Volume 10, Issue 10
May 31, 2002
Vegetables
Vegetable Insects
-
Cabbage.
Along with diamondback and imported cabbageworms, be sure to sample carefully for thrips activity on susceptible varieties. A treatment is recommended if 20% of the plants are infested. On highly susceptible varieties, a treatment should be applied as soon as populations start to increase, and before they have moved deep into the wrapper leaves. Capture, Spintor or Warrior has provided control.
Cucumbers.
Both pickles and slicers should be watched for increases in aphid and cucumber beetle populations. Fresh market cucumbers are very susceptible to bacterial wilt vectored by cucumber beetles. Although pickling cucumbers grown in high-density rows can compensate for about a 10 percent stand loss, beetle feeding can reduce plant growth. If moderate feeding can be found on the cotyledons and/or the first true leaves and there is a history of bacterial wilt on your farm, a cucumber beetle spray should be applied. Actara, Thiodan, a pyrethroid or Lannate will provide control. A treatment should be applied if 10 to 20 percent of the plants are infested with aphids. Actara, Thiodan or Lannate will provide aphid control.
Melons.
Economic levels of cucumber beetles, aphids and spider mites continue to be found. As vines begin to run, be sure to sample carefully for spider mites. The threshold is 20- 30% infested crowns with 1-2 mites per leaf. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. Agri-Mek, Kelthane, Danitol or Capture will provide spider mite control. Actara, Fulfill, Lannate and Thiodan are the labeled on melons and will provide melon aphid control. Actara, Lannate and Thiodan will also provide cucumber beetle control. Capture will provide cucumber beetle and spider mite control. We have had reports of high levels of thrips reducing plant growth. Although no thresholds are available for thrips damage on melons, a treatment may be needed if plant growth is significantly reduced. Capture, Dimethoate, or Lannate should help to reduce populations.
Potatoes.
Corn borer egg masses continue to be found and the first stem tunneling has been detected. Be sure to check our website (http://www.udel.edu/IPM/traps/latestblt.html) for the most recent moth catches in your area. If trap catches are being used to time sprays, the first application will be needed during the next 7-day period. Ambush, Baythroid, Penncap, Pounce or Spintor will provide control. .In general, 2-3 sprays of these materials are needed to provide corn borer control. If you are scouting for infested terminals, the first treatment should be applied when 20-25% of the terminals are infested. Furadan or Monitor will provide the best control if you are waiting until you see infested terminals. A second spray will be needed if you continue to see an increase in the number of infested terminals. Continue to sample for potato leafhopper adults and nymphs. As a general guideline, controls should be applied if you find ½ to one adult per sweep and/or one nymph per every 10 leaves. A pyrethroid, dimethoate, Actara or Provado will provide control.
Snap
Beans.
We continue to see an increase in leafhopper and thrips activity, especially in seedling stage 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. Lannate, Asana, Capture, or dimethoate will provide control of both insect pests.
Sweet
Corn.
Continue to watch the earliest planted fields for corn borer
larvae. Economic levels have been
detected in the earliest planted fields. A treatment should be applied if 15%
of the plants are infested. The best timing for a treatment is just as the
tassels are emerging from the whorls. In recent years, the best corn borer
control has been achieved with Ambush, Pounce, Penncap
or Warrior. As soon as ear shanks are present, the first silk sprays will be
needed. In
Pea Irrigation and Pea Harvest Progress - Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu
Pea Harvest is probably 15-20% complete and in most fields, yields have been good, some exceeding 4,000 pounds per acre. Maintaining yields as the weather warms will be dependent on adequate rainfall or good irrigation practices. Remember, when peas are in the flowering or pod fill stages, and temperatures are 90 degrees or above, their evapotranspiration rate is 0.25 inches of water per day. Maintaining adequate soil moisture is key to setting and filling out pods.
Accent for Grass Weed Control in Sweet Corn - Mark VanGessel, Extension Weed Specialist, mjv@udel.edu
Accent was labeled for sweet corn a few years ago. Accent is labeled only for use on processing sweet corn (Bonus, Excalibur, GG-43, GG-55, More, Reward, Viking and Zenith only varieties labeled). Accent can not be used on sweet corn that was treated with Counter due to crop injury. We tested Accent on Bonus and observed some yellowing and stunting, but yield was not reduced. My caution when using Accent on sweet corn, even labeled varieties, is to expect some injury, and should only be used when grasses are a severe problem. The label recommends the addition of nitrogen, but this is liable to further increase injury.
Vegetable Diseases
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Potatoes.
Late Blight Advisory
Disease Severity
Value (DSV) Accumulations as of
|
Date |
Total DSV |
Spray
Recommendation |
|
5/1 |
12 |
None |
|
5/11 |
19 |
5 days, low rate |
|
5/19 |
23 |
10 days, low rate |
|
5/22 |
23 |
10 days, low rate |
|
5/27 |
27 |
10 days, low rate |
|
5/29 |
30 |
7 days, low rate |
Potatoes that have reached greenrow (50% emergence) by April 28 have all reached more than 18 DSV’s. Fields that reached greenrow after May 2 have not accumulated 18 DSV's yet and would not need to be sprayed. Spray recommendations are generated by the Wisdom potato software program.
For this greenrow date and location, we have accummulated 334 P-days as well. P-days are a measure of potato plant growth somewhat similar to growing- degree- days. When 300 P-days have been exceeded, conditions for early blight infection are favorable and sprays for early blight susceptible varieties should begin if early blight is expected to be a problem.
Growers should apply at least 1-2 sprays of Dithane or Bravo before plants canopy. Late blight has not
been a problem here in
If pink rot or leak has been a problem in the past and you did not apply a fungicide in the furrow for control, the first foliar application of Ridomil Gold MZ, Ridomil Gold/Bravo or Fluoronil should be made between when tubers are nickel-sized and flowering then repeated 14 days later. Apply the fungicide in as much water as possible. Try to get some coverage of the soil for root uptake as well. Pink rot generally occurs in poorly drained areas or where water stands due to compaction from spray rows.
Vegetable Diseases -
Kate Everts, Extension Vegetable Pathologist,
University of
Watermelons.
From the
Latest EFI values from local weather stations
Any questions please call (410) 742-8788
EFI Values (Environmental Favorability Index)
Do
not use MELCAST if there is a disease outbreak in your field, it is a preventative program.
Location
Charles Co. 0 3 3 6 3 1 0
Collins Farms 2 2 2 2 1 1 0
Galestown, MD 2 2 3 1 1 0 0
Glenville, MD 1 3 4 8 4 0 0