Progress 10/01/02 to 09/30/08
Outputs
OUTPUTS: European red mites can be serious pests of grapes in the northeast with many vineyards sustaining severe leaf injury (bronzing) due to feeding by these mites even though recommended tolerable levels of European red mite are only 2-5 per leaf, a density considerably less than that necessary to cause visible leaf damage. There is also considerable use of miticides by vineyardists, at times when densities of mites are very low. These apparent contradictions could be due to several reasons; what is clear though, is that quantitative research that relates mite injury to berry yield and quality has been lacking, and this contributes to vagueness over the need to control European red mite in northeast grapes. Experiments were conducted to relate mite injury to fruit yield and quality using single panels of grapes (3 or 4 vines) as experimental units. Mite densities were managed to reach a range of cumulative miteday levels. Vine response measurements included bloom, leaf photosynthetic rates, fruit yield and quality, bud winter-hardiness, and cluster development in overwintering buds. In many perennial plant systems, plant-feeding mites are controlled by phytoseiid mites. Persistence of these predators on plants is more important to biological control than the rate of pest mite consumption. The lack of leaf trichomes (hairs or bristles on the underside of leaves) can be an important obstacle to mite biological control. Plants that lack leaf trichomes usually have low predator numbers and may therefore sustain pest mite attack. We assesed three possible solutions to this problem: applying trichome-mimics to plants that lack leaf trichomes. arranging plants with and without leaf trichomes within a planting to provide for greater densities of predators throughout the group of plants, and breeding plants with leaf trichomes. To do so we determined how physical characteristics, density and spatial pattern of leaf trichome mimics influence predator mite behavior and retention on plants; we determined whether the arrangement of plants with leaf trichomes among plants without leaf trichomes can provide for retention of phytoseiids and biological mite control for the entire plant ensemble; and we developed a moderately saturated genetic map segregating for leaf trichomes in grape and identifed genetic markers that can be used for marker-assisted selection. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Photosynthesis declined in relation to increasing mite-feeding damage in two years out of three. We measured yield of fruit in relation to cumulative mite density in three of the four years of the study; in one year berries failed to develop thereby precluding yield assessments. Our measurements showed no relation between fruit yield, as assessed by berry and cluster weights, and cumulative mite densities. In contrast to fruit yield, we did observe an effect of mite feeding damage on fruit quality measurements. In one year, we observed a decrease in %Brix with increasing cumulative mite density: At the highest level of mite injury (ca 1500 mitedays), %Brix was reduced by 10%. In two other years we observed no influence of mite feeding damage on %Brix. Cold hardiness of buds was assessed as an indicator of vine vigor and hardiness. Based on the data gather over three years, there is little evidence to suggest that there is a statistical influence of mite feeding injury on low temperature exotherms and hence cold hardiness. Similarly, three years data effect of mite levels on dormant bud "fruitfulness" lead us to conclude that there is no consistent relationship between mite density and "fruitfulness". We demonstrated that artificial trichomes can be used to imitate natural trichomes and plants that lack leaf trichomes and do not retain phytoseiids can be transformed to plants that retain phytoseiids through the addition of trichome mimics. We showed that phytoseiid retention on plants in relation to leaf trichomes varies among species of phytoseiids; however, several species (those with a Type III life history) respond to leaf trichome abundance. We hypothesized that juxtaposition of plants with leaf trichomes among plants without trichomes would increase phytoseiid abundance in the plant assemblage; however, experiments at several spatial scales refute this idea. We found that phytoseiid abundance in relation to leaf trichomes is independent of scale; results are similar for individual leaves, single plants and assemblages of up to 16 field-grown grape plants. We have developed a genetic linkage map in a population segregating for trichomes and have associated trichome formation with regions of the grape genome influencing this trait. Overall this project will help to identify tactics that can be used to augment mite biological control in perennial crops. On perennial plants that lack leaf trichomes mite biological control is hampered because the plants do not support adequate numbers of predacious mites. If this limitation can be overcome, mite biological control can be more readily realized,. Mixing plants with and without leaf trichomes does not offer a solution. In the long term, breeding plants with leaf trichomes is the best strategy. For this to occur tools are needed that a breeder can use to select superior breeding lines. Many modern breeding programs use a method called "marker assisted selection" for this purpose. We are developing DNA markers that are associated with grape leaf trichomes which a breeder can use to assure that new cultivars have leaf trichomes.
Publications
- Loughner R, Wentworth K, Loeb G, Nyrop J 2010. Influence of leaf trichomes on predatory mite density and distribution in plant assemblages and implications for biological control. Biol. Control. 54:255-262.
- Loughner R, Wentworth K, Loeb G, Nyrop J 2009 Leaf trichomes influence predatory mite densities through dispersal behavior. Entomol Exp Appl 134:78-88
- Loughner R ; Goldman K ; Loeb G ; Nyrop J. 2008 Influence of leaf trichomes on predatory mite (Typhlodromus pyri) abundance in grape varieties. Experimental and Applied Acarology 45:111-122
- Luczynski A, Nyrop JP, Shi A 2008 Pattern of female reproductive age classes in mass-reared populations of Phytoseiulus persimilis (Acari: Phytoseiidae) and its influence on population characteristics and quality of predators following cold storage. Biological Control. 47:159-166
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Progress 10/01/06 to 09/30/07
Outputs
Mass produced predatory mites, Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae), have been extensively used for the biological control of the two-spotted spider mite, Teranychus urticae Koch (Acari: Tetranychidae) on a variety of greenhouse and field crops. The efficacy of the biological control programs relying on these predators has been primarily attributed to appropriate release rates and the quality of mass-produced populations. In the past several years, quality assessment of several biological control agents has received considerable attention. The International Organization for Biological Control (IOBC) has developed guidelines for quality assessment of mass-produced P. persimilis, in an effort to ensure that cultures produced in commercial insectaries meet minimum performance standards. However, commercial P. persimilis cultures are routinely cold-stored following harvest, and they are shipped in cooled containers without food, treatments that
could potentially affect predator quality at the final destination. The IOBC standards and guidelines do not consider the effects of cold-storage and starvation and it remains uncertain whether assessments conducted immediately after harvest are reliable indicators of P. persimilis quality following storage and shipment. We exposed mass-produced Phytoseiulus. persimilis to 5C or 10C for 0, 6, 12 or 18 days to determine the influence of cold on the fecundity and longevity of individual predators, on their dispersal and survival patterns following storage, and on the reproductive age structure in populations of females. When P. persimilis populations were tested shortly after harvest or delivery to their final greenhouse destination, the distribution of reproductive ages was consistently biased towards older and non-producing females, with overall average fecundity of ca 13 eggs and longevity ca 7 days. The number of live predators gradually declined as the length of storage increased
at either 5C or 10C. In contrast, the capability of predators to disperse upward was only reduced after 18 days of storage at 5C. The proportion of reproductively young females increased in populations that survived 18 days of storage at either 5C or 10C, and this was reflected in significantly higher mean oviposition period and fecundity than in the remaining three treatments. Our results reveal that the ability of P. persimilis females to tolerate cold storage and starvation is strongly tied to their reproductive age and that reproductively young females are capable of tolerating prolonged exposure to low temperature and starvation without compromising their quality. Fecundity of P. persimilis assessed shortly after harvest met the expectations outlined in IOBC guidelines. We found a positive linear relationship between the directly measured total fecundity and the results of a short-term (5-day) IOBC fecundity test, indicating that the IOBC test reliably predicts the reproductive
potential of P. persimilis females. However, the proportion of surviving predators did not meet IOBC guidelines.
Impacts
We found that the distribution of reproductive age classes of commercially produced P. persimilis was strongly biased toward reproductively older females. A similar pattern was also observed in P. persimilis populations that were delivered to commercial greenhouses. It is unclear why we observed a high proportion of older females in mass- produced populations, but the combination of hunger, temporary arrestment of the dispersal behavior and the propensity for cannibalism in P. persimilis offers a plausible explanation. Results from our storage experiments indicate that the ability of P. persimilis females to tolerate stress induced by cold and starvation is strongly tied to their reproductive stage; reproductively young females are more likely to survive and continue reproducing following prolonged storage without food. The IOBC quality guideline for P. persimilis specifies that females are expected to produce a minimum of 2 eggs/female/day over a 5-day test period
(day 1 to 6) and a minimum of eighty percent of these females are expected to survive to the end of the fifth day. When we tested predators shortly after harvest, their fecundity met this IOBC standard, but the proportion of surviving predators did not. An adequate number of released predators for a specific level of spider mite infestation and a high fecundity of released predators are among the key determinants of biological control efficacy of P. persimilis. It is therefore a matter of concern that there are several reported inconsistencies between the expected number of predators per shipment and the actual number supplied. Furthermore, we have identified low fecundity in commercial supplies of P. persimilis. Increased consistency in the number of supplied predators along with improved fecundity of the P. persimilis at the time of release, both have the potential to improve the effectiveness of biological control when using this predator.
Publications
- No publications reported this period
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Progress 01/01/06 to 12/31/06
Outputs
One reason proposed for increased number of phytoseiids found on plants with leaf trichomes is that these structures increase the depth of the boundary and thereby mediate the adverse effects of low relative. We tested this hypothesis through a series of experiments in which eggs were placed on substrates that varied in their putative ability to mediate ambient low relative humidity. These substrates consisted of a glass slide, a respiring leaf with no trichomes, and a respiring leaf with trichomes. If the aforementioned hypothesis is true, then, at low relative humidity, egg hatch should be highest on the respiring leaf with trichomes and lowest on the inert, glass surface. Survival of eggs placed on the glass slide would reflect the effect of the ambient relative humidity. Respiring leaves create a boundary layer about the leaf surface, which, under conditions of low ambient relative humidity, will have an elevated relative humidity and should allow for greater egg
survival and hatch compared to eggs placed on the glass surface. Respiring leaves with trichomes should generate a boundary layer that is deeper than that on leaves with no trichomes and this deeper boundary layer should result in greater mediation of low humidity conditions and increased phytoseiid egg hatch. We conducted experiments using the phytoseiid Typhlodromus pyri and with transpiring leaves that lacked trichomes, that had natural trichomes, and that had artificial thrichomes made from cotton fibers. When plants with and without natural trichomes were compared, different species of plants were used (bean and apple). When artificial trichomes were compared, the same species of plant was used (bean). None of the experiments provided any evidence that substrate influenced hatch of T. pyri eggs though the effect of humidity was clearly and consistently shown. The results conclusively show that, for the conditions under which the experiments were conducted, neither respiring
leaves or the addition of trichomes to respiring leaves, mediated the adverse effects of low relative humidity on survival and hatch of T. pyri eggs. These results are perplexing because it has long been accepted that a plant's evapotranspiration combined with the boundary layer above a leaf surface, should ameliorate the adverse effect of low humidity. Several explanations for our results need to be considered. One possibility is that the plants used were not transpiring; however, there was no evidence of wilt among the plants and the bean plants showed visible growth. Another possibility is that airflow in the environmental chambers caused leaf movement and hence disrupted the boundary layers. However, video cameras showed there was no leaf movement. A third possibility is that previous studies that showed an influence of a live leaf on phytoseiid egg hatch allowed phytoseiids to oviposit on leaves with spider mite webbing whereas we used leaves with no spider mite webbing. Spider
mite webbing is hygroscopic and coupled with evapotranspiration and the boundary layer, may have had a mediating effect on low humidity whereas the leaf alone did not produce such a measurable effect.
Impacts
These studies are of a discovery-based nature; there is no direct application to biological control or crop improvement for biological control. However, it is clear that for some species of phytoseiid predators, the presence of leaf trichomes is a requisite for the predaceous mites being abundant on the plants and hence able to exert control over pest mites. Understanding the ultimately causes of these difference in predator numbers will enable researchers to better ensure that leaf trichomes are expressed in new cultivars and varieties and may provide clues about other management practices that might ameliorate the effects of no leaf trichomes on phytoseiid abundance.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
The objective of this project is to quantify the influence of European red mites (Panonychus ulmi) on grape yield, quality and vigor. European red mites can be serious pests of grapes in the northeast. Over the last several years, many vineyards have sustained severe leaf injury (bronzing) due to feeding by these mites even though recommended tolerable levels of European red mite are only 2-5 per leaf, a density considerably less than that necessary to cause visible leaf damage. There is also considerable use of miticides by vineyardists, at times when densities of mites are very low. These apparent contradictions could be due to several reasons; what is clear though, is that there is no quantitative research that relates mite injury to berry yield and quality, and this lack of knowledge contributes to vagueness over the need to control European red mite in northeast grapes. During the past three years experiments have been conducted to relate mite injury to fruit
yield and quality. Experimental units have consisted of a single panel of grapes comprised of 3 or 4 vines, with 30 to 40 panels used for each experiment. Cultivars have been Cabernet Sauvignon or Cabernet Franc. European red mite densities were estimated in each panel every 10 to 14 days from a sample of 15 leaves and cumulative mitedays calculated as the area beneath the trajectory of density. When targeted miteday levels were reached, a panel was treated with a miticide to eliminate the mites. Response measurements have included bloom, leaf photosynthetic rates, fruit yield and quality, bud winter-hardiness, and cluster development in overwintering buds. In 2005 experiments were conducted in two grape plantings, one on Long Island and one in the Finger Lakes region. At the Long Island site only fruit quality was measured. At the Finger Lakes site, photosynthesis, fruit yield and quality, and winter-hardiness and cluster development were assessed. At the Long Island site cumulative
mite densities (mitedays) ranged from a low of 20 to a high of 1340. There was no affect of mite injury on the weight of a 100-berry sample from each panel or on the soluble solids and acids in these berries, At the Finger Lakes site mite days ranged from 5 to 1100. There was no relationship between mite injury and any of the crop performance variables measured. In 2003 we found that European red mite damage to grape leaves significantly reduced photosynthesis and led to reduced fruit maturation (percent Brix) and lower levels of total acidity. In contrast to these results, mite injury did not influence photosynthesis in 2004. Unfortunately, no harvest data could be collected in 2004 due to winter-injury to fruit buds. In 2005 we observed no influence of mite injury (up to 1300 mite days) on fruit yield and quality. Thus, in the three vineyards where experiments have been conducted, mite induced damage was only observed in one. Based on data from the same three experimental sites
there is little evidence that damage from mites results in reduced cold hardiness. Similarly, the effects of mite injury on dormant bud fruitfulness are not discernable.
Impacts
Published research led to recommendations that no more than 2 to 5 European red mite per leaf be allowed in vineyards, a density well below that required to cause visible leaf injury. However, the research upon which recommended tolerable levels of mites were determined was not quantitative. More recent, quantitative research suggested grape vines are able to tolerate significant numbers of mites before berry yield or quality is affected. In one study infestations up to 3500 mitedays (a maximum density of approximately 60 mites per leaf) resulted in no decrease in photosynthesis and only an 8.7 percent reduction in transpiration. The same study found that similar levels of mite feeding had no effect on total yield or the number of berries per cluster, must soluble solids, total acidity, or pH . Our results are not fully in accord with these finding yet at the same time, our results do suggest that grape plants can sustain significant mite injury without adverse
affects on yield or quality. These results will allow us to revise action thresholds and thereby reduce the need for and use of miticides on grape.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
Two studies are reported on that contribute towards improved management of European red mite (ERM). The objective of the first study is to quantify the influence of ERM on grape yield, quality and vigor. For the second year mite densities were manipulated to achieve cumulative miteday levels ranging from near 0 to ca. 1500. Experimental units consisted of a single panel of grapes comprised of 4 vines. Response measurements of bloom, leaf photosynthetic rates, fruit yield and quality, bud winter-hardiness, and cluster development in overwintering buds were collected. Unfortunately, harvest data were not usable because severe winter injury resulted in abnormal fruit development. There was no relation between mite injury in 2003 and bloom in 2004. ERM densities reached a maximum of approximately 45 per leaf with a corresponding cumulative density of about 1500 mitedays. Vines with the highest mite densities showed severe leaf bronzing. No effect of mite injury on
photosynthesis was detected. We found no influence of mite damage on cold hardiness. There was little effect of mite injury on bud development and cluster differentiation although buds from vines with the very highest mite levels were less developed than vines with lower levels of mite injury. In 2003 we found that European red mite damage to grape leaves significantly reduced photosynthesis and led to reduced fruit maturation (%Brix) and lower levels of total acidity. In 2003 we did not detect any influence of mite injury on fruit yield. In 2002 and 2003, patterns of photosynthesis reduction due to mite damage were similar, with a logarithmic decline in relation to cumulative mite density best explaining the data. In contrast to these results, mite injury did not influence photosynthesis in 2004. Unfortunately, harvest data from 2004 could not be compared to previous results. As in 2003, we found no relationship between cold hardiness and mite injury. The objective of the second
study is to understand phytoseiid behavioral response to leaf trichomes. Experiments were conducted using bean plants and artificial trichomes to determine who leaf trichomes affect retention of phytoseiids. Longer fibers and higher fiber density resulted in increased retention of Typhlodomus pyri. Retention of five phytoseiid species increased with increasing fiber density; however the magnitude of this increase varied greatly among species. Relatively modest levels of trichome mimics resulted in greatly increased retention of T. pyri and Amblysieus andersoni, a result roughly in accord with field data from grapes. These results buttress the theory that dispersal behavior is a proximate cause of different phytoseiid numbers on plants with varying levels of leaf trichomes. The presence of leaf trchomes likely determines whether certain phytoseiid species can be successful biological control agents.
Impacts
European red mites are common in commercial vineyards; however, their rational management is hindered by two knowledge gaps. First, the impact of these plant-feeding mites on grape yield and quality has heretofore not been quantified in the northeast. As a result, pesticides might be applied when the economic benefit is insufficient to justify use. Conversely, pesticides might not be applied when their use would result in better yield and quality. Closing this knowledge gap will identify conditions where actions should be taken to limit pest mite numbers. A second knowledge gap is the extent to which trichomes and hairs on grape leaves dictate the effectiveness of mite biological control. Predaceous mites can, under the right management regime, obviate plant-feeding mites as pests. However, these beneficial mites are usually scarce to non-existent on plants that lack leaf trichomes and hairs. Better understanding of this relationship will allow prediction of grape
cultivars that are not suitable for mite biological control. Overall, results from this project will allow more rational and integrated control of pest mites.
Publications
- Roda, A., J. Nyrop and G. English-Loeb. 2003. Leaf pubescence mediates the abundance of non-prey food and the density of the predatory mite Typhlodromus pyri.. Exp. Appl. Acarol. 29:193-211.
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Progress 01/01/03 to 12/31/03
Outputs
The objective of this experiment is to quantify the influence of European red mites (Panonychus ulmi) on grape yield, quality and vigor. In 2003 mite densities were manipulated in a vinyard planted to Cabernet Sauvignon grapes. Experimental units consisted of a single panel of grapes comprised of 4 vines and 30 panels were used. European red mite densities were estimated in each panel every 10 to 14 days and cumulative mitedays calculated as the area beneath the trajectory of density. When targeted miteday levels were reached, a panel was treated with a miticide to eliminate the mites. Response measurements of leaf photosynthetic rates, fruit yield and quality, bud winter-hardiness, and cluster development in overwintering buds were collected. European red mite densities reached a maximum of approximately 75 per leaf with a corresponding cumulative density of about 1700 mitedays. Vines with the highest mite densities showed severe leaf bronzing. Leaf injury inflicted
by the mites had a significant and consistent effect on leaf photosynthesis with measured photosynthetic rates declining exponentially with increasing mitedays. For the highest recorded cumulative mite density, photosynthesis rates late in the growing season were reduced by approximately 35%. There was no effect of mite damage on fruit yield. Mite injury did, however, result in a decrease in %Brix and titratable acids (20% maximum). We found no influence of mite damage on winter hardiness or on bud development. Our results indicate that European red mite damage to grape leaves can significantly reduce photosynthesis and lead to reduced fruit maturation (%Brix) and lower levels of total acidity. Furthermore, the patterns of these relationships do not suggest a threshold response, wherein some level of mite damage is tolerated before effects on photosynthesis and fruit quality are manifest, but rather a nearly instantaneous and continuous reduction in response to mite injury. In both
2002 and 2003, patterns of photosynthesis reduction due to mite damage were similar, with a logarithmic decline in relation to cumulative mite density best explaining the data. The relationship between cumulative mite density and %Brix in 2003 was also best described by a logarithmic decline in relation to mite injury. In 2002, there was no evidence that cumulative mite density up to 800 mitedays was related to declines in fruit quality. In both 2002 and 2003 we observed no effect of mite injury on fruit yield, vegetative maturation as evidenced by cold hardiness, or, in 2003, on bud development.
Impacts
This project will quantify the impact of European red mite on grape yield and quality in the northeast. This quantification will allow for more rational management of European red mites and will help vinyardists avoid crop losses and unnecessary pesticide applications.
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
An experiment was conducted to assess the impact of European red mite on grape leaf photosynthesis, fruit yield and quality, and vine vigor as indicated by cold-hardiness. Mite densities were manipulated in a 15-year-old Chardonnay planting. Experimental units were groups of 4 vines (panels) planted between trellis posts. Mite density was blocked among 25 experimental units (100 vines) and there was a maximum cumulative density (mitedays) of 800 recorded between 15 July and 1 September. Leaf photosynthesis was measured twice in September with measurements taken from 10 mid-shoot leaves from each of 10 panels having the complete range of recorded mitedays. At harvest, the number and weight of the fruit clusters were determined for each vine. A subset of fruit were retained for use in determining percent Brix and titratable acids. Fruit weight, percent Brix and titratable acid were regressed on mitedays, the number of fruit clusters per vine and the product of mitedays
and number of fruit clusters per vine. The latter variable accounted for the possibility that the impact of mite injury would be greater with larger crop loads. Buds representative of those to be left for pruning were sampled and assessed for mid-winter bud cold hardiness. Buds were severed from the canes, placed on thermo-electric plates, placed in a freezer and cooled until they released a low temperature exotherm (LTE), which signaled bud death. European red mite injury had a significant effect on leaf photosynthesis with measured photosynthetic rates declining exponentially with increasing mitedays. For the highest recorded cumulative mite density (nearly 800 mitedays), photosynthesis rates were reduced by nearly 30 percent compared to leaves that were not damaged by European red mite. Linear models were fit to the data using a stepwise backward elimination procedure. None of the independent variables (mitedays, fruit clusters per vine, or the product of mitedays and fruit
clusters) were significantly related to the dependent yield or quality parameters. We found no influence of mite damage on median LTE. Therefore, vines subjected to the greatest level of mite injury suffered no less winter protection than did vines that had no mite injury.
Impacts
In this experiment, grapevines were subjected to nearly 800 mitedays with a maximum European red mite density of approximately 30 per leaf, a density greatly in excess of current recommended treatment thresholds. Thus, from the perspective of measurable impact on vine vigor and fruit yield and quality, our results indicate that current treatment thresholds for European red mite are overly conservative. If this conclusion withstands further testing, mite management recommendations can be revised and pesticide treatments can likely be reduced.
Publications
- No publications reported this period
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Progress 01/01/01 to 12/31/01
Outputs
In 1999, we initiated an experiment to assess the impact of EBDC fungicide use in grapes on the predatory mite, Typhlodromus pyri. At each of 9 vineyards, we established two plots, 0.5 to 1 acre each. One of these plots was treated with EBDC fungicides, the other with non-EBDC fungicides. Within each plot, 4 sub-plots were established and T. pyri were released into 2 of these sub-plots. We found that T. pyri densities were reduced approximately two-fold by EBDC applications but that release of T. pyri had no significant effect on predator abundance. Thus, T. pyri were indigenous to these vineyards at the start of the experiment. We also found that over the three-year course of the study, T. pyri densities increased nearly 10 fold. No influence of EBDC applications on European red mite densities was observed; however, there were more (9 vs 4) instances where average densities of European red mite exceeded 1 per leaf for the entire season when grapes were treated with
EBDC fungicides. From this experiment, we conclude that EBDC applications do reduce T. pyri numbers and that in some instances, these reductions may be sufficient to cause problematic numbers of European red mite. However, EBDC applications do not, in general, lead to outbreaks of European red mite. The results from this experiment also reinforce the efficacy of T. pyri as a biological agent. Plots with moderate to high (>0.5 per leaf) seasonal densities of T. pyri never had problematic European red mite numbers (>1 per leaf over the entire season); whereas, 30% of the sites with fewer than 0.5 T. pyri per leaf developed European red mite numbers in excess of 1 per leaf. We repeated a study in which the leaf topography of several grape cultivars grown in a common garden were characterized and T. pyri densities on these cultivars were estimated with the aim to confirm a previously determined relationship between leaf topography and predator abundance. We also conducted an experiment in
which potted grape plants consisting of the same cultivars as those sampled from the common garden were subjected to one of three treatments: European red mite and T. pyri added, T. pyri added alone, and European red mite added alone. Ten cultivars were used and each treatment was replicated 10 times. Each year an index of domatia size and ranks of leaf hairs were significant predictors of T. pyri density with these variables accounting for approximately 80% of the variation in predator numbers. These results show that T. pyri densities are strongly influenced by leaf characteristics and that cultivars with leaves having few trichomes and no domatia have very low numbers of predators. On the potted plants, cultivars with high numbers of T. pyri were generally the same cultivars that harbored high densities in the common garden. Highest numbers of European red mite were recorded on the cultivar with the fewest T. pyri and that lacked domatia and had few trichomes (Dechaunac). A similar
pattern was observed in a commercial planting consisting of Baco Noir, Concord, Dechaunac, Elvira and Niagara.
Impacts
These results show that EBDC fungicide applications do not, by themselves, cause European red mite outbreaks, that conserving T. pyri in grapes results in effective mite biological control and that grape cultivars that lack domatia and leaf trichomes may not support sufficient T. pyri to realize biological control.
Publications
- No publications reported this period
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Progress 01/01/00 to 12/31/00
Outputs
In 1999, we initiated an experiment to assess the impact of EBDC fungicide used in grapes on the predatory mite, Typhlodromus pyri. Previous research has shown that application of these fungicides may prevent establishment of the predators and disrupt biological control. At each of 9 vineyards, we established two plots, 0.5 to 1 acre each. One of these plots was treated with EBDC fungicides, the other with non-EBDC fungicides. No insecticides detrimental to T. pyri were used in either plot. Within each plot, 4 sub-plots were established that consisted of 3 panels in each of 3 rows. Into 2 of these sub-plots, T. pyri were released by affixing 50 apple flower blossoms that harbored predators to the vines in each panel. Inoculation was repeated by affixing 50 apple leaves with predators to the grape leaves in each panel. In 1999, there was no evidence that predator releases increased the numbers of T. pyri. There was some evidence that EBDC fungicide applications reduced
predator numbers approximately two fold; however, predator densities were very low. Typhlodromus pyri were found in all the plots regardless of release status and European red mite (Panonychus ulmi) were scarce. In 2000, there again was no evidence that release of the predators resulted in an increase in abundance. However, T. pyri were 2-8 times more abundant where EBDC fungicides were not applied. Densities of European red mite were generally low except at two sites where pest mite numbers in EBDC treated plots were 10-15 times higher than in plots where EBDC fungicides were not used. We also examined the influence of domatia and grape leaf trichomes on T. pyri by performing counts of predators on different grape cultivars, and conducting experiments to study adult movement and oviposition behavior, and thrips predation on T. pyri eggs. Variation in numbers of T. pyri on different grape cultivars was related to the density of leaf trichomes and to the size of domatia. Analysis of
predator counts over time showed that T. pyri densities varied among cultivars and over time; however, the numbers of mites on each cultivar relative to the other cultivars did not change. Laboratory experiments showed that T. pyri preferred leaves with domatia over leaves covered with felty, matted hairs and lacking domatia, and over leaves that were nearly glabrous. Leaf topography did not influence T. pyri oviposition rates. Leaf trichomes and domatia afforded predator eggs protection from thrips predation and the data suggest that this protection is obtained even from low densities of trichomes and small, poorly developed domatia. These data suggest that on grape cultivars lacking leaf trichomes and domatia, T. pyri probably will not attain sufficient densities to provide biological control.
Impacts
These results show that conserving T. pyri in grapes results in effective mite biological control; however, grape cultivars that lack domatia and leaf trichomes may not support sufficient T. pyri to realize biological control.
Publications
- No publications reported this period
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Progress 01/01/99 to 12/31/99
Outputs
An experiment was conducted in 10 vineyards to test the hypothesis that T. pyri could be established and provide biological control of European red mite when EBDC fungicides were not used. At each site, a split-plot design was used where sub-plots with and without predator releases were nested within plots with and without EBDC fungicides. Typhlodromus pyri densities were very low at all but one site where they were abundant, but twice as numerous in plots without EBDC fungicides. In plots where predators were not released, no predators were recovered in five EBDC treated plots compared to two such plots not treated with EBDC fungicides. When no predators were found in the control plots, there were more predators in the release plots. There were also more predators in non-EBDC treated plots than in EBDC treated plots. Sampling of a grape planting with several varieties revealed large differences in T. pyri abundance among varieties. Using 29 sets of 50-leaf counts of
European red mite, we found that 24 sets could be described by a negative binomial distribution and that the variance could be described as a function of the mean. These two models are sufficient to describe the proportion of samples with more than T organisms as a function of the mean. By doing so, the proportion of samples with more than T mites can be used in lieu of complete counts. We developed two sampling procedures that classify mite densities into one of three categories: 1) density well below the action threshold and sampling again is not needed for about 14 days, 2) density less than that requiring control, but sampling needed again in about 7 days, and 3) density greater than the action threshold and intervention is suggested. The first sampling procedure is designed to be used during the first half of the growing season and is based on an action threshold of 5 mites per leaf. It uses T = 2 so leaves with two or mites are scored as positive whereas all other leaves are
scored as negative. The second sampling plan is to be used during the second half of the growing season and has an action threshold of 7.5 and T =4.
Impacts
(N/A)
Publications
- No publications reported this period
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Progress 01/01/98 to 12/31/98
Outputs
In 1998 we repeated two experiments also conducted in 1987 to assess the impact of EBDC fungicide applications on an established and abundant population of Typhlodromus pyri. The first experiment used individual trees as experimental units. The treatments, omitting controls, consisted of a seasonal EBDC fungicide program, EBDC fungicides applied before bloom only, and EBDC fungicides applied after bloom only. Treatments were applied using a hand gun. Experimental units for the second experiment consisted of plots of trees and treatments were applied with a speed sprayer. This experiment was replicated twice in each of 3 blocks. In both years we found that when using a handgun to apply treatments, seasonal applications of EBDC fungicides reduced T. pyri populations 70% in June, 60% in July and by August, densities were approximately equal in the treated trees and controls. Applications of EBDC fungicides before bloom did not affect T. pyri numbers. We also found in
both years that applications made using a speed sprayer did not affect predator densities. Experiments were also conducted to assess the influence of pollen augmentation on T. pyri. Cattail (Typhus) pollen was applied weekly for seven weeks to each of 5 Macintosh and Red Delicious trees and predator densities measured. Repeated measures analysis of variance revealed higher predator numbers on Red Delicious pollen treated trees but no differences on Macintosh trees.
Impacts
(N/A)
Publications
- No publications reported this period
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Progress 01/01/97 to 12/31/97
Outputs
In 1996 and 1997 we conducted experiments to assess the impact of EBDC fungicide applications on an established and abundant population of Typhlodromus pyri. The experiments were conducted in an apple planting with experimental units consisting of individual trees with one tree buffers on all sides. In 1996 there were 4 replicates per treatment and in 1997 there were 6. The treatments, omitting controls, consisted of a seasonal EBDC fungicide program, EBDC fungicides applied before bloom only, EBDC fungicides applied after bloom only, and EBDC fungicides applied on a seasonal basis for two years. Mite densities were estimated weekly by brushing mites from twenty five leaves collected from each tree. Data were analyzed using repeated measures analysis of variance. In 1996 we found that seasonal applicatons of EBDC fungicides reduced T. pyri populations 70 percent in June, 60 percent in July and by August, densities were approximately equal in the treated trees and
controls. In one treatment European red mite populations exploded to over 70 per leaf. In 1997 we obtained similar results with the exception that pest mite numbers never exceeded 5 per leaf. There were no differences among 3 EBDC fungicides tested. Applications of EBDC fungicides before bloom did not affect T. pyri numbers and that there was no carry-over of treatment effects from 1996.
Impacts
(N/A)
Publications
- Nyrop, J. P., G. English-Loeb and A. Roda. 1997. Conservation biological control of spider mites in perennial cropping systems. In: "Perspectives on the Conservation of Natural Enemies of Pests". P. Barbosa [ed]. Academic Press, New York.
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Progress 01/01/96 to 12/30/96
Outputs
A five year record of dynamics between European red mite and the mite predators Typhlodromus pyri and Amblysieus fallacis were kept in an orchard at Geneva. In this orchard, T. pyri were released into 2 of 4 blocks of trees and A. fallacis naturally occurred in the other two blocks. One year after the release of T. pyri, European red mite were controlled in the blocks where T. pyri were released without the use of any pesticides. This pattern was repeated for the years 1993-1996. In contrast, A. fallacis failed to keep pest mite numbers below damaging levels unless a miticide was used early in the growing season. Reasons for the difference in the effectiveness of the two predators are two-fold. First, A. fallacis that spend the winter in trees, suffer much higher levels of mortality some years than do T. pyri. During two of four years for which winter survival was estimated, Amblysieus fallacis in trees were reduced to such low numbers in the spring that they were not
found even with intensive sampling. Second, even when A. fallacis survive well during the winter, they are often absent in the spring, probably because they disperse out of the tree when they first become active, which is before European red mite eggs hatch. In 1996, A. fallacis survived in trees until mid-April. However, four samples of 150 leaves each that were collected during late May and June to estimate predators numbers produced no A. fallacis.
Impacts
(N/A)
Publications
- VAN DER WERF, W., J. P. NYROP, AND M. R. BINNS. 1997. Monitoring European red mites using adaptive frequency classification: Development and evaluation of a new monitoring methodology. Exp. Appl. Acarol. (In Press).
- LAWSON, D. S., J. P. NYROP AND T. J. DENNEHY. 1996. Aerial dispersal of European red mites (Acari: Tetranychidae) in commercial apple orchards. Exp. Appl. Acarol.20:193-202.
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Progress 01/01/95 to 12/30/95
Outputs
We developed a new method (Adaptive Frequency Classification or AFC) for monitoring pests over a growing season, and applied the method to monitoring red spider mite in apples. We evaluated the performance of the monitoring method in this system by simulation experiments and a field test in 28 orchard blocks in New York State (USA) in 1995. The method is based on serially linking sample occasions (bouts) in time. At each sample occasion, the monitoring procedure decides between intervening or not intervening. In case of no intervention, the procedure schedules the next sample bout on the basis of an estimate of current density, a descriptive population growth model (exponential for mites), and intervention thresholds. The next sample bout is scheduled when the risk of pest density becoming greater than a future intervention threshold exceeds a specified tolerance. The sampling protocol is constructed by combining a sequential probability ratio test for taking quick
intervention decisions at high density, with fixed sample size estimation for obtaining estimates of current density when density is low. The density estimates are used for calculating waiting times until the next sample. Simulation suggested that AFC would have performance characteristics similar to those of an existing monitoring method when monitoring rapidly growing populations, while substantial savings on the number of sampling occasions were obtained with slowly growing populations. The latter prediction was corroborated in th.
Impacts
(N/A)
Publications
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Progress 01/01/94 to 12/30/94
Outputs
Crop protection decisions are often based on classifying pest abundance with respect to a predetermined threshold. The performance of sampling plans used for this purpose can be compared based on a) the cost of taking a sample and b) the cost of misclassifying pest abundance and thus making an inappropriate decision. The probability that a sample will classify a pest population into one category or other can be summarized by the operating characteristic (OC) function: The OC function shows, for any true mean, the probability that density will be classified as less than the threshold. When sampling plans are used repeatedly to monitor population density over time, the probability of classifying populations as being above the nominal threshold increases, and this could result in unnecessary intervention. Sampling plans that categorize density into three classes (tripartite plans) rather than two classes (dichotomous) provided more information and are more effective
constituents of monitoring protocols. When tripartite plans are used to monitor population density, overall probability of never recommending intervention is less influenced by the process of repeated sampling. Two principles can guide selection of tripartite classification sampling plans for use in monitoring protocols. First, thresholds must often be raised if erroneous decisions to intervene are to be minimized. Second, because monitoring with tripartite classification plans allows a wrong decision not to intervene to be corrected,.
Impacts
(N/A)
Publications
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Progress 01/01/93 to 12/30/93
Outputs
Further work was completed on two methods that can be used to monitor populations through time. This is especially useful when assessing biological control. One method is based on cascading sampling plans that sequentially classify density into one of three categories (tripartite sequential classification, TSC). The other protocol is constructed by cascading sampling plans based on a combination of sequential classification and estimation of density (adaptive frequency classification, AFC). Binomial count TSC sampling plans that used a tally threshold of 4 were much more precise than plans that used a tally threshold of 0. However, the overall performance of a monitoring protocol based on tally 0 sampling plans did not greatly differ from a monitoring protocol based on tally 4 sampling plans. Simulated performance of the tally 0 protocol was corroborated by field evaluation. The monitoring protocol based on tripartite classification required 30 to 45 percent fewer
sample bouts than a protocol based on conventional sequential classification at weekly intervals. The monitoring protocol based on tripartite classification was also better able to schedule intervention when needed compared to a protocol based on conventional classification at two week intervals. When monitoring protocols were compared, those based on AFC sampling plans required fewer sampling resources than protocols based on TSC plans.
Impacts
(N/A)
Publications
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Progress 01/01/92 to 12/30/92
Outputs
Four studies were conducted whose goals were to determine the importance of vegetation beneath apple trees on the dynamics of the mite predator Amblyseius Fallacis (Garman). Withholding herbicide applications in the spring to allow ground cover to grow beneath trees did not result in greater numbers of A. fallacis in trees during the summer compared with plots where herbicides were applied and ground cover was greatly reduced. A survey of 23 commercial orchards revealed that A. fallacis overwintered on trees in 14 sites. Typhlodromus pyri was also found. In two orchards that were part of the 23 surveyed, phytoseiids and European red mite, Panonychus ulmi (Koch) were sampled the following spring and summer. Amblyseius fallacis were found in the trees at bloom (10 May) and there was no evidence that they first increased in the ground cover and then colonized trees. Overwintering predator populations were repeatedly sampled in six orchards during fall, winter, and spring
1991- 1992. A. fallacis as well as T. pyri overwintered in high numbers in the trees. A. fallacis was also found in high numbers in the ground cover as were fewer T. pyri. Both predator species suffered high overwintering mortality. Treatment of ground vegetation with a pyrethroid insecticide in the spring did not affect arboreal A. fallacis densities during the summer; however, treatment of trees with the insecticide greatly reduced A. fallacis densities.
Impacts
(N/A)
Publications
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Progress 01/01/91 to 12/30/91
Outputs
Amblysieus fallacis is a mite predator common in New York apple orchards and known to be capable of providing biological control of European red mite. Previously A. fallacis was thought to overwinter in ground cover beneath apple trees and to colonize tree canopies as phytophagous mite numbers increased there. Management principals that resulted from this inferred biology were the importance of ground cover beneath apple trees and the freedom to use pesticides toxic to A. fallacis early in the season because the predator was not yet in the tree canopy. Research has now unequivocally shown that A. fallacis overwinters in both apple trees and in the ground cover beneath apple trees; however, ground cover beneath trees appears to have little influence on A. fallacis dynamics in the tree. We now hypothesize that the inference frequently made that A. fallacis is a poor biological control agent because it does not colonize trees until late in the growing season and after
European red mite have reached problematic numbers is incorrect. A more likely explanation of the observation that A. fallacis numbers are often low until late in the season is that pesticides toxic to A. fallacis are used early in the season. Another phytoseiid species that apparently is capable of providing biological control of European red mite has been identified in commercial New York apple orchards. This predator is Typhlodromus longipilles.
Impacts
(N/A)
Publications
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Progress 01/01/90 to 12/30/90
Outputs
An impediment to biological control of mites in apples is destruction of naturalenemies through the use of chemical pesticides. Leafrollers frequently require control using insecticides toxic to mite natural enemies. Bacillus thuringiensis (Bt) is not toxic to mite predators and may provide effective leafroller control. Tests of Bt were conducted in large unreplicated, adjacent plots in 3 commercial orchards. A treatment consisting of Dipel mixed with 1/10th rate Asana performed best. Dipel alone performed as well as the best carbamate insecticide. Unfortunately, the low rate of Asana (1/10th rate) is still very toxic to the mite predator Typhlodromus pyri. The mite predator A. fallacis is hypothesized to move in and out of apple trees on a seasonal basis and ground covers are thought to provide an alternate habitat for A. fallacis. Ground cover composition may influence A. fallacis abundance. Experiments were conducted to study this relationship. Samples were
taken to estimate densities of European red mite (ERM) (Panonychus ulmi) and A. fallacis in an orchard with 3 ground cover treatments: 1) an 8-foot living mulch of crown vetch, 2) an 8-foot preemergent herbicide strip, and 3) mowed sod. A. fallacis and ERM densities did not differ among the 3 ground cover treatments. In the fall and winter, samples of ground cover and apple tree twigs were placed in Berlese funnels to extract predators. A. fallacis were found overwintering on the tree as well as in the ground cover.
Impacts
(N/A)
Publications
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Progress 01/01/89 to 12/30/89
Outputs
A study was initiated to elucidate the importance of orchard ground covers on the dynamics of Amblysieus fallacis (Acari: Phytoseiidae) in apple orchards. In each of three orchards, herbicides were eliminated from each of two plots consisting of 9 to 20 trees in order to foster the development of weedy growth beneath the tree canopy. Samples of vegetation were collected from these plots three times during the spring and early summer and placed in Berlese funnels to extract arthropods. Only 3 A. fallacis were recovered from these samples even though a control experiment showed that up to 70 percent of A. fallacis in herbaceous vegetation could be extracted using this procedure. A. fallacis populations did appear in the trees until late summer (around Aug. 10) and at this time there were no differences due to herbicide treatments. A second study was started to investigate the potential for recolonizing Typhlodromus pyri (Acari: Phytoseiidae) in apple orchards where
it currently is not found. Colony-reared T. pyri were released in 4 trees in a commercial orchard in early summer (June 10). These trees and adjacent trees were then monitored. T. pyri populations increased in the release trees to 0.32 adults per leaf in early September. No T. pyri were found in trees adjacent to the release trees.
Impacts
(N/A)
Publications
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Progress 01/01/88 to 12/30/88
Outputs
The toxicity of orchard insecticides, acaricides, and fungicides to several lifestages of Typhlodromus pyri and Amblyseius fallacis was examined using two laboratory assay methods, a closed petri dish and a leaf assay method. Lower or equal mortality occurred with the leaf method than with the dish method. High adult female mortality was observed for methomyl, oxamyl, dimethoate, methidathion, phosphamidon, fenvalerate, and formetanate hydrochloride. Chlorpyrifos only caused high mortality with T. pyri. Phasolone only caused high mortality with A. fallacis. High immature mortality occurred with dicofol, oxythioquinox, mancozeb, and chlorpyrifos. Only benomyl caused reproductive effects in A. fallacis. Phytoseiids were identified from western NY leaf samples taken from commercial orchards. A sharp increase in the incidence of A. fallacis relative to T. pyri in the recent survey compared to a 1974 survey indicates a species shift likely due to pesticide use.
Impacts
(N/A)
Publications
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Progress 01/01/87 to 12/30/87
Outputs
An investigation of the dynamics which occur between the mite predator Typhlodromus pyri and the European red mite, Panonychus ulmi was completed. This investigation consisted of field studies at three locations and development of a simulation model. Results clearly show that T. pyri is an effective biological control agent under New York conditions. Once established in an orchard, T. pyri will maintain P. ulmi densities at very low levels. T. pyri cannot, however, overtake an expanding P. ulmi population due to its relatively slow rate of increase. The utility of a previously developed prey-predator ratio sequential sampling plan was greatly improved by replacing counts of mites on leaves with presence-absence sampling. The new sampling scheme compares favorably to the older one in terms of OC and ASN function while also greatly reducing the time needed to make a classification.
Impacts
(N/A)
Publications
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Progress 01/01/86 to 12/30/86
Outputs
The spatial distribution of European red mite (ERM) and Typholodromus pyri (TP) were studied with the following results: a) leaf densities of ERM and TP are approximately independent; b) most variation in prey and predator densities occur on a between-leaf basis; c) Taylor's power law precisely describes the variance-mean relationship for ERM and TP; d) TP displays a strong thigmotactic behavior, but forages over an entire leaf surface. A sequential procedure was developed which simultaneously classified prey to predator ratios and the density of prey. The ability of TP to regulate ERM was assessed using a simulation model and field experiments. A ratio of prey to predator of ca. 7.5 and less results in biological control. Work was continued on validating proposed action thresholds for ERM.
Impacts
(N/A)
Publications
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