Crop Profile for Wheat in Delaware

Prepared: April, 2002
Revised: August, 2006^[1]

Wheat production for Delaware (no-till) (2, 3)

A timely planted wheat crop germinates, emerges, and tillers before winter dormancy begins in December. Autumn dry matter production and nitrogen (N) requirements are low, but 20-30 lb N/ac is needed to establish the crop and promote root growth and tiller production. This reduces winter-kill and enhances nutrient and moisture use during spring growth. Excessive fall growth from over-fertilization with N can produce wheat susceptible to disease and winterkill. Over-fertilization with N also increases the potential for leaching losses during dormancy. Wheat uses little N during winter dormancy. Wheat breaks dormancy and resumes growth ("greenup") in late February or early March.

The no-till system has been employed successfully for wheat since 1980. In Delaware research trials, yield for no-till wheat was within 0.6 bu/A of the yield of conventionally planted wheat. In all cases, the key to a successful no-till small grain system is good management. Good management involves the selection and calibration of a no-till drill, proper lime and fertilizer planning, careful variety and seeding rate selection, and attention to weed, disease, and insect management.

No-till can substantially reduce the time interval between corn, sorghum, or soybean harvest and small grain planting. When planting date runs into November, any delay in planting results in reduced yield potential and possible crop failure. Labor and fuel savings also accrue by eliminating fall tillage.

PLANTING EQUIPMENT

No-till drills require special attention to planting speed and depth settings based on soil conditions and the amount and type of residue/vegetation. No-till drill planting accuracy improves when planting on level soil surfaces and when the crop residue has been spread uniformly during the previous crop harvest. The combine or mower should always be adjusted to spread the crop residue as uniformly as possible. In addition, certain types of no-till drills may require that grain sorghum or corn stalks be mowed before planting small grains. When situations are encountered where the no-till drill will not satisfactorily perform, conventionally planted small grain would be superior to no-till.

LIMING

Soil pH is critical in small grain production. Wheat is sensitive to both high and low soil acidity levels. Soil pH must be adjusted based on soil type and manganese availability. Light sandy soils should be maintained at a pH from 5.8 to 6.0. Medium textured soils, such as a Sassafras sandy loam, should be maintained at a pH to 6.0 to 6.2. The heavier soils of northern Kent and New Castle counties can range from 6.2 to 6.5. Soil pH is especially important in the lighter soils since manganese deficiency can occur when the soil pH is over 6.0.

FERTILITY AND TOP DRESSING

Small grain phosphorus (P) and potash (K) requirements are the same for both tillage systems. No differences in wheat yields have been shown between fall or spring applied P and K on a medium or higher fertility soil. Required P and K for double-cropped soybeans or grain sorghum can be applied on the small grains.

An important difference between no-till and conventionally tilled small grains relates to the nitrogen (N) response. Research indicates that on no-till wheat 20 to 30 lbs N/A is needed above spring N top dressing normally applied to conventionally-planted small grains. Up to 20 lbs N/A of fall applied N can be beneficial to a small grain crop planted following a high yielding corn crop since little soil N remains, especially on light soils. Fall N may also be beneficial if planting grain late in the season.

The most important fertilizer application is N top dressing in the spring. Research results indicate that on a yield basis ammonium nitrate is superior (3 to 5 bu/A yield advantage) to other N sources. No yield differences have been found between using 30 percent UAN (urea-ammonium nitrate solution) or ammonium sulfate (20-0-0-21.5) although UAN solution offers the advantage of applying N and herbicides (Harmony, 2,4-D, or Banvel) simultaneously. However, ammonium nitrate is generally more expensive and somewhat more difficult to acquire. If a 3 to 5 bu/A yield increase translates into added profits after subtracting the additional cost of using ammonium nitrate, then it is the preferred source. Otherwise, use UAN solution or ammonium sulfate. If a complete fertilizer is needed, the ammoniated phosphate sources can be used.

Urea should not be used to top-dress N on small grains unless rain or irrigation will follow within 24 hours after application. Urea N can readily be lost to the air when applied on a trash or vegetative surface or during warm, humid weather. If a complete analysis fertilizer is used and the material is a blended fertilizer, make sure that urea is not used as the N source. Unless urea N is incorporated by either tillage or watering (rain or irrigation), N loss as great as 40 percent can rapidly occur.

Unlike vegetables and fruit crops, there are no worker hand activities in wheat which would cause pesticide exposure. As with any pesticide, applicators might be exposed during mixing/ loading/ application. Parathion, however, can only be applied by air using a closed system. The use of a closed system as well as other restrictions have significantly reduced any potential worker exposure. The Delaware Department of Agriculture reports that they have had no worker exposure violations or complaints related to pesticide use on wheat. Field crop extension agents in Delaware also report no incidents with worker exposure in wheat.

In Delaware, insects can attack wheat in the fall and spring. Soon after planting in the fall, Hessian fly and multiple aphid species are potential pest problems. Once spring growth resumes, aphids, cereal leaf beetle, true armyworm and grass sawfly can cause economic losses. In recent years, the cereal leaf beetle has become an important pest of wheat grown in the Mid-Atlantic region

Aphid Species

Biology and Life History: The most common aphid species found in Delaware wheat-  fields are the English grain aphid, oak-bird cherry aphid, corn leaf aphid and the greenbug. These four species overwinter on small grains as eggs or females which give rise to offspring in the spring. Wingless females will produce offspring without mating for a number of generations. As small grains mature in late spring to early summer, winged females move to other wild or cultivated grasses for the summer. In the fall, they return to newly-planted small grain fields to overwinter. 

Damage: Although aphids can injure small grains by removing plant juices from the leaves, stems and grain heads, this direct feeding rarely causes economic damage. Generally, there are two exceptions to this rule: (1) Greenbug Aphid Damage: This species secretes a toxic substance into the plants that kills plant tissue. Extensive feeding in the fall and early spring may result in circular yellow to brown spots with dead spots in the center. Infested plants appear stunted and discolored. (2) Aphids Feeding on Grain Heads: Significant damage can occur when large numbers of aphids feed on the grain head causing shriveled or blasted heads. This damage can result in reduced yield and test weight of the grain. This generally occurs when spring conditions are unusually cool resulting rapid aphid development but reduced natural enemy reproduction. The most important losses from aphids occur when aphids vector barley yellow dwarf virus. This occurs when aphids carrying the virus move back into fields in the fall from their wild or cultivated grass hosts.

Monitoring and Decision Making: In areas where Barley Yellow Dwarf virus (BYDV) have been detected in previous seasons, field should be scouted for aphids during the first 30-60 days after emergence in the fall. Examine 5 linear foot of row in 10 areas of a field. Examine areas that exhibit plant stress. At each site, count or estimate the number of aphids per linear foot of row. If BYDV is know to occur and you can find 10-15 aphids per linear foot of row, a treatment is recommended. In the late winter/early spring, sampling should resume, especially if the winter has been mild, up until stem elongation occurs (Feeke’s Stage 4). A treatment will be needed if you find 150-200 aphids per foot of row. If plants are stressed, the treatment should be reduce to 10-15 per foot of row. During heading, check 50 to 100 heads throughout a field. A treatment may be needed if you find 20-25 aphids per head and beneficial insect activity is low. While counting aphid populations, be sure to check for natural enemies. Lady beetle adults and larvae, syrphid fly maggots, lacewing larvae, damsel bugs, and parasitic wasps often help to keep aphid populations in check. A ratio of one predator to every 50 to 100 aphids is sufficient to achieve biological control.

Controls:

Biological: Lady beetle adults and larvae, syrphid fly maggots, lacewing larvae, damsel bugs, and parasitic wasps often help to keep aphid populations in check. A ratio of one predator to every 50 to 100 aphids is sufficient to achieve biological control. One exception should be noted. During cool, spring weather conditions, the beneficial insect development often lags behind resulting in aphid explosions and the need to apply an insecticide.

Cultural:  Although varieties vary in their susceptibility to BYDV, there are no varieties that exhibit a high level of resistance to the virus. The avoidance of early planting, especially before the Hessian Fly Free date, can also help to reduce the potential for aphid-vectored BYDV problems. 

Chemical:

• Cruiser 5FS Seed Treatment -  Applied at a rate of 0.75 - 1.33 fl. oz per 100 lbs. of seed. Provides excellent control of aphids and significantly reduces the damage from BYDV. Recently labeled (Fall 2000) so no 2000/2001 acres treated. Currently has 120-day plant back restriction to soybeans so will not be used in our area unless restriction changes.
• Gaucho Seed Treatment – Applied at a rate of 0.8 - 2.4 fl oz per 100 lbs of seed. Provides excellent control of aphids and significantly reduces the damage from BYDV;  used on 2-3% of the acreage due to cost and the unpredictable nature of BYDV.

• Dimethoate 4EC Applied at a rate of 0.5 – 0.75 pt/acre. Provides good control except when temperatures are below 60 degrees F; applied to less than 5 % of the acreage.

• Lannate LV – Applied at a rate of 0.75 to 1.5 pt/acre. Provide good control, applied to less than 2% of the acreage.
• Malathion 8 EC – Applied at a rate of 1.5 pt/acre. Provides very good control; applied to less than 5% of the acreage
• Penncap 2-FM – Applied at a rate of 2-3 pt/acre. Provides fair control; applied to less than 2% of the acreage
• Warrior T – Applied at a rate of 2.56 oz/acre. Provides excellent control; applied to 10-15% of the acreage.

Cereal Leaf Beetle

Biology and Life History: Overwintering adults emerge in late March and begin to lay eggs after 2 to 3 weeks of feeding. Since females prefer to lay eggs on young plants, spring-planted oats and late-planted wheat are the predominant hosts. In general, barley is more advanced in the spring and less attractive to egg -laying adults. Newly emerged larvae will feed voraciously for 10 days to 3 weeks. Larvae cover themselves with a brown or black coating of fecal material causing them to appear "slug-like". Summer adults emerge during late June and early July, feed on corn and wild grasses, then enter a summer dormancy. Only one generation occurs per year.

Damage: Both larvae and adults feed on the upper leaf surfaces of wheat and oats. Larvae feed on the outer surface of the leaves, giving the plants a silver or "frosted" appearance. Adults feed between the leaf veins, resulting in longitudinal streaks on the leaves.

Monitoring and Decision Making: Begin sampling fields in early April as soon as adult beetles are observed. Examine 5-10 tillers (entire stems) in at least 10 locations throughout a field. Count the number of eggs and larvae per stem and estimate the percent defoliation. If only eggs are found, the field should be re-sampled at a later date when eggs have hatched and larvae are detected. An earlier-triggered threshold is now recommended which allows more lead time to take action and apply controls; The new treatment threshold is 25 eggs and/or larvae per 100 tillers. Treatment is suggested when the egg threshold is reached and more than 50% of the sample consists of larvae, i.e. 50% egg hatch. If the egg threshold is not used, an insecticide is needed if you find 0.5 larvae per tiller, defoliation is greater than 10 %, and larvae are still small enough to cause additional damage. Research from Virginia and North Carolina indicates that the greatest damage can occur between flowering and the soft dough stage. Once the wheat reaches the hard- dough stage, the beetle has little effect on yield so no controls will be needed.

Controls:

Biological: A number of introduced parasites are being evaluated to help keep populations below an economic level. Although they have been evaluated on a small scale in Delaware, they have not provided effective control, especially when other insect pests are present and insecticide treatments are needed.

Cultural: No commercial varieties are available that provide effective cereal leaf beetle control.  Planting wheat immediately after the "Hessian Fly-Free Dates" has helped to suppress populations. 

Chemical:

• Furadan 4F – Apply at a rate of  0.5 pt/acre; Provides good control; used on less than 2% of the acreage
• Lannate LV – Apply at a rate 0f 0.75 – 1.5 pt/acre; Provides good control but no residual; applied to 5% of the acreage
• Malathion 57%EC – Apply at a rate of 1.5 pt/acre; Provides good control; applied to less than 2% of the acreage
• Sevin XLR Plus – Apply at a rate of  2 pt/acre; Provides fair control; applied to less than 2% of the acreage
• Warrior T – Apply at a rate of 2.56 oz/acre: Provides excellent control; applied to 70% of the acreage

True Armyworm

Biology and Life History: Armyworms overwinter as partially grown larvae in the soil and in plant debris of crops and woodland. Moth emergence and egg laying begins in late April. Moth activity peaks by late April. Egg laying is often concentrated in weedy and lodged areas of a field. The first small larvae can be found on lower leaf tissue in early May. Larval development takes 20-28 days. In late May through June, larvae often move to other crops. Mature larvae burrow into the soil or under debris to pupate. Three to four generations occur each year, but only the first one attacks small grains.

Damage: Young larvae (less than 1/2 inch long) generally feed on the upper leaf surface. Larger larvae feed heavily on the leaf blades and weeds. The last instar( 1.5 inches long and greater) will consume 80 percent of all the plant material eaten during their larval development. This stage lasts six to eight days before moving into the soil to pupate. Heavy defoliation of the flag level can result in significant economic loss. Unlike the sawfly, armyworms begin head clipping only when all vegetation is consumed and the last succulent part of the plant is the stem just below the grain head. Larvae can feed on the kernel tips of wheat, resulting in premature ripening and lower test weight.

Monitoring and Decision Making: Sampling should begin in late April to detect small larvae before head clipping begins. Examine fields for clipped heads and larvae throughout the field as well as along field margins and in lodged areas.  Armyworms often escape detection during the day since they hide under debris and weeds and feed at night. Check for small armyworms curled in a C-shape at the base of plants or under debris and weeds. Examine 5 linear foot of row in at least 10 locations through out a field, count the worms and note any head clipping. Treatment should be applied when you find 2 armyworm larvae per foot of row. In high management wheat, a treatment is needed if you find 3-5 larvae per square foot.

Controls

Biological: None Available

Cultural: None Available

Chemical:

• Lannate LV – Apply at a rate of 0.75 – 1.5 pt/acre; Provides good control; used on 25% of the acreage
• Penncap 2-FM – Apply at a rate of 2-3 pt/acre; Provides fair control, only effective on small larvae; used on less than 5% of the acreage
• Sevin XLR Plus – Apply at a rate of 2-3 pt per acre; Provides fair control, only effective on small larvae; used on less than 2% of the acreage
• Warrior T – Apply at a rate of 2.56 oz/acre; Excellent control; used on 60% of the acreage

Grass Sawfly

Biology and Life History: Adult sawflies emerge in early April, mate and begin to lay eggs in the leaf margins of small grains. Most egg laying is complete by early May. The first larvae can be found by early May feeding on the lower leaf blades. Mature larvae can be distinguished by their solid green color, amber head with a brown band and many legs. Larval development takes approximately 21-30 days. By mid-June, larvae burrow into the ground and begin a period of summer diapause (hibernation) in the prepupal stage

Damage: Sawfly larvae prefer to feed on the stems and are potentially more damaging than armyworms. Larvae begin to climb and feed on stems when the larvae are half grown and the grain is in the tiller to head stage. Stem clipping often occurs before leaf feeding is complete and/or the grain reaches physiological maturity. Head clipping often peaks by May 10, ten days before peak armyworm damage. 

Monitoring and Decision Making: Sampling should begin in late April to detect small larvae before head clipping begins. Although sawflies tend to be found earlier than armyworms, they are often found together. Examine fields for clipped heads and larvae throughout the field as well as along field margins and in lodged areas. Young sawflies often blend into the vegetation. A sweep net is helpful in detecting the initial presence of sawflies in a field. Since sawflies feed during the day and can be found on the plants, sample plants by shaking the wheat stalks of two rows toward the innerspace between the rows. Examine 5 linear feet between two rows in at least 10 sites. Count the number of worms and note any head clipping at each site. A treatment is recommended if you find 0.4 larvae per foot of row.

Controls:

Biological: None Available

Cultural: None Available

Chemical: No insecticides are labeled for grass sawfly control. However, the insecticides labeled on wheat, have provided consistent grass sawfly control and can be used under Section 2EE of FIFRA.

Hessian Fly

Biology and Life History: The Hessian fly has traditionally been an insect pest of wheat grown in the Midwestern states. In recent years, populations have been increasing in the Mid-Atlantic region and economic losses are starting to occur as a result of changes in wheat production practices. In the Mid-Atlantic region, there are generally 2 generations per year. Adults emerge in September from the "flax seeds" (puparium) that survive on wheat stubble throughout the summer.

Damage: If fall damage is extensive, plants will appear weakened and stunted. Spring infestations generally result in lodged plants as a result of maggots feeding on the first or second joint. During the last three years, Hessian fly has caused varying levels of yield loss. Fields planted in continuous wheat and/or no-till situations where volunteer small grains are present at the time of planting suffer the greatest yield loss. Entire fields can be severely stunted due to fall infestations. Spring infestations often result in lodging ranging from 5 to 25%.

Monitoring and Decision Making: Currently, no methods are available for effectively monitoring Hessian Fly populations. Yellow sticky traps have been used to monitor for presence of adult flies.

Controls

Biological: None available

Cultural: Since chemical controls have still not proven to be an economic alternative, a combination of the following cultural practices still provide the best control: complete plowing of infested wheat stubble soon after harvest, crop rotation (do not plant wheat in the same field 2 years in a row), elimination of  volunteer wheat before planting to prevent early egg laying, avoiding the use wheat as a fall cover crop near fields with infestations the previous season, planting after the fly free date (Oct 3 – New Castle County; Oct 8 – Kent County; Oct 10 – Sussex County) and the use of resistant varieties. 

The use of avoidance, i.e. using the Hessian Fly Free Date, should still be used as a part of a total management program. However, changes in current management practices and warmer fall weather have made this tool less effective in recent years. The recent development of varieties with resistance to Biotype L, the predominant Hessian fly biotype in Delaware, may provide effective Hessian Fly management. However, these varieties have just been released and are currently being evaluated under commercial conditions.

Chemical:

1. Cruiser 5 FS Seed Treatment : Cruiser 5FS Seed Treatment -  Applied at a rate of 0.75 - 1.33 fl. oz per 100 lbs of seed. Provides fair control. Recently labeled (Fall 2000) so no 2000/2001 acres treated. Currently has 120-day plant back restriction to soybeans so will not be used in our area unless restriction changes.
2. Gaucho Seed Treatment: Applied at a rate of 0.8 - 2.4 fl oz per 100 lbs of seed Provides fair control; currently not used in Delaware for Hessian fly control due to cost and variability of the control

Annual and Perennial Broadleaves and Grasses

Frequency of Occurrence: Annually.

Damage Caused: Reduced yields from weed competition, and loss due to interference with harvesting equipment.  Crops can become contaminated with weed plant parts (e.g. wild garlic, Canada thistle buds) during harvesting that can result in reduced selling price or in severe cases, rejection of the crop. 

% Acres Affected: 100%

Pest Life Cycles: A wide range of winter and summer annual and perennial weed species may be present in winter wheat fields in DE.  Some of the more common ones include mustard species, common vetch, field pansy, henbit (deadnettle), horseweed, chickweed, common lambsquarters, and common ragweed, wild garlic, annual bluegrass, brome species, ryegrass, and Canada thistle.

Timing of Control: Preplant, at planting, and postemergence.

Yield Losses: Can be as high as 100% in severely infested fields.  Fields with infestations of weeds posing contaminant problems (Canada thistles, wild garlic) can be passed over for harvesting.

Regional Differences: Weeds are a common problem throughout the state.

Cultural Control Practices: Cultivation is not a viable option after the wheat has been planted.

Biological Control Practices: None.

Post-Harvest Control Practices: Application of herbicides after harvest can control perennial weeds and aid in long-term control.

Other Issues: Research on winter wheat weed control is ongoing.

Use in IPM Programs: Use of these herbicides is consistent with IPM recommendations.  Postemergence herbicides support the use of scouting and as-needed applications.

Resistance Management: Hoelon-resistant ryegrass has been reported in VA and is suspected in DE, although it has not been confirmed as of yet.  Most growers are using Harmony Extra exclusively for weed control in fields planted to small grains.  They are being encouraged to tankmix Harmony Extra with 2,4-D whenever possible to minimize the risk of resistance.

Efficacy Issues: The listed herbicides have different but often overlapping spectra of species control.  Currently there are no labeled herbicides for control of Hoelon-resistant ryegrass, annual bluegrass, or brome species.  Some of the herbicides being used in the mid-west and western portions of the US, are not appropriate for the Mid-Atlantic region.

Alternatives:  Other new herbicides under research carfentrazone, AEF130060, AEF 107892, flufenacet, metolachlor, clodinofop, sulfosulfuron, chlorsulfuron, and metsulfuron.

Diseases of wheat are: seed decay, seedling blights, powdery mildew, loose smut, leaf rust, septonia leaf, tan spot, glume blotch, and scab.  No Organo-phosphate or Carbamate pesticides are used to treat these diseases.  Mancozeb, a potential carcinogen, is applied as a foliar fungicide to treat septoria leaf, glume blotch and tan spot.

When no-tilling wheat into corn stubble, there is an increased risk of head scab. Scab-causing spores produced on corn stubble move in air currents up to wheat plants. Head infection occurs when moist, warm weather occurs during flowering. Depending on time of infection, one or more spikelets or the entire head is bleached. Infected grain may contain mycotoxins that are harmful to non-ruminant livestock.

When wheat follows wheat for several years in the same field, a disease known as take-all can develop. The disease usually affects small areas in a field, but unless the field is rotated out of wheat, these areas can enlarge and result in substantial yield losses. Symptoms include a black lesion near the base of each stem, poor root growth causing the plant to be easily pulled out of the ground, shortened plants, and sterile, whitened seed heads.

Subject matter contacts at the University of Delaware, College of Agriculture and Natural Resources:

Joanne Whalen
Bob Mulrooney
Mark Van Gessel
Ed Kee
TracyWootten

Authors:

Joanne Whalen - INSECTS
Mark VanGessel - WEEDS
Susan Whitney - General Information

1. Delaware Agricultural Statistics Summary.  Wheat: Acreage, Average Yield and Production.  Delmarva 1998-1999. http://www.nass.usda.gov/de/p11.htm
2. Walker, Derby and Richard Taylor.  1998.  NO-TILL WHEAT AND BARLEY PRODUCTION  FOR DELAWARE. Agronomy Facts Series: AF-14.  http://ag.udel.edu/extension/information/af/af-14.htm
3. Vadas, Peter A. And Tom Sims.  Current Status of Soil and Plant Nitrogen Testing for Winter Wheat.   http://www.udel.edu/DSTP/FactSheets/sto13.htm

[1] FOOTNOTES:
Captan is not labeled for wheat. It has been deleted from this crop profile for use against wheat diseases.
Di-Syston is not labeled for wheat. It has been deleted from this crop profile for use against aphids and Hessian Fly.
Adage was renamed to Cruiser. The rates and pests (aphids and Hessian Fly) remain the same.