On-Farm Use of a Hybrid Vetch Cover Crop to Reduce Fusarium Wilt in Seedless Watermelon

View the project final report

• 2007 annual report

Commodities

• Fruits: melons

Practices

• Crop Production: cover crops, application rate management, tissue analysis
• Education and Training: demonstration, extension, on-farm/ranch research, participatory research
• Farm Business Management: budgets/cost and returns
• Pest Management: chemical control, cultural control, eradication, integrated pest management, mulching - plastic
• Soil Management: green manures, organic matter

Fusarium wilt is the most wide-spread, damaging soilborne disease of watermelon in the South. Cropping the same fields again and again to watermelon without rotation or with short rotations selects the specialized form of the soilborne fungus Fusarium oxysporum, F. oxysporum f. sp. niveum that attacks watermelon. Because this fungus lasts indefinitely in infested soil, It can reduce the yield, acreage, and economic return of watermelon crops, both crops grown now and those planted in the future. Although hybrid seeded cultivars resistant to race 1 were useful in the past, the watermelon market has shifted to seedless cultivars, which are susceptible to Fusarium wilt.
A new management tactic for Fusarium wilt is the production of watermelon following a fall-planted hairy vetch cover crop that is killed in the spring and turned into the soil as a green manure. One problem is that hairy vetch is a good host of Southern root-knot nematode (Meloidogyne incognita), the predominant root-knot species in the South. However, a hybrid cultivar of common vetch ‘Cahaba White’ (V. sativa x V. cordata) is a poor host and so is resistant to Southern root knot nematode. 'Cahaba White' vetch will be tested for suppression of Fusarium wilt on a commercial seedless watermelon farm in Fairfax, SC.
This project directly includes three elements of sustainability: cover crops, integrated pest management, and nutrient management. It also fits under two of the three goals of sustainable agriculture with the potential to increase environmental stewardship and farm income.

In this project we will use the seedless watermelon cultivar ‘Sugar Heart’, which is susceptible (91% wilt) to all races of FON. The O’Neal’s have grown ‘Sugar Heart’ for a number of years. Results with this susceptible cultivar can be transferred to all farms infested with FON regardless of which race of FON is present on a given farm.
We will compare ‘Cahaba White’ hybrid vetch with rye (the negative control) for suppression of Fusarium wilt. The project will be done on Coosaw Farms, Fairfax, SC, in a field naturally infested with FON. Each plot will be three rows wide (8-ft spacing between rows) and 200 ft long. The three treatments and four replications will be laid out in a randomized complete block experimental design. The three treatments will be:
1) rye, the negative (no effect) control treatment expected to have the highest level of Fusarium wilt of all three treatments;
2) ‘Cahaba White’ hybrid vetch; and
3) vetch plus fumigant, a treatment suggested by the cooperating grower (phone conversation on 2 November 2006).
These treatments will allow us to find out:

i) the contribution of vetch to control of Fusarium wilt by comparing vetch with rye;
ii) the contribution of the fumigant by comparing vetch plus fumigation with vetch alone; and
iii) the contribution of vetch plus fumigation by comparing vetch plus fumigation with rye.
The research technician assigned to this project will lay out the field plots in late August 2007 and supervise seeding of the cover crops and incorporation. The cooperating grower will seed vetch and rye in early September 2007, at 65 lb/A and 30 lb/A, respectively. In late November 2007, the grower will incorporate the vetch and rye by flattening them, and disking to a depth of at least 6 inches. Rye plots will be worked before vetch plots to avoid mixing soil between treatments. Raised beds will be shaped, and a single drip irrigation tube will be placed in the center of the row. The beds will be covered with black polyethylene mulch. Methyl bromide fumigation will be applied to one-half of the vetch plots.
In March 2008, three-week-old triploid watermelon seedlings will be planted into the plots under supervision of the research technician. The diploid pollenizer (source of pollen) ‘SP-4,’ a watermelon that does not produce marketable fruit, will be planted in the row between every fourth watermelon transplant. The cooperating grower will spray the plots as needed with the fungicides Pristine alternated with mancozeb or chlorothalonil to control gummy stem blight and other foliar diseases, so that they do not interfere with the yield of watermelon.
The amount of Fusarium wilt will be checked and recorded three times during the 2008 growing season. Ripe fruit will be harvested three times, and weight and number of fruit will be measured and counted. Wilted vines will be collected during the harvest period and cultured in the laboratory to confirm the presence of FON in each plot that has symptomatic vines. In fall 2008, greenhouse tests with three differential watermelon cultivars will be done to identify the race of each FON isolate (Egel et al., 2005). The cost and economic return of each treatment will be calculated using a partial budget approach, a simplified method in which only the inputs unique to each treatment are used to calculate the cost of production (Estes et al., 1985).
Soil samples will be collected three times from each of the 12 plots: 1) fall 2007 when cover crops are planted, 2) spring 2008 when watermelon is transplanted, and 3) summer 2008 at the end of the project. We will count the number of Fusarium colonies that develop from tiny amounts of a soil suspension spread on culture medium that favors growth of Fusarium oxysporum (Komada, 1975). From the same soil samples, the number of nematodes will be counted and the total nitrogen content determined at the Clemson University Agriculture Service Laboratory.
The following data will be analyzed statistically: Fusarium wilt percentage at each of the three ratings, area under the disease progress curve (a sum of all ratings over time), fruit weight, number of fruit, number of Fusarium colonies recovered from soil at three samplings, and change in number of Fusarium colonies between samplings 1 and 2, 1 and 3, and 2 and 3.