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Insect Management in Wheat 1
Richard K. Sprenkel 2The release of several adapted varieties has led to a renewed interest in planting wheat in Florida. Generally, wheat has fewer insect problems than other agronomic crops. However, a number of insects can reduce yields and growers need to be able to identify the major pests and respond with appropriate management practices to avoid unnecessary losses.
Description of Major Insect Pests
Aphids and Greenbugs
Aphids, including the corn leaf aphid, the English grain aphid, and greenbugs feed by sucking plant juices from leaves, stems, and wheat heads. In addition, several species of aphids are capable of transmitting barley yellow dawarf virus. Greenbugs also pose a threat to wheat because while feeding, they inject toxic juices which cause the plant to discolor and, in severe cases, cause the death of the plant. A greenbug has a pale green body with a dark green stripe down the center.
Figure 1. Greenbug on wheat Aphids vary from pale green to nearly black, depending on the species. Aphids and greenbugs are small insects (1/8 of an inch or less in length) and are capable of reproducing rapidly. As a result, they may build up quickly in the spring when the plants begin to joint. In most situations, predators such as lady beetles, syrphid fly maggots and others keep the aphid population in check. Generally, aphids and greenbugs are not able to reduce yields after wheat has reached the soft dough stage.
Armyworms
True armyworms tend to be more common in wheat that has rank growth due to high plant populations, excessive fertilization, wet growing conditions or a combination of these factors. Female armyworm moths lay their eggs in masses of up to 300 on lower leaves. Armyworms feed on leaves and are capable of stripping the plant. Large worms may also feed on stems causing the seed heads to fall to the ground. Armyworms are nearly 1 1/2-inches long when fully grown and are greenish-brown with two orange to cream-colored stripes on both sides of their bodies. They feed for approximately three weeks before entering the soil where they change into the pupal stage. In addition to the true armyworm, the fall armyworm will occasionally cause damage to wheat. The damage of the fall armyworm is similar to that described for the true armyworm.Chinch Bugs
Chinch bugs occasionally cause yield losses in wheat. They are common in dry years and prefer thin stands of wheat. Generally, the newer varieties that are adapted to Florida conditions produce thick stands of plants that are unfavorable for chinch bug development. As a consequence, the chinch bug is a less severe problem on wheat than it was several years ago. Newly hatched chinch bugs are reddish with a white band across their backs. As the nymphs mature, their reddish color becomes darker.
CREDITS: University of Florida, Institute of Food and Agricultural Sciences
Figure 2. Chinch bug nymphs. The adult chinch bug is 1/5 inch long with a black body. It has white wing covers, each with a black triangle at the middle of its outer margin. Chinch bug feeding causes wheat fields to have areas of dead and dying plants early in the spring.
CREDITS: University of Florida, Institute of Food and Agricultural Sciences
Figure 3. Adult chinch bugs. Generally these areas are limited to those spots where plant growth is poorest.
Grasshoppers
Grasshoppers feed on a wide variety of plants. Generally, they begin feeding in fence rows, ditch banks, and roadsides around wheat fields. As they outstrip their food supply in these areas or as the wheat becomes more attractive as a food source, grasshoppers may move into grain fields.
CREDITS: University of California (http://www.ipm.ucdavis.edu/PMG/r730301411.html)
Figure 4. Grasshopper resting on wheat blade. Usually the damage is confined to field borders, however, occasionally grasshoppers may infest entire fields. Grasshoppers damage wheat by stripping leaves, feeding on developing grain, and cutting off seed heads.
Hessian Flies
Before the use of resistant varieties and later planting dates, the Hessian fly was capable of causing serious yield losses in wheat. Fall infestations of the Hessian fly cause stand reductions, and spring feeding causes lodging. The Hessian fly passes winter as a full-grown maggot in a brown puparium which is commonly called flaxseed. These flaxseed are located between the leaf sheaths and stems.
CREDITS: R.K. Sprenkel, University of Florida
Figure 5. Flaxseed stage of a Hessian fly on a wheat shaft. The adults emerge in the spring about the time the plants begin to grow actively. The adults are small (1/8 inch long), two-winged black flies that resemble mosquitoes. The female Hessian fly lays its reddish-colored eggs in the grooves on the upper leaf surface.
CREDITS: R.K. Sprenkel, University of Florida
Figure 6. Female Hessian fly on wheat leaf. The eggs hatch in about seven days and the maggots feed behind the leaf sheath. Infested stems usually break over when the heads begin to fill. Use of resistant varieties has been shown to be the best management practice for the control of the Hessian fly in Florida. Distribution of crop residues by deep plowing as soon as possible after harvest is useful in reducing future populations. Gaucho seed treatment will provide some protection from the Hessian fly in the fall. Chemical control is seldom practical.
Stink Bugs
At least two species of stink bugs are capable of causing yield losses to wheat in Florida. The rice stink bug is a tan to straw-colored bug that is approximately 3/8 inch long. It has distinct points on its "shoulders" that are directed nearly straight forward. The southern green stink bug can be very common in wheat in early spring.
CREDITS: Frank Suber, University of Georgia
Figure 7. Stink bug. They have a wide host range including many wild plants and cultivated crops. They are approximately 1/2 inch long and have the characteristic shield shape of stink bugs. Both the rice stink bug and the southern green stink bug feed on the developing wheat kernels leaving an empty seed coat. Although stink bugs may be found in wheat fields before heading, they apparently do very little damage to the plant.
Scouting Wheat for Insects
Although wheat grown in Florida generally does not have many insect pest problems, scouting on a regular interval is strongly recommended. Scouting on a weekly interval permits a grower to identify pest infestations early and avoid yield loss through timely application of control measures.Samples should be selected at random and be representative of the field scouted. Approximately 20% of the samples should be taken on the edge of the field and the remainder in the interior of the field. From late tillering through dough stage wheat should be checked weekly for insect pests. One sample should be taken for each five acres of field size with a minimum of five samples per field. Each sample consists of examining the ground, foliage, and seed heads for insect pests and damage within a 2 X 4 foot area. Since wheat is commonly planted with a grain drill with rows spaced on seven inch centers, three rows four feet long would be sampled.
Estimate the total number of aphids, greenbugs, and chinch bugs on the wheat plants contained in the sample area. Determine the number of aphids, greenbugs, and chinch bugs per linear foot of row from the estimates.
Count the number of armyworms in the area to be sampled. Also, check for armyworm damage (striped leaves or clipped heads). Armyworms commonly feed during late afternoon, night, or early morning hours and remain hidden on the soil at the base of the plant during the remainder of the day. This behavior can make them difficult to detect. When checking for armyworms, pay particular attention to any areas of the field that may have rank growth. These areas are preferred by the armyworm moths and are usually the first to become infested.
Grasshoppers tend to be more common on edges of fields. If grasshoppers are found in the field, check for leaf feeding or cut heads and note the area involved in the infestation.
Stink bugs have the potential for causing the greatest yield loss during the grain filling and soft dough stages. Check heads carefully during this period for either the rice stink bug or the Southern green stink bug. Record the total number of stink bugs found in each sample and calculate the number per linear foot of row. At the same time aphid and greenbug populations are estimated, note the presence of predators feeding on the pests. Pay special attention to the foliage at the base of plants in thin stands of wheat. Chinch bugs prefer these sites and may usually be found there first.
Action Thresholds for Insect Pests
Detailed studies on the action thresholds of the common insect pests of wheat under Florida conditions have not been conducted. Those thresholds given below are suggested as guidelines to assist you in making pest control decisions, see Table 1.Aphids and greenbugs are usually controlled by predators in the spring in Florida. However, when few predators are present, and aphid and greenbug populations exceed 100 per linear foot of row, chemical treatment is usually justified.
An average of 16 or more armyworms 1/2 inch or more in length per 2 X 4 foot sample usually justifies treatment. If large worms are present and not clipping heads, and if the wheat is nearly mature (hard dough stage), then chemical control is not recommended.
Chemical control of chinch bugs is rarely justified. Chinch bugs normally prefer thin stands of wheat that has only limited yield potential. However, controls may be justified if chinch bug damage (areas of dead and wilted plants in early spring) is evident and chinch bugs are numerous (50 or more per linear foot of row).
Spot treatment of wheat is usually all that is required for control of grasshoppers in Florida. Chemical control is usually recommended if head damage or clipping is common and if grasshoppers are numerous.
Stink bug control is usually recommended only during the period of early to mid-grain development. Chemical control in wheat before heading or when the grain is mature is not advised. During the grain fill period, chemical control may be justified if there are one or more stink bugs per two linear feet of row.
Disclaimer: The use of trade names in this publication is solely for the purpose of providing specific information. It is not a guarantee or warranty of the products named and does not signify that they are approved to the exclusion of others of suitable composition.
Pesticide Restrictions
Di-Syston 15 G: Do not make more than 1 application per season and do not use for forage within 75 days of treatment. Do not place treated zones closer than 6 inches apart.Furadan 4F: Current wheat label only for grasshoppers in Florida. Do not make more than 2 foliar applications per season.
Lannate: Do not apply more than 1.8 lb ai/acre/crop. Do not make more than 4 applications per crop.
Mustang Max: Extremely toxic to fish and bees. Do not make applications less than 14 days apart. Do not apply more than 0.125 pounds ai/acre.
Phaser: Do not apply after heads begin to form. Do not feed treated forage to livestock. Do not make more than 2 applications per year. Do not exceed 1 lb ai/acre/year.
Sevin: Do not apply more than 3 ¾ pounds of Sevin 80 WSP or 3 quarts of Sevin 4F or XLR Plus per crop. Do not reapply within 14 days. A maximum of 2 applications per season is allowed.
Tracer: Do not apply more than 9 ounces of Tracer (0.28 lb of spinosad) per acre per year.
Warrior Z: Do not apply more than 0.06 lb ai/acre/season.
Tables
Table 1. Control of specific insect pests in wheat.
Trade Name (Common Name)
lb ai/a
Formulation/a
a/gal or lb
Min Days to Harvest and Restrictions
APHIDS
Methyl 4EC (methyl parathion)
0.25-0.75
1/2 -1 1/2 pt
16-5.3
15-grain
Dimethoate 400 (dimethoate)
0.25-0.37
1/2-3/4 pt
16-10.7
35-grain; 14-grazing
Di-Syston 15 G (disulfoton)
6.7 lb max
0.15
75-grazing, forage. Apply 1.67 oz/1000 ft of row in the drill or broadcast at planting.
Di-Syston 8 (disulfoton)
0.25-0.75
4-12 oz
32-10.7
30-grain. Do not graze or cut for forage. Only one application per growing season.
Lannate 2.4 LV (methomyl)
0.225-0.45
3/4-1 1/2 pt
10.7-5.3
7-grain, 10-grazing
Malathion 8 Flowable (malathion)
0.8-1.0
1-11/4 pt
8-6.4
7-grain. For English grain aphid.
Mustang Max (zeta-cypermethrin)
0.02-0.25
3.2-4.0 oz
5-4
14-grain, forage and hay
Phaser 3 EC (endosulfan)
0.5-0.75
2/3-1 qt
6-4
See restrictions
Warrior Z (lambda cyhalothrin)
0.02-0.03
2.56-3.84 oz
50-33
30
ARMYWORMS
Lannate 2.4 LV (methomyl)
0.225-0.45
3/4-1 1/2 pt
10.7-5.3
7-grain, 10-grazing
Malathion 8 Flowable (malathion)
0.8-1.0
1-11/4 pt
8-6.4
7-grain.
Mustang Max (zeta-cypermethrin)
0.011-0.025
1.76-4.0
9-4
14
Sevin 80 WSP (carbaryl)
1-1.5
1 1/4-1 7/8 lb
0.8-0.53
7-forage; 21-grain
Sevin XLR and 4F (carbaryl)
1-1.5
1-1 1/2 qt
4-2.7
7-forage; 21-grain
Tracer (spinosad)
0.047-0.094
1.5-3 oz
85-43
21-straw, grain; 14-forage or hay.
Warrior Z (lambda cyhalothrin)
0.02-0.03
2.56-3.84 oz
50-33
30
CHINCH BUGS and FALSE CHINCH BUGS
Methyl 4EC (methyl parathion)
0.45
1 1/2 pt
5.3
15
Mustang Max (zeta-cypermethrin)
0.02-0.25
3.2-4.0 oz
5-4
14-grain, forage and hay
Warrior Z (lambda cyhalothrin)
0.03
3.84 oz
33
30
CUTWORMS
Mustang Max (zeta-cypermethrin)
0.008-0.025
1.28-40 oz
12.5-4
14-grain, forage and hay
Methyl 4EC (methyl parathion)
0.37-0.5
3/4-1pt
10.7-8
15-grain For climbing cutworm.
Warrior Z (lambda cyhalothrin)
0.015-0.025
1.92-3.2oz
67-40
30
FALL ARMYWORMS
Mustang Max (zeta-cypermethrin)
0.02-0.25
3.2-4.0 oz
5-4
14-grain, forage and hay
Sevin 80 WSP (carbaryl)
1-1.5
1 1/4 - 1 7/8 lb
0.8-0.53
7-forage; 21-grain
Sevin XLR and 4 F (carbaryl)
1-1.5
1-1 1/2 qt
4-2.7
7-forage; 21-grain
Tracer (spinosad)
0.047-0.094
1.5-3 oz
85-43
21-straw, grain; 14-forage or hay.
Warrior Z (lambda cyhalothrin)
0.02-0.03
2.56-3.84 oz
50-33
30
GRASSHOPPERS
Dimethoate 400 (dimethoate)
0.37
3/4 pt
10.7
14-grazing, 35-grain
Di-Syston 15G (disulfoton)
1
6.7 lb max
0.15
75-grazing, forage. Apply 1.67 oz/1000 ft of row in the drill or broadcast at planting.
Furadan 4F (carbofuran)
0.13-0.25
1/4-1/2 pt
32-16
See note below.
Note: Carbofuran (Furadan) is a chemical which can travel (seep or leach) through soil and can contaminate ground water which may be used as drinking water. Carbofuran has been found in ground water as a result of agricultural use. Users are advised not to apply carbofuran where the water table (ground water) is close to the surface and where the soils are very permeable, i.e., well-drained soils such as loamy sands. Your local agricultural agencies can provide further information on the type of soil in your area and the location of ground water.
Malathion 8 Flowable (malathion)
0.8-1.0
1-11/4 pt
8-6.4
7-grain.
Methyl 4EC (methyl parathion)
0.5
1 pt
8
15-grain
Mustang Max (zeta-cypermethrin)
0.02-0.25
3.2-4.0 oz
5-4
14-grain, forage and hay
Thimet 20G (phorate)
0.98
4.9 lb
0.2
70-harvest or grazing foliage. Apply granules in the seed furrow at the rate of 1.2 oz/1000 ft of row.
Tracer (spinosad)
0.047-0.094
1.5-3 oz
85-43
21-straw, grain; 14-forage or hay For suppression only.
Warrior Z (lambda cyhalothrin)
0.02-0.03
2.56-3.84 oz
50-33
30
GREENBUGS
Dimethoate 400 (dimethoate)
0.25-0.37
1/2-3/4 pt
16-10.7
14-grazing; 35-grain
Di-Syston 8 (disulfoton)
0.25-0.75
4-12 oz
32-10.7
30-grain. Do not graze or cut for forage. Only one application per growing season.
Di-Syston 15G (disulfoton)
1
6.7 lb max
0.15
75-grazing, forage. Apply 1.67 oz/1000 ft of row in the drill or broadcast at planting.
Malathion 8 Flowable (malathion)
0.8-1.0
1-11/4 pt
8-6.4
7-grain. For English grain aphid
Mustang Max (zeta-cypermethrin)
0.02-0.25
3.2-4.0 oz
5-4
14-grain, forage and hay
Warrior Z (lambda cyhalothrin)
0.03
3.84 oz
33
30
HESSIAN FLIES
Di-Syston 15G (disulfoton)
1
6.7 lb max
0.15
75-grazing, forage. Apply 1.67 oz/1000 ft of row in the drill or broadcast at planting.
Thimet 20G (phorate)
0.98
4.9 lb
0.2
70-harvest or grazing. Apply granules in the seed furrow at the rate of 1.2 oz/1000 ft of row.
Warrior Z (lambda cyhalothrin)
0.03
3.84 oz
33
30 Apply when adults emerge.
LEAFHOPPERS
Methyl 4EC (methyl parathion)
0.75
1 1/2 pt
5.3
15-grain
MITES
Dimethoate 400 (dimethoate)
0.17-0.25
1/3-1/2 pt
24-16
14-grazing, 35-grain. For control of brown wheat mite.
Di-Syston 15G (disulfoton)
1
6.7 lb max
0.15
75-grazing, forage. Apply 1.67 oz/1000 ft of row in the drill or broadcast at planting.
Di-Syston 8 (disulfoton)
0.25-0.75
4-12 oz
32-10.7
30-grain. Do not graze or cut for forage. Only one application per growing season.
Methyl 4EC (methyl parathion)
0.5
1 pt
8
15-grain For brown wheat mite and western wheat mite.
STINK BUGS
Methyl 4EC (methyl parathion)
0.25-0.75
1/2-1 1/2 pt
16-5.3
15-grain
Mustang Max (zeta-cypermethrin)
0.02-0.25
3.2-4.0 oz
5-4
14-grain, forage and hay
Warrior Z (lambda cyhalothrin)
0.03
3.84 oz
33
30
THRIPS
Methyl 4EC (methyl parathion)
0.25-0.37
1/2-3/4 pt
16-10.7
15-grain For barley thrips.
Mustang Max (zeta-cypermethrin)
0.02-0.25
3.2-4.0 oz
5-4
14-grain, forage and hay
Footnotes
1. This document is ENY-408 (IG067), one of a series of the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date: October 12, 1993. Revised: December 2005. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.2. Richard K. Sprenkel, professor, Department of Entomology, North Florida Research and Education Center--Quincy; Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.
Use pesticides safely. Read and follow directions on the manufacturer's label. All chemicals should be used in accordance with directions on the manufacturer's label. Check the label carefully as this information does change and our publications may not have the latest information. The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition.
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Copyright Information
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