Volume 9, Issue17 July 20, 2001
Volume 9, Issue17 July 20, 2001
Vegetables
Vegetable Insects - Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Cucurbits.
Aphid populations continue to increase and in some cases leaf curling can be found. Treatments should be applied when 20% of the plants are infested but before leaves are curled. Actara, Fulfill, Lannate and Thiodan will provide aphid control in cucurbits. If bees are foraging, Fulfill or Thiodan should be used.
Lima Beans.
Be sure to watch for economic levels of leafhoppers. Most labeled insecticides will provide 7-10 days of leafhopper control. In fields with pin pods, you should sample for earworm, lygus and stinkbugs. A treatment should be applied if you find one corn earworm per 6 foot of row or 15 tarnished plant bugs and/or stinkbugs per 50 sweeps. Lannate or Capture can be used to control all 3 insects on lima beans.
Peppers.
At the present time, all peppers that have fruit ½ inch in size or larger should be sprayed on a 7-10 day schedule for corn borer and pepper maggot control. We are also starting to see an increase in aphid populations in peppers. Remember a continuous pyrethroid program should not be used to avoid aphid explosions.
Potatoes.
Continue to sample fields for potato leafhoppers and aphids. At this time, the aphid threshold is 10 per leaf. Potato leafhoppers still remain active in later planted fields. The potato leafhopper threshold is 5-10 leafhoppers per 10 sweeps and/or 1 nymph per every 10 leaves.
Snap Beans.
Corn borer trap catches have started to increase, so all snap beans in the bud and pins stages should be treated for corn borers. We continue to find defoliators feeding on the pin pods. In areas where corn borer catches remain low, a treatment should be applied if defoliators are feeding on pin pods. Lannate, Asana or Capture will provide the best control of defoliators.
Sweet Corn.
Fresh market silking sweet corn should be sprayed on a 3-4 day schedule in Kent County and in the Laurel area. A 4-5-day schedule is adequate for the rest of Sussex County. In areas where corn earworm pressure is low, sap beetle populations continue to be high. In addition to insect frass, beetles are attracted to plants during the pollination period. Therefore, a 4-5-day spray will be needed if sap beetles are present and corn earworm trap catches remain at less than one moth per night.
Internal Rind Necrosis on Watermelon – Derby Walker, Sussex County
Extension Agent, derby@udel.edu
Internal rind necrosis has been found in a couple of fields in Sussex County. Both seeded and seedless varieties of watermelon were affected. The fields were watered with trickle irrigation. We hope the following color pattern information will be a good indicator of fruit to cull out. On the melons that were observed with internal rind necrosis, the seedless varieties with a white cast were more likely to have the problem. Seeded varieties that appeared to be sunburned (yellow cast on the exterior – not necessarily a “true sunburn”) seemed to be affected. A very subtle knobbiness on the exterior may be observed.
Internal rind necrosis is a noninfectious disorder that appears to affect only watermelon. It has been associated with drought stress. The disorder appears to affect the crown fruit at a greater percentage than later harvests.
Internal Rind Necrosis on Watermelon
Photos taken from Diseases
and Pests of Muskmelons and Watermelons, Richard Latin, Purdue University
Cooperative Extension Service 8/93
Vegetable Diseases
- - Bob Mulrooney,
Extension Plant Pathologist; bobmul@udel.edu
Sweet Corn.
Be on the lookout for sweet corn rust. Look for the small red pustules. Once observed on corn in the whorl stage or earlier, apply a fungicide such as Bravo (fresh market only), mancozeb, or Tilt for control. Older corn will not benefit from an application.
Lima Bean Downy
Mildew.
At the present time the best program we have for fungicide
control of lima bean downy mildew is the application of fixed copper, Champ DP
or Kocide 2000, at 2.0 lb per acre on a 7 day interval when conditions are
favorable for infection. From previous years plot work this has been the best
of the labeled fungicides. Ridomil Gold/Copper has provided good control as
well and work is currently underway in the IR-4 program to establish a
tolerance so it can be labeled in the future. It is my opinion that using the
old Hyre forecasting system can help determine the time to begin fungicide
applications, then applications need to be made on a preventative basis. It can
take up to seven days for symptoms to appear in a field (from the time that
spores land on the plants until mildew is seen). If downy mildew is found in an
area, spraying to protect nearby healthy fields would be highly recommended.
Spray coverage is important so using as much water as possible would also be
encouraged. Races D and E of Phytophthora
phaseol , the fungus that causes downy mildew, are present and are both a
threat to lima bean production in the region.
Potatoes.
Early blight is beginning to appear in potatoes at low levels on susceptible varieties. Apply Quadris at the 6.2 fl oz rate/A on a 14-day schedule. Apply mancozeb or Bravo between Quadris applications. Look on the oldest leaves first for symptoms of early blight. Early blight produces small circular, brown spots that look like target boards with concentric rings of dead tissue.
Late Blight Update
|
Date |
Total DSV |
Spray Recommendation |
|
5/16 |
0 |
|
|
5/17 |
11 |
|
|
5/20 |
29 |
|
|
5/30 |
51 |
5-day, low rate |
|
6/3 |
57 |
5-day, low rate |
|
6/5 |
57 |
5-day, low rate |
|
6/7 |
57 |
7-day, low rate |
|
6/11 |
59 |
10-day, mid rate |
|
6/13 |
60 |
10-day, mid rate |
|
6/17 |
76 |
7-day mid rate |
|
6/20 |
76 |
7-day high rate |
|
6/24 |
88 |
7-day high rate |
|
6/27 |
88 |
7-day high rate |
|
7/1 |
89 |
10-day, high rate |
|
7/4 |
90 |
10-day, high rate |
|
7/8 |
92 |
10-day, high rate |
|
7/11 |
94 |
10-day, high rate |
|
7/15 |
94 |
10-day, high rate |
|
7/18 |
99 |
7-day, high rate |
Thursday’s weather allowed for 5 severity values. There have been no reports of late blight on
potatoes from our region, but there have been several occurrences from
Wisconsin and one in Michigan.
Early blight is now evident on the oldest leaves in many
plantings. As vines run out of nitrogen
and senesce, look for more early blight to occur.
For late maturing varieties or early blight susceptible varieties,
control is necessary.
Vegetable Diseases - Kate
Everts, Extension Vegetable Pathologist, University of Delaware and University
of Maryland; everts@udel.edu
Pumpkins.
Developing a spray program for foliar diseases of pumpkins is difficult because many diseases (some controlled by different fungicides) must be considered. The following is a schedule that is designed to be effective and take economics into consideration. The core of the program is broad spectrum products, maneb, chlorothalonil, and Quadris. This program will control most diseases of pumpkin, but it is still necessary to scout for development of powdery mildew and downy mildew.
Early in the season, when disease pressure is low and the plant canopy is relatively open, apply Maneb 75DF 2.0 lb/A. When disease pressure begins to build up, or powdery mildew is observed (threshold of one lesion on 45 old leaves), switch to an alternation of fungicides. Alternate chlorothalonil (such as Bravo Ultrex 2.7 lb/A or Terranil 3 pt 6L/A) plus Nova 40WP 2.5 oz/A with Quadris 12 oz./A. For protection against Phytophthora blight, add copper (such as Kocide DF 1.5 lb/A) to each fungicide application. If Phytophthora occurs, both Delaware and Maryland have been given a Section 18 approval for the use of Acrobat on pumpkin. Acrobat 50 WP may be applied up to 5 times per season.
These fungicides should be applied at regular intervals depending on the susceptibility of the pumpkin variety. Our data indicate that maximum yield on susceptible varieties can be achieved only with weekly sprays. However for varieties with some tolerance to powdery mildew (such as Magic Lantern or Merlin) grown on a cover crop (which reduces black rot pressure) a 14-day schedule does a good job of controlling diseases.
Downy mildew is not usually present here on the Delmarva Peninsula until very late in the season (mid August or September). In some years it is not present at all because it requires high rainfall. Symptoms of downy mildew on pumpkin begin as angular yellow or chlorotic areas on the upper surface of leaves. Sporulation occurs on the underside of leaves and appears brown to gray. The sporangia can be seen with a 10X hand lens and appear as barely distinguishable black or purple specks. Scout your field for the presence of downy mildew and apply Ridomil Gold or Ridomil Gold/Copper if it occurs.
Anthracnose on Watermelon.
Anthracnose on watermelons is present in several local fields. Disease development often occurs in low areas in the field (the disease is spread by splashing water). To manage anthracnose, apply chlorothalonil (Bravo, Equus, or Terranil) at 2-3 pt 6F/A. Benlate or Topsin M (0.5 lb/A) can be added to chlorothalonil to improve control. Quadris will also manage anthracnose however, because gummy stem blight is also present in many fields chlorothalonil is a better choice. Resistance to Quadris has been found in the fungus that causes gummy stem blight.
Anthracnose on Watermelons
Photos taken from Diseases
and Pests of Muskmelons and Watermelons, Richard Latin, Purdue University
Cooperative Extension Service 8/93
EFI Values (Environmental Favorability Index)
Do
not use MELCAST if there is a disease outbreak in your field, it is a preventative program. Any questions,
please call David Armentrout at (410) 742-8788 or e-mail: da88@umail.umd.edu
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Location |
7/11 |
7/12 |
7/13 |
7/14 |
7/15 |
7/16 |
7/17 |