Vol. 5 No. 4 April 25, 1997

Weekly Crop Update
University of Delaware Cooperative Extension

Volume 5, Issue 5

May 1, 1997

Field Crops:

Field Crop Insects -

Joanne Whalen, Extension IPM Specialist.

Field Corn - Low levels of cutworm leaf feeding activity have been observed in the earliest planted corn. With the higher than normal pheromone trap catches and the cool, wet weather, fields should be scouted at emergence for the presence of leaf feeding, cut plants and larvae. A treatment will be needed if you find 10% leaf feeding or 3% cut plants and larvae are present. Rescue treatments should be applied before larvae are one-inch long. Asana, Ambush, Pounce or Warrior will all provide control.

Small Grains - Although cereal leaf beetle egg hatch was significantly reduced by the cold spring weather and freezing night temperatures, adults can still be found mating and laying eggs. In addition, the first grass sawfly larvae have been found on the lower eastern shore. So far, no armyworm larvae have been detected. As temperatures increase, all three insects could be found in wheat. The following thresholds can be used to make a treatment decision: cereal leaf beetle - 0.5 per leaf; grass sawfly - 0.4 per linear foot of row; and armyworm - 1-2 per foot of row. Remember, armyworms can cause greater damage in barley so the lower threshold should be used. When all three insects are present, the threshold of each should be reduced by at least one-third. If all 3 insects are present in wheat, Warrior, Lannate, or Parathion will provide the best control. Remember only Lannate and Parathion are labeled on barley. Also, Parathion can only be applied by air and has set back restrictions.

Soybeans - If you plan to plant full season no-till soybeans, be sure to treat the seed for seed corn maggot. Flies are still laying eggs and larvae will be present in fields with high amounts of organic matter. A seed treatment containing diazinon will be needed to control seed corn maggot larvae.

Herbicide News -

Mark VanGessel, Extension Specialist.

ISK Biosciences will discontinue the production of Dacthal. Dacthal inventories will be depleted with time. It is estimated that there is an 18 months supply of Dacthal. Expect prices to increase as supply declines.

Speaking of prices, BASF manufacturer of Poast and Poast Plus, has decided to reduce the price of Poast. The reduction will bring the cost of amount active ingredient to about the same level for both Poast and Poast Plus. Remember the formulations are not the same for Poast 1.5L and Poast Plus 1.0L, so price per gallon will not be the same. This will reduce the cost of postemergence grass control in vegetables.

Field Crop Diseases -

Bob Mulrooney, Extension Plant Pathologist.

Wheat. Keep checking for powdery mildew. Disease development is progressing. Depending on the variety susceptibility, stand, nitrogen fertility, and the weather. Tyler, Pennmore, and Mason have significant mildew at the present time in the New Castle county test plots near Middletown. Barley yellow dwarf symptoms have been seen in several areas in Sussex county. Infected wheat will be yellow, slightly to severely stunted, and surrounded by normal wheat. It often occurs in spots where aphids have fed or are feeding. Leaf discoloration can vary including shades of yellow, red, or purple. Discoloration often occurs from the tip to the base of the leaf and from the margin to the midrib. The only definite way to confirm the diagnosis is by a serological test.

Lastly, I have detected some Septoria leaf spot caused by Septoria nodorum, on some lower canopy leaves from Georgetown. So be on the lookout for Septoria as well.

Plant Soybeans Early -

Richard W. Taylor Extension Agronomist, and Bob Uniatowski, Extension Associate for Field Crops

Although it=s the first of May, you probably aren=t planning to plant soybeans just yet. But, farm and research experience suggests that the first full week of May is the best time to plant varieties from maturity group IV and V. Based on a 4-year project sponsored by the Delaware Soybean Board, delaying planting until the first of June reduced yield by an average of 10 to 15 bu/A depending on variety.

What about earlier-maturing varieties, maturity group III and II? For group III beans, the ideal planting date was mid-May and for group II beans it was mid-June. Yield potential declined after the ideal date and by late-June and early-July yield reductions of 1 to 1.25 bu/A/day occurred.

If you have some fields that are fit for soybean planting and your corn fields are still not fit to plant, switch over and plant your group IV and V soybean varieties and see how they respond to early planting.

Some Keys to Successful Soybean Planting -

Richard W. Taylor, Extension Agronomist, and Bob Uniatowski, Extension Associate for Field Crops

In the previous article, we mentioned what early planting can do for your soybean yields but there are other keys to success too. Most importantly, success depends on establishing a vigorous stand of beans. The following are some ideas on ensuring a vigorous stand.

First, use high quality seed of a high performing variety. Many studies have compared bin-run seed to Certified seed. On average, Certified seed will yield 3. 5 bu/A more than bin-run seed. If you choose to use bin-run seed, be certain to treat it special from the time it is planted until its harvested, and then treat it even more special during harvest and during storage. Have it cleaned of weed seeds and broken or damaged beans. Have a germination test run. Although soybean seed is not traditionally treated with a fungicide or insecticide, early planting in cooler and wetter soil conditions may make seed treatments pay. After mid-May when soils are warmer, seed treatments will not be required unless the germination percentage falls below 80 percent. Seed with a germination of 70 percent or less should not be planted.

Once you purchase quality seed, remember to handle it carefully as soybean is more sensitive to rough handling then most other crop seed. Check you planters to be sure the seed coat is not being broken during planting.

A seeding depth between 1 and 1.5 inches is best for soybeans. Emergence problems can occur at seeding depths greater than 2 inches. At the deeper seeding depths, emergence is slower and can increase the chance for damage from insects and diseases.

Consider using a soybean inoculant (Bradyrhizobia) if you haven't used one in your field recently. Many new inoculants are available on the market. The inoculant organism is what supplies the soybean plant with nitrogen. Research by Dr. Jeff Fuhrman with the University of Delaware's Department of Plant and Soil Sciences has demonstrated that many of the native Bradyrhizobia bacteria in our soils are either not very effective at fixing -nitrogen or actually produce a toxin that can limit soybean yields. It only takes a few minutes to treat your soybean seed with the inoculants and costs less than $2 per acre.

Once planted and emerged, scout your fields to guard against early insect problems, weed breaks, and nutrient imbalances.

Follow these suggestions and you should end up with a vigorous stand with top yield potential.

Vegetable Crops:

Vegetable Crop Insects -

Joanne Whalen, Extension IPM Specialist.

Asparagus - With the warmer temperatures, we are starting to see an increase in asparagus beetle activity. Spot treatments along field edges will only work if the beetles have not moved into the field. A treatment is recommended if you find 5 or more beetle per plant and/or egg laying has begun. Sevin, Ambush, or Pounce will provide cost effective control.

Seed Corn Maggot - Adult flies continue to lay eggs and larvae can be found feeding on the seeds and in the stems of spring planted vegetable crops. Unfortunately, once damage occurs there is no cost effective rescue treatment. Since the potential for damage will continue throughout the month of May, preventative controls should be applied in all spring planted vegetable crops. If a seed treatment is a viable option, be sure to choose a product that contains diazinon or chlorpyrifos. Although not available for all crops, research from New York still indicates that a chlorpyrifos seed treatment is the best option. In many cases, a broadcast application of diazinon is the only available control option. In order to be effective, it should be incorporated into the top 3-4 inches of soil immediately before planting.

Section 18 Granted For Pre-emergence Use of Command on Watermelons -

Ed Kee, Extension Vegetable Specialist

The EPA has approved a Section 18 Emergency Label for the pre-emergence use of Command on watermelons. A maximum of one application of Command 4EC may be applied using ground equipment at a rate of 0.3 to 0.4 pint of product/acre (0.15 to 0.20 a.i./acre) when applied pre-emergence and at a rate of 0.4 to 0.5 pint of product/acre (0.2 to 0.25 lb a.i./acre) for pre-plant incorporated applications. Command may be applied in a band over the row, adjusting the rate and carrier volume to the band width. Do not exceed 0.25 lb a.i./acre per year. A preharvest interval of 80 days is required. Follow all directions on the label.

Sinbar, a broadleaf material, has also been submitted. When we receive the EPA rating, we will advise you.

Vegetable Crop Diseases-

Kate Everts, Extension Plant Pathologist,

Universities of Maryland and Delaware

Cucurbits - As early transplants of muskmelon, squash or watermelon go the field, they are at risk of developing scab. This fungal disease is favored by cool wet weather. To control, apply a chlorothalonil product (Bravo or Terranil) every 5 to 7 days.

Phytophthora Root and Crown Rot of Cucurbits - Losses to Phytophthora root rot on peppers and squash were severe in 1996. Field location and field preparation should be made with those losses in mind, since chemical control of Phytophthora is difficult to achieve. Peppers and squash should not be planted into fields which have been cropped to cucurbits, tomatoes, eggplant or pepper within the last 3 years. Phytophthora root rot development is favored by warm, wet weather and begins in areas of the field where excessive water accumulates as a result of high rainfall or poor drainage. Ideally these crops should be planted on well prepared raised beds where water from heavy rain will not pool around the base of the plant (subsoil if necessary to improve drainage). A soil application of Ridomil before or just after planting or transplanting may be beneficial. The key is to plan ahead to avoid disease outbreaks wherever possible.

Spinach - White rust on spinach is present and severe in some areas due to our cool wet weather. If Ridomil 2E was applied at planting on the spring crop, the spinach will be protected in the early season. However, intensive scouting should now be underway. The disease usually appears first on the edges of the field. Apply fungicides when the first sign of disease appears.

Vegetable Diseases -

Bob Mulrooney, Extension Plant Pathologist.

Snapbeans. If damping-off and root rot are a concern in early plantings, apply Ridomil Gold 2E in a 7-inch band over the row at seeding, or apply Ridomil Gold PC-11G in the furrow at planting.

Potatoes. Growers should note the date when each field emerges. Field emergence is defined as the time when a green row can be seen or 50% of the plants have emerged. This date will be used later for determining disease severity values (DSVs). The late blight hotline will be in service this week, hopefully. The number will be 831-6400 in New Castle county, and 1-888-831-SPUD for long distance callers. We are looking forward to providing this information again this year.

Upcoming Meetings:

Quarterly Pesticide Applicator Training and Exam


June 3 & 4, 1997


Delaware Department of Agriculture Conference

Center, Rt 13

Dover, Delaware

Training Date &Time:

June 3 - 8:30a.m.- 4:00p.m.

June 4 - 8:30a.m.- 12 noon

Exam Time:

June 4 - 1:00p.m.- 3:30 p.m.

To register, contact the Delaware Department of Agriculture at 302-739-4811 or 1-800-282-8685 (DE only) and ask for the Pesticide Compliance Section.

Compiled & Edited By:

Tracy Wootten

Extension Associate - Vegetable Crops

Weather Summary

University of Delaware,


Week of April 26 to May 1, 1997


1.02 inches: April 28

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



Ranged from 74EF on May 1 to 60EF on April 27.


Ranged from 49EF on April 28 to 40EF on April 26 & 30.

Soil Temperature:

55.5EF. Average for the week.


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.