David Owens, Extension Entomologist, owensd@udel.edu
Sweet Corn
Scout early whorl stage corn for armyworm – both fall and yellow striped. Thresholds for whorl damage are 15% active infestation. You may see windowpaning but not find a larva.
Brown stink bugs are present in some fields, particularly near weedy edges. Of the materials labeled for ear protection, bifenthrin and a pyrethroid/methomyl mix are the most effective options towards control. Bifenthrin has the most stink bug activity among the pyrethroids, and can be found in Brigade (and other generic formulations), Hero, and the diamide premix Elevest.
We have not been able to test many moths in our vial tests this week due to low flight numbers. Last week we were at close to 45% survivorship in pyrethroid-treated vials. Do not use a pyrethroid alone to manage corn earworm.
Thursday trap counts have decreased a bit in most of our trap locations:
| Trap Location | BLT – CEW | Pheromone CEW |
| 3 nights total catch | ||
| Dover | 1 | 27 |
| Harrington | 1 | 65 |
| Milford | 0 | 26 |
| Rising Sun | 0 | 25 |
| Wyoming | 0 | 3 |
| Bridgeville | 2 | 41 |
| Concord | 1 | 24 |
| Georgetown | 1 | 12 |
| Greenwood | 1 | 36 |
| Laurel | 2 | 41 |
| Seaford | 1 | — |
| Millsboro | 2 | 12 |
| Lewes | — | 33 |
Squash
Squash bugs are very active right now, and squash vine borer is a continued threat, particularly in smaller plantings. Squash bug thresholds are 1 egg mass per plant. If upon a casual inspection you see an egg mass on every other or every third plant on the upper side of the leaf, you most likely have many more that are present underneath of the leaf. This threshold is also on a per plant basis, not a per leaf basis. While squash bugs are known to transmit a yellowing disease to squash, it appears that this is extremely uncommon. Labeled materials include carbaryl, various pyrethroids, acetamiprid, and Sivanto. Use of other neonicotinoids should be avoided at this stage due to bee toxicity, and especially towards cucurbit specialists like squash bee. Eggs are almost impossible to kill with an insecticide, we need to wait until they hatch before we treat. Eggs take about 10 days to hatch. During that time, you may have other egg masses laid; thus these insects sometimes require multiple applications to control. Adults like to hide near the base of the plants, in the mulch or weeds, and as such can sometimes be difficult to find and to contact with treatment. Assail and Sivanto are unlikely to flare up mites in the same way that carbaryl and most of the pyrethroids can. Sivanto is primarily an aphid material. Assail is also very good on cucumber beetles. The disadvantage comes with managing for squash vine borer: only pyrethroids are effective. Furthermore, melon aphids are starting to move into fields, and by frequent pyrethroid usage alone for squash bug or vine borer, you might flare up aphids. There are many good aphid materials, including diamides, Beleaf, acetamiprid, Sivanto, Torac, PQZ, and Sefina.
Watermelon
The entire pest complex is now present in watermelon fields, with most being generally low in abundance. Pay special attention to fields that are currently being harvested, as the harvesting process stresses plants out and can lead to extremely rapid mite population increases and impact to plants. Watch out for blocky areas of yellowing. First-generation striped cucumber beetle emergence from the soil seems to have peaked. These beetles can feed on the rinds, and if severe enough, can render a melon unmarketable. Various species of worms are active, including yellow striped armyworm and corn earworm, both of which can be aggressive rind feeders. Finally, aphids are beginning to move into fields. It is very unlikely that aphid populations will increase to the point of causing economic damage, but scouting is still extremely important.