Monitor Beet Armyworms in Cotton

Key Points

  • Beet armyworm larvae move from Palmer amaranth into B.t. cotton in locations across the Southern United States.
  • Genuity® Bollgard II® Cotton offers suppression of small (less than 1/4-inch) beet armyworms.
  • Bollgard® 3 technology is designed to significantly improve beet armyworm, fall armyworm, and cotton bollworm protection.

Causes

figure 1 

Figure 1. Pigweed in a cotton field that should be controlled to help prevent beet armyworm damage.

Beet armyworm (BAW) is a pest of cotton throughout the growing season, but can be more prevalent under droughty conditions and fields with pigweed. Mild winters, delayed planting, heavy early-season application of broad spectrum insecticides, and fields with open canopies can also contribute to the presence of BAW. Regular scouting to identify BAW should occur on a five to seven day schedule throughout the growing season.1

Management

Technology selection. Small BAW can be suppressed by Genuity® Bollgard II® Cotton. Bollgard® 3 XtendFlex® technology offers three modes of action against BAW and other cotton pests. This wider spectrum of larval control can translate into fewer insecticide applications and less potential injury to cotton during the growing season. Bollgard®< 3 technology combines the proven performance and control of Bollgard II® with the Vip3A protein.

figure 2 

Figure 2. Young BAW with a small black dot above middle true legs. John C. French Sr., Retired, Auburn University, University of Georgia, Clemson University, and University of Missouri, Bugwood.org.

Weed control. Remove weeds from the field throughout the season. BAW larvae will feed on lambsquarters and pigweed (Figure 1) first, growing larger and more tolerant of B.t. cotton.2,3

Planting. Timely planting, good stand establishment, and avoiding skip-row planting can help reduce the risk of a BAW infestation.

Scouting. Fields should be scouted every five to seven days. Pheromone traps may be used.3 Inspect cotton leaves, blooms, and squares for injury. Damage to the mainstem can cause the terminal to abort. Insecticide application should be considered for BAW more than 1/4-inch in length and if threshold levels are met.2

Economic thresholds. A general threshold is 10 active hatchouts, or active clusters of small larvae, per 300 row feet. However, where BAW have moved from pigweed to cotton, it is recommended to treat when 10 percent of blooms, squares, or terminals are damaged.2,4

Beneficial insects. It is important to identify beneficial insects correctly in the field to help prevent unnecessary insecticide applications that can disrupt beneficial lifecycles.

Insecticide applications. There are several insecticides available that are effective against BAW, see Table 1 for information about potential options.

table 1 
 
 

Identification

Damage. BAW are primarily foliage feeders but may also feed on cotton squares, blooms and occasionally small bolls.1 The larvae can bore into the main stem causing injury to the terminals. Larvae feed for three weeks as they progress through five growth stages.1

Larvae. Young BAW larvae are pale green to yellow in color and can be identified by a small black dot directly above the middle pair of true legs (Figure 2).1,3 As they mature, BAW become darker in color and form dark lateral stripes as they reach the fourth instar (Figure 3).3

figure 3 

Figure 3. BAW with lateral dark stripe.

Adults. Moths are gray to brown with two yellowish spots near the middle of the wings. Width of wingspan is 1 to 1.5 inches.

Eggs. White to pale green in color and round. Laid in clusters and covered with cottony white scales.3 BAW females can lay an average of 500 to 600 eggs in a 4 to 10 days, with each egg mass containing 40-80 eggs.1

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