Vol. 5 No. 4 April 25, 1997

Weekly Crop Update

University of Delaware Cooperative Extension

Volume 5, Issue 7

May 15, 1997


Field Crops:

Field Crop Insects -

Joanne Whalen, Extension IPM Specialist.


Field Corn. Black cutworm activity remains high in both no-till and conventionally tilled fields. Leaf feeding damage ranges from 10 to 50%. In general, larvae are still small - c to3 inch long. A treatment is recommended if you find 10% leaf feeding or 3% cut plants in spike to 4-leaf stage corn. Late planted corn will be very susceptible to attack. If you are unable to scout your field from the spike to 4-leaf stage and you have had a history of cutworm problems, a pyrethroid tank mixed with a herbicide will provide cost effective control, especially if you are planting into a poorly drained field with a lot of chickweed growth. In situations where you are planting into a burned down small grain cover, true armyworms could also be a problem. A pyrethroid tank mixed with the herbicide will also provide control of true armyworm. Stand losses are starting to show up from white grub damage, especially in no-till fields. Unfortunately, there is no rescue treatment and grubs will continue feeding for another couple of weeks. If a replant decision is made, a soil insecticide will still be needed unless you can find grubs that have begun to pupate.


Small Grains. Although grass sawfly and true armyworm adults can be found laying eggs, worm populations are extremely light. Economic levels of cereal leaf beetle can be found in sporadic locations, especially in thinner stands. When scouting fields, be sure to look for small cereal leaf beetle larvae being found in the lower plant canopy. Although insect populations are very light this year, there is still a chance that economic levels of worms will be found in small grains, especially after a period of warm weather.


Water Soluble Packs Require Agitation -

Mark VanGessel, Extension Weed Specialist.



Water-soluble packs are being used more often by pesticide manufacturers for personal safety, environmental, and convenience considerations. Often these packets are used in combination with other pesticides. But there has been some comments about the difficulty in getting these packets dissolved. First of all, water soluble packets require vigorous agitation. The spray tank should be filled only 1/4 to 1/3 full before adding the required number of packets. Packets should be added while the water is agitating and should be allowed to agitate for 5 minutes to allow the packets to completely dissolve. While agitation continues, add additional water and other materials.

Also, putting chemicals in the tank in the wrong order can result in difficulty in getting pesticides into solution. The result is that the pesticides are not compatible with one another. Sometimes the pesticides will settle out (form gunk) even when the proper order is followed, in which case a compatibility agent is needed. The order of putting pesticides in the tank is based on the formulation. The general order for mixing is as follows:

1. Water soluble packets

2. Compatibility agent - (if needed)

3. Wettable powders - (first mixed with water in a bucket to form a slurry)

4. Dry flowables or water dispersible granules

5. Liquids - (these are the true liquids, they do not turn the solution white when added to water)

6. Emulsifiable concentrates (these do turn white when added to water)

7. Surfactants or crop oil

8. Nitrogen fertilizer


Field Crop Diseases -

Bob Mulrooney, Extension Plant Pathologist.



Wheat. Powdery mildew is still the predominant disease, but in general levels are low. Once wheat reaches flowering and the flag leaf and the leaf below are free of disease the crop will not respond to fungicides. Keep checking wheat for the lens shaped lesions of Septoria (Stagnospora) leafspot. Wheat spindle streak mosaic virus appears to be present in some fields. The cool weather is favorable for infection and symptom expression. Samples are being checked now to confirm the presence of this disease.


Corn Replant Decision Making -

Richard W. Taylor, Extension Agronomist.



Since early planted corn is now either just emerged or in the 1- to 3-leaf stage, it's time to scout your early planted fields to decide if any of them need to be replanted. There are reports of some poor stands in early planted corn. The earlier you can make the decision to replant, the less yield you risk loosing.

There are seven steps to follow to improve your chance of making the "right" decision. First, determine the cause for the poor stand (if uncorrected, replanting will only result in another poor stand). Second, determine the number and distribution of viable corn plants. Third, determine the yield potential of the existing stand (the fact sheet, AF-4, cited below has tables that have been validated in Delaware to estimate yield potential). Fourth, determine the yield potential of a replanted stand (estimate when you could replant the field and use the tables in AF-4). Fifth, determine the yield advantage for replanting. Sixth, estimate the cost of replanting. Finally, determine the net economic gain or loss from replanting.

Stand reductions in irrigated corn are often more damaging than on dryland corn. Also, replanted irrigated corn often will have a higher yield potential than under similar dryland conditions.

For tables of predicted yield values and additional information about corn replant decision making, request agronomy fact sheet number AF-4 entitled "Corn Replant Decisions" from your county agricultural Extension agent.


Avoid Bloat Problems When Grazing Alfalfa -

Richard W. Taylor, Extension Agronomist.



Bloat can be a problem when ruminants are grazed on young, lush legumes and especially when grazing alfalfa. Bloat can be controlled by management practices, feeding poloxalene, or a combination of the two. The new grazing-type alfalfa cultivars are just as likely to cause bloat as the traditional hay-type cultivars. To avoid bloat problems with your management, try these tips.

T Fill animals with another roughage such as hay or grass before turning them onto alfalfa the first time. Remember, hungry animals may over-eat when moved to fresh pasture and this can lead to bloating.

T Over a 5 to 6 day period, gradually increase the time that animals have access to alfalfa pasture. Don't just put them on lush alfalfa pasture and leave them there.

T Observe animals twice a day when first turned on to alfalfa. Some animals are chronic bloaters and should be watched carefully and removed if necessary.

T Begin feeding poloxalene 2 to 5 days before turning animals on to alfalfa pasture. Use higher dosages initially and reduce the rate if no problems occur.

T Once animals adjust to alfalfa pasture, leave them on the pasture constantly even at night as you rotate through paddocks.

Other points to remember are more mature alfalfa is less likely to cause bloat; animals on lush, immature alfalfa will require more poloxalene than those on more mature alfalfa; minimize your risk by initially turning animals on alfalfa that has reached the bloom stage; use extra caution during wet, cloudy periods especially in early spring when alfalfa is rapidly growing; and do not put animals on alfalfa pastures if a heavy dew is present.


For more information about bloat, request agronomy fact sheet number AF-7 entitled "Bloat on Legume Pastures" from your county agricultural Extension agent.


Nutrient Management Planning--Saving Fertilizer Dollars

Richard W. Taylor, Extension Agronomist.



It's a busy time of year but just a few minutes to review your current nutrient management plan may help save you money. A nutrient management plan is like a shopping list. When I go to the grocery store and don't take a list with me, I frequently end up spending many dollars more than I had intended. Like a good shopping list, a nutrient management plan can help you resist putting extra pounds of fertilizer on your crops. The plan also can help you avoid buying the high priced shotgun treatments that cost many dollars and return little to nothing. A good rule of thumb is that for every dollar of inputs you should gain four dollars in gross income. This spread is to account for the inherent risk involved in farming.

But, you say you don't have a written nutrient management plan. Until you have time to either write a detailed plan yourself or have your crop consultant, certified crop adviser, or other nutrient management consultant write one for you, take just an hour or two to sketch out a nutrient management plan for each of you fields. Even a brief outline of a plan is better than not having one at all. Use your outlined plan as your shopping list for this growing season so you don't spend unnecessary dollars on unneeded nutrients. Make a note for yourself to develop a complete detailed nutrient management plan at season's end.


Vegetable Crops:

Vegetable Crop Insects -

Joanne Whalen, Extension IPM Specialist.



Peas. Fields should be sampled on a weekly basis from bloom through harvest for pea aphids. At this time, populations are lower than normal and beneficial insects appear to be helping to control the population. When plants are small, count the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. A treatment is recommended if you find 5-10 aphids per plant or 50 or more per sweep. Dimethoate, Lannate, or Penncap-M will provide control. Be sure to read the label for application restrictions during bloom.


Potatoes. CPB egg laying activity is light and no insecticide applications should be needed until small larvae are detected. The treatment threshold is 4 small larvae per plant. Corn borer nightly moth catches are ranging between 2 and 9 (Harrington area) per night. Once moth catches reaches 10 per night, fields should be scouting for egg masses and/or percent infested terminals.


Apples. Pyramite from BASF has recently received a federal registration for mite control in apples. In our 1996 demonstration, Pyramite provided excellent summer mite control and will be an excellent tool for mite explosions in season. It works as a contact miticide; therefore, thorough leaf coverage is critical.


Sinbar for Watermelons Receives Section 18 -

Ed Kee, Extension Vegetable Crops Specialist



The EPA granted a Section 18 Emergency label for Sinbar on Watermelons in Delaware, Maryland, and Virginia. It is labeled as a pre-emergence treatment at 3 to 4 ounces/acre. We recommend 3 ounces per acre, especially when used in combination with other herbicides. The three ounce rate is also appropriate for our sandy soils, which is where most of the watermelons are grown.

A Curbit (1.5 oz./A) and Sinbar (3 oz./A) combination will provide excellent grass and broadleaf control. Command (5 oz./A) and sinbar (3 oz./A) will also provide excellent grass and broadleaf control. These are for use with direct-seeded crops only. Sinbar can be used with transplants. Temperatures early in the season may inhibit growth, but the watermelons will usually grow out of it as warm weather takes over. The stunting that may occur during cold conditions results from Curbit.

If some sort of stand failure occurs, re-seeding can occur, but it is best not to work the soil, but plant no-till, if possible, in order to not disturb the weed control.


Sweet Corn Herbicide Choices -

Ed Kee, Extension Vegetable Crops Specialist



Sweet Corn growers have several options to choose from when developing a sweet corn herbicide program. With planting still in progress, there is still time to evaluate options.

The standard program, especially with early plantings where double-cropping to soybeans or vegetables is expected, is Dual or Lasso for grass control, plus Bladex for broadleaf weed control. This has worked well over the years, with good weed control, good crop safety, and little residual problems to succeeding crops.

Dual or Lass, plus Atrazine is another major standard, and used when double-cropping is not an issue with later planted sweet corn. Dual does have a significant advantage over Lasso in controlling nutgrass.

Recently, Frontier, or Guardsman has been labeled for Sweet Corn. Frontier is a grass herbicide, and Guardsman is a packaged mix combination of Frontier and atrazine. We have not listed Frontier for sweet corn in our Commercial Recommendation Book because it has a 12 month rotation restriction for many vegetable crops. The Guardsman combination on sweet corn can be effective, but be aware of its weed spectrum and the rotation restrictions.


Some Summer Meeting Dates


Last summer there were several days when two or more grower meetings where scheduled, creating some conflicts. As an early announcement to allow for scheduling and to avoid conflicts, the following are dates, meeting title, location, and time (if available):

June 11, 1997 -

Pea Variety Twilight Field Meeting, U of D Research & Education Center, 5 PM

 July 3, 1997 -

Crop Consultant Diagnostic Day, U of D Research & Education Center, 9 AM

 August 13, 1997 -

Farm & Home Field Day, U of D Research & Education Center, 8 AM

 August 21, 1997 -

Crop Management Farmers Tour - Begins @ U of D Research & Education Center, Time to be Announced


More details will be forthcoming as these dates approach.


Vegetable Crop Diseases

Bob Mulrooney, Extension Pathologist.



Potatoes. Conditions for late blight have not been favorable. The DSV accumulations are as follows: Baldwin (Bridgeville) 6, Jackewicz (Rising Sun) 0, Zimmerman (Rt 9, Dover) 0, Baker ( Mt. Pleasant) 7. The threshold for initiating sprays for late blight is 18 DSVs. The DSVs are not accumulating in spite of the cool weather because relative humidity above 90% for 10 hours or more is not occurring frequently. Some fields have plants that are large enough that plants are touching down the row, and some growers may want to spray a low rate of a protectant fungicide such as mancozeb or chlorothalonil at this time.

The late blight occurrence in North Carolina that I referred to in last weeks newsletter was a situation where the grower had not made any fungicide applications before late blight occurred. This situation illustrates several points that I have been stressing with our growers: 1) that you buy disease free seed, and 2) spray protectant fungicides. It is important to know your seed source. Buy good seed from good sources. Follow a protectant fungicide program. I have seen plenty of good to excellent seed from Maine this year and the year before, unfortunately this infected seed reportedly came from Maine, and if the grower had sprayed he may have never seen late blight.


Vegetable Diseases

Kate Everts, Extension Plant Pathologist, Universities of Maryland and Delaware


Peas. Bacterial blight on peas is present in some early-planted fields. This bacterial disease is primarily a seed transmitted disease. The pathogen arrives in fields within or on pea seed, and therefore is restricted to specific seed lots (other sources of infection are much less common). Since the seed has been well mixed in during harvest, processing, and then in the planter box, infected seed will be planted randomly throughout the field. If conditions are not favorable for development of the disease, it will not spread. However, under weather conditions the 1997 early pea crop was exposed to (wet soil at emergence, hard rains, wind, blowing sand and frost) infected spots have developed in some fields. Control is best achieved by planting clean seed. Once the disease has been found in a field, avoid working the field while wet to minimize spread. Development of resistant varieties would be an excellent control method for this disease.

Another Adisease" of peas is actually nutrient toxicity, which occurs in peas planted in soils which are low in pH. This malady is characterized by small rust or brown spots on the lower leaves of the plant. Symptoms appear somewhat like those of Aschochyta blight, however in the case of Aschochyta the spots will not be confined to the edge of the leaves. While this disease is considered minor in importance, it can be avoided by monitoring pH and applying lime to raise the pH above 6.0.


Free Drinking Water Supply Evaluation -

Helen Waite, Extension Associate - Water Quality


Ever wonder about the quality of your drinking water? "Is my well safe? Septic system OK?"

From May through September for Delaware residents, Cooperative Extension will offer a free assessment of your farmstead. An Extension professional will work with you using Farm*A*Syst, a program designed to enable you to assess your property for protection of your water supply.

Ninety-five percent of families living in southern Delaware use ground water to supply their drinking water needs. This source can be very safe, supplying clean, potable water. However, if water supply systems are not properly constructed and/or maintained, bacteria and other pollutants may contaminate this source of drinking water.

Pollution is a serious threat to available fresh water supplies, which make up only one-half percent of the world's total water supply. You can protect your drinking water supply by learning to recognize potential sources of pollution and working to reduce or eliminate them. For more information or an appointment, please call (302) 856-7303 and ask for Helen Waite.


Out of State

( The Following is taken from a vegetable newsletter that I receive from Cornell)

Ontario, Wayne, Yates Counties and Steuben Muck Report - 5/7/97

In general, cool, moist weather has slowed planting on all but very well drained soil. The earliest planting of onions are up. Some western New York onion plantings sustained wind damage the first week in May. Tomatoes have been put out under plastic row covers. Carrot planting continues.


Lake Plains Region - 5/6/97

Plastic corn now has 5 leaves. Harvest of lettuce that had been under row covers is expected this week.


Wisconsin - 5/1/97

Temperatures in the southern part of the state have hovered near normal or slightly below for this time of year. Growing degree days statewide are still behind normal but with the recent mild weather, will soon be catching up. Growers are beginning to get out into their fields in most parts of the state. The first Colorado potato beetle adult was seen this week at the Hancock Research Station


Weather Summary

University of Delaware,


Week of May 9 to May 15, 1997



0.06 inches: May 9

0.61 inches: May 10

0.04 inches: May 15

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




Ranged from 75EF on May 10 to 63EF on May 14.


Ranged from 58EF on May 13 to 40EF on May 14.



Soil Temperature:

58.5EF. Average for the week.





Compiled & 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.