Weekly Crop Update

University of Delaware Cooperative Extension

Field Crops:

Field Crop Insects -

Joanne Whalen, Extension IPM Specialist

Small Grains. As a result of warmer, late winter temperatures, aphids can be found in small grain fields at this time. If temperatures remain warm, beneficial insects should be able to keep these populations in check and prevent population explosions seen in 1996. Fields should be scouted by early April for potential aphid problems. Be sure to include sites that are showing plant stress in your sampling plan. Plant damage may appear as circular yellow to brown spots with dead plants in the center. Treatment may be needed if you find 150 aphids per linear foot of row throughout the field and beneficial activity is low. Dimethoate (wheat only, do not apply when temperatures are below 60EF), Disyston, Malathion, Penncap-M and Warrior (wheat only) will provide control.

Field Corn. The decision to use a soil insecticide should be based on a combination of factors including field scouting, history of a pest problem, planting date and conditions favoring a pest problem. If scouting and/or field history information is not available the following factors can be used to determine the potential for a soil insect problem:

(Pest Species/Conditions favoring Outbreaks)

Cutworms

Late planted corn (black cutworm); Combination of poorly drained soil, heavy broadleaf weed growth, soybean stubble, reduced tillage.

Seed Corn Maggot

Cool and/or wet springs with delayed germination; Warm weather in late winter resulting in early fly emergence and egg laying before spring tillage; Early planting in fields with poor drainage, heavy crop residues, and/or manure applications.

White Grubs

Planting into old sod, pasture, hay or set aside acreage; Planting into double crop or full season soybean stubble, especially fields with heavy grass infestations the previous season.

Wireworms

High organic matter soils, sod covers, and heavy grass pressure the previous season; More prevalent in continuous corn with the above conditions.

Rootworms

Continuous corn planted on heavier soil types; rotated corn planted on heavier soils following soybeans with heavy infestation of volunteer corn or weeds.

Changes in Corn Herbicides for 1997 - Mark VanGessel, Extension Weed Specialist.

There will be a few new herbicides available for corn in 1997. Some of these are new products, others are old products just re-packaged and renamed. Many will be in limited supply for the Delmarva region but undoubtedly you will you hear of them.

Balance (Rhone-Poulenc). Preemergence use for annual broadleaf control and some grass suppression. It needs more research in our area to determine effective rates that minimize crop injury.

Basis (DuPont). Pre-package mix of matrix plus pinnacle for early postemergence use. Early postemergence means maximum corn size is 4th leaf stage. Has soil insecticide restrictions similar to Accent. Excellent product for lambsquarters and pigweed (triazine resistant and susceptible) and good on a variety of annual weeds. Check the label for precautions when tank-mixing with Basis. It is labeled for preemergence use but none of the universities in the Mid-Atlantic region have looked at this application timing.

Basis Gold (DuPont). Pre-package mix of matrix plus accent plus atrazine for postemergence use. Has soil insecticide restrictions similar to Accent. This product does not have pinnacle in it and as a result it is weak on triazine resistant pigweed and lambsquarters. Check the label for precautions when tank-mixing with Basis Gold.

Broadstrike (DowElanco). Preemergence use by itself. Can be a help with triazine lambsquarters and pigweed management. Use it in later planted fields to minimize crop injury or use with IR corn hybrids.

Fultime (Zeneca). Pre-packaged mixture of topnotch plus atrazine for preemergence use. Topnotch is the encapsulated form of acetachlor (Harness, Surpass). It still has ground-water restrictions (ground water is less than 30 feet deep and soil texture is sand with less than 3% organic matter; or soil texture is loamy sand and less than 2% o.m.; or soil texture is sandy loam and less than 1% o.m.).

Hornet (DowElanco). New name for Broadstrike Plus, pre-package mixture of broadstrike plus stinger for preemergence application. Use it in later planted fields to minimize crop injury or use with IR corn hybrids. Stinger will control Canada thistles emerged at time of application.

Liberty Link corn (AgrEvo). Corn hybrids genetically altered for resistance to Liberty herbicide. Liberty is a broad spectrum herbicide that will kill conventional corn hybrids. Liberty can be weak on larger grasses and velvetleaf. It is doubtful that one application of Liberty by itself will provide full-season control. Liberty does not provide residual weed control. Current recommendation is to use a soil-applied program and then use Liberty as the postemergence product.

Sethoxydim Resistant corn (SR) (BASF). Corn hybrids genetically altered for use with Poast Plus herbicide. This can be a big help in fields with bermudagrass (wiregrass) or severe crabgrass infestations. There is little to no resistance of SR corn to other postemergence grass herbicides such as Select, Assure II, or Fusilade. Headline is a co-pack of Poast Plus and Laddock (atrazine plus basagran). Headline is weak on triazine-resistant pigweed and lambsquarters.

Touchdown (Zeneca). Burn-down herbicide for use with no-till. Similar properties to Roundup and should be used a similar manner.

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. 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 (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. These viruses can be confused with manganese deficiency caused by high pH, so take a soil test also and check the pH from the good and bad areas.

Soybeans. It is still not too late to check for the soybean cyst nematode. Soil samples can be checked for the presence of SCN at any time of the year as long as the ground is not frozen or flooded. If you are planting susceptible soybeans in an area where SCN is present, I would not plant them without a nematode test. Nematode Assay bags are available from each of the county Extension offices. The Delaware Soybean Board pays for half the cost with check­off funds. Growers in Delaware pay $5.00 per sample. If a soybean grower with a 40 acre field with a yield potential of 40 bushels per acre, plants a susceptible variety on SCN infested ground, he can lose 3­50% of the yield to SCN. If you figure a 30% loss which is 12 bu/A over the 40 acres that is 480 bushels lost at $6.50/bushel. This results in a loss of $3,120 as a result of not taking a $5.00 Nematode Assay Test. Can you afford not to test? PP­2 Management of Soybean Cyst Nematode has recently been revised. This fact sheet outlines the SCN situation in Delaware, and makes management suggestions for growers. If you have not received a copy yet, please stop by a county office or request one. A list of some SCN resistant varieties was recently revised as well, request PP­13 Soybean Variety Reactions to SCN and Root Knot Nematodes.

What Temperature Did You Store Your Herbicides? -Mark VanGessel, Extension Specialist/Weed.

The ideal situation for pesticide storage is a dry room with a temperature above 50EF. But many pesticides are stored in unheated facilities where temperatures drop below freezing. Low temperatures can cause the active ingredient of certain pesticides to breakdown and the pesticide loses its effectiveness. Below is a series of tables for minimum temperatures for some of the common herbicides. This is not meant to be a comprehensive list. If your herbicide is not listed, check the label, or with your county agent, or your dealer for this information. Note this list does include Adry" herbicides as well as Aliquids". The majority of herbicides can be stored at any temperature without a problem.

Do Not Store	Do Not Store	Do Not Store
Below 40EF	Below 32EF	Below 0EF
Broadstrike + Treflan	Basagran	Buctril
Command 4EC	Blazer	Bullet
Commence EC	Devrinol 2E	Laddock
Frontier	Gramoxone Extra	Micro-Tech
Prefar 4-E	Hoelen EC.	Roundup
Prowl 3.3	Kerf 50-W	Weeder 64
Pursuit Plus Lares DF	Poast and Poast Plus
Squadron
Treflan EC	Pursuit
TRI-4	Ramrod
Tri-Scept	Reflex
	Scepter
	Stinger
	Storm

Grain Marketing Highlights - Carl German, Extension Crops Marketing Specialist

Delaware farmers should note two interesting points reported in the grain markets this past week:

• Ownership of mid-western 1996 (old crop) corn production is now primarily in the hands of the grain dealers and handlers in the Mid-West.

• The Chicago Board of Trade 1996 (old crop) soybean price has to rise in order to ration and keep the U.S. from running out of supply before the end of the marketing year, which ends September 30, 1997.

These two key points have resulted in significant price increases in corn and soybeans since the end of February. Cash forward pricing opportunities are available to contract initial 1997 intended production at $3.00 or better of corn and $7.00 or better for soybeans. For further information contact me at 302-831-1317.

Access the Weekly Crop Update on the Internet -

The Weekly Crop Update can be accessed on the World Wide Web at the following address:

http://laurie.rec.udel.edu

Hourly weather information and a daily summary from the Campbell Weather Station located at the University of Delaware Research and Education Center can also be accessed at this site. Past issues of Update from 1996 are also available. We encourage those of you who are currently using the internet, to obtain this information from Athe Web@. It=s fun and it=s free!

Vegetable Crops:

Assure II - New Postemergence Grass Herbicide- Ed Kee, Extension Vegetable Specialist

Assure II is now cleared for postemergence control of grasses in peas and beans. In peas, it may have its best fit to control volunteer small grains. These can be a special problem after plowing during a wet spring, when the small grain tillers back. The grain, especially barley, can be a real quality control problem when mixed in with the peas at harvest. Assure II is labeled at 6 to 12 ounces and can be used with either crop oil concentrates or nonionic surfactants. Check the label for the precise rates of the additives. Repeated applications are allowed, however, the total amount applied cannot exceed 14 ounces. The preharvest interval is a minimum of 15 days.

Matrix - A new Herbicide for Potatoes - Ed Kee, Extension Vegetable Specialist

Matrix is a new herbicide for potatoes that has been tested by University researchers in the mid-Atlantic area and has even been put out in limited commercial trials. However, it is important to note that the formulation of Matrix that is now available is rimsulfuron only. Several years ago, many of us tested a Matrix formulation that was a combination of rimsulfuron and metribuzin (Sencor or Lexone).

Matrix is labeled for preemergence uses, in combination with many standard grass control materials. However, its best fit in Delaware may be as a postemergence material, used after the standard preemergence materials, for example, Dual and Lorox. Matrix may be applied postemergent when the potatoes are emerged but before the crop reaches 14 inches in height. Excellent control of many grasses and broadleaves can be achieved (See label). The material will also provide suppression and some control of purslane.

The postemergent rate is 1 to 1.5 ounces/acre, combined with a nonionic surfactant. Please read the label carefully for all details. There are crop rotation restrictions that must be considered and are listed on the label.

Vegetable Crop Insects - Joanne Whalen, Extension IPM Specialist

Seed Corn Maggot. The warm temperatures in late winter has favored early fly emergence and in many cases egg laying has occurred before spring tillage operations. If spring conditions turn cool and wet and crop germination is delayed, seed corn maggot problems will be seen in many spring planted vegetables. Unfortunately, there are few materials available for effective seed corn maggot management. In addition, chemical controls alone may not always provide adequate control. The most effective controls will be achieved when early, complete tillage is combined with a seed treatment (containing diazinon or chlorpyrifos) and/or a soil insecticide. If surface vegetation is still exposed after tillage, egg laying flies will still be attracted to the field. All the soil insecticides labeled for sweet corn (Counter, Lorsban, Fortress, and Force) will provide seed corn maggot control. However, if conditions are extremely favorable then a seed treatment and complete tillage will also be necessary. In most other spring planted vegetables, a broadcast application of diazinon is the only available soil insecticide. The diazinon must be applied immediately before planting and incorporated in the top 3-4 inches of soil to be effective.

Winter Temperature Index For Predicting Stewarts Wilt in Delaware Sweet Corn ­ 1997 - Bob Mulrooney, Extension Plant Pathologist

The winter temperature index is severe for both Georgetown and Newark. The mean temperature for Dec., Jan., and Feb. were measured at both sites. The sum of these averages provides the bacterial wilt index for predicting Stewarts wilt severity. Since the disease is transmitted by overwintering, the sum of these averages provides the bacterial wilt index for predicting Stewarts wilt severity. Since the disease is transmitted by overwintering

flea beetles that have the bacteria in their alimentary tracts, conditions affecting flea beetle survival influence the occurrence of this disease.

The index is as follows:

Index:	Predicted Severity
< 90 90­100 >100	Usually absent Intermediate Usually severe

foliar insecticides if needed is another option.

Vegetable Diseases -

Kate Everts, Extension Specialist, Vegetable Pathology

Universities of Maryland and Delaware

Spinach. Begin scouting for white rust on fall planted spinach fields which have overwintered. Due to our winter weather conditions, spinach die back was light this year and the abundant green tissue may harbor infections. White rust has been found in Sussex County. Now that the weather is warming up, not only will the plants begin to grow again, so will any disease which is present. Initial symptoms of white rust are chlorotic lesions on the upper surface. The under side of the leaf. Will have white circular pustules, often in the shape of concentric rings. Because much of the leaf tissue which has overwintered is chlorotic, flip the leaves over to look for the white concentric ring shaped pustules in order to confirm the diagnosis. Leaf spots and anthracnose are often prevalent in fall planted overwintered fields. Once the plants begin growing in the spring, apply a copper containing fungicide such as Champ 2, Kocide LF, or Ridomil/Copper for white rust, leaf spots and anthracnose, or Alliette primarily for white rust. Remember that you should not plant a spring crop of spinach near overwinter fields.

Subscribers May Have the Weekly Crop Update Faxed to Them Each Week -

If you would like to have the Weekly Crop Update faxed to you instead of mailed, please indicate so on your subscription form. Your faxed copy should be received no later than Friday afternoon. If we are unable to fax the Update due to electronic malfunction or lighting strike (it has happened once in the past) you will receive your copy by first class mail until the problem is resolved. We will do our best to provided you with this service.

Compiled & Edited By:
Tracy Wootten

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.

Extension Associate - Vegetable Crops