MONITOR BEET ARMYWORMS IN COTTON

  • Beet armyworms (BAW) larvae have been known to move from Palmer amaranth into B.t. cotton in some locations across the southern United States.
     
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  • Genuity® Bollgard II® with Roundup Ready® Flex cotton offers some suppression of small (less than 1/4-inch) BAW. 
     
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  • Bollgard® 3 technology is designed to significantly improve BAW, fall armyworm, and cotton bollworm protection.
     
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Considerations

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Figure 1. Beet armyworm. Alton N. Sparks, Jr., University of Georgia, Bugwood.org
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Hot and dry conditions are ideal for BAW to proliferate on Palmer amaranth in some cotton fields. Once BAW caterpillars strip the Palmer amaranth leaves, they may move into cotton fields. BAW larvae can damage cotton plants and potentially reduce yield potential. Small BAW may be suppressed by Genuity Bollgard II with Roundup Ready Flex cotton. Farmers should scout regularly to monitor all cotton for BAW and other caterpillars more than 1/4-inch in length and consider applying insecticides if threshold levels are reached.

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Bollgard® 3 XtendFlex® technology offers three modes of action against BAW and other cotton pests. This wider spectrum of worm control can translate into fewer sprays and less potential damage to cotton during the growing season. Bollgard® 3 technology combines the proven performance and control of Bollgard II® with the Vip3A protein. 

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Extension Recommendations

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Table 1. Effect of Genuity® Bollgard II® Technology and Bollgard® 3 Technology on Cotton Insects.
Insects
Genuity Bollgard II Technology Activity
Bollgard 3 Technology Activity
Tobacco Budworm
Control
Control
Pink Bollworm
Control
Control
Cotton Bollworm
Spray may be needed
Suppression*
Beet Armyworm
Suppression
Control/
 
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Fall Armyworm
Little Activity
Control/
 
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Source: G. T. Bohmfalk, Texas Agricultural Extension Service: Blake Layton, Mississippi State Cooperative Extension Service. *Incomplete data.
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Cotton growers must be aware of BAW activity in their fields. Larvae may begin feeding on Palmer amaranth in a field and as they grow larger move into B.t. cotton. Large BAW larvae that moves to a B.t. cotton plant may survive.

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BAW larvae can be identified by a small black dot directly above the middle pair of true legs. BAW are primarily foliage feeders but are known to also feed on cotton squares, blooms and occasionally small bolls.1 The larvae can bore into the main stem a couple of nodes below the terminal and may damage the terminals. (Figure 1). 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 Larvae will feed for 3 weeks while they pass through 5 growth stages. BAW egg masses that are laid and hatch on Bollgard II with Roundup Ready Flex cotton will be suppressed by the technology.

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Observational scouting should occur every 5 to 7 days during the growing season. BAW infestations may be spotty, so care must be taken to cover entire fields.1 Only a portion of a field may reach thresholds and need treatment. Areas of a field with higher weed populations, especially Palmer amaranth, should be carefully scouted. Threshold levels for BAW vary depending on the cotton growth stage, the percentage of infested plants, and whether or not fruit feeding is detected.

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According to University of Georgia Cooperative Extension, thresholds for beginning control of BAW with insecticides are 10% damaged squares, 10% infested blooms, 10% damaged terminals, or when 10 active “hits�? are observed per 300 feet of row.2 To reduce the risk of killing beneficial insects, farmers should be cautious to spray insecticides before BAW or other caterpillars reach threshold levels.

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Universities list multiple insecticides that are effective against BAW, including: Coragen®, Denim®, Dimilin®, Belt®, Steward®, Intrepid®, Diamond®, Prevathon®, Tracer®, and Blackhawk®. Refer to your local extension for threshold levels and application rate recommendations. Planting cotton varieties with Bollgard 3 technology may allow for fewer insecticide applications and reduced potential damage to your cotton all season long.

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