David Owens, Extension Entomologist, owensd@udel.edu
Cucurbits
Squash vine borer and Squash bug continue to attack summer squashes. Treat for squash bug when there is an average of 1 egg mass per plant once egg masses begin hatching. You may have a staggered egg cluster age, so it may take 2 applications to achieve adequate control. The pyrethroids will also help reduce squash vine borer damage. Be sure though to scout for aphids to ensure that they are not increasing because of the pyrethroids.
On watermelons, rind feeding is becoming a concern. Photos were sent earlier this week of cucumber beetle larva and a caterpillar that looked suspiciously like melonworm or pickleworm causing rind injury. Spider mites are also present in most plantings and with hot dry weather, their populations can increase up to 10x per week. Pyrethroid and Carbaryl application will make them worse. Avoid unnecessary pyrethroid applications. Cucumber beetle adults will probably begin appearing at some point during this week but may not be a concern until after mid-July. Insecticide seed treatment should provide sufficient cucumber beetle control in recently planted pumpkins.
Sweet Corn
Moth counts continue to decline, most sites are suggesting a 4-day spray schedule, and some even a 5 day. 5 days makes me very hesitant to recommend. If the previous application contained a diamide and the crop is not in the first 7 days of silking (silks are aging), then it may well be sufficient, otherwise, a 3- or 4-day interval should provide excellent control.
Spider mites have been observed in some fields. There are no thresholds for them listed in the MidAtlantic Production Recommendations guidebook as damaging populations are very uncommon. Some state extension services recommend treating only young corn less than 4 feet tall if small colonies are found on the lower leaves throughout the field. We only have two options: Zeal and Oberon. Oberon has a 4-day PHI, Zeal has a 21 day. If stippling and colonies are observed on husk leaves or ear leaves, control may be warranted on fresh market sweet corn. Keep overhead irrigation up. While irrigation is not a silver bullet when it comes to spider mites, it does help by reducing somite reproduction.
By the way, if any of you know someone who needs rebar for a project, let me know and I can get them one without having to take one of my trap stands!
Thursday trap counts are as follows:
| Trap Location |
BLT CEW |
Pheromone CEW |
| 3 nights total catch | ||
| Dover | 1 | 7 |
| Harrington | 0 | 7 |
| Milford/Canterbury | 0 | 15 |
| Rising Sun | 1 | 3 |
| Wyoming | 0 | 0 |
| Bridgeville/Redden | 0 | 4 |
| Concord | 1 | 0 |
| Georgetown | 0 | 1 |
| Woodenhawk | 0 | 5 |
| Laurel | 0 | 8 |
| Lewes | ||
| Middletown | ||
Potatoes
Colorado potato beetle adults are increasing and may be a significant threat late. These beetles are laying eggs right now. Also scout for potato leafhopper, their numbers are increasing in alfalfa.