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Department of Entomology

Department of Entomology
123 W. Waters Hall
1603 Old Claflin Place
Kansas State University
Manhattan KS 66506-4004

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entomology@ksu.edu

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Sorghum Insects

Greenbug, Schizaphis graminum.

Sorghum>Greenbug nymphs

Greenbug nymphs.

Sorghum>Greenbug damage

Nymphs with feeding damage to leaf.

 Sorghum>Greenbug damage to sorghum

Sorghum showing greenbug damage on lower leaves.

flowers

Damaged panicle resulting from greenbug-induced flower sterility. Note telltale chlorosis on stalk.

Greenbugs are small, lime-green or yellow aphids that concentrate in colonies on the undersides of leaves. They have a dark green line down the middle of the back and antennae that are as long or longer than their body. Their reproductive capacity is very high. All individuals are female and mature in five to seven days in warm weather, producing several offspring per day for up to two weeks. While feeding, greenbugs inject saliva that is very toxic to sorghum, destroying chlorophyll in the leaves and turning them a red or rusty brown. As host plants deteriorate, winged forms develop that are capable of wind-assisted dispersal over great distances. Greenbug damage to sorghum in Kansas has declined in recent years, but could resurge at any time.  Injury may occur at any time during the growing season, from seedling through soft dough stages. Empty panicles can result from flower steriilty induced by greenbug feeding.

More detailed information on greenbug biology can be found here.

Resistance to Insecticides

Greenbugs have developed resistance to various insecticides over the years. The proportion of resistant individuals within the population will likely increase with the frequency of insecticide applications, so decisions to spray should always be tempered by concern for potential resistance. Insecticide resistance is independent of greenbug biotypes, which are defined by the reactions of specific sorghum varieties to greenbug feeding. Resistance management refers to strategies for mitigating the development of resistance in insect populations to ensure the continued efficacy of registered insecticides. This is best accomplished by rotating materials with different modes of action, applying only recommended rates, opting for spot treatments whenever feasible, and by using chemical control only when populations reach economic thresholds.

Using the Greenbug Treatment Guide

The greenbug treatment guide (in the table below) describes threshold values for various growth stages. For example, an infestation of 10 to 25 greenbugs per plant (based on counts from 25 plants or more) is considered threatening if found early in the season on one-leaf stage plants. Depending on conditions, the infestation may persist and build, or it may decline. A field should be monitored and treated if populations increase. If the infestation at the one-leaf stage averages 25 to 50 greenbugs per plant, the risk is higher, and serious stand loss is likely. Prompt control would probably be recommended. As plants develop, beneficial insects become increasingly important as sources of greenbug control, and their relative abundance should temper treatment decisions.

Greenbug Treatment Guide (Susceptible Hybrids)1

 Based on Avg. No. of
greenbugs per plant
 
Plant growth stage2Threatening
level
Treatment level3Based on visual rating3
0 to 1 leaf stage10 - 2525 - 50Colonies or numerous winged adults present on majority of plants. May be risky to wait until visible damage is obvious.
3 leaf stage2550-100As above, before general signs of stress are visible. Light to threatening levels often declinenaturally.
5 leaf stage50150-300When majority of plants are infested with rapidly increasing colonies of greenbugs and initial signs of reddening start to appear.
Mid-whorl stage, about one month
after emergence
200300-600When majority of plants are infested with rapidly increasing colonies, but before leaves begin to die. Damaging levels uncommon at this stage, but beginning infestations are often starting to
appear.
Late whorl
through soft
dough stages
7001,000Some lower leaves beginning to become wet and sticky with honeydew. Some leaves yellowing and reddening with occasional leaves drying. Small to large colonies present and increasing on the majority of plants.

1Some upward adjustment in numbers and damage is usually indicated to justify treatment on resistant hybrids particularly in early growth stages.
2One leaf stage means collar of first leaf visible, same system for third and fifth leaf stages.
3Assumes minimal beneficial activity. Remember frequent field visits are usually necessary to make wise decisions.

Management

Greenbugs are best managed with an integrated approach (IPM). This means employing a combination of different tactics to mitigate crop losses, rather than depending exclusively on one control method. The following list of tactics all contribute to protecting sorghum from greenbugs. It is up to producers to determine which combination of tactics is most economic and practical for their enterprise and location.

Resistant Hybrids

Resistant hybrids can be a useful way of reducing greenbug damage if the hybrid is resistant to the greenbug biotype that dominates in the region where it is planted. Biotype I is still the predominant biotype in Kansas. Biotype K has overcome resistance to most biotype I resistant sorghums, but this strain has not yet become common. All new sorghum hybrids where once screened for susceptibility to greenbug damage, but this is no longer the case. However, hybrids with various levels of resistance to biotype I are still available. While resistant hybrids are not a perfect or complete solution, they are compatible with all other tactics for greenbug management and should be considered in areas prone to greenbug infestations. Check with local seed suppliers for greenbug resistant hybrids adapted to your area.

Seed Treatment

Seed treated with commercially applied systemic insecticides provides good early season protection against greenbugs. Because Cruiser, Gaucho and Poncho are neonicotinoid insecticides, they should be effective against greenbugs resistant to organophosphate and carbamate insecticides. However, resistant greenbugs have likely declined because of reduced insecticide pressure. Seed treatment is an attractive option for regions where greenbugs and chinch bugs are a problem shortly after crop emergence. Seed treatments are a relatively selective form of insecticide delivery and are more compatible with biological control than broadcast applications.

Clothianidin (Poncho)

Seed is commercially treated with 5.1 to 6.4 fl. oz. of Poncho 600 per cwt. of seed. Do not use treated seed for feed or food. Read label for other use directions and safety cautions.

Imidacloprid (Attendant, Dyna-Shield Imidacloprid, Gaucho, Imida, Senator and possibly others.)

Reference labels for information on how these products should be applied. Some products indicate that they are to be commercially applied and others allow end-use seed treatment on agricultural establishments in liquid or slurry treaters at or immediately before planting. Do not graze or feed livestock in treated areas for 45 days after planting. Follow any listed rotational restrictions on the seed tag. Treated seed must not be used for food or feed.

Thiamethoxam (Cruiser)

Use seed commercially treated with 5.1 fl. oz. of Cruiser 5FS per hundredweight of seed. Follow label precautions and directions for use. Do not use treated seed for feed or food.

Soil Treatment

Soil treatments applied at planting time are useful for early-season protection when there are significant flights of greenbugs during planting. Treatments are particularly useful in eastern regions of the state where protection from chinch bugs is also desirable. Terbufos is only labeled for a band or a knifed-in application since it can be phytotoxic. Soil treatments may not be effective where insecticide-resistant greenbugs are present.

Terbufos (Counter 1 5G) Restricted Use

Band application. For use in Lock ‘n’ Load systems. Apply 1 lb. a.i./acre. Follow label directions for application rate depending on formulation and row width. Place granules in a 5- to 7-inch band directly behind the planter shoe in front of the press wheel and incorporate lightly with drag chains or tines. Use only one application per year. Knifed-in application. Apply 1 to 2 lb. a.i./acre. Follow label directions for application rate depending on formulation and row width. Drill granules 1 to 4 inches directly below the seed or 1 to 4 inches below and up to 5 inches to the side of the seed. PHI is 50 days for forage and 100 days for fodder or grain.

Biological Control

Four families of beneficial insects contribute to control of greenbug populations in Kansas – lady beetles, lacewings, hoverflies and parasitoid wasps. See KSRE publication MF2222: Biological Control of Insect Pests of Field Crops in Kansas for more details on these insects. Several species of lady beetles feed on greenbugs, but the most important in Kansas is the convergent lady beetle. These have two convergent white lines on the pronotum (area behind the head), and orange wing covers that sometimes have black spots and markings. The bright orange eggs are laid in clusters on the undersides of leaves near aphid colonies. The larvae resemble little alligators with orange markings. Parasitoid activity can be assessed by looking for brown, dried-up aphids (mummies) on the surfaces of greenbug-infested leaves. Take note of these insects when scouting for greenbugs. If they are abundant in new greenbug colonies, control measures may not be required and treatment may be postponed until observations confirm continued growth of greenbug populations. This is especially true for resistant varieties that slow greenbug reproduction, which enhances the effect of beneficial insects. There is no evidence that biological control can be improved in the field by purchasing these beneficial insects from mail order sources and releasing them to augment naturally occurring populations. Large numbers will migrate naturally into sorghum fields as wheat and weeds dry down and populations of other aphids decline. Recruitment of natural enemies is enhanced when corn leaf aphids colonize the crop in the whorl stage.

Cultural Control

Research has shown that reduced tillage or no-till planting reduces greenbug infestations. Migrating winged aphids respond to the contrast between bright green, growing plants and the dark color of bare soil to find host plants. Crop residues on the soil surface may diminish this response.

Rescue Treatment

Foliar sprays may be used to control infestations that develop when early-season control tactics fail. The decision to treat should be made after field scouting and using the greenbug treatment guide to determine the relative severity of the problem. Treatment thresholds can be adjusted upward for fields with sorghum hybrids with resistance to greenbug biotypes I and K. Resistant hybrids suffer less damage and usually support fewer aphids, but yield loss can still result from heavy infestations.

Please refer to the most recent version of the Sorghum Insect Management Guide for specific control recommendations.

Page last updated on 12/3/2014 by J.P. Michaud.