David Owens, Extension Entomologist, owensd@udel.edu
Potatoes
Scout for Colorado potato beetles. Warm weather during the previous week may allow them to fly into new plantings from further away. The neonics used at planting should provide about 45 days or so of control (some places may have more), we are right on that cusp of having to start thinking about them. Neonics should also provide considerably longer potato leafhopper protection.
Snap Beans
It may be time to begin thinking about potato leafhopper in snap beans. This is about the time of the year they move up into our area, and the recent above average temperatures will help them move. Thresholds are high, at 5 per sweep. I doubt we would see that many for another few weeks at the earliest.
Cucurbits
Striped cucumber beetles are rolling into fields now! This is about a week earlier than usual. Remember to check multiple locations throughout the field and field edges. Thresholds are two beetles per plant (watermelon) and 1-2 beetles per plant for other cucurbits. There are three ways to control them: neonicotinoid application via drip or foliar, carbaryl, or call your Extension entomologist to collect them all out of the field. Carbaryl is going to have a relatively short residual but is very efficacious. It may be enough though to disrupt the beetles aggregation pheromone and response. If using a neonicotinoid through the drip, remember to check your application rate against the label’s rate per 1000 ft row. If your row spacing is not on the label’s charts, an easy way to figure out how much material should be put down is to divide 43,560 by your row spacing. Seven ft is common and would give 6,223 row ft of drip. If using a product that has a rate of 10.5 fl oz, then 10.5/6223 = 1.7 fl oz product per 1000 row ft. The key here is that you use your bed spacing, NOT your bed width. Plot work performed in 2020 suggested that a drip treatment could reduce the emerging summer beetle population from the plants root system by at least 50%.
Sweet Corn
Begin scouting sweet corn for signs of cutworm.
Cole Crops
Scout for worms and for harlequin bugs. While the imported cabbageworm is the most common species (green with a velvety appearance) the other main cole crop pests are also active and can be more challenging to control To best preserve susceptibility to insecticides in the worm populations, particularly diamondback moth, use a treatment window approach. A treatment window is about a month period of time in which two insecticide modes of action are used, then rotated to a completely different set of MOAs. If using a Bt product, use high gallonage to achieve good coverage. I like Bt early when plants are small and good coverage is attainable. Bt also is not or minimally disruptive toward parasitic wasps that can destroy a large proportion of worms.