Progress 09/30/06 to 08/31/09
Outputs
OUTPUTS: New practices that were developed and evaluated as part of this project (use of green manure cover crops of Vicia vilosa or V. sativus x V. cordata, and use of resistance inducers to reduce Fusarium wilt and improve yield,) have been disseminated to growers in the mid-Atlantic and southeast regions of the U.S. Extension presentations were used to teach vegetable farmers in Maryland, Delaware and South Carolina. Extension articles have been posted to websites, and online and print newsletters, e.g. University of Delaware's Weekly Crop Update http://agdev.anr.udel.edu/weeklycropupdate/ . Additional outreach has been conducted through twilight and grower field days in three states. Plant Disease Management Reports (American Phytopathological Society) were published to rapidly disseminate the results to plant pathologists, horticulturists, extension specialists, extension educators, consultants and others in many states. During the project period, growers in Delaware, Maryland, and South Carolina trialed the use of hairy vetch on their farms. These "early adopters" reported good success with the new practice. A few concerns remain (growers sometimes have concern about carry over seed) however these early adopters have continued with the practice. PARTICIPANTS: Kathryne L. Everts is stationed at the Lower Eastern Shore Research and Education Center, which is a facility of the University of Maryland, located in Salisbury, MD. Dr. Everts has a joint appointment with the University of Delaware. Xin-Gen Zhou, who was a post-doctoral researcher at University of Maryland, Plant Science Dept., is now an Assistant Professor & Research Plant Pathologist of Rice and Bioenergy Crop Diseases at Texas A&M Research and Extension Center at Beaumont. Dr. Anthony P. Keinath and Dr. Richard L. Hassell are faculty at Clemson University. They are located at Clemson University's Coastal Research and Education Center, Charleston, SC. TARGET AUDIENCES: The target audience for this project was watermelon farmers in the mid-Atlantic and southeastern U.S. Farmers who classify their production as conventional, sustainable or organic will be able to use the practices that were evaluated. Organic growers will need to modify the method of killing the cover crop, and cannot use Actigard. However the use of cover crops is a common practice in organic and conventional production. The non-pathogenic F. oxysporum strain CS20 is a biological control that has the potential to be incorporated into many farm operations. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
There has been an increase in prevalence and severity of Fusarium wilt of watermelon in the eastern U.S. following the loss of the use of methyl bromide and the increase in production of seedless cultivars, which often lack resistance. Our project increased the knowledge of management of Fusarium wilt of watermelon with the following information: A green manure of hairy vetch (Vicia villosa) but not rye (Secale cereal) reduced Fusarium wilt of watermelon in Maryland. Hairy vetch also increased yield compared to rye. The reduction in wilt and increase in yield following hairy vetch was similar to that achieved with soil fumigant, K-Pam (Potassium N-methyldithiocarbamate). Stem infection by Fusarium oxysporum f. sp. niveum in greenhouse grown watermelon was reduced by Actigard and by non-pathogenic F. oxysporum CS-20, practices which induce the plant defense response. As Actigard and CS20 concentration increased, stem colonization decreased, although the highest rates of Actigard induced phytotoxicity. In field trials conducted in Maryland, wilt incidence was lower and yield was higher in plots treated with CS20 both years, with Actigard one year, and their combination (both years), compared to untreated controls. There was no additional benefit to use of both Actigard plus CS20 vs. either one alone. In South Carolina however, where wilt incidence was low neither resistance inducer reduced wilt. Actigard did increase yield in one year in South Carolina. Because hairy vetch is a host of root knot nematode, this project examined Cahaba White, a hybrid common vetch (V. sativus x V. cordata), which is a non-host of root knot nematode, as an alternative to hairy vetch. Biomass produced by Cahaba White was similar or greater to that produced by hairy vetch. In South Carolina, wilt incidence was lower after Cahaba White than after rye in one year, but did not differ among cover crops in a second year. In Maryland, both vetches reduced wilt incidence compared to rye in both years and improved marketable weight of fruit in one year. Cahaba White was as effective as hairy vetch in reducing wilt, and is recommended for fields that are infested with root knot nematode. In all experiments, wilt incidence of Revolution was lower than wilt incidence of Sugar Heart, and yield of Revolution was double the yield of Sugar Heart. Economic analysis indicated that growing a race-1 resistant cultivar on a cover crop of hairy or Cahaba White vetch would provide the best net return in both South Carolina and Maryland. Further research is needed to elucidate how location and environment influence the reduction in Fusarium wilt in watermelons grown after vetch. Research on management of the hairy vetch or Cahaba White vetch to reduce the development of volunteer plants in subsequent crops would also hasten the adoption of this practice.
Publications
- Keinath, A.P., Hassell, R.L., Everts, K.L. and Zhou, X.G. 2010. Cover crops of hybrid common vetch reduce Fusarium wilt of seedless watermelon in the eastern United States. Online. Plant Health Progress. doi: 10.1094/PHP-2010-0914-01-RS.
- Zhou, X.G., Everts, K.L., Keinath, A.P. and Hassell, R.L. 2009. Evaluation of cover crops and cultivar resistance for management of Fusarium wilt in seedless watermelon, 2008. Report 3:V090. doi: 10.1094/PDMR03.
- Zhou, X.G., Everts, K.L., Keinath, A.P., Hassell, R.L. and Fravel, D.R. 2009. Evaluation of resistance inducers and cover crops for management of Fusarium wilt in seedless watermelon, 2008. Report 3:V091. doi: 10.1094/PDMR03.
- Keinath A. P. and Hassell R. L.,2009 On-farm evaluation of hairy vetch and fumigation for integrated control of Fusarium wilt on seedless watermelon, 2008. Report 3:V035. doi: 10.1094/PDMR03.
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Progress 09/30/07 to 09/29/08
Outputs
OUTPUTS: Two experiments were conducted in Maryland and South Carolina during the reporting period. In Maryland the experiments were established at the University of Maryland's Lower Eastern Shore Research and Education Center, Salisbury. In South Carolina the experiments were conducted at Clemson University's Coastal Research and Education Center, Charleston. The following procedures were used in Maryland and similar procedures were used in South Carolina. The first experiment was designed to determine if the hybrid common vetch cultivar Cahaba White, which is resistant to southern root knot nematode, suppressed Fusarium wilt similar to the more widely-used cultivar Unspecified. The experiment was conducted as a split-plot design. Whole plots consisted of three cover crop treatments: rye, Cahaba White and Unspecified; subplots consisted of two triploid (seedless) watermelon cultivars with a different level of wilt resistance: Sugar Heart and Revolution, susceptible and moderately resistant to Fusarium wilt, respectively. Rye and both vetch cultivars were seeded in the fall of 2007 and disked and incorporated into soil in the spring. Fertilizer was applied before bedding based on the estimated nutrient contribution of each cover crop. Plots were covered with polyethylene mulch and watermelons were transplanted. In Maryland, the percent Fusarium wilt in plots where Cahaba White was incorporated was lower than in the rye plots, and was similar to that in plots where Unspecified was incorporated. However in South Carolina, where overall wilt incidence was low, percent wilt did not differ between cover crop treatments. A second field experiment to evaluate host plant resistance inducers Actigard (acibenzolar-S-methyl) and non-pathogenic Fusarium oxysporum strain CS-20 alone and in combination with a hairy vetch cover crop on Fusarium wilt also was conducted at both locations. The treatments were main plots, which were one of three cover crop treatments (Cahaba White, rye, or rye plus the fumigant K-pam (metam potassium)) and subplots, which consisted of 1) Actigard, 2) CS20, 3) both Actigard and CS20, and 4) nontreated control. Vetch and rye were seeded in the fall of 2007 and disked and incorporated into soil the following spring. Fertilizer was applied as in the previous experiment. K-pam was injected into the soil and covered immediately with polyethylene mulch. Watermelon Sugar Heart was seeded in a greenhouse. CS20 was added to treatment plug cells at seeding and 1 week prior to transplanting. The pollenizer SP4 was inter-transplanted between every other seedless watermelon plant within each row. Actigard was applied 1, 3, 5 and 7 weeks after transplanting. In Maryland, vetch green manure significantly reduced percentage wilt and increased fruit yield as compared with the rye control or the fumigation treatment. The combined use of Actigard with CS20 reduced wilt and increased fruit yield and CS20 alone reduced wilt incidence and had the highest fruit yield. However, results differed in South Carolina, where there were no differences among treatments due to cover crop or resistance inducer. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Several outreach activities were accomplished during the reporting period. In addition to the on-farm research trial described previously, talks were given at the Organic Farming Twilight Tour in Salisbury, MD, watermelon twilight tour at the University of Delaware Research and Education Center, Georgetown and at the University of Delaware, Newark. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
To increase outreach, an experiment was conducted on a commercial watermelon farm in Hampton County, South Carolina, in a portion of a 50-acre field in which Fusarium wilt was diagnosed in previous watermelon crops. Four treatments, fallow, hairy vetch, Wren's Abruzzi rye, and hairy vetch plus methyl bromide-chloropicrin, were arranged in a randomized complete block design in one field block (six planted rows between a drive row). The hairy vetch plus Telone C-35 treatment was located in an adjacent field block. All five treatments were replicated three times. Hairy vetch at 65 lb/A and rye at 120 lb/A were seeded in the fall of 2007 and incorporated in the spring by cultivating with a disk. Watermelon rows were planted on raised beds, which were covered with black polyethylene mulch. Selected plots were fumigated with 400 lb/A methyl bromide-chloropicrin (50/50) or 35 gal/A Telone C-35 as mulch was laid. The triploid watermelon cultivar 7167was planted in rows 1, 3, 4, and 6. A mixture of the seedless cultivar and equal numbers of two seeded diploid pollenizers, Mickey Lee and Summer Flavor 800, was planted in rows 2 and 5. Plants that had wilted or died were counted on 30 Apr and 20 May. Symptomatic plants of 7167 in rows that also contained the pollinizers were collected in the fallow, hairy vetch, rye, and hairy vetch plus methyl bromide-chloropicrin treatments in block 1. Discolored vascular tissue was cultured on Komada's medium. Fruit in rows 1, 4 and 6 were counted on 10 Jun. Counts of fruit per plot were divided by the number of surviving plants per plot to account for differences in survival. Fusarium wilt was very severe in the area of the field where the experimental plots were located. All 23 symptomatic plants collected yielded F. oxysporum. Many symptomatic plants in the nonfumigated treatments were completely wilted and stunted, whereas most plants in the two fumigated plots were normal size and only partially wilted. At the first rating, mean wilt incidence was higher in the four rows with only seedless watermelon than in the two rows with a mixture of seedless and pollenizer watermelons (paired t test, P=0.0075). Hairy vetch plus Telone C-35 reduced wilt incidence in all rows, whereas hairy vetch plus methyl bromide-chloropicrin reduced wilt only in the rows with a mixture of seedless and pollenizers. Wilt incidence increased greatly in the hairy vetch plus Telone C-35 treatment between 4 and 7 weeks after transplanting At the second rating, wilt incidence was lower in the hairy vetch plus methyl bromide-chloropicrin treatment than in all other treatments for rows with seedless watermelons and the mixture of seedless and pollenizers. Number of fruit set near the crown of plants was greater in the fumigated treatments than in the nonfumigated treatments. The grower had seeded the remainder of the field to hairy vetch. Yields of watermelon in that part of the field were approximately 40,000 lb/A, which exceeded expectations for yields in a field infested with F. oxysporum f. sp. niveum.
Publications
- Zhou, X.G., Everts, K.L., Keinath, A.P. and Hassell, R.L. 2008. Evaluation of resistance inducers and cover crop for management of Fusarium wilt in triploid watermelon, 2007. Report 2:V074. DOI: 10.1094/PDMR02.
- Zhou, X.G., Everts, K.L. and Fravel, D.R. 2008. Greenhouse evaluation of effective rate of Actigard and CS20 for management of Fusarium wilt in watermelon, 2007. Report 2:V073. DOI: 10.1094/PDMR02.
- Zhou, X.G., Everts, K.L., Keinath, A.P. and Hassell, R.L. 2008. Comparison of vetch cultivars for suppression of Fusarium wilt in triploid watermelon, 2007. Report 2:V072. DOI: 10.1094/PDMR02.
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Progress 09/30/06 to 09/29/07
Outputs
One greenhouse and two field experiments were conducted during the reporting period. The greenhouse experiment was conducted to determine the effective rates of Actigard and CS20 (nonpathogenic F. oxysporum) for suppression of Fusarium wilt of watermelon. The experiment was a split-plot design, where the main units were four rates of Actigard (acibenzolar-S-methyl, 0, 20, 100 and 500 ppm); and subunits were four concentrations of CS20 (0, 1000, 10,000, 100,000 CFU/g soil). Actigard 38WG was applied to the foliage until run off at 2 and 4 weeks after seeding; a conidial suspension of CS20 was added into soil at the time of seeding and 3 weeks after seeding. Two sub-experiments were conducted with different pathogen inoculation methods and plants that were not inoculated with the pathogen served as negative controls. Symptoms were evaluated using a stem colonization assay. At 3 weeks after inoculation, three plants were collected from the remaining live plants, their
lower stem sections were sampled, and homogenized tissue was serially diluted and placed on Komada's medium. A field experiment was conducted to determine if the hybrid common vetch cultivar Cahaba White, resistant to Southern root-knot nematode (Meloidogyne incognita), had a similar effect as the Unspecified cultivar, susceptible to root-knot nematode, for suppression of Fusarium wilt in watermelon. The experiment was conducted as a split-plot design with four replications. Whole plots consisted of three winter cover crop treatments (rye, vetch cultivars Cahaba White and Unspecified); subplots consisted of two triploid watermelon cultivars (Sugar Heart and Revolution, susceptible and moderately resistant to Fusarium wilt, respectively). Rye (140 lb/A) and both vetch cultivars (30 lb/A) were seeded on 10 Oct 06. On 9 and 16 May 07, rye and vetch cover crops were disked two times, and incorporated into soil. Before bedding, fertilizer was applied to plots based on cover crop biomass
and N content. Plots were covered with black polyethylene mulch and a pollinizer was inter-transplanted between every other seedless watermelon plant within each row. A second field experiment consisted of main plots, hybrid common vetch cv. Cahaba White, rye, and rye plus the fumigant K-pam; and subplots, Actigard, CS20, both Actigard and CS20, and nontreated control. Vetch and rye cover crops were planted, incorporated and fertilized as described previously. K-pam (metam potassium) was injected into the soil and covered with mulch. Sugar Heart was seeded in a greenhouse on 2 May. At seeding and 1 week prior to transplanting, 3 ml of a conidial suspension of CS20 (2 x 1,000,000 microconidia/ml) was added into each cell. Watermelon seedlings and pollinizers were transplanted as described previously. Actigard 38WG was applied at 0.33, 0.5, 0.5 and 0.75 oz/A at 1, 3, 5 and 7 weeks after transplanting, respectively, using a tractor-mounted sprayer. For field experiments the percent of
plants showing symptoms of Fusarium wilt was assessed on 13 Jun and 18 Jul. Total fruit yield was weighed on 13 Aug, and sugar content in three fruit from each plot was determined with a hand-held refractometer.
Impacts
Phytotoxic symptoms (yellowing lesions on sprayed leaves and stunted plants) were observed in the greenhouse experiment on plants sprayed with Actigard at 500 ppm (equivalent to 3 oz/A) but not at lower rates. All rate treatments of Actigard except at 20 ppm, equivalent to 0.12 oz/A, in experiment 1 significantly reduced stem infection by F. o. f. sp. niveum in both experiments when compared to the nontreated control. However, the high rate (100 ppm, equivalent to 0.6 oz/A) was more effective than the low rate (20 ppm, equivalent to 0.12 oz/A). Similarly, all concentrations of CS20 significantly decreased stem colonization relative to the nontreated control in both experiments. The greatest CS20 concentration (1 x 100,000 CFU/g soil) resulted in the least pathogen CFU followed by the treatment of 1 x 10,000 CFU/g soil. Actigard at a rate between 0.12 and 0.6 oz/A and CS20 at the concentration of 1 x 1000 CFU/g soil or above could be safe and effective to suppress
Fusarium wilt in watermelon. In the field experiment to compare Cahaba White and Unspecified hairy vetch, on both 13 Jun (early season) and 18 Jul (late season), percent wilt in Cahaba White vetch plots was significantly lower than that in the rye control plots and was similar to the Unspecified hairy vetch treatment. The partially resistant watermelon cultivar Revolution had a lower level of Fusarium wilt compared to the susceptible cultivar Sugar Heart. A similar effect of these treatments was observed on marketable fruit yield, although the fruit yields were generally low. The Cahaba White cultivar treatment had a yield level similar to the Unspecified cultivar treatment, which was significantly higher than the rye control. Sugar content in watermelons did not differ among treatments. The Cahaba White cultivar of common vetch was as effective as the Unspecified cultivar of hairy vetch for suppression of Fusarium wilt in triploid watermelon. Fusarium wilt was severe in the second
field trial. However, vetch green manure significantly reduced percent wilt and increased fruit yield as compared with the rye control. These effects were comparable to improvements achieved by K-pam. The use of Actigard, CS20 and the combination significantly decreased percent wilt on 18 Jul (late season) but not on 13 Jun (early season). These treatments did not improve fruit yield. Sugar content in watermelons did not differ among treatments.
Publications
- No publications reported this period
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