Progress 08/01/04 to 07/31/07
Outputs
OUTPUTS: The twospotted spider mite (TSSM) is a key pest of vegetables in western and central North Carolina. Infestations are particularly problematic on tomatoes, where growers spend as much as $100 per acre to manage this pest. Little was known about the population dynamics of TSSM in relation to vegetables in this region of the state. The goal of this project was to better understand the area-wide population dynamics of TSSM so as to identify risk factors for mite infestations in individual fields, and to development strategies for minimizing acaricides use on vegetable crops. Specific objectives include: 1) identify factors contributing to the susceptibility of vegetable fields to infestation by TSSM; 2) determine the effect of late-season weed control in the border of tomato fields on overwintering populations of TSSM; 3) determine the mite density-yield relationship on sequential plantings of tomato. To accomplish these objectives, more than 100 field locations were sampled
over a three year period to determine mite phenology in tomato fields and surrounding crop (soybean, corn, strawberry, pepper, cucurbits) and non-crop (weeds) habitats. These data, along with tomato production practices associated with individual tomato fields (location, planting date, rotation, and pesticides applied) were subjected to multiple regression to identify factors important in predicting mite infestations on tomatoes. To more clearly understand the movement TSSM populations into and out of tomato fields, field studies were conducted to determine the distance of mite migration from tomatoes in the autumn. Finally, to examine the impact of mite infestations on the yield, quality and economics of early and late-planted tomatoes, economic threshold studies were conducted in field trials.
PARTICIPANTS: Individuals: James F. Walgenbach - principal investigator responsible for all aspects of project. George G. Kennedy - co-PI. David W. Monks - co-PI Elijah Meck - M.S and PhD student conducted research as part of thesis. Hourly employees - Tom Hoyt, Jason Livingston, Anna Hinshaw. Training development: Project providing training in IPM to one graduate student and three undergraduate students during summer months. Training of vegetable extension agents and producers occurred at field days.
TARGET AUDIENCES: Extension Agents, vegetable growers, pest control industry, agrochemical industry, and general public.
Impacts
A number of different factors were associated with high mite densities in tomato fields, including previous crop, acaricide use, insecticide use, and mite intensity in weeds surrounding fields. Acaricide use and mite intensity in the weeds were important factors associated with the maximum mite intensity in tomatoes. Year, location, planting date, and acaricide use were all important factors associated with the time it took for tomato fields to reach their maximum density. Upon further analysis, it was found that none of the dependent variables (year, location, previous crop, adjacent crop, planting date, acaricide use, insecticide use) were associated with seasonal mite intensity in weeds or mite intensity in weeds on the last two sample dates. However, previous crop and insecticide use were significant factors associated with mite intensity in weeds on the first two sample dates. Furthermore, seasonal mite intensity in weeds was significantly correlated with seasonal
and maximum mite intensity in tomato fields. While previous crop, current season insecticide use, and mite intensity in weeds were factors associated with mite intensities in the field, high overwintering mortality appeared to negate the effects of these factors; consequently it was not possible to predict in advance fields that were most susceptible to high mite infestations. Acaricides will likely remain a key management strategy in the near future, and the use of thresholds will be important to use these materials in a judicious manner so as to avoid resistance development. Two vegetation management techniques (herbicide and cultivation) plus an untreated control plot were established around senescing tomato plants. Twospotted spider mite dispersal was monitored by planting chickweed trap plants at 2, 6, and 12 m from the tomatoes. Sampling took place in the fall of 2004 & 2005 and the spring of 2005 & 2006. Only a small number of mites were collected in the 2004-2005 sampling
period, making it difficult to draw conclusions. The 2005-2006 sampling period showed that herbicide-treated soil facilitated mite dispersal in the fall, while there were no differences in mite populations among treatments in the spring, suggesting a high rate of overwintering mortality. Finally, TSSM threshold studies on tomatoes in 2006 and 2007 showed that mite populations built to higher densities on early vs. later planted tomatoes, and mite-induced fruit quality effects included reduced total yields and increased levels of gold flecking disorder. On early and late-planted tomatoes, total yields in the controls were reduced by as much as 31.1 and 15.7% compared to the low threshold treatment. In addition, net profits in the early planting were reduced from $14,663 in the low threshold treatment to $2,158/acre in the control. A provisional economic threshold level for twospotted spider mite on tomatoes is 3 mites per terminal leaflet.
Publications
- No publications reported this period
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Progress 08/01/04 to 07/31/06
Outputs
Studies were conducted on the population dynamics and management of twospotted spider mite in relation to vegetable crops in central and western North Carolina. To identify factors that contribute to mite infestations on tomatoes, 57 tomato fields were sampled at 2-week intervals to follow mite population buildup in tomato crops, adjacent weeds, and nearby fields of corn, soybean, and strawberries. Multiple regression analysis showed that the only factors associated with mite density was location - fields at lower elevation (275 to 325 meters) had higher mite densities than those at higher elevation (>600 meters). Mite densities in adjacent weeds or crops, previous crop in the field, and type of insecticides applied were not significant. An experiment was conducted to determine the impact of different soil management practices on the dispersal of mites from tomatoes to overwintering weeds in the fall. Mites dispersed at equal densities to trap crops of chickweed at 2,
6 and 12 meters from tomatoes when trap crops were surrounded by bare soil treated with herbicide or abundant weeds. However, mite dispersal to trap crops located 6 and 12 meters was reduced when trap crops were surrounded by soil cultivated every two weeks. Frequent soil cultivation may serve to reduce mite migration from tomatoes to overwintering weeds in the fall. But, high mite mortality during the winter months resulted in similar mite densities in all trap crops the following April. Studies to assess the impact of different mite densities on the yield and quality of tomatoes revealed that mites only affect yield, not quality of tomatoes. A provisional threshold level to dictate the need for miticides to minimize adverse effects of mites on yield was 3-8 mites per leaflet.
Impacts
Identifying overwintering sites of spider mites and the susceptibility of different fields to infestation and development of damaging populations will help to determine the risks associated with mite infestations in vegetables, and aid in reducing chemical input into the environment. This research will aid in helping to minimize chemical miticide applications to vegetables and reduce grower costs.
Publications
- No publications reported this period
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Progress 10/01/04 to 09/30/05
Outputs
Twospotted spider mite populations were monitored in a diversity of crops and non-managed habitats in the piedmont and mountainous region of western North Carolina, with the objective to determine the role of vegetables (primarily tomato) in the in the area-wide population dynamics of this pest. Mites overwintered in relatively low densities on broadleaf weeds and strawberries, and moved to vegetables upon senescence of these plants in May and June. There was a lag time in the buildup of mites on vegetables, with populations being highest from August to September. With the exception of one pepper field in the mountain region, mites infested all 25 tomato fields sampled, which included a diversity of planting dates and cultivars. Mite populations built to higher densities on early and late planted fields compared with early plantings (April and May), and were higher in the piedmont compared with mountain fields, due to the lower temperatures and higher rainfall in the
mountains. Bioassays to detect resistance to the miticide abamectin were conducted with a laboratory susceptible population and a field population collected from tomato fields sprayed frequently with this miticide, and none was detected. Field studies were also conducted in the autumn to determine the dispersal distance of mites from tomatoes to overwintering chickweed planted various distances from tomatoes. At the first sample in November, more mites were detected in weeds planted at 7 and 21 ft compared with 35 ft. Sampling of weeds in the spring (April) detected very few mites, indicating high mortality of mites during the winter months.
Impacts
Identifying overwintering sites of spider mites and the susceptibility of different fields to infestation and development of damaging populations will help to determine the risks associated with mite infestations in vegetables, and aid in developing cultural management programs. This research will aid in helping to minimize chemical miticide applications to vegetables.
Publications
- No publications reported this period
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