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Stop the March: Starting Your Wheat Season Off Right with Fall Armyworm Management
Ashleigh M. Faris, State Specialist for Cropping Systems Entomology
As Oklahoma summer crops are winding down, we are seeing an increase in fall armyworm reports. Fall armyworms are posing a significant risk of economic damage to our upcoming winter wheat crop. These summer crops and weeds have supported lush vegetation, creating highly attractive habitats for female moths to lay eggs, which can subsequently move into newly planted wheat.
Here is what wheat producers need to know to identify, manage, and prevent fall armyworm infestations this planting season.
Fall Armyworm (FAW) Identification and Life Cycle
Fall armyworms have a distinct, broad, white inverted “Y” present on the front of their head capsule (Fig. 1). Their body varies from light tan to green to dark brown or nearly black in color with three widely separated narrow, yellowish-white stripes down their back (Fig. 2). There are four distinct black dots arranged in a square on the top of the 8th abdominal segment.
Fig. 1 Fall armyworm. Note the white inverted “Y” on the head capsule. Credit: Mitchell Alcala, OSU Agriculture.
Fig. 2. Fall armyworm. Credit: Pat Porter, Texas A&M AgriLife Extension.
The adult moth will lay their eggs that hatch as caterpillars (the damaging stage). Adult moths migrate from Mexico and Texas to Oklahoma usually by late June. Eggs are laid in clusters on host plants and appear pale yellow but darken as they age turning black just before hatching (Fig. 3). Larvae will feed on foliage for 2-3 weeks, increasing with size as they progress through 6 larval instars, then dig into the soil to pupate. A new generation of moths emerge about 2 weeks later. Because there are several overlapping generations in Oklahoma, extending into October and November, protecting wheat stands and monitoring for FAW can be critical for crop establishment. Keep in mind that FAW do not overwinter in Oklahoma; the first killing frost of the season should eradicate the population.
Fig. 3. Fall armyworm eggs laid on grass. The fuzzy appearance is due to scales that are deposited between and over the eggs. Credit: Desiree van Heerden, Syngenta.
Signs of FAW Damage, Scouting, and Economic Threshold
The earliest sign of infestation is “windowpane” damage, where tiny, newly hatched FAW larvae chew off a single layer of leaf tissue, leaving behind transparent patches (Fig. 4). Within a few days, the growing FAW caterpillars can consume entire leaves. Because 90% of crop damage happens during the insect’s final two growth stages, FAW can quickly decimate seedling stands, sometimes forcing producers to completely replant their winter wheat.
Fig. 4. Small FAW larvae will scrape off the top layer of leaf tissue when they feed, leaving behind a “windowpane” appearance. Credit: Lanie Hale, Wheeler Bros.
To scout for FAW, check your fields regularly (e.g., every other day in the evenings), looking closely at the base of newly emerged seedlings. Focus on field borders and edges near grassy or weedy areas where FAW often start. During the day FAW will hide under residue and at the base of the plant, scouting early morning or in the evenings is the best time for spotting FAW in the crop canopy. Look closely and carefully for early instars, as these are very small (Fig. 5).
Fig. 5. Small, early instar FAW can be difficult to see against wheat and residue, especially when scouting in full sun. Red circles highlight the FAW hiding in this image. Credit: Dr. Amanda Silva, OSU Small Grains Extension Specialist.
The economic threshold for FAW in winter wheat is 3 – 4 larvae per linear foot of row alongside visible feeding damage. Alternatively, treat when there are 4 or more larvae (1 inch or longer) per square foot threatening the stand. If 25-30% of plants show window-pane injury, monitor the field daily and treat immediately if the stand is in danger.
Planting Practices: Cultural Control & Insecticide Seed Treatments
Keeping your field and its surrounding borders completely weed-free, in additional to removal of volunteer wheat for at least two weeks before planting is one way to make sure your wheat season starts off on the right foot. This removes early food sources and makes the area less attractive for egg-laying female moths.
Another way to get your season off on the right foot is to consider using an insecticide seed treatment but make sure it is specifically labeled for FAW. This is because not all insecticides are effective against FAW. Seed treatments containing the active ingredient Chlorantraniliprole (Group 28), such as Cedocor CPL and Lumivia, are effective options labeled to control or suppress FAW. These products also provide protection against wireworms, cutworms, and grasshoppers. Insecticide seed treatments can provide protection for four to six weeks.
How do you know if you should invest in a seed treatment? Consider your planting timing and intended use for your wheat. Planting wheat early for use as a dual-purpose crop significantly increases the prevalence of several diseases and damage caused by viruses, fungi, and by insect pests compared to planting wheat later for grain-only. You should also consider the history of the field. If you have seen issues in a particular field, then it may be worth planting treated seed. If you don’t know the history of the field, work with your local agronomist to determine what insects are likely an issue in those fields.
If you are using treated seed, remember that combinations of some fungicidal and insecticidal seed treatments can be toxic to the seed. Read the label carefully before mixing insecticides with fungicides. Also be sure to follow required grazing restrictions and intervals listed on the label. Equipment such as augers and trucks to deliver grain should not be contaminated by treated grain.
Foliar Chemical Control Options
It is critical to treat fields while FAW caterpillars are on the small side meaning less than half an inch long; larger caterpillars do the most damage and can be highly resilient to insecticides. Effective foliar products typically include active ingredients like chlorantraniliprole, lambda-cyhalothrin, spinetoram, or cyfluthrin. Options labeled for FAW control include Coragen eVo, Tombstone, Warrior II, Mustang Maxx, Besiege, and Radiant SC. When selecting an insecticide, it is important to consider if the option is broad spectrum. Broad spectrum insecticides can reduce natural control such as lacewing and syrphid larvae, as well as lady beetles that may be keeping other pests like aphids under threshold. Always read and follow all label instructions to ensure you are applying at the correct rate and adhering to the required pre-harvest and grazing intervals.
This fall, the OSU Cropping Systems Entomology team will be conducting field trials to evaluate the efficacy of insecticide seed treatments and foliar insecticides on FAW in hard red winter wheat. These trials are made possible through support from industry partners and the Oklahoma Wheat Commission. Trial results will be shared at future OSU Field Days and grower meetings.
Protect Your Emerging Stands: True Armyworm Movement from Maturing Wheat to Summer Crops
Ashleigh M. Faris, Cropping Systems Extension Entomologist & IPM Coordinator
As the Oklahoma winter wheat crop reaches maturity, producers and crop consultants should prepare for the annual migration of true armyworm larvae. While true armyworms are a common fixture in small grains, their movement out of maturing wheat and into newly emerged corn, soybeans, and sorghum can lead to stand thinning or loss if not monitored closely.
True Armyworm Migration Timeline
True armyworm moths typically migrate into Oklahoma from the south in early spring with infestations typically occurring in late April through the first two weeks of May. The first generation is typically laid in winter wheat. Once the larvae currently finish their development in wheat, they will soon seek new food sources as the wheat crop dries down. This transition period is the most critical time for scouting summer crops, especially those adjacent to wheat fields.
True Armyworm Life Cycle and Identification
Armyworms overwinter as pupae or as mature larvae which pupate in the spring. Moths emerge in the spring, mate, and lay eggs in masses on hosts plants (mostly in the grass family). Female moths deposit their eggs in low-lying areas on wheat or pasture ground, as well as field margins or fields with dense, grassy weeds like Johnson grass. Larvae feed for about 4 weeks but do most of their damage during the last 10 days of this period. They then pupate in the soil. A new generation of moths emerges about 1 week later. There are 4 generations per year in Oklahoma.
True armyworms have a smooth body and can be variable in color, ranging from green, tan, orange, and black, with distinct pale orange or reddish stripes running along the sides (Figure 1). A key identifier is a dark diagonal band on each of the abdominal prolegs; there are four pairs of prolegs (Figure 2). The head capsule is light brown with a distinct “net-like” or honeycomb pattern of dark lines (Figure 2).
Figure 1. Four true armyworm larvae. One is dark (right) and three are light colored (left). Photo by Ashley Dean, Iowa State University Extension.
Figure 2. True armyworm. A) Dark band on prolegs. B) Orange head capsule with dark net-like pattern. Photos by Adam Varenhorst, Iowa State University Extension.
True Armyworm Management Cutoff in Wheat
A common question during this window is whether to treat armyworms in maturing wheat. Once wheat reaches the soft dough stage, the crop has generally accumulated its yield. Unless larvae are actively head-clipping (cutting the wheat heads off the stems), chemical control is rarely economical at this stage. Instead of treating the wheat, focus on young stands of summer crops. As wheat turns brown, larvae will move toward the nearest green tissue—often your emerging corn or sorghum.
Scouting, Damage, and Economic Thresholds for Summer Crops
Armyworms are whorl feeders in grass crops like corn and sorghum and will also feed on soybean leaves. True armyworms hide in the soil, crop residue, or whorls during the heat of the day and feed at in the early morning, evening or late when it is cool outside. When it is warm, larvae will hide in the soil, crop residue, or the whorl of corn plants. Large larvae consume more tissue but will generally be done feeding in a few days. Insecticides should target young, small larvae that will be feeding for a long time; however, you may see a range of larval sizes in a single field.
Corn, Sorghum, and Soybean Damage
True armyworm feeding typically begins at the leaf edges, leaving ragged holes and edges (Figure 3). As this leaf tissue is removed, the larvae will move to the upper leaves and continue feeding. True armyworms do not tunnel into the stalk and generally do not feed on the growing point of larger corn and sorghum plants. While not the preferred host, true armyworms will move into soybeans if no grasses are available. Larvae typically cause defoliation (Figure 4); however, soybeans are quite resilient to early-season leaf loss, but scout for stand-thinning if larvae are clipping seedlings.
Figure 3. True armyworm feeding on young corn plant. Photo by Adam Varenhorst, Iowa State University Extension.
Figure 4. Soybean leaves with true armyworm feeding damage. Photo by Meaghan Anderson, Iowa State University Extension.
Corn Threshold: Small plants typically recover from true armyworm feeding and outgrow the defoliation. Per Kansas State Extension, treatment is justified only when larvae are less than 1.25 inches long and present on 30% of plants with 5 – 6 extended leaves, or when 75% of plants have one or more larva per plant. There is risk of yield loss if defoliation during reproductive stages approaches the ear zone before hard dent. Lower thresholds may apply if the plants are subject to additional stresses.
Sorghum Threshold: Sorghum is very tolerant of defoliation, so insecticide control is rarely justified. For early infestations (5-7 leaf stage, prior to panicle development) at the vegetative stages where true armyworms may be in the whorl, do not initiate controls unless 40% or more of the plants in a field are infested. Because the worms are only defoliating at this point in the sorghum plant’s development, economic damage is not a concern and there would likely be no return on investment for spraying before panicle development.
Soybean Threshold: Once grasses are fed upon or harvested, true armyworms can turn tobroadleaf crops, including soybean. While soybean is not a preferred host, the growing point is exposed early in the season, making them susceptible to stand loss. Management is suggested if soybean defoliation is greater than 35% – 40% during the vegetative stages.
True Armyworm Insecticide Management Options for Summer Crops
True armyworm is generally easier to control with pyrethroids than fall armyworm. Ensure high-volume water (10-15 GPA ground) is used to get the product into the whorl or canopy where the larvae hide. Remember that most insecticides work via contact; if true armyworm larvae are feeding or hiding under dense residue, insecticides are unlikely to make contact and are ineffective. Target applications when larvae are actively feeding on foliage to ensure good contact. Follow all instructions on the insecticide label to ensure good control.
For a complete list of recommended insecticides and rates for these crops, please consult the following OSU Fact Sheets: CR-7167: Management of Insect and Mite Pests in Corn and Sorghum and CR-7115: Management of Insect and Mite Pests in Soybean.
The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.
Down and Dirty with NPK 