Vol. 5 No. 4 April 25, 1997

Weekly Crop Update

University of Delaware Cooperative Extension

Volume 5, Issue 9

May 30, 1997


Field Crops:

Field Crop Insects -

Joanne Whalen, Extension IPM Specialist.



Field Corn.

Although cutworms can still be found in later planted field corn, the number of fields with economic levels appears to be declining. We have received a number of reports where grubs and wireworms are causing damage. Remember, there is no rescue treatment for these two pests. Lorsban 4E sprayed over the top has only worked once for grubs in my 18 years experience and only did so because of a heavy rain immediately after application. It is also very expensive and the success is rare so this is not a recommended option. As cereal leaf beetle pupate and small grains begin to dry down, you will begin to see adults moving to nearby corn fields. Most of our experience as well as information from North Carolina indicates that economic damage rarely occurs. Most of the damage is usually confined to field edges. As a general guideline, no controls will be needed unless you find 10 or more beetle per plant and 50% of the plants with damage throughout a field.


Small Grains.

Once wheat fields are past the soft dough stage, no controls will be needed for cereal leaf beetle. Armyworms can now be found starting to clip barley heads in Sussex County with worms ranging from 1/4 to 3/4 inch long. Economic levels can also be found in wheat but in general they are staying in the lower plant canopy. The treatment threshold in barley is 1 per foot of row. In wheat, the treatment threshold is 2 per foot of row. In barley, Penncap, or Lannate will provide control if the worms are small. Remember, Penncap should not be used if bees are foraging in the area. If worms are mixed in size then Lannate is the best choice. In wheat, Warrior can still be used if you have 30 days to harvest.



As the first plants emerge and the weather turns warmer, watch for leaf feeding by bean leaf beetle. Adults chew circular holes between the leaf veins and can cause stand reductions. Controls are not needed unless you find 2 beetle per foot of row and stands are reduced by 25%. A pyrethroid or Sevin will provide control.


Grain Marketing Highlights -

Carl German, Extension Crops Marketing Specialist, University of Delaware


As we near the end of May the grain market is in an oversold situation.

This means that we will see some near term price improvement, yet not quite back to pre-planting levels. Summer weather will now become the focus of attention for commodity traders. Any `weather market' developing for the 1997 crop is likely to be extremely explosive for soybean prices, that in turn will have a spillover effect for the grains. Further sales decisions should be placed on hold.

Vegetable Crops:

Vegetable Crop Insects -

Joanne Whalen, Extension IPM Specialist.



Colorado potato beetle eggs laying and hatch has started to increase. The treatment threshold is 4 small larvae per plant. Agri-Mek, cryolite or Provado will all provide control if larvae are found. Recent corn borer moth counts are lower due to the cool evenings. In areas where rain was heavy, many small larvae were killed. Only the tallest potatoes may need a corn borer treatment . So far, very few infested stems have been detected so a better timing would be early next week, especially if you intend to use Furadan or Monitor.



As vines begin to run on the earliest plantings, be sure to watch for both melon aphids and mites. Low levels of mites have been detected in Sussex county but no treatments should be needed until 10-15% of the crowns are infested. In general, melon aphids are usually found in fields in early June. Infestations are generally higher during hot, dry periods following a cool spring when natural enemies lag behind. A treatment should be considered when 10-20% of the runners are infested with 5 or more aphids per leaf and beneficial activity is low. Lannate is the only material labeled on cucurbits for melon aphid control. Dimethoate will not control melon aphids.


Sweet Corn.

Continue to watch for small ECB larvae feeding in the whorls of the earliest planted sweet corn, Controls will not be needed until 15% of the plants are infested. The best control options are Ambush, Pounce, Penncap, or Warrior. As cereal leaf beetle pupate and small grains begin to dry down, you will begin to see adults moving to nearby sweet corn fields. Most of our experience indicates that economic damage rarely occurs. Most of the damage is usually confined to field edges. As a general guideline, no controls will be needed unless you find 10 or more beetle per plant and 50% of the plants with damage throughout a field.


Update on Lima Bean Variety -

Ed Kee, Extension Vegetable Crops Specialist.


There has been some confusion about the downy mildew resistance of the variety >Packers.= The developers of >Packers,= Ferry-Morse Seed Company, indicate that this variety has resistance to all 4 races of Downy Mildew. This is based on evaluations made on the variety by the USDA-Beltsville in the mid-eighties.


Pea Harvest Begins -

Ed Kee, Extension Vegetable Crops Specialist.


Pea Harvest will begin on May 29-30. Many of the fields look good, the cool spring has been beneficial to the crop, although fields are often shorter in height than other years, primarily because of the cooler conditions this year.


Vegetable Crop Diseases -

Bob Mulrooney, Extension Plant Pathologist, University of Delaware



Late Blight Update

May 28, 1997

Weather conditions for late blight development have been unfavorable until last Sunday. Severity values were recorded at all the weather monitoring stations. Remember that in order to have a disease, you need a susceptible crop which we have, a disease causing agent (pathogen) and favorable weather for infection. We hopefully have late-blight-free seed. The weather has been very unfavorable for late blight this spring. The low temperature and low humidity have not permitted the accumulation of many Disease Severity Values (DSV=s) until this last rainy period. The threshold for initiating sprays for late blight control is 18 DSV=s. Some growers may not want to wait until 18 DSV=s are reached. Applications when plants begin to touch down the row would be the next suggested time to begin spraying with a protectant fungicide such as mancozeb, metiram, chlorothalonil, copper, etc. Under these conditions low rates would be recommended.


The DSV accumulations as of May 26 are as follows:

Baldwin, Sussex County, Emergence Date - 4/20, 8 , no spray.

Jackewicz, Kent County, Emergence Date - 4/26, 5, no spray.

Zimmerman, Rt.9, Kent County, Emergence Date - 4/28, 4 , no Spray. The only accumulation occurred on 5/24-25.

Baker, New Castle County, Emergence Date - 5/7, 17, no spray. If potatoes emerged after 5/9/97, DSV=s are at 10, no spray


Note: There was a favorable period in this area on May 8 that accumulated 8 DSV=s.

Growers in New Castle County may want to be ready to spray soon.


Pink Rot.

Early potato plantings are approaching bed development, which is a reminder that the first pink rot spray, if needed, should be applied at flowering and 14 days later. Ridomil Gold MZ should be applied in as much water as possible. I have had excellent results with 30 gallons/acre. Test plots have indicated that two applications beginning when the first tubers are nickel-sized also provides very good control.


Crop Report For Delaware

( Sussex County)


Barley is at the soft dough stage. Harvest is expected in approximately two weeks.


Most wheat fields are at the milk stage. It has been observed that some fields have been affected by dry weather. In some cases, the flag leave was burned by drying winds and lack of rainfall. The recent rain should help finish-off the crop.


Most corn planting is done except in poorly drained areas. Some sections of fields have had to be replanted due to sand and wind damage. Damping-off has also been a problem is poorly drained areas of fields and these areas are being replanted. White grub injury has also been observed this spring with thin stands as a result of this damage.


Early plantings of soybeans are in and have emerged. At this time, plantings look good.


As reported last week, strawberries are in season, but have been slow to ripen due to the cool weather.


Early plantings of cantaloupes and watermelons have been held back by the cool weather. Wind damage is also evident in many fields. These early plantings are just starting to grow, and as a result, later plantings are at approximately the same stage of growth as the earlier plantings.


Out-of-State Reports

New Jersey

Field Crops - 5/15/97

Field Corn planting had been going strong but many producers are still waiting for poorly drained fields to dry out enough to get in them. Corn planted 2-3 weeks ago is just starting to germinate, or is in the spike to early growth stages. The wheat crop is in the jointing growth stage and overall appears very good.

Vegetable Crops - 5/21/97

Conditions have not been favorable for the development of late blight. The late blight forecast system in South Jersey has not produced any DSV=s to date. Pepper transplants have sustained wind damage. Marginal blight has been observed in several lettuce fields and is the result of sand blasting during sudden rains. Growers are reporting losses of cucurbits from seed corn maggot and asparagus beetle populations are still very high.


New York State Regional Reports

Ontario, Wayne, Yates Counties & Steuben Muck Report - 5/21/97

In general, cool, wet weather continues to slow both planting and development of planted crops. Frost was reported on May 18 in low lying areas of Yates Co. Sweet corn is growing very slowly. Corn under plastic is quite a bit ahead of bare ground. Processing sweet corn planting is just getting started. Some melon transplants have been planted. Row covers have been especially helpful this year due to cold weather and wind. Onions are growing very slowly. The earliest planted potatoes, on sandy soils, have finally come up, and Colorado Potato Beetle have been seen.

Lake Plains Region (WNY): 5/21/97

Emergence and growth of many crops and planting of some crops is slow due to cool weather. Asparagus harvest is on the light side due to cool temperatures. Pea planting is on schedule and Processing sweet corn planting has begun. Potatoes are being planted at full speed on the muck.


Sweet Corn that was planted under plastic mulch the last week of March stands about 6 to 8 inches tall. Sweet corn that was planted 4 weeks ago in bare ground, is up with some parts of fields at spike and other parts that will probably never come up. Growers are replanting and in some cases, rotary hoeing to break soil crust that has formed hoping to improve stand/emergence. Cabbage is growing well. Melon transplants are being seeded.

Illinois - 5/14/97

In the south, cool and cloudy days are still plaguing vegetable producers. A few vegetables are in the ground, and those that are look very good. In the southwest, vegetable growers are now getting most warm season crops in the ground. Soils were approaching the dry side. Early sweet corn plantings are up and looking good. In the north, temperatures remain on the cool side.

Michigan - 5/14/97

East: The rain has been just enough to keep most growers out of the field. Potatoes that have been in the ground six weeks are beginning to emerge. Tomatoes are being planted on a small scale. Cabbage has been in the ground for more than six weeks is still growing very slowly. Central: Crop germination and growth are significantly behind normal. Light frost was widespread on May 13. Snap bean planting has started. The earliest pea plantings are emerging slowly. West: Asparagus volume is slow due to cool weather. Most growers are on their third or fourth harvest, with a 3-4 day interval between harvests.

Weather Summary

University of Delaware,


Week of May 23 to May 29, 1997


1.24 inches: May 26

0.08 inches: May 27

Readings taken for the previous 24 hours at 8 a.m.



Ranged from 81EF on May 25 to 62EF on May 28.


Ranged from 58EF on May 26 to 39EF on May 29.

Soil Temperature:

63EF. Average for the week.


Complied & Edited By:

Tracy Wootten

Extension Associate - Vegetable Crops


Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State College and the United States Department of Agriculture cooperating, John C. Nye, Dean and Director. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age or national origin.