The caterpillar (larval) stage of beet armyworm feeds on leaves and reproductive parts of the plant. The use of Bt cotton varieties has greatly reduced the risk of infestations, and economically damaging infestations in cotton are rare. Also, newer insecticide chemistries have made infestations easier to control. For more information on Beet Armyworms visit the Cotton Insects Beet Armyworm Fact Sheet (W029).
Egg masses and freshly hatched larvae are typically found on the undersides of the leaves in the mid and lower canopy. Small larvae feed in a group and leave a windowpane-like feeding sign on the leaves. The larvae can be recognized by a characteristic small black dot directly above the second true leg. Scout by counting the numbers of “hits” (active clusters of small larvae) observed while walking down a row. Infestations are often worse where wide- or skip-row spacing is used, and they are sometimes associated with the presence of alternate hosts like Palmer amaranth or other pigweed species.
Prior to August 15, treat for beet armyworm when an average of 5-6 “hits” (active clusters of small larvae) are found per 300 row feet. After August 15, treat when 10 or more “hits” are found per 300 row feet.
|Insecticide (Trade Names)|
for BEET ARMYWORM
|Lb Active Ingredient|
|chlorantraniliprole (Prevathon 0.43 SC)||0.067 - 0.09||20 - 27 oz||9?|
|chlorantraniliprole, λ-cyhalothrin (Besiege)||See label||8 - 12.5 oz||9?|
|emamectin benzoate (Denim 0.16)||0.0075 - 0.01||6 - 8 oz||9|
|indoxacarb (Steward 1.25)||0.09 - 0.11||9.2 - 11.3 oz||9|
|methoxyfenozide (Intrepid 2)||0.06 - 0.16||4 - 10 oz||9|
|spinetoram (Radiant SC 1)||0.033 - 0.0625||4.25 - 8 oz||9|
|spinetoram, methoxyfenozide (Intrepid Edge)||See label||4 - 8 oz||9|
|spinosad (Blackhawk 36% WDG)||0.056 - 0.072||2.4 - 3.2 oz||9|
- Production of an early crop and preservation of beneficial insects will reduce the risk of a beet armyworm outbreak.
- Bt cottons generally provide good control of beet armyworms. Supplemental insecticide applications are unlikely unless infestation levels are unusually high.