Weekly Crop Update

University of Delaware Cooperative Extension

Volume 5, Issue 20

August 14, 1997

Field Crops:

Field Crop Insects -

Joanne Whalen, Extension IPM Specialist.




Although most of our attention has focused on spider mite problems, be sure to scout fields for the presence of corn earworm larvae. Corn earworm moth catches have been relatively low this season; however, a combination of migratory moths and a resident population now leaving drought stressed field corn will be attracted to soybeans. Fields that have been sprayed multiple times for mites may also be more prone to corn earworm problems due to a reduction in beneficial insect activity. Begin scouting fields as soon as flowering occurs. The treatment threshold is 3 per 25 sweeps in narrow row beans and 5 per 25 sweeps in wide row beans. Ambush, Asana, Larvin, Pounce or Warrior will provide control.

Short of Forage? What Can You Do Now?

Richard W. Taylor, Extension Agronomist


Bob Uniatowski, Extension Associate - Field Crops



With drought conditions existing in many areas of the state, livestock and dairy producers may be faced with a shortage for forage. It's too late now to obtain much growth from warm-season annuals such as the millets, sudangrasses, or sorghum-sudangrass crosses. However, there still are options available as noted below.


Grazing Options:

1. Spring oats can be seeded during August and early September. Seed at about 3 bu/A either under conventional tillage or no-tillage. Generally, no added inputs are needed especially if the crop is seeded after drought-stressed corn.


2. Barley, rye, winter oats, and triticale (the winter grains) can be seeded in early September for fall and spring grazing. Again, seed at heavier rates than usually used for grain production. Unless you expect high residual nitrogen (N) levels (for example, after drought-stressed corn or early harvested beans), apply 30 to45 lbs N/A to stimulate fall vegetative growth. Limit fall grazing so that the grains enter the winter with at least 2 to 3 inches of growth. Spring grazing is also possible without significant yield reduction if cattle are removed prior to stem elongation or Feeke's growth stage 6 (first node visible above soil surface).


Silage Options:

1. Spring oats--see above.

2. A mixture of spring oats and winter grains can be used. Since winter grains are leafy and produce no stem material in the fall, making silage is difficult unless mixed with spring oats. Plant about 2 bu/A of spring oats along with 1 to 1.5 bu/A of a winter grain. The winter grain can be harvested the next spring for either silage or grain. Rye is the most commonly used winter grain as it has the most winter hardiness and can be planted the latest of the winter cereals. It does drop in quality faster than the other cereals, so it must be harvestedin the boot stage (prior to head emergence) for best quality. Blending rye with wheat or triticale can help maintain quality if rye harvest is delayed past head emergence.

Harvest maturity of the winter grains can be ranked (earliest to latest) as follows: Rye > Barley > Wheat > Triticale. Management for forage is similar to that for grain except that seeding rates should be increased as the seeding date is delayed and spring nitrogen must not be delayed. Apply the required amount of N at the first sign of green-up in early spring to stimulate additional tillering (this can increase dry matter production). Fall N should also be used if adequate residual is not available from the soil.

3. Soybeans - At least through early August, soybeans are an option, either by salvaging a drought-injured crop or planting late for emergency silage. Soybeans can be planted up until early August. Plant as late a season variety as possible so it will continue to grow until the temperatures approach freezing in the fall. Seed with a grain drill at 300,000 seed/A on narrow row spacing. Harvest for silage prior to a killing frost to keep as much leaf material as possible. Yield will depend on planting date, maturity group, and available soil moisture from late-season rains but range up to 1 to 1.5 ton/A if conditions are favorable for growth.

Root Stimulators on Wheat

Richard W. Taylor, Extension Agronomist


Bob Uniatowski, Extension Associate - Field Crops



We recently saw a research report on Amisorb from Dr. Lloyd Murdock, Extension Soils Specialist from the University of Kentucky. Amisorb is another of the root stimulating products (others include ACA and Asset) reported to increase nutrient plant uptake and availability and to stimulate root growth. He applied 1 qt/A of Amisorb in the fall and again in late winter (Feb. 14) along with 30 lb nitrogen (N)/A. Another 60 lb N/A was applied in March. The wheat was planted at 35 seeds/ft2 on October 16. There were no visual differences between the treatments throughout the growing season, no differences in chlorophyll readings, and no differences in yield. The control averaged 104 bu/A and 2 qt/A of Amisorb averaged 101 bu/A. Dr. Murdock concluded that, at this point, Amisorb does not show promise as an effective additive to a wheat fertility program.

 In work that we conducted at sites in Georgetown and Middletown, we found no difference in wheat yields between a control (no ACA or Asset) and various treatments (1/3, 2/3, and 1 pt/A) of the root stimulators with a N application rate of 75 to 90 lb N/A. Several other researchers in the region also have failed to find any yield benefits for these additives although one researcher has consistently seen yield responses, generally under low fertility conditions. Before using these products, you will need to decide whether under your growing conditions and cultural practices they will add enough to your bottom line to justify their use. If you soil test and your fertility program is up to par, we have seen little if any benefit to these soil additives.


Grain Marketing Highlights -

Carl German, Extension Specialist, Crops Marketing


With the release of the USDA August crop report, which is the first report for the 1997 crop based upon field surveys, some key points should be noted. First, although the remaining soybean supply for old crop beans is in short supply (at 125 million bushels) the production forecast for the 1997 new crop is 2.74 billion bushels, leaving the projected carryover at an estimated 305 million bushels, a 180 million bushel increase. This production forecast is 9% higher than the 1994 record year. World soybean supplies (stated in million metric tons) are projected to increase inoverall production and in ending stocks when compared to the current crop year. Production shows an estimated 10% increase and ending world stocks a whopping 36% increase. The relatively short supply for old crop beans has resulted in a season average soybean price of $7.38 per bushel for the 1996/97 old crop. However, for new crop U.S. beans to remain competitive in the world market, USDA is projecting the 1997 new crop soybean price to range from $5.40 to $6.60 per bushel, likely a realistic estimate. The current preferred sales method for old crop and new crop beans is to make cash sales.

 The current forecast for U.S. corn production is 9.28 billion bushels, down 424 million from last month and slightly below last year. This estimate came in well below average trade expectations and has provided a rally in the corn market with spillover support to wheat and soybeans. Ending U.S. corn stocks are projected at 847 million bushels, a 94 million bushel drop from last year. The $2.60 December corn put may be a possibility for those needing to contract more 1997 corn production.

Roundup Ultra plus Insecticides -

Mark VanGessel, Extension Weed Specialist.


Some of the double-cropped soybeans planted with Roundup Ready varieties are needing both a herbicide and an application for mites. Tank-mixing dimethoate with Roundup Ultra is not a problem. The formulation of dimethoate (an emulsifiable concentrate - EC) may cause some flecking on the leaves, but nothing to be concerned about. Also, other miticides are not a problem when tank-mixing with Roundup.

Field Crop Diseases -

Bob Mulrooney, Extension Plant Pathologist.



Be on the lookout for charcoal rot. This soil inhabiting fungus can cause problems in short to mid season varieties planted full season. This fungus disease is favored by hot dry weather. Symptoms usually appear after flowering and during pod fill. Irregular spots of wilting plants appear in the field. Charcoal rot is primarily a root and basal stem disease, but may be seen on aboveground parts of infected plants. Diseased tissue in the taproot and lower stem develops a grayish discoloration. Eventually the lower stem is girdled, causing wilting and death. Infected soybeans have many tiny, black specks (sclerotia) on the roots and lower stem just beneath the epidermis or bark. The sclerotia resemble a sprinkling of powdered charcoal, hence the name charcoal rot.

Field Corn.

Since the end of July southern corn leaf blight, race O, has been seen in lower Delaware. It has been seen primarily on the lower leaves, and in most cases has not been a threat to yields. Spots (lesions) caused by southern corn leaf blight are usually tan, narrow 2 to3 inch wide by : inch long. The lesions often have a brown to reddish-brown border and can be numerous. Under favorable weather conditions lesions can merge, blighting whole leaves. The lack of rainfall thus far will greatly limit the development of many fungal leaf spots in non-irrigated corn.

Vegetable Crops:

Vegetable Crop Insects -

Joanne Whalen, Extension IPM Specialist.



Economic levels of diamondback and cabbage looper larvae can now be found in cabbage. In most cases, diamondback larvae can be found in the heart of the plant and cabbage looper on the undersides of the leaves. A treatment is needed if 5% of the plants are infested with larvae (a single species or combination of the two), especially if they are feeding in the hearts of the plants. If larvae are small, a combination of a Bt plus a pyrethroid has provided good control when both insects are present.

 If most diamondback larvae are large at the time of treatment, Monitor ( 1 qt/acre, 35 days to harvest) or Thiodan plus a Bt have provided the best control. Remember, Monitor will not provide adequate cabbage looper control.

Lima Beans.

As corn begins to dry down and corn earworm moths migrate from the south, be sure to begin sampling fields for earworm larvae. Whenever possible, fields should be scouted twice a week since populations can increase quickly and we are limited in our chemical selection. Lannate is the only effective insecticide labeled for earworm control in lima beans. Rate selection is dependent on the size of larvae at treatment time. If most larvae are small, 1.5 to 2 pt/acre of Lannate LV will provide control. However, 3 pt/acre should be used if the worms are large.


Corn borer and fall armyworm are the primary insect pests of concern at this time. Since corn borer catches have significantly increased, sprays should be applied on a 5-7 day schedule. In most cases, Orthene is the material of choice since corn borer and fall armyworm are the predominant pest. In areas where corn earworm blacklight trap catches are above 10 per night, Lannate should be used.

Pickling Cucumbers.

Be sure to watch small seedling plants for melon aphids. Economic levels can still be found and will quickly cause damage in hot, dry weather. Fields should be treated if 20% of the plants are infested with aphids. Lannate LV (1.5 pt/acre) is the only effective labeled insecticide for melon aphid control on cucumbers. Pickleworms can be readily found in the terminals of plants that have begun to form runners. Infestation levels range between 1 and 6% infested terminals. In some cases 2-3 larvae can be found in each terminal. If you plan to harvest the field within 4 days and only small larvae are found in the terminals, no spray should be needed since larvae do not start moving to the fruit until they are half grown. However, if you are greater than 4 days from harvest and/or larvae can be seen moving out from the terminals, Lannate LV at 1.5 pt per acre should be used. If a second application is needed, Asana XL (8 oz/a) should be applied.

Snap Beans.

Processing - Corn borer pressure has significantly increased in a number of locations throughout Delaware and Maryland. In order to prevent larvae from tunneling into the stems of plants, the bud spray of Orthene should be applied one week before buds are found or at the earliest sign of buds. Since corn earworn moths are starting to leave drought stressed corn, a combination of Orthene plus Asana should be used at the pin spray. After the pin spray, controls should be applied on a 5-6 day schedule except in the Harrington and Leipsic areas where sprays are needed on a 4 day schedule.

Sweet Corn.

All fresh market silking sweet corn should be sprayed on a 3 day schedule. Corn borer, fall armyworm and corn earworm all pose a threat to sweet corn at this time. At this time, the mid-range rate of Warrior (3.5 oz/a) or the high rate of Baythroid (2.8 oz/a ) should be used. If Lannate, Larvin Ambush, Asana or Pounce are being used, a combination of the mid-range rate of the pyrethroid plus Lannate (1.5 pt/a) or Larvin (30 oz/a) should be used.


U of D Crop Pest Hotline:

In State: 1-800-345-7544

Out-of-State: 302-831-8851


Field Crop Diseases -

Bob Mulrooney, Extension Plant Pathologist




Maintain applications of Bravo every 10 days for the control of leaf spots especially Alternaria.

Sweet Corn.

Rust is still present in some fields. Scout young plantings especially if older plantings are infected. If rust is seen prior to whorl development, apply a fungicide for control.

Pumpkin and Winter Squash.

Maintain foliar applications of Bravo plus a copper fungicide every 7-10 days for the control of foliage and fruit diseases.


If bacterial spot is present, do not work in the fields when the leaves are wet and apply a foliar spray of a copper fungicide plus maneb every 7 days for control. Bacterial spot produces numerous small, angular, brown spots on the leaves.


UpComing Events...


Crop Management Tour

Thursday, August 21, 1997

9:00 a.m. - 12:00 p.m.

Lunch will be served at 12:30 p.m. at the Research & Education Center in the grove

 Please contact the Research & Education Center at 302-856-7303 to reserve a spot on the bus and lunch.

University of Maryland

Wye Research and Education Center

Field Day

August 21, 1997

Registration 8:30 a.m. - Noon

Concurrent Tours, 8:30 a.m. - 11 a.m.

  • Field Crops and Soils

    Horticultural Crops

    Animal Sciences

  • IPM Orchard Tour

    Raspberry Improvement

    Aquatic Toxicology/Water Quality Tour

  • Crab Feast, 3:30 p.m. - 6 p.m.

  • Exhibits - All Day


    Weather Summary

    University of Delaware,

    Georgetown, DE

     Week of August 8 to August 14, 1997


    0.45 inches: August 14

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



    Ranged from 93F on August 14 to 82F on August 8.


    Ranged from 71F on August 14 to 57F on August 8 & 10.

    Soil Temperature:

    73.6F. 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.


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