High armyworm numbers alert producers

July 10, 2017

by Tyler Mays, Texas A&M AgriLife Extension Agent, IPM

High numbers of fall armyworm moths (Spodoptera frugiperda) have been trapped at both moth traps. Higher numbers of cotton bollworm moths (Helicoverpa zea) have also been seen at both trap locations in Gaines County. Traps in Yoakum County are also seeing higher flights of both fall armyworm and cotton bollworm moths. Terry County traps are catching higher fall armyworm moths than last week.

These higher catch numbers, especially the Gaines County traps are a sign that we will start seeing egg lays and eventually larvae of both fall armyworm and in some areas cotton bollworms.

These high counts of fall armyworms in Gaines County mean that we need to be on the lookout for populations reaching economic thresholds in our area crops. Crops most susceptible to fall armyworm damage now are corn, sorghum, hay grazer, alfalfa, and peanuts. Scouting should be started immediately, and continue until these trap catches go down.

Scouting methods for fall armyworms depend on the growth stage of corn and sorghum. When both corn and sorghum are in the whorl stage before tassel emergence in corn and head emergence in sorghum, whorls should be pulled from approximate 20 plants in 5 different sections of the field and inspected for fall armyworm presence keeping track of the number found in each whorl. Also, while at each plant inspect the underside of the leaves for the presence of egg masses, keeping track of the number of plants inspected and the number of egg mass observed.

Once corn begins to develop ears, roughly 20 ears in 5 different areas of the field should be inspected by peeling back the husk and counting the number of fall armyworms in each ear, and keep track of the number of worms found and the number of ears check. The lower sides of leaves should be inspected for egg masses.

Once the panicle of sorghum emerges, scouting for fall armyworms should be done by beating head in a white bucket or a milk jug with the bottom cut out. In each field, 20 panicles should be inspected in four to five different areas of the field, keeping track of the number of fall armyworms found in each head, and use the sorghum head worm calculator to determine if the field is at population that would benefit from an insecticide application.

Fall armyworms vary in color from white with a black head when first hatched, to greenish-brown. Identification characteristics also include a white line down the top of the back, a brownish-black stripe above the midline, and a pale stripe with a reddish-brown tinge below.

The easiest way to distinguish between fall armyworm and cotton bollworm in on the head capsule, on fall armyworms there is a very visible white inverted Y on the front of the head, which is not present on the head of cotton bollworms.

This increase in corn earworm moths indicates that there is a decent egg lay going on. This is as expected because there is typically an egg lay of bollworms around the fourth of July, and with a full moon starting on Saturday we could see even more moths caught next week.

Scouting cotton for bollworms should be done by inspecting whole plants include bracts of squares, leaves, stems, and bloom tags if present for bollworm eggs which are laid singly. A total of 10-20 plants in 5 areas of the field should be inspected keeping track of the number of eggs found and the number of plants checked.

There is no economic threshold for cotton bollworm based on egg number, but observing the color of the eggs can give you a rough estimate of when you could expect to see them hatching. When bollworm eggs are first laid they are white in color and as they age develop a brown tint, which indicates the egg is roughly 3 days from hatching.

To scout for cotton bollworms full plant inspection should done for small larvae, checking the terminal inside the bract of squares, around bolls if present, and checking in the bloom tags if they are present. A total of 10-20 plants in 5 random areas of the field should be inspected, keeping track of the number of worms present at each plant, to calculate the number of bollworms per 100 plants.

The amount of fruit which includes both squares and bolls should also be estimated by pulling 100 random squares and boll throughout the field.

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Category: Agriculture