Volume
10, Issue 15
July 5, 2002
Volume
10, Issue 15
July 5, 2002
Vegetables
Vegetable Insects
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Cucumbers.
With the continued hot, dry weather, continue to watch both pickles and slicers for increases in aphid populations. A treatment should be applied for aphids if 10 to 20 percent of the plants are infested with aphids. Actara, Fulfill, Thiodan or Lannate will provide control. Be sure to watch for bees foraging in the area and avoid insecticide applications on blooming crops.
Lima
Beans.
Continue to scout fields for lygus bugs and stinkbugs. Treatment should be considered if you find 15 adults and/or nymphs per 50 sweeps. Lannate, Capture or Mustang can be used if both species are present.
Potatoes.
Aphid populations have started to increase in later planted fields. A treatment should be considered if you can find 4 aphids per leaf. Remember, green peach aphids are generally found on the underside of the lowest leaves, so be sure to sample the correct area of the plant. Actara, Fulfill or Provado will provide green peach aphid control. We have had reports of growers describing significant levels of corn borer damage. Upon examination of fields, most of the damage has not been caused by corn borer. Although low levels of corn borer stem infestations are present, the greatest damage has resulted from bacteria splashing into the leaf petioles ("aerial stem rot"). This often occurs when growing conditions are dry, fields are constantly irrigated and windy conditions persist. No controls are available for this "aerial stem rot".
Melons.
Economic levels of spider mites, thrips and aphids can still be found in melon fields. A treatment will be needed if you find 20-30% of the plants infested with 1-2 mites per leaf. Agri-Mek, Kelthane and Capture have provided effective control this season. Be sure to watch for an increase in aphid populations. A treatment is needed if 20% of the plants are infested with 5 or more aphids per leaf. High numbers of thrips can still be found in later planted melons. No thresholds are available, but a control may be needed if plants are stressed and populations continue to increase. A pyrethroid or dimethoate should help to reduce populations.
Peppers.
Corn borer controls are needed in areas where pepper fruit is ½ inch in size or larger. If acephate (Address/Orthene) is not being used, then dimethoate should be added to the mix for pepper maggot control.
Snap
Beans.
Fresh market and processing snap beans in the bud to pin stage will need to be sprayed for corn borer control. Seedling beans should still be watched for thrips and leafhopper activity. If both insects are present, the threshold for each should be reduced by 1/3. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. We have started to find defoliators feeding on the pin pods. Even though corn borer counts remain low, a treatment should be applied if defoliators are feeding on pin pods. Lannate, Asana, Capture or Mustang will provide the best control of defoliators.
Sweet
Corn.
Fresh market silking sweet corn
should be sprayed on a 4-5 day schedule. Be sure to make the first application
when ear shanks are first visible. The first fall armyworm has been found in
whorl stage corn, so be sure to sample all late planted fields for fall
armyworm larvae. No controls will be needed until 15% of the plants are infested.
Diagnosing
Nutritional Disorders -Ed Kee,
Extension Vegetable Crops Specialist; kee@udel.edu
When confronted with diagnosing a possible deficiency in plant nutrients, it is helpful to remember which elements are immobile in the plant and which are mobile. The deficiency symptoms of immobile elements appear on the young tissue, because they are not easily translocated from older leaves to newer leaves. Iron and manganese are the two elements that will appear as a deficiency on new and recently maturing leaves.
Nitrogen, Phosphorus, Magnesium, and Potassium will exhibit deficiency symptoms on mature leaves, because these elements move readily to active tissue sites such as young leaves. Each element will have specific symptoms, but the location of the symptoms brings into focus the possibilities.
Perhaps the most common deficiency occurs with nitrogen, usually due to leaching or some factor that has limited nitrogen application. It is a general light green or yellow-green chlorosis of the entire leaf tissue beginning on mature leaves, but over extended periods will involve the new growth. Growth is eventually retarded, but is easily corrected with the application of nitrogen. If it has gotten that severe, yield and quality of vegetables will be negatively affected.
Vegetable Diseases
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Ozone
and Watermelons.
Current weather conditions have resulted in high ozone levels. Ozone injury, chlorosis and scorching of the upper leaf surfaces, is present in watermelons. Damage is most prevalent in older, crown leaves. Little can be done to protect the current crop. To reduce ozone damage on future crops, plant cultivars that are ozone tolerant such as Millionaire, Millennium, or Tri-X-313. Avoid cultivars that are sensitive to ozone such as Sugar Baby, Crimson Sweet or Fiesta. See the Commercial Vegetable Production Recommendations 2002 for more information on cultivar sensitivity or tolerance.
Fusarium Wilt.
Fusarium wilt in watermelon is present in several fields on Delmarva. Symptoms often appear when the vines produce runners and become more severe as fruit are increasing in size. Symptomatic plants appear water-stressed when soil moisture is adequate. Crown leaves wilt first, followed by runners and eventually the whole plant. Infected stems may have a red, brown or black gummy exudates and the vascular system of the plant is discolored.
Management of Fusarium wilt has
been accomplished in the past through long rotation (5 to 6 years), planting
resistant cultivars and fumigation.
However, fumigation may fail to control disease because Fusarium can quickly reinvade fumigated ground. A new aggressive form of the pathogen (Fusarium oxysporum
f. sp niveum, race 2) has been detected in
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. 1 0 0 0 8 7 3
Collins Farms 2 1 2 2 3 2 0
Vincent Farms 3 3 2 3 4 3 0