Volume 9, Issue 12 June15, 2001
Volume 9, Issue 12 June15, 2001
Vegetables
Vegetable Insects - Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Potato Leafhoppers.
Be sure to watch carefully for leafhoppers in alfalfa, soybeans, snap beans, and potatoes. We are starting to see increases in populations of adults and nymphs in all of the previous crops. The recent hot weather will result in increased damage from nymphs. In addition, adults have been laying eggs for approximately one month and the warm weather will result in significant egg hatch. Once you see damage (yellowing, stunting, or "hopper burn" on leaf edges), yield loss has already occurred. Be sure to apply treatments soon after threshold levels are detected to avoid yield loss. The following treatment thresholds should be used:
|
Crop |
Treatment Threshold |
|
Alfalfa |
3 inch or less in height - 20/100 sweeps 4-6 inch in height - 50/100 sweeps 7-11 inch in height - 100/100 sweeps 12 inches or taller - 150 /100 sweeps |
|
Soybeans |
8 per sweep |
|
Potatoes |
0.5 - 1 per sweep or 1 nymph/10 leaves |
|
Snap Beans |
5 per sweep |
Melons.
Aphid populations have increased again so be sure to scout carefully and apply treatments before significant leaf curling occurs. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. Actara, Fulfill, Lannate and Thiodan are labeled on melons and will provide melon aphid control.
Peppers.
In areas where corn borer trap catches are above 2 per night and pepper fruit is ½ inch in size or larger, fields should be sprayed on a 7-10 day schedule for corn borer control. If Orthene or Address are used, it will also control pepper maggot. If Lannate, Spintor or pyrethroids are used, then dimethoate should be added to the mix. Be sure to check local trap catches updated on the IPM website three times per week (http://www.udel.edu/IPM/traps/latestblt.html ).
Potatoes.
We have started to see an increase in green peach aphid activity in fields where Admire was not used at planting. Before 2 weeks from harvest, the threshold is 4 aphids per leaf. Within 2 weeks from harvest, the treatment threshold increases to 10 aphids per leaf. Provado or Fulfill will provide control.
Snap Beans.
In the Dover, Laurel, Greenwood and Seaford areas, fresh market and processing snap beans in the bud to pin stage should be sprayed for corn borer. Orthene or Address should be used at the bud and pin stages on processing beans. Once pins are present on fresh market snap beans, a 7-10 day schedule should be maintained for corn borer. Lannate, Asana or Capture are labeled. We continue to see an increase in thrips activity in seedling stage snap beans. A treatment is needed if you find 5-6 thrips per leaflet. Asana, Capture, Dimethoate or Orthene will provide thrips control.
Sweet Corn.
Economic levels of corn borer continue to be found in whorl stage corn. From the whorl to pretassel stage, a treatment should be applied if 15% of the plants are infested. Early planted sweet corn should be sprayed on 6-day schedule in most areas of the state except in the Bridgeville area where sprays should be applied on a 4-5 day schedule. Be sure to check local trap catches updated on the IPM website three times per week ( http://www.udel.edu/IPM/traps/latestblt.html ).
Peas – Water Congestion and Irrigation - Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu
During the week of June 4, we experienced heavy rains at some locations. Some pea fields experienced what is known as “water congestion.” First symptoms appear as very small water-soaked spots near the outer edge and underside of the foliage. These spots can increase in size and number until the outer and terminal portions of leaves and stipules are completely water-soaked and appear darker green than normal tissue. Eventually these areas die. Severe water congestion can destroy 75% of the foliage at one to several nodes. Fortunately, we have not seen anything close to this level of damage.
It is caused by the growing conditions of high humidity, high temperatures, and high soil moisture. Simply said, the water does not transpire out of the leaves, but water logs that tissue, causing death.
Sunny weather reduces or stops the condition.
With high temperatures we are now experiencing, it is important to remember that peas are using as much as a quarter-inch of water per day. Keeping adequate soil moisture is critical to setting and filling pods to their potential. Manage the irrigation to maintain soil moisture, but stop irrigating early enough to facilitate harvest operations. Keeping in touch with your processing company field staff is important.
Vegetable Diseases
- - Bob Mulrooney,
Extension Plant Pathologist; bobmul@udel.edu
Potatoes.
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 |
Potatoes that have reached greenrow (50% emergence) since May 18, have all reached more than 18 DSV’s.
Growers should be applying a fungicide for late blight control at this time. Early blight susceptible varieties will also benefit from a fungicide application now that 363 P-days have accumulated. The early blight prediction model indicates that early blight spores may be present now.
To control pink rot caused by Phytophthora erythroseptica and P. nicotianae, and leak caused by Pythium apply Ridomil Gold MZ, Ridomil Gold /Bravo, or Flouronil between the time the potatoes are nickel-sized until flowering, and repeat 14 days later.
Vegetable Diseases - Kate Everts, Extension Vegetable Pathologist, University of Delaware and University of Maryland; everts@udel.edu
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
|
Location |
6/6 |
6/7 |
6/8 |
6/9 |
6/10 |
6/11 |
6/12 |
6/13 |
|
Bridgeville, DE |
|
1 |
1 |
1 |
0 |
0 |
1 |
0 |
|
Laurel, DE (Collins Farms) |
|
1 |
1 |
1 |
1 |
3 |
2 |
2 |
|
Galestown, MD |
|
1 |
1 |
1 |
1 |
1 |
2 |
2 |
|
Georgetown, DE |
1 |
2 |
1 |
1 |
1 |
0 |
2 |
1 |
|
Hebron, MD |
|
1 |
1 |