Vegetable Crop Insect Scouting

David Owens, Extension Entomologist; owensd@udel.edu

Cucurbits
Spider mites have been observed in a few fields at low numbers. Most mites have been observed near field edges immediately adjacent to other crops or woodlines. With the warm weather, I am beginning to find spider mites on edge-weeds such as pokeweed. Last year, every pokeweed plant I looked at by mid-July had large spider mite populations on it, and quite a few predators too. Spider mites can also ‘balloon’ into fields, meaning that a population can start in the field interior.

Our lab examined rye strips from several fields at the beginning of May looking for spider mites. We collected 20 row feet of the windbreak foliage, washed it in soapy water, and filtered the water. We did not observe spider mites in the rye samples. However, this is like looking for a tiny needle in a large haystack. One of the fields we sampled had spider mites early, likely coming in from the greenhouse. This can be reduced by keeping greenhouses weed-free when not in use, and especially in late summer through fall.

The table below lists the miticide active ingredients and their mode of action group for watermelon. There are generic formulations of some of the chemicals, this list is not meant to serve as an endorsement.

Please note that avermectin is in the same mode of action class as abamectin. Do not apply one right after the other. Also, some of these products will stop mite feeding quickly, but the mite will take a few days to die. If you have sprayed a field and see mites a couple of days later, wait another few days and resample. Also, many of these products have a long residual activity, meaning that if it is not active immediately on eggs, it should still be around once the eggs hatch. This year, we have plans to test these products at our research station. As always, read the label thoroughly for further guidance. Some products have restrictions on reapplication interval, and restrictions on consecutive applications. There are also requirements on some for spray adjuvants to avoid illegal residues. Good coverage is key for miticide efficacy, even on those that are translaminar. Also, be mindful of products that are in a tank-mix. For instance, Zeal may have some reduced efficacy when mixed with Boron, and stickers or ‘sticky’ fungicides can interfere with Agri-mek. Both Agri-Mek and Magister can be very toxic to pollinators, while Portal and Kanemite are not generally considered toxic to bees. All of the others advise caution.

Cucumber beetles are still moving into new plantings.

Sweet Corn
Sweet corn pheromone and blacklight traps are checked twice weekly on Mondays and Thursdays. By Tuesday and Friday morning, data is uploaded to our website: https://agdev.anr.udel.edu/trap/trap.php. For reference, action thresholds based off of blacklight and pheromone trap can be found here: http://extension.udel.edu/ag/insect-management/insect-trapping-program/action-thresholds-for-silk-stage-sweet-corn/. Moth counts continue to be elevated, and seem to be higher and a little earlier than last year. Thursday’s trap capture is as follows: