Vol. 5 No. 4 April 25, 1997

Weekly Crop Update

University of Delaware Cooperative Extension

Volume 5, Issue 23

September 4, 1997


Field Crops:

Field Crop Insects -

Joanne Whalen, Extension IPM Specialist.

joanne.whalen@mvs.udel.edu

 

Soybeans.

Low levels of small corn earworm larvae can now be found in some double crop fields. Although we do not expect widespread problems from corn earworms, you expect to see isolated fields with economic threshold levels. In most areas blacklight trap catches have increased to 20 to 50 moths per night, so you should start to see small larvae in the next 7-10 day period. At this time, most full season soybeans should escape damage. The predominant fields to watch are soybeans behind barley and irrigated wheat beans where flat pods are present and have just begun to fill. The treatment threshold is 3 larvae 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.


 

Grain Marketing Highlights -

Carl German, Extension Specialist, Crops Marketing

clgerman@udel.edu

 

USDA's weekly crop condition report rated 14 % of the U.S. corn crop excellent, a 1 % decline from the previous week and 12 % of the U.S. soybean crop as excellent, unchanged from the previous week. Beans rated good increased 1 % from the previous week. With the corn and soybean crops beginning to shut down in some areas of the country, we are not likely to see further improvement in the weekly ratings. With the next USDA crop report just a week away, the market is said to be trading a 9.05 to 9.2 billion bushel corn crop and a 2.65 to 2.76 billion bushel soybean crop. Prices are currently reflecting strong new crop export sales, the threat of cooler temperatures, and the market being oversold. The market is currently in a seasonal trend where we can expect prices to rally into September, before harvest and the release of the September 12 crop report. Once harvest is underway we are likely to see a seasonal decline in corn and soybean prices. For further information contact Carl German @ 302-831-1317.

 


 

Understanding High-Oil Corn: Part 1--Top Crosses, What are They?

Richard W. Taylor, Extension Agronomist

rtaylor@udel.edu

Bob Uniatowski, Extension Associate - Field Crops

bobuni@udel.edu

 

There are two approaches currently being used to create high-oil corn hybrids or blends. These are the conventional high-oil corn hybrid and the top cross blend. These types can be described as follows:

 Conventional high-oil corn hybrid: a new hybrid is bred with traditional plant breeding techniques to have a larger embryo, thus increasing the oil content of the grain.

 Top Cross or TC Blend seed corn: The blend consists of two components; a female, or grain parent, composing 90 to 95 percent of the blend and which is male sterile; and the male, or special pollinator, composing 8 to 10 percent of the blend. A currently adapted hybrid is selected to be the female (grain-bearing) parent and the male sterile gene is bred into this adapted hybrid. A special male pollinator licensed to each seed company by DuPont is used as the male line to provide pollen in the field. The large-embryo trait is carried in the genes of the pollen and is expressed (xenia) in the resulting grain from the fertilization of the female parent by the pollen from the special pollinator. If foreign pollen fertilizes the female parent, the grain produced will not have a larger embryo and will have only the normal oil content of corn. The male pollinator is a synthetic inbred. It produces little in the way of grain for yield, but it is thought that this trait will change with time as better synthetics are created by the breeders.

 To understand how Top Cross blends are created and how they work, it's necessary first to define some of the terms used.

 Top cross: A cross between a selection, line, clone, etc., and a common pollen parent which may be a variety, inbred line, single cross, synthetic, etc. The common pollen parent is called the top cross or tester parent. Top cross or open-pollinated progeny are the result of a selected plant (in this case our male-sterile female grain parent) crossing on a random basis with any plants in the area (in the high oil situation, pollination is restricted by a physical barrier--distance from other corn pollen sources--to a synthetic male pollinator line).

 Xenia: The effect of pollen on the embryo and endosperm. For high oil corn, the male line carries the gene for a larger embryo and thus a higher oil content.

 Next week, we will review the quality characteristics that make high-oil corn attractive to the feed industry.

 


 

Fall Harvest Management For Alfalfa -

Richard W. Taylor, Extension Agronomist

rtaylor@udel.edu

 

Fall harvest management of alfalfa is all about protecting the winter hardiness of the crop. In the fall, alfalfa plants are developing cold resistance in response to the shortened day length and cooler day and especially night temperatures. We call this process hardening. It entails a reduction in top growth (harvestable dry matter) production and an increase in carbohydrate storage in the tap root and crown. Next spring (and after each cutting during the growing season), the carbohydrates stored in the root (about 50% remain) will be removed and used to fuel top growth until it is 6 to 8 inches in height. At that point, carbohydrates begin to accumulate in the roots again.

 

Hardiness and winter survival and spring regrowth are possible only if enough carbohydrate storage occurs before cold weather kills the alfalfa top growth in the fall. Traditionally, we recommend not to cut alfalfa 4 to 6 weeks before the first killing frost. In our area, this means that the last cut before a killing frost should not be taken after September 15 to 20. Cut after this period, the new regrowth may not be sufficient to restore root carbohydrates levels before a killing frost and this can increase the risk of winter kill.

 

An article in the "Pennsylvania Forage and Grassland News" suggests that management practices and planning can minimize the potential for winter injury from fall harvest stress. The article listed the following items:

Young stands are less susceptible to winter injury due to fall harvesting than older stands.

Length of harvest interval during the growing season is more important than the date of fall harvest in determining alfalfa stand survival. Delaying at least one harvest during the season until 50 percent bloom reduces the risk of all harvest compared to taking fall harvests at late bud or first flower.

Maintaining soil fertility levels (especially potash but also phosphorus, sulfur, and boron) is extremely important in reducing the risks associated with fall harvest.

Use of disease resistant and winter hardy alfalfa cultivars will reduce the risk.

Environmental conditions either moderate or aggravate the effects of fall harvesting. These include:

• Temperatures of 5 to 150 F. injure alfalfa crowns and roots. Soil and snow can insulate the crown and roots. So can companion crops such as orchardgrass and ryegrass.

• Amount of snow cover determines the amount of protection (>6 inches are adequate for insulation)

• Wet soils cool faster than dry soils and can lead to lower soil temperatures. Wet soils also freeze and thaw more extensively, which increases the potential for heaving.

Finally, play it safe. Use a late summer or early fall fertilization plan and avoid cutting after September 15 to 20. Cutting after a killing frost is okay if you need the hay and if you leave enough stubble to catch snow for a cover. Remember that the amount you remove after the killing frost is about equal to the reduction in yield you will see the following spring.


 

Field Crop Diseases -

Bob Mulrooney, Extension Plant Pathologist

bobmul@udel.edu

 

Small Grains.

Fungicide seed treatments, properly applied, are highly recommended and can be considered as inexpensive stand establishment insurance. Seed treatments minimize losses from seed decay, seedling blights, and seed and soilborne diseases. Some products have enough systemic fungicide activity to provide early spring disease control, e.g. Baytan. The following table taken from EB 237, 1997 Pest Management Recommendations for Field Crops, indicates disease control efficacy for small grain seed treatments. Wheat varieties with high levels of disease resistance may only need a seed treatment such as Raxil-thiram or Vitavax 200 for loose smut, seed rots and seedling decay, while powdery mildew susceptible varieties may need Baytan or Dividend.

 

Comparison of effectiveness of seed treatments in the management of diseases that typically occur in the Mid-Atlantic region.

 

 

 

Seed Treatment

 

Rate

(fl oz/cwt)

 

Wheat

Loose

Smut

Early

Season

Powdery

Mildew

 

Seedborne

Scab

 

Early

Season

Septoria

 

Barley

Loose

Smut

 

Barley

Stripe

Baytan + Captan

1.25 + 2.0

E

E

F

G

E

G

Dividend

0.5

E

P

P

F

NR

NR

Dividend

1.0

E

F

F

G

NR

NR

Flo-Pro IMZ

0.25 - 0.5

N

N

F

q

N

E

Raxil + Thiram

3.5

E

P

G

q

E

G

Vitavax 200

3.0 - 4.0

G

N

G

N

G

F

Key: E= excellent, G=good, F=fair, P=Poor, N=no control, NR= not registered, q = information not available.


Vegetable Crops:

Vegetable Crop Insects -

Joanne Whalen, Extension IPM Specialist.

joanne.whalen@mvs.udel.edu

 

Cole Crops.

A mixture of imported cabbageworm, cabbage looper and diamondback can be found in most cole crop fields. If you are only concerned with imported cabbageworm, then a Bt alone will provide effective control. However, a combination of cabbage looper and diamondback can be found in most fields. Treatments should be applied when 5% of the plants are infested. A combination of a Bt plus a pyrethroid will provide control. Since cabbage looper egg laying has increased, you may need to apply controls on a 5 day schedule until the egg laying period is over.

 

Lima Beans.

Be sure to watch for an increase in corn earworm egg laying and larval activity during the next week. Corn earworm blacklight trap catches have increased to 20 - 50 per night in many areas and moths will be very attracted to fields in bloom. A treatment should be applied when you find one corn earworm larvae per 6 ft of row. Lannate LV should be applied at a rate of 2 - 3 pt per acre depending on the size of the larvae at treatment time. Green cloverworm can also be found in most lima bean fields. Controls are not needed until you find at least 20- 30 worms per 6 foot of row, especially if worms are small. In addition, larval populations have started to crash as a result of natural controls from fungal diseases.

 

Peppers.

In most areas, peppers should be sprayed on a 7 day schedule for the insect complex present. In areas where corn borer catches are above 20 per night, sprays should be applied on a 5 day schedule. Be sure to check the Crop Pest Hotline for the most recent nightly blacklight trap catches. Since corn earworm pressure has significantly increased and corn borer pressure is still high, Lannate or a combination of Orthene and a pyrethroid will be needed to provide control of both species.

 

Processing Snap Beans.

In areas where corn borer catches are above 20 per night, you may need to consider 3 Orthene treatments from the prebud to pin stage to avoid stem entrances and plant lodging. Treatments may need to be applied on a 5 day schedule to be within the 14 day preharvest interval for Orthene. In areas where corn earworm catches are above 20 per night, Asana should be combined with Orthene at the pin spray for corn earworm control. After the pin spray, sprays should be applied on a 5 day schedule except in the Harrington area where sprays are needed on a 4 day schedule.

 

Sweet Corn.

Any remaining fresh market sweet corn should be sprayed on a 2-3 day silk spray schedule until the end of the season.


 

Vegetable Crop Diseases -

Bob Mulrooney, Extension Plant Pathologist

bobmul@udel.edu

 

Tomatoes.

Powdery mildew has been identified in New Jersey and New York this summer infecting field grown tomatoes. Previously powdery mildew had been seen only in greenhouse production and just within the last two years in New York. Infected tomato leaves are chlorotic and the fungus produces white, talcum-like growth typical of the powdery mildews on the lower leaf surfaces. Powdery mildew is certainly a common disease on the eastern shore, but not on tomatoes. Powdery mildew is more common in the western growing regions. It has been reported that Bravo provides control if complete coverage of the leaves can be obtained. Be on the lookout for this new disease on tomatoes. Please let the county agents know if you spot this disease in Delaware either in commercial production or in home gardens. If there is any question concerning identification of powdery mildew, place infected leaves in a zip-lock bag and submit samples to the county agents or myself at 154 Townsend Hall, Newark, DE 19717.

 

Spinach.

For fall planting, be sure to rotate away from spinach for 2 years to avoid white rust and apply Ridomil Gold as a pre-emergence spray application for control of pre-emergence damping-off and early season control of blue mold and white rust.

 

Snap beans.

Be on the lookout for bean rust. Rust can be a problem on fall-planted crops. Planting resistant varieties for the fall crop is the best control, but if rust should appear, spray with Bravo every 7 days. Rust is easily identified by the presence of small, yellow, circular spots with a reddish-orange, powdery spore mass in the center.

 

Lima beans.

Remember that favorable weather in the fall can mean downy mildew. If 1.2 inches of rain falls within a 7 day period and the average daily temperature is 78F, downy mildew can occur on a susceptible variety if the fungus is present. If a period of 90 F occurs during this time, the disease will not develop. Keep an eye on the weather and spray accordingly with tri-basic copper sulfate.

 

Fall sampling for nematodes in vegetable crops.

Fall is the best time to determine nematode levels in production fields. Nematode levels are usually the highest in the fall following harvest. This is particularly true if root knot nematode is a potential problem. Melon growers particularly are encouraged to sample fields for next years production after fall harvest. Spring samples are not reliable in detecting damaging levels of root knot nematode. Sample directions and nematode test bags are available from each county Extension office. This inexpensive test can pay big dividends, so as the soil test folks say, Don’t guess, soil test.


 

Weather Summary

University of Delaware,

Georgetown

 

Week of August 29 to September 4, 1997

 


Rainfall:

0.83 inches: Sept. 2

0.05 inches: Sept 3

0.03 inches: Sept. 4

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

 


Temperature:

 

Highs

Ranged from 89 F on September 2 to 77 F on September 4.

Lows

Ranged from 69 F on September 3 to 49 F on September 4.

 


Soil Temperature:

73 F. Average for the week.

 


http://laurie.rec.udel.edu


 

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.