Extended-duration row covers to suppress bacterial wilt on muskmelon: optimizing a new management strategy for organic growers

View the project final report

• 2010 annual report

Commodities

• Fruits: melons

Practices

• Crop Production: application rate management
• Education and Training: demonstration, extension, networking, on-farm/ranch research, participatory research
• Pest Management: cultural control, disease vectors, integrated pest management, mulching - plastic, row covers (for pests)
• Production Systems: organic agriculture

Field experiments using different row cover removal strategies on organically-grown muskmelon and butternut squash were carried out in 2010 and 2011 in Iowa. Little or no bacterial wilt was observed both years. In 2010, in the absence of bacterial wilt, row cover treatments reduced the need for fungicide sprays, increased yield, and enhanced earliness of muskmelon. This effect was not observed in 2011. On squash, season-long row covers and no row covers obtained the highest yield. In addition, six on-farm trials were carried out to demonstrate the use of delayed row cover for bacterial wilt management.

Introduction:

Cucurbits are among the most important vegetable crops in the U.S. In 2007, cucumbers, melons (including muskmelon), pumpkins, and squash were produced in approximately 50,500 ha in the U.S. (FAO, 2008), with a farm gate value exceeding $400 million a year. Striped (Acalymma vittatum) and spotted (Diabrotica undecimpunctata) cucumber beetles are the most important insect pests of melons and cucumber in the eastern half of the U.S. Cucumber beetles not only inflict direct feeding damage, but also vector the bacterium Erwinia tracheiphila, the causal agent of bacterial wilt. Bacterial wilt causes up to 80% crop loss in muskmelon (Latin, 1993) if the beetles are not controlled effectively. The bacteria are harbored in the beetle’s digestive system (Garcia-Salazar et al., 2000) and transmitted through direct contact of the mouth parts and frass (feces) to feeding wounds on stems and leaves.

Once in the plant’s vascular system, E. tracheiphila multiplies and blocks the water flow, causing wilting and death. No resistant varieties of muskmelon have been developed. Therefore, growers need to prevent the beetles from feeding and inoculating plants. Both conventional and organic growers struggle to contain bacterial wilt when beetles are numerous. The situation is especially challenging for organic growers, since organic insecticides are often ineffective deterrents of cucumber beetles. Many organic vegetable growers in the Upper Midwest avoid growing muskmelon after discouraging experiences with bacterial wilt. Clearly, there is a pressing need for alternative strategies that can deliver effective control of this devastating insect-disease complex.

Deploying row covers to provide a sheltered environment from transplanting until anthesis (start of flowering) has been a standard practice for many Midwest muskmelon growers for decades. Field experiments at ISU showed that this practice could delay the onset of bacterial wilt (Mueller et al., 2006), but did not provide acceptable season-long suppression. Recently, ISU researchers borrowed an idea that had been pioneered in Canada and Africa (Gaye et al., 1991; Vassiere and Froissart, 1996): extending the length of time that the muskmelons remain under row covers. By delaying row cover removal until 10 days after anthesis, the ISU team discovered that bacterial wilt could be suppressed throughout the remainder of the growing season (Jesse et al., 2007) without using any chemical insecticides. Pollination during the extended row cover period was accomplished by either opening the ends of the row covers or inserting a bumble-bee box under the cover. When transplanting was delayed several weeks due to wet weather, however, removing row covers at anthesis controlled wilt as effectively after 10 days (Saalau et al., 2008). These results suggest that timing of transplanting may be critical in gaining the benefits of the delayed row cover removal strategy, probably due to timing of vectoring by the cucumber-beetle vectors. This project will perform the additional experiments necessary to develop grower guidelines for consistent success.

The aim of this project was to provide a feasible strategy to control bacterial wilt and other insect pests on muskmelon and butternut squash in an organic management system. The first objective compared the use of row covers with different times of removal to prevent the incidence of bacterial wilt on both crops. The second objective was to involve organic growers in on-farm trials and demonstrate the use of extended duration row covers on cucurbits. Trial results were communicated to growers by presentations at a regional grower meeting, a field day, creation of a website, and newsletter publications.