Vol. 5 No. 2 April 10, 1997

Weekly Crop Update

University of Delaware Cooperative Extension

Volume 5, Number 2

Thursday, April 10, 1997

Field Crops:

Field Crop Insects -

Joanne Whalen, Extension IPM Specialist.

Small Grains. Cereal leaf beetle eggs can be easily found in most wheat fields. Eggs are elliptical in shape and are yellow to burnt orangish-yellow in color. Although eggs can be found in most fields, adults prefer to lay eggs in late planted fields and in thinner stands. Larvae will appear slug-like in shape and resemble small Colorado potato beetle larvae except for the color. The head and legs will be brown-black and the body orange-yellow in color. Scouting should begin by mid-April to determine if egg hatch has begun. As soon as the weather turns warmer, you should begin to see egg hatch. In warmer weather, damage can occur in as little as five days. Examine 10 tillers (stems) in 10 locations for the presence of larvae and eggs. In most cases, the treatment threshold of 0.5 per stem will provide timely control. Remember, this was a new threshold in 1996 reflecting research results from North Carolina and Virginia. Their 1996 research results indicate that this threshold may need to be reduced even further, especially in higher management wheat and in areas at higher risk (i.e. high egg counts, problems the previous season). In addition, if aerial application is delayed, larvae could reach damaging levels before controls can be applied. If fields are at high risk for damage, one should consider a treatment when 50% of the eggs have hatched and you find a total of 25 eggs and/or larvae per 100 tillers. Lannate, Furadan, Malathion, Sevin, and Warrior all provide beetle control.

Field Corn. High levels of black cutworm moths have been found in pheromone traps in Maryland and Delaware. In recent years, these traps have provided a good indication of the potential for economic infestations in field corn. Since trap catches are higher than normal, all fields should be scouted at emergence for the presence of feeding damage and/or cut plants. A rescue treatment will be needed before the 3-leaf stage if 10% or more of the plants show leaf feeding or 2% of the plants are cut and larvae are present. If a field has a history of cutworm problems, it will be late-planted, and you are unable to scout the field in a timely manner, an insecticide should be applied at planting or tank mixed with the herbicide within a week of planting. If a soil insecticide is used, Force and Lorsban have provided the most consistent control. Fortress is also labeled for cutworm control. If an insecticide is tank-mixed with the herbicide, Ambush, Asana, Pounce, or Warrior will provide the best control.

Alfalfa. Begin sampling for alfalfa weevil larvae feeding in the tips of plants. Check 10-20 plants per field for the presence of feeding damage which appears as small holes in the leaves. If feeding damage is observed, randomly walk through the field collecting 30 stems and place them top first in a bucket. In addition, measure the stem height at 5-10 sites to get an average stem height per field. If alfalfa is less than 12 inches tall, the treatment threshold is 0.7 per stem. Once alfalfa reaches 12 inches in height, the threshold increases to 1 per stem. In recent years, Furadan, Imidan, and Penncap-M have provided the most consistent control.

Broadstrike Label Changes -

Mark VanGessel, Extension Weed Specialist.

Broadstrike SF + Dual and Hornet (formerly called Broadstrike Plus) have been used in Delaware for management of triazine-resistant lambsquarters and pigweeds in corn. However, Broadstrike has injured corn in certain situations. To minimize the risk of crop injury, labels of Broadstrike products have been changed. Broadstrike products should be used in corn when 1.) soil temperature is consistently >50F, 2.) soil organic matter is at least 1.5 %, 3.) corn is planted at least 1.5 inches deep and 4.) Counter is not used as a soil-insecticide. If all of the restrictions are not met, then use a IR corn hybrid. Broadstrike can help with triazine-resistant weed management, but planning is required to minimize the risk of crop injury.

Preparing Fields for No-till Corn -

Mark VanGessel, Extension Weed Specialist.

As you consider burn-down herbicides for no-till corn fields a few things to keep in mind. Gramoxone or Roundup will not provide residual control and if they are used alone, you may need a second application at planting to control weeds emerging closer to planting. Consider using atrazine and a grass herbicide in combination with Roundup or Gramoxone to control those later emerging weeds. Extrazine (pre-mix of atrazine and Bladex) applied 2 to 3 weeks before planting, in combination with Princep or 2,4-D ester, has provided good burndown activity and provided residual control. Finally, if using a residual grass herbicide (Dual, Micro-Tech, Frontier, Harness, Surpass etc.) two weeks or longer before planting, the rates are higher than if these herbicides were applied at planting - check the label.

Agricultural Crop Additive - ACA - Does it Pay? -

Ed Kee, Extension Vegetable Crops Specialist.

ACA, has been sold locally for several years on Delmarva as a crop stimulant or yield enhancer. ACA stands for Agricultural Crop Additive. It was developed in the early 1970's and sold as an additive for anhydrous ammonia. ACA is formulated by combining acetic acid, water, anhydrous ammonia, and zinc oxide to make a product with a guaranteed analysis of 15% nitrogen and 17% zinc, by weight. It weighs 10.55 lb./gallon.

It has been suggested that it acted as a nitrification inhibitor, although this has been proven not to be the case. It has been speculated that the zinc has been providing a micronutrient response. More recent indications are that some sort of plant regulatory action is occurring. Reported responses to ACA include more fibrous and extensive root systems, increase in the number of brace roots, faster and more vigorous early plant growth, wider and darker green leaves, and heavier ear and kernel weight.

Positive yield responses have been the exception rather than the rule in controlled, replicated experiments conducted both in the Mid-Atlantic region and in the Midwest. A three-year study in Michigan did report slight increases in grain yield of field corn (3 to 4 bushels) when ACA was sidedressed with N, but not when applied pre-plant. Studies in Minnesota report moderate increases in one year, no responses in two other years. Studies in Wisconsin did not generate higher yields in field corn.

The results in the Mid-Atlantic region have, with a few exceptions, failed to demonstrate yield increases in several agronomic and vegetable crops. The University of Maryland has shown responses in small grains, but Virginia studies have not shown similar responses. There have been no responses in several vegetable crops tested in the region in the early 1990's. Recent work in potatoes and sweet corn in Wisconsin have not shown a conclusive positive response to ACA.

The inconsistencies in yield response suggest that further research is needed to determine the application, environmental, and varietal interactions that affect the ability of ACA to pay back the growers investment with significantly increased yield. Currently, I do not recommend its use, because the evidence accumulated to date does not indicate good chances for yield increases. Growers who wish to evaluate this material, and others like it, need to make a true Awith and without comparison on their farm. That is the ultimate test.

1996 Variety Trial Results. -

Bob Uniatowski, Extension Associate IV, Agronomy.

The 1996 variety trial results are available from your County Extension Office. Ask for bulletin #63 for corn hybrids, #65 for soybeans, and #66 for sorghum.

If there are any varieties that you would like to see in the soybean or sorghum variety trials, please let me know (302) 831-2531 or your county agent.

The 1997 small grain variety trials are available for viewing. The New Castle County plot is located 1 mile east of Rt. 896 on Marl Pit Road, in Kent County across from the Honda dealership on Rt. 13 south of Dover, and in Sussex County between the farm complex and the administration offices at the Research and Education Center.

Field Crop Diseases -

Bob Mulrooney, Extension Plant Pathologist.

Wheat. Early season diseases that may be present now are powdery mildew, Ascochyta leafspot, barley yellow dwarf virus, and soil­borne wheat mosaic virus. Powdery mildew is very easy to diagnose. Look for white to tan masses of fungal growth on the leaves. Jointing or growth stage 6 (Feeks), is a good time to begin checking for powdery mildew. It is generally to early to take any action at this time, but monitor disease development.

Ascochyta leafspot often appears at green­up and resembles Septoria leafspot. Symptoms include large gray­brown spots on the lower leaves that tend to be oval shaped. It will also produce small black to brown pin­head sized fungal structures in the dead leaf tissue. This fungus leafspot gets established on winter damaged tissue, but has been of minor importance and does not need to be controlled. This early in the season if you see circular areas in the fields where the wheat is shorter than the surrounding areas and lighter in color barley yellow dwarf virus(BYD) or wheat soil­borne mosaic virus (WSBM) may be the cause. Closer observation may reveal that the oldest leaves are bright yellow which may mean BYD, if leaves are mottled yellow­green it may indicate WSBM. The only way to be sure is to have a sample of infected plants tested for the presence of the virus. BYD is transmitted by aphid feeding in the fall and spring, WSBM is transmitted by a soil inhabiting fungus.

Split Nitrogen Applications -

Richard W. Taylor, Extension Agronomist, Univ. of Delaware

Some growers prefer to apply spring nitrogen (N) in a split application. This can often be beneficial especially in seasons with above average rainfall or when particularly heavy rainfall events cause high N loss. When applying liquid urea-ammonium nitrate (UAN), growers using split applications often experience significant leaf burn following the second N application. This can be avoided by diluting the N solution with water. Ron Mulford, Farm Superintendent at the University of Maryland Popular Hill facility suggest the following dilution rates. For 60 lbs N/A, you will need about 18.5 gal of 30 percent UAN plus 9 to 10 gal of water per acre and for 40 lbs N/A you will need about 12.5 gal of 30 percent UAN plus 7 to 8 gal of water per acre. Dilution will minimize any negative effect on yield from leaf burn. Adjust your spray volume to deliver the desired number of units of nitrogen.

Grain Marketing Highlights -

Carl L. German, Extension Specialist, Marketing

This report is being issued a day ahead of the monthly USDA Supply and Demand Estimate revisions that are scheduled for release on April 10, 1997. Interestingly, the trade speculation holds that we are likely to look for a further reduction in the soybean carryover estimate. In the

March report, USDA put the soybean carryover at 140 million bushels; corn carryover stocks were estimated at 959 million bushels; and wheat carryover stocks were placed at 379 million bushels. The reason for this speculation is a day after the issue of the March 31 Grain Stocks Report a correction was made in the Mississippi figure that reduced total soybean stocks by 22 million bushels. So the trade is anxiously awaiting the April Supply and Demand update. We are generally in a tight world supply situation for soybeans and oilseeds. This has translated into good pricing opportunities for old crop and new crop beans. The question of "how long do I wait to make a decision to price" will eventually be somewhat dictated by the 1997 U.S. growing season. We are entering a period of extremely volatile commodity prices. Cost of production and profits need careful consideration in deciding when to pull the sales trigger.

For further information contact Carl German @ 302­831­1317

Vegetable Crops:

Vegetable Crop Insects -

Joanne Whalen, Extension IPM Specialist.

Asparagus. Asparagus beetles are now active. Edge treatments should be applied before beetles move into the main field. Ambush, Pounce, or Sevin will provide control.

Seed Corn Maggot. Flies can be readily found laying eggs in freshly plowed ground. At this time, all direct seeded crops should receive a seed treatment containing diazinon or chlorphrifos (Lorsban). In situations where a combination of the following conditions occur, a seed treatment and soil insecticide will be needed: 1) manure has been applied to a field, 2) a cover crop or crop residue is plowed under late, or 3) the field has a high organic matter content.

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.