David Owens, Extension Entomologist, owensd@udel.edu
Cucurbits
All major cucurbit pests are either active or soon will be. Cucumber beetles continue to be active, although perhaps with somewhat less intensity than in previous years. Watermelon thresholds are between 2-5 beetles per plant. If injecting product through the drip, pay special attention to label rate conversion charts for guidance on how much product to inject per 1000 ft based on your row spacing. This is important so as to not under-treat. Although I have not yet received reports of much mite activity in melon plantings, recent hot, dry weather will force them out of perennial or early season weeds earlier. Also, be sure to check any late transplants that are still on wagons or in greenhouses. We have seen more mite activity this week in greenhouses than we did at the beginning of May. Recent reports from Virginia indicate squash bugs are active in summer squash, and we will have enough degree days this week for squash vine borer to emerge. Squash bugs tend to hide during the day, seeking shelter in planting holes and under residue. Look for their coppery egg masses underneath leaves and on leaf stalks. Time a treatment for after egg hatch. Squash vine borer is probably the hardest of the cucurbit pests to manage. It lays single eggs, usually on the stem or leaf stalk. Once inside the plant, the caterpillar is largely protected. Thus, weekly sprays focused at the stem are often necessary in small plantings of winter squash. When the worm has invaded the stem, you may see a single leaf wilt, or you may see a small amount of frass near the entry point (often near a leaf stalk). Other management options include dissecting out the worm and covering the nodes with soil to encourage adventitious root development.
Solanaceous Crops
Continue scouting for Colorado potato beetle (potato, tomato, and eggplant), flea beetles (tomato, eggplant), and potato leafhopper (potato). See last week’s post for threshold and treatment suggestions.
Sweet Corn
Sweet corn will soon be silking. Right now, our traps are catching low levels of moths, but this will increase. We typically see an early to mid-June peak in activity. Until that happens, first sprays might not be necessary until 50% first silk. During the August and September moth flights, I time my first treatment for 10% first silk. Next week we will be reporting trap counts in the WCU. Trap counts along with spray thresholds can also be found at https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/insect-trapping/. Be sure to scout fields with emerging tassels for signs of larval corn earworm infestation. Thresholds are near 15% infested tassels. Larvae that are pushed out with the developing tassel may damage the developing ear and require a pre-silking spray. We have several additional pre-silk spray options including Lorsban, Intrepid, Intrepid Edge, and Avaunt.
Early in the season, we tend to see greater pyrethroid susceptibility, but this rapidly changes in July. That said, last year we had a greater percentage of moth survivorship early, likely impacted by the mild 2019-2020 winter. We will be resuming vial tests soon. Please be aware that while susceptibility tends to be greater during the early season, pyrethroids cannot necessarily be relied upon alone to give acceptable control. In 2019 and 2020, beta-cyfluthrin provided greater ear protection than other pyrethroids tested in Georgetown. However, Dr. Tom Kuhar’s tests at Painter, VA revealed a different pattern, with Hero providing the best level of efficacy among the pyrethroids tested. Be sure to follow label guidance in terms of application number and amount for the active ingredient bifenthrin.
Cole Crops
As a general reminder, thresholds for cole crops are 5% infested plants during head formation. Pay special attention to pre harvest intervals. Several worm products have pre harvest intervals of 3 days or less, but others have PHIs of 7 days. Pay special attention to labeled pests and what worms are currently in your field. Some products have reduced efficacy for different species (ex cabbage looper). The Vegetable production guide also lists Spear Lep with a 0-d PHI. This product needs to be tank mixed with a Bt for efficacy. If treating with a translaminar active (such as the group 28 diamides and spinetoram), do not use a sticker adjuvant.