Muskmelon is grown on >70,000 acres in the United States, generating >$319 million [U.S. Department of Agriculture (USDA), 2014]. Direct marketing of muskmelon is well suited for diversified organic farms in the eastern half of the United States. The U.S. organic industry continues to expand, with organic food sales increasing nearly 8% in 2010 [Organic Trade Association (OTA), 2011] and valued at over $39 billion in 2014 (OTA, 2015).
In much of the eastern half of the United States, muskmelon growers rank the cucumber beetle/bacterial wilt complex as their most important pest problem (Bessin et al., 2003; Hoffmann, 1999). Striped and spotted cucumber beetles can cause direct feeding damage and vector E. tracheiphila, the causal agent of bacterial wilt of cucurbits. Bacterial wilt can reduce yields by 80% on unprotected muskmelon (Sherf and MacNab, 1986) and cucumber [Cucumis sativus (Latin, 1993)] and is also a serious threat to pumpkin (Cucurbita maxima), winter squash (Cucurbita sp.), and zucchini (Cucurbita pepo) (McGrath, 2001).
On conventional farms, insecticides are the primary tool for bacterial wilt control. Recommendations for timing of insecticide applications in conventional production vary from calendar-based timing beginning at plant emergence (Sánchez et al., 2013) to sprays based on cucumber beetle scouting thresholds. Unfortunately, the few insecticides available to organic growers are largely not highly effective against cucumber beetles.
Spunbond polypropylene rowcovers exclude cucumber beetles and other insect pests (Bextine et al., 2001; Perring et al., 1989; Saalau Rojas et al., 2011), thereby eliminating the need for insecticide applications during the protected period. Rowcovers are often used to accelerate crop development and protect against environmental extremes from transplant until flowers appear (Soltani et al., 1995; Taber, 1993). In IA, removing rowcovers at bloom temporarily suppressed bacterial wilt in muskmelon, but this effect was overcome once covers were removed and plants were exposed to cucumber beetles (Mueller et al., 2006). Interestingly, delaying rowcover removal in IA until 10 d after perfect flowers appeared resulted in bacterial wilt incidence of <20% at harvest compared with >80% without the 10-d delay (Saalau Rojas et al., 2011). However, to determine the value of this strategy to organic producers it must be field tested in regions with different climates and levels of bacterial wilt and cucumber beetle pressure. Pest exclusion must also be balanced with providing pollinator access, since muskmelon requires insect pollination and rowcovers exclude pollinators.
In addition to pest control, nutrient management can be challenging on organic farms (Clark et al., 1999; Pimentel et al., 2005), in part because nutrient sources generated on the farm, such as compost, release nutrients slowly. Nutrient availability is also unpredictable; for example, N mineralization rates depend on soil temperature, microbial activity, and organic matter incorporation (Richard, 2004). Combining organic nutrient sources such as compost with rowcovers can also increase yields by contributing to vegetative plant growth characteristics (Nair and Ngouajio, 2010).
The goal of the present study was to develop a coherent management approach for bacterial wilt and using compost for organic muskmelon production in PA, IA, and KY. We investigated the single and combined effects of various rowcover timing strategies and compost application rates on bacterial wilt incidence and marketable yield.
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