Vegetable Crop Insect Scouting

David Owens, Extension Entomologist,

Cucurbit Crops
Striped cucumber beetles are moving into fields quickly. These beetles aggregate in a field, and can develop high populations in fairly small areas of a field, thus you need to check multiple locations in the field. This is particularly important for cantaloupe or musk melon, as these aggregations result in a feeding frenzy with numerous beetles defecating on the same leaf. Morning dew or other leaf wetness washes fecal matter into the wounded plant tissue which is how Bacterial wilt is introduced into the plant. Watermelon is resistant to this disease, but it is still important to manage these beetles now so that the summer generation which feeds on rinds will be suppressed. Watermelon thresholds in our region are 2 beetles per plant, although some recent research from Purdue University suggests this threshold could be as great as 5 per plant.

The most common insecticide control is a neonicotinoid application through the drip, and care needs to be taken not to accidentally overthink a chemigation rate and under-apply. Essentially, the label foliar rate needs to be applied on the same field footprint, not plastic footprint. Many labels have rate charts for drip irrigation depending on bed spacing. Pay special attention to these. However, some of the earliest fields may be flowering very soon and have bees on them in less than 2 weeks. In these fields, pay special attention to aggregations and thresholds, and consider using a foliar treatment of Assail.

There are two diamides labeled for cucumber beetle control, Harvanta and Exirel. In our tests, they do not kill adults at the same level as the neonics, but treated beetles stop feeding. These materials are probably best deployed during the summer months when Lepidopteran rind feeders also need to be managed as they are excellent worm products unmatched by either neonic or pyrethroid.

Solanaceous Crops
Continue scouting for Colorado potato beetle in potato and eggplant. Adults can fly once the temperature reaches 80 degrees. There are many modes of action available for CPB control. If the crop has been previously treated with a neonicotinoid, rotate to a different chemistry, as this insect is especially prone to resistance.

Flea beetles may also cause problems in eggplant. Their feeding is a characteristic small shot hole over the entire leaf. Thresholds depend on size; small transplants less than 3 inches are 2 beetles per plant. Admittedly, two beetles per plant can make an eggplant look terrible quickly. Many of the same modes of action for Colorado potato beetle are effective on flea beetles, including neonics, Entrust, Torac, Verimark, and Harvanta.

Begin scouting potato for potato leafhopper. They typically begin arriving in early June, although with hot, dry conditions they may migrate into fields earlier. Thresholds are 1 adult per sweep or 1 nymph per 10 leaves. The only product labeled for both leafhopper and CPB is Torac and various neonicotinoids. Several other materials are labeled, and leafhoppers are sensitive to pyrethroids.

Snap Bean
Begin scouting potato for potato leafhopper. Thresholds in snap beans are 100 nymphs per 20 sweeps.