Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Cucumbers
Continue to scout all fields for cucumber beetles and aphids. Cucumber beetle populations have exploded this past week. Fresh market cucumbers are susceptible to bacterial wilt, so treatments should be applied before beetles feed extensively on cotyledons and first true leaves. Although pickling cucumbers have a tolerance to wilt, a treatment may still be needed for machine-harvested pickling cucumbers when 5% of plants are infested with beetles and/or plants are showing fresh feeding injury. With the predicted increase in temperature, you should watch carefully for an increase in aphid activity. A treatment should be applied for aphids if 10 to 20 percent of the plants are infested with aphids with 5 or more aphids per leaf.
Melons
Continue to scout all melons for aphids, cucumber beetles, and spider mites. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. Be sure to also watch for beneficials. We are starting to find the first spider mites in commercial fields. The threshold for mites is 20-30% infested crowns with 1-2 mites per leaf. Acramite, Agri-Mek, bifenthrin, Danitol, and Oberon are labeled on melons for mite control. We also saw a significant increase in cucumber beetle activity this past week. Since beetles can continue to re-infest fields as well as hide under the plastic, multiple applications are often needed. Foliar products labeled for cucumber beetle control on melons include a number of pyrethroids, Assail, Lannate, Sevin, and Thionex. Venom 70SG also has a 2ee label for cucumber beetle control on cucurbits (http://www.cdms.net/LDat/ld76N019.pdf). Be sure to check all labels for rates, precautions and restrictions, especially as they apply to pollinators.
Peppers
Continue to sample for thrips. We continue to hear reports of high thrips activity on crops in Virginia. You should also continue to sample for corn borers and watch carefully for egg masses. Before fruit is present these young corn borer larvae can infest stems and petioles. Be sure to also check local moth catches in your area by calling the Crop Pest Hotline – in state: 1-800- 345-7544; out of state: (302) 831-8851; or visiting our website at (http://ag.udel.edu/extension/IPM/traps/latestblt.html). You should also watch for an increase in aphid populations. A treatment may be needed prior to fruit set if you find 1-2 aphids per leaf for at least 2 consecutive weeks and beneficial activity is low.
Potatoes
Fields should be scouted for Colorado potato beetle (CPB), corn borers (ECB) and leafhoppers. Adult CPB and small larvae can now be found. 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. A corn borer spray may be needed 3-5 days after an increase in trap catches (http://ag.udel.edu/extension/IPM/traps/latestblt.html) or when we reach 700-degree days (base 50). If you are scouting for infested terminals, the first treatment should be applied when 10% (fresh market) or 20-25 % (processing) of the terminals are infested. As a general guideline, controls should be applied for leafhoppers if you find ½ to one adult per sweep and/or one nymph per every 10 leaves.
Snap Beans
Continue to sample all seedling stage fields for leafhopper and thrips activity. Both insects can be found in seedling stage snap beans. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. If both insects are present, the threshold for each should be reduced by 1/3. If both insects are present, Lannate, bifenthrin, Proaxis and Warrior (lambda-cyhalothrin) are labeled for both insect pests on snap beans. In addition, continue to watch for bean leaf beetle. As a general guideline, a treatment should be considered if defoliation exceeds 20% prebloom. A pyrethroid, dimethoate or Sevin are labeled for control. As a general guideline, once corn borer catches reach 2 per night, fresh market and processing snap beans in the bud to pin stages should be sprayed for corn borer. Sprays will be needed at the bud and pin stages on processing beans. Once pins are present on fresh market snap beans and corn borer trap catches are above 2 per night, a 7 to 10-day schedule should be maintained for corn borer control.
(http://ag.udel.edu/extension/IPM/traps/latestblt.html)
Sweet Corn
Continue to sample seedling stage fields for cutworms and flea beetles. You should also sample all fields from the whorl through pre-tassel stage for corn borers and corn earworms. Both species can now be found feeding in whorls and tassels of sweet corn. A treatment should be applied if 15% of the plants are infested with larvae. We have also seen high earworm catches in a number of locations, especially the Bridgeville and Laurel areas. Virginia is also reporting high earworm catches. The first silk sprays will be needed for corn earworm as soon as ear shanks are visible. On silking sweet corn, sprays are needed on a 3-day schedule. Blacklight trap catches in the Bridgeville and Laurel areas indicate that a 2 to 3-day schedule is needed on silking sweet corn. Let’s hope these trap catches drop soon! Be sure to check trap catches since the spray schedules can quickly change. You can call the Crop Pest Hotline for the most recent trap catches – in state: 1-800-345-7544; out of state: 302-831-8851 or check our website at http://ag.udel.edu/extension/IPM/traps/latestblt.html.