Vegetable Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Snap Beans – Stand, PLH, BLB

Scout for stand loss. Reports came in this week of unusually late seedcorn maggot damage. While checking stands, be on the lookout for both bean leaf beetle and for potato leafhopper. Leafhoppers cause hopperburn on plants – a yellowing around the leaf margins. They have moved into our area. The threshold is 5 per sweep.

Eggplant

Flea beetles have been very active on eggplant this year. In some cases, insecticide treatment appears to have not provided the expected control. There can be several reasons for this. Seedling drenches, seed treatment and even foliar treatment only provide a couple of weeks of control at best. This season we have had several bouts of wet, cool weather in which plants grow slowly if at all. This combines to both leach active ingredient out of the root zone as well as reduce plant uptake because plants are not actively growing. In other crops, high pressure can overwhelm seed treatments, particularly when adverse weather occurs. Our cool spring has started, in spurts, to give way to summer heat, possibly leading to a more intense migration period into the crop. We have several options for flea beetles, including pyrethroids, neonics, Torac, Verimark, and Botani Gard. If Colorado potato beetles are present, consider a non-pyrethroid. Also scout for two spotted spider mites. A study in the Marianas Islands with a related Tetranychus species suggested a threshold of 4-8 mites per leaf. Mites LOVE eggplant. Scout carefully.

Tomato

Scout for flea beetles and for two spotted spider mites, especially in high tunnels where the tomatoes have a full fruit load. Spider mite thresholds from North Carolina are 2-4 mites per leaflet on an upper canopy terminal leaflet.

Cucurbits

Continue scouting for striped cucumber beetle. Remember they aggregate in fields so portions of a field may not have large numbers while other portions may be defoliated by them. Also begin to scout for spider mites. Our nominal action threshold is to apply when mites reach 2 per leaf on half of the crown leaves sampled.

Sweet Corn

The earliest sweet corn may have just begun silking or is about to. As a reminder, we have a corn earworm pheromone and black light trapping network spread across Kent and Sussex counties. Traps are checked Mondays and Thursdays and data uploaded to our website by the next day. You can find our trap data and our spray thresholds at https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/pest-management/insect-trapping/. Many thanks to Dick Monaco, Morgan Malone, and Morgan Marzec for trap checking and data entry.

Trap counts from Thursday are as follows:

Keep in mind, our spray thresholds are a bit conservative. The most important period to control earworm is the first 10 days to 2 weeks of silking. One recommendation that is not on the website (I still need to update it) is to tighten spray intervals by 1 day when the temperatures are above 82 degrees. This is especially important late in the season under high pressure environments and especially when following a pyrethroid application. I am not convinced that with our conservative thresholds that it is entirely necessary following a Besiege or Elevest application.

I think of our season as 2 phase: before mid-July and after mid-July. After mid-July our moth pyrethroid susceptibility decreases significantly in our vial tests (we will have our first vial test data next week). Generally low to moderate populations tend to be easier to control, especially with our conservative spray schedule and I see little treatment differences in spray trials performed prior to August. After August, there can be very significant differences. In recent years, Hero at its HIGH rate has outperformed all others, followed by BaythroidXL which is as good as or slightly better than Brigade which is as good as or significantly better than Warrior II. The most effective and simplistic rotations in my trials have been Besiege or Elevest rotated with BaythroidXL. I tend not to apply much Lannate in my spray trials, and for producers who are concerned about its toxicity, trials last year indicated Intrepid Edge or Radiant + BaythroidXL would perform quite well, if a bit pricey. I also only tested those two at their high rates.

Elevest is a recent market introduction, consisting of chlorantraniliprole plus bifenthrin. In some trials it performs a little bit better than Besiege, and in other trials they are equal. It could help if you have stink bugs in the mix. Unless you have a significant amount of worm feeding in the tassel as it is being pushed out, or if armyworm is in the mix (usually not the case until sometime around early to mid-July), I do not see any benefit to a pre silk application.