Monitor for insect pests in your cucurbit crops

It’s early July and squash vine borers and squash bugs are now active in many parts of the state.

Squash vine borers

Adult squash vine borers can be monitored with a pheromone trap, which can be purchased from Great Lakes IPM (See their lures or traps.). Monitoring with the pheromone trap will help detect first activity of adults. It is useful to find out when egg laying is occurring because management options are limited to controlling the hatching larvae (first instars) before they enter the plant stem. Once the larvae are inside the stem, there is little that can be done to kill them.

There are no threshold guidelines regarding how many frass-damaged plants or how many captured adult moths in the trap indicate a need for chemical control. The most practical way to prevent widespread damage is to detect the earliest signs of adult activity using the traps. An insecticide application is most effective just as the larvae are hatching from their eggs and before they burrow into the stem. Since eggs hatch in about 7 to 10 days, time the insecticide application a week to 10 days following the time of first sustained moth presence in your traps. To learn more about the damage symptoms and biology of squash vine borers, visit the VegEdge web site from the University of Minnesota.

Since the pheromone trap may attract a variety of clearwing borer moths, identification and knowledge of clearwing borer moths will be necessary. Remember that just because you see borers in your traps, it doesn’t necessarily mean you have squash vine borers. There are many species of borers flying around at this time and getting caught in the traps. View pictures of the squash vine borer moths and how to identify them.

Squash bugs

To detect squash bugs in the field, regular scouting of leaves is necessary. The damage symptoms include wilting of leaves initially, and ultimately, the damaged leaves will appear black or dried out. Later in the season, these insects will also feed on fruits.

Threshold is reached when the average number of egg masses (meaning groups of eggs) is greater then one egg mass per plant. Seedlings, new transplants, and flowering plants are the most critical growth stages to monitor, as these are the stages when the most damage can occur. If the threshold is exceeded, an insecticide application is warranted.

To see photos of the squash bug adults, nymphs and eggs, and to read more on its biology, check out this factsheet from the University of Minnesota.

To find out which insecticides are registered for use in your crop for these pests, check out Michigan State University Extension’s E312 Extension bulletin.

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