Jerry Brust, IPM Vegetable Specialist, University of Maryland;email@example.com
On several farms I have visited lately with squash I was surprised to see several wilted plants (Fig. 1) that upon further inspection had squash vine borers. Some of these squash plants were pretty young with the base of the plants being < ½ inch in diameter, but there was one small entrance hole (Fig. 2) and one squash vine borer in the base of the stem (Fig> 3). Usually the plants need to be older and have a larger base to support borers. The vine borer over winters in the same field where they attacked plants the year before; therefore crop rotation is a good management tactic. Adults emerge sometime in mid to late June, mate and females begin to lay eggs. Most of the eggs she lays (78%) will be laid at the base of a squash or pumpkin plant. Once larvae are in the stem nothing will control them—systemic insecticides will not work at this point and heaping soil at the base of the plant will not work. On several of the farms I saw female moths; they are day flyers, flying in and around squash plants. The moths lay eggs over a 4-6 week period, if you have SQVB moths you’ll need to protect the base of your squash or pumpkin plants from now until early August.
Figure 1. Wilted squash plant
Figure 2. Squash vine borer larva entrance hole in stem (arrow)
Figure 3. Squash vine borer larva with brown head capsule
The other problem that I commonly saw in these cucurbit fields was squash and pumpkin leaves with a great many squash bug eggs (Fig. 4). I usually do not see this density of eggs until late August or early September. The squash bug adults were usually found at the base of the plant where they feed and mate (Fig. 5). It would be a good idea to mark a few egg masses and when you observe them hatching in the next week or so you could time your sprays better—small nymphs are much easier to kill than large ones.
Figure 4. Two sets of squash bug eggs on underside of pumpkin leaf
Figure 5. Three squash bug adults at base of plant (arrows)