However, some symptomatic or asymptomatic immature plants may collapse suddenly in the middle of the season or just after fruit set. Typically, all the leaves turn yellow within a few days, starting about a week or two before harvest. Terminal leaves stand erect, fail to expand, and the margins curl inwards. Older leaves develop scorched margins and may die. The phloem in the crown and lower stem turns honey-colored. Eventually, the root begins to decompose, a process that is hastened by secondary rot organisms, and the whole plant begins to decline and die. Watermelon fruit turn yellow as the leaves begin to discolor. Other fruit usually fail to show symptoms.
It is critical to control early-season adult squash bugs as they colonize the field to successfully manage this disease. Insecticide applications should target young seedlings (< 3-5 true leaves) as soon as squash bugs are present on the plants. New generation synthetic pyrethroids (i.e. Capture) tend to work better than most other materials to control the squash bug. Spraying seedlings with synthetic pyrethroids should also control cucumber beetles and bacterial wilt. Thionex may also be effective on the squash bug and cucumber beetle. Sevin is no longer effective for squash bug control in CT. Since most fruit is not affected, fruit from infected pumpkins, winter squash, cantaloupe, or muskmelon vines should be harvested and marketed early to avoid crop loss.
In Texas, many growers have successfully used early-planted straightneck summer squash ('Lemon Drop'or 'Hyrific') as a trap crop in the border rows of their watermelon fields to attract and control squash bugs to manage CYVD.
Trap crop plants should be 2-3 weeks older than the main crop to attract the bugs. One researcher said that up to 100% of the bugs will be attracted to the border rows and killed by insecticide applications, and that the technique has almost eliminated CYVD in his region over the past 5 years. This trap crop technique is remarkably similar to the perimeter trap crop system New England growers have been using to control cucumber beetles and bacterial wilt on cucurbit crops. Squash bugs are most attracted to Hubbard squash, summer squash, pumpkins, watermelons, muskmelons, cucumbers, and butternut squash in decreasing order. Using our existing perimeter trap crop system, with early-planted 'Blue Hubbard' around later planted pumpkins (or other cucurbits), may control four pests (squash bugs & CYVD, cucumber beetles & bacterial wilt) with as few as one border spray. Time the trap crop spray just prior to main crop emergence, and if a second application is needed, at the first true leaf stage of the main crop.
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T. Jude Boucher, University of Connecticut