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

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

Summary

The causal agent of cucurbit bacterial wilt, Erwinia tracheiphila, is transmitted by striped and spotted cucumber beetles. Management strategies against bacterial wilt rely mostly on controlling vectors and are often ineffective and costly for organic farmers. In order to validate the effectiveness of row covers against bacterial wilt, 3 row cover treatments with different timing of removal were compared as follows: 1) row covers removed at anthesis; 2) row cover ends opened at anthesis, and then removed 10 days later; and non-covered control. Bacterial wilt was not detected in our field trial; however, the effect of row covers was assessed on yield, fruit quality, and earliness.

Objectives/Performance Targets

The aim of this project was to provide a feasible strategy to control bacterial wilt on muskmelon 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. 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.

Accomplishments/Milestones

A field trial comparing 3 row cover treatments was carried out at the Iowa State University Horticulture Research Station (Gilbert, IA) in 2010. Treatment subplots consisted of a non-covered control and 2 row cover treatments with different timing of removal: 1) row covers deployed at transplant and removed at anthesis; 2) row covers deployed at transplant and removed 10 days after anthesis. At anthesis, both ends of the row cover were opened to allow pollination. Although no bacterial wilt was detected in 2010, the effect of row on fruit number, quality, and earliness was compared. The analysis of variance shows that both row cover treatments had significantly higher fruit number and marketable weight than the control (no row covers). Fruit quality, measured by sugar content in fruit at harvest, was also significantly higher when row covers were implemented. Earliness was enhanced by row covers when compared to the control. This effect could be valuable for growers, since early harvests usually obtain premium prices in local markets. The total number of cull fruit due to small size was not significantly different in both row cover treatments. In previous trials using extended-duration row covers, it has been observed that delaying the removal by 10 days after flowering may significantly reduce the incidence of bacterial wilt. Our 2010 results suggest that in the absence of bacterial wilt, opening the ends of row covers during 10 days may provide sufficient access to pollinators in order to obtain adequate fruit size.
Three on-farm trials were carried out to demonstrate the use of extended-duration row covers. No bacterial wilt was observed in 2 of the 3 on-farm trials. The absence of bacterial wilt may be related to the low cucumber beetle numbers and their appearance relatively late in the growing season. However, at Growing Harmony Farm (Nevada, IA), extended-duration row covers provided an effective control against bacterial wilt. The added protection from row covers increased yield when compared to the uncovered control.

• Table 1. Effect of row cover treatment on muskmelon (ISU Horticulture Research Station, Gilbert, IA).

Impacts and Contributions/Outcomes

Management of cucurbit bacterial wilt is often challenging to organic growers in the Midwest. Organic strategies to control cucumber beetles transmission of bacterial wilt are often inefficient and costly to implement. In previous trials we have proven that row covers may be an efficient strategy in muskmelon production, however, the purpose of this project was to optimize this strategy under an organic production system. Our field results are encouraging, although there was no bacterial wilt present in our trials, we have provided useful and practical information about the added benefits of row covers in the Midwest. We have also demonstrated the use of extended-duration row covers at a field day with an attendance of over 100 growers (ISU Horticulture Research Station, Gilbert, IA). We have presented the results at a regional grower meeting (IFVGA Annual Meeting, Jan 30 2010, Des Moines, IA) and demonstrated the use of extended-duration row covers at 3 on-farm trials. The creation of a website focused on organic cucurbit production, has also provided access to information about our trials, results, and ongoing research (http://organiccucurbit.plp.iastate.edu/).

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