Joanne Whalen, Extension IPM Specialist;jwhalen@udel.edu
Leafminers in Vegetable Crops
Each spring, we receive reports of leaf miners attacking spring planted vegetable crops. There are a number of potential species that attack vegetables including the vegetable leafminer, serpentine leaf miner, spinach leafminer and beet leafminer. Leaf miners can be difficult to control and we have limited experience with control strategies in our area. The following links provide information on some of the potentially important species:
http://entnemdept.ufl.edu/creatures/veg/leaf/vegetable_leafminer.htm
http://entnemdept.ufl.edu/creatures/veg/leaf/a_serpentine_leafminer.htm
http://extension.umass.edu/vegetable/insects/leafminer-beet-and-spinach
Cabbage
Continue to scout for diamondback and imported cabbageworm larvae. A treatment should be applied when 5% of the plants are infested and before larvae move to the hearts of the plants.
Melons
Continue to scout all melons for aphids and cucumber beetles. Aphids can be found in some of the earliest transplanted fields. As a general guideline, a treatment should be applied for aphids when 20 percent of the plants are infested with 5 aphids per leaf and before significant leaf curling occurs.
Potatoes
Continue to sample for Colorado potato beetle adults and egg laying. A treatment should be considered for adults when you find 25 beetles per 50 plants and defoliation has reached the 10% level. Once larvae are detected, the threshold is 4 small larvae per plant or 1.5 large larvae per plant.
Snap Beans
All seedling stage fields should be scouted for thrips activity. The thrips threshold is 5-6 per leaflet. Be sure to also watch for bean leaf beetle feeding. Damage appears as circular holes in leaves and we have seen significant damage in recent years on the earliest planted fields. As a general guideline, a treatment should be considered if you defoliation exceeds 20% prebloom.
Sweet Corn
Continue to sample for cutworms and flea beetles. As a general guideline, treatments should be applied if you find 3% cut plants or 10% leaf feeding. In order to get an accurate estimate of flea beetle populations, fields should be scouted mid-day when beetles are active. A treatment will be needed if 5% of the plants are infested with beetles.