Taking an environmentally sensitive approach to pest management


Integrated Pest & Crop Management



AUTHOR

Wayne C. Bailey
University of Missouri
Division of Plant Sciences
(573) 882-2838
baileyw@missouri.edu

Potential for late season fall armyworm in grass pastures and alfalfa.

Wayne C. Bailey
University of Missouri
(573) 882-2838
baileyw@missouri.edu

Published: September 19, 2011

Although no reports of fall armyworm damage in grass pastures and alfalfa have been received at this time, the potential does exist for this pest to infest and damage grass pastures and fall seeded alfalfa fields during the next few weeks. Damage from fall armyworm larvae can be substantial during late summer and fall when larval numbers often peak. Fall armyworm larvae tend to feed on all tender green tissue which give infested pastures the appearance of drought. If heavy feeding occurs, grass plants may become severely stunted or killed. Damage may occur on 60 different hosts with tall fescue and orchardgrass being favored host plants. Damage in newly seeded alfalfa can be severe with complete stands of seedling alfalfa destroyed in a matter of a few days.

Several generations of fall armyworm occur in Missouri each year. Larvae produced in spring and summer tend to be light in color ranging from light green to tan. Larvae produced during fall generations often are dark to completely black in color. Both color phases of this insect will possess stripes running the length of the body. Identifying characteristics of the larvae include an inverted Y on the face of the insect, four black spots or bumps found on the top of each segment with those on the last segment of a worm arranged in a square pattern, and three white lines on the back of the segment located just behind the head capsule. Sometimes the three white lines will extend to additional segments. Larvae typically grow through 6 "worm stages" often reaching a length of 1 ¼ to 1 ½ inches.

Damage in grass pastures often "just appears overnight" as growing larvae become large enough to consume substantial amounts of forage in short periods of time. Larvae are especially active both early and late in the day. Scouting is best accomplished during these periods to gain an accurate estimate of larval numbers. The economic threshold for this pest in grass pastures is three or more larvae per square foot. Insecticides labeled for use on this pest in grass pastures can be found in the following table. Best control is achieved if 20 gallons or more of water is applied per acre. Be sure to follow all label precautions and restrictions.

Recommended Insecticides for Fall Armyworm Larvae in Grass Pastures

Control: Treatment is justified when 3 or more larvae are present per square foot. Best to apply insecticide applications early or late in day when larvae are most active.
Common Name Trade Name Rate of formulated
material per acre
Pre-Harvest/Grazing
Intervals Days
zeta-cypermethrin *Mustang Max 3.2 to 4.0 fl oz 0/0
carbaryl Sevin XLR Plus 1 to 1 1/2 quarts 14/14
lambda-cyhalothrin *Warrior II 1.28 to 1.92 fl oz 7
*Designates a restricted-use pesticide. Use is restricted to certified applicators only. Regardless of the formulation selected, read the label to determine appropriated insecticide rates, directions, precautions, and restrictions.

Recommended Insecticides for Fall Armyworm Larvae in Alfalfa

Insect Pest - Fall Armyworm larvae
Chemical Name Common Name Rate of formulated
material per acre
Pre-Harvest Intervals Days Comments
Beta-cyfluthrin *Baythroid XL 1.6 to 2.8 fl oz/acre 7 days 1st & 2nd Instars only
Chlorpyrifos +
gamma cyhalothrin
*Cobalt
19 to 38 fl oz/acre 7-14 days May cause temporary phytotocity
Chlorpyrifos *Lorsban Advanced
*numerous products
1 to 2 pts/acre
see specific labels
14 - 21 days
14 - 21 days
 
Zeta-cypermethrin *Mustang Max 2.8 to 4.0 fl oz/acre 3 days  
Gamma-cyhalothrin *Proaxis 2.56 to 3.84 fl oz/acre 1 day forage
7 day hay
1st & 2nd Instars only
Carbaryl Sevin 4F 1 - 1 1/2 qt/acre 14 day forage
14 day hay
 
Carbaryl Sevin XLR Plus 1 - 1 1/2 qt/acre 14 day forage
14 day hay
 
Zeta-cypermethrin *Stallion 9.25 to 11.75 fl oz 7 days coverage essential for control
Lambda-cyhalothrin
+ chlorantraniliprole
*Volian xpress 6.0 to 9.0 fl oz
1 day forage
7 day hay
 
Lambda-cyhalothrin *Warrior II with ZT 1.92 to 3.2 fl oz/acre 1 day forage
7 day hay
Use higher rate for large larvae
Lambda-cyhalothrin *Numerous products see specific labels 1 day forage
7 day hay
Use higher rate for large larvae
Use higher rate for large larvae
*Designates a restricted-use pesticide. Use is restricted to certified applicators only. Regardless of the formulation selected, read the label to determine appropriated insecticide rates, directions, precautions, and restrictions.
   About IPM     Contact Us    Subscribe     Unsubcribe

Copyright © 2018 — Curators of the University of Missouri. All rights reserved. DMCA and other copyright information. An equal opportunity/access/affirmative action/pro-disabled and veteran employer.

Printed from: https://ipm.missouri.edu
E-mail: IPM@missouri.edu

REVISED: September 27, 2011