David Owens, Extension Entomologist, owensd@udel.edu
Early Transplant Loss Culprits
Both insects and diseases can cause rapid wilting of young transplants. The most likely insect culprits would be seedcorn maggot and wireworm. Wireworm is going to be very patchy, hitting a plant here and there, concentrated on heavier soil areas of fields. You will see tunnelling just below or at the soil line. Seedcorn maggot would generally be more uniform across a field, the stems below ground would have a swollen appearance, and if you open the stem up, the inside is going to look shredded, hollow, and off-color. Every now and then pavement ants can also cause problems. You would see tunneling in the stem, girdling at the soil line, and evidence of ant activity at the base of the plant. Last year, a report came in of suspected wireworm damage to transplants. The farmer dug up a wilting transplant and found a wireworm in the hole. However, the culprit was disease. The damage was uniform, consistent, and no signs of holes or chewing on the stems. Wireworms are going to be more inconsistent. A report came in earlier this week of wireworm damage to melon transplants. Imidacloprid tray drenches are for aphid management only and should be factored in when making later chemigation applications.
For instance, Admire Pro has a tray drench rate of 0.44 fl oz/10,000 plants, or for melons, about 3 acres worth. This is considerably lower than a chemigation max rate of 10.5 fl oz per acre. The label is a bit ambiguous as to whether or not to penalize a chemigation rate if a tray drench had been used. If we err on a conservative side, we can tray drench and then apply a maximum of roughly 10.35 fl oz per acre in the drip line. One could also use Platinum instead. I don’t know if this would help with wireworm, and it does seem a bit early for cucumber beetle efficacy. Another possible option would be bifenthrin.
For ants, there are various ant baits on the market. If you have to deal with ants, be sure to look for something labeled for pavement ant. A few years ago, we tested an imidacloprid drench on ants that were feeding on transplants. It worked, but a proof-of-concept idea is a far cry from saying it would work if injected into drip lines if ants were to be a problem.
Potatoes
Colorado potato beetle is active and moving into fields. Adults fly once the daily high temperature is near 80F. Based on Tom Kuhar’s work on the Eastern Shore, we can expect about 50 days of control from a neonic, and perhaps a bit longer from a diamide. Any field that did not receive an insecticide at planting should be scouted for CPB. Look for the striped adults and the bright orange egg clusters laid on the underside of leaves. Thresholds are 1 adult per stem or 50 adults per 50 stems. Also, if a field was treated with a diamide, you will want to scout for potato leafhopper towards the later half of next month.
Asparagus
Scout asparagus for asparagus beetle activity, especially with warm weather allowing beetles to be active. The threshold is 10% spears with beetles or 1-2% of spears with eggs.
Tomato/ Eggplant
One of the greater threats to young tomato and eggplant is flea beetle. Thresholds for small eggplant are 2 beetles per plant. Neonics, Pyrethroids, Verimark, Torac, Botaniguard, and spinosyns (Entrust, Radiant) are effective on flea beetles.
Cole Crops
Continue scouting young broccoli, cabbage, and napa cabbage for worms and for flea beetles. The threshold for young plants is a 20% infestation; that increases a bit as plants grow vegetatively. When plants are young and when caterpillars are young, B.t. should provide excellent control. Flea beetles are typically an early spring, cool weather pest. Thresholds are 1 beetle per transplant or 5 per 10 plants during cotyledon/first leaf stages. There are several effective products for flea beetles, most of which have cross-efficacy with other cole crop pests. Pyrethroids, Torac, and Verimark have activity on cabbage maggot, which should be active now. Those three products are also effective on cabbage whites, and Torac and Verimark are effective on diamondback moth (assuming your local population is not resistant to them). The main worm threats for right now are diamondback moth and imported cabbageworm.