How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

Eggs of the armyworm and beet armyworm are pale green to pink, striated, and deposited in a mass that is covered with a white cottony material. At first, the tiny, newly hatched larvae feed in a colony, skele­tonizing the first few leaves on which they feed. The larvae are about 1.25 inches long when full grown. Armyworms are greenish brown in color with several longitudinal stripes, while beet armyworm are mottled olive green to almost black.

Eggs of the western yellowstriped armyworm are similar to those of the beet armyworm. The egg masses are larger and covered by a gray cottony material. Newly hatched larvae also feed in colonies; mature larvae attain a length of 1.5 to 2.0 inches and are black with a prominent yellowish stripe and several narrow bright ones on each side of the body. An intense black spot is usually visible on each side of the first legless segment behind the head.

DAMAGE

Newly hatched armyworms feed in colonies and skeletonize leaves. Larvae that are half grown or more will feed singly on leaves, in the ear, or on the tassels. Damage by army­worm to the ears resembles that caused by corn earworm. Because of the damage to tassels and ears, tolerance for armyworm damage in sweet corn is very low.

MANAGEMENT

Armyworms are often attracted to fields with barnyardgrass. When they are done feeding on barnyardgrass, larvae move to corn so it is important to control this weed.Specific treatment thresholds have not been established for armyworms on field corn, but treatment is seldom necessary. Sweet corn, however, has a greater potential for damage and may require treatment. While these pests may be present any time from June through September, populations are usually most damaging in late summer. For sweet corn, phero­mone traps may be useful to determine the timing of moth flights and subsequent larval infestations. In those rare instances where control measures are required, the beet army­worm is more difficult to control than the western yellowstriped armyworm and may require the higher treatment rate of the materials recommended below. Insecticide applica­tions will be most effective if applied against small larvae. Frequently, spot treatments are sufficient.

Organically Acceptable Methods
Controlling weeds, especially barnyardgrass, and applying sprays of Bacillus thuringiensis are organically acceptable management tools.

Common name		Amount/Acre**	P.H.I.+
(trade name)			(days)
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies. Also consider information relating to water quality when choosing a pesticide.
A.	INDOXACARB
	(Avaunt)	2.5–3.5 oz	Sweet corn: 3
			Fodder/stover: 35
	MODE OF ACTION: An oxadiazine (Group 22)1 insecticide.
	COMMENTS: For use on sweet corn only. Can only be used before silking. Do not apply more than 14 oz product/acre/crop and allow at least 3 days between sprays.
B.	METHOXYFENOZIDE
	(Intrepid) 2F	4–8 oz	Field: 21
			Sweet corn: 3 (ears/forage)
			21 (dry fodder)
	MODE OF ACTION: An insect growth regulator (Group 18)1 insecticide.
C.	METHOMYL*
	(Lannate SP)	0.25–0.5 lb	See label
	MODE OF ACTION: A carbamate (Group 1A)1 insecticide.
	COMMENTS: Do not apply more than 2.25 lb a.i./acre/crop for field and popcorn, and 6.3 lb a.i./acre/crop for sweet corn. Phytotoxicity may occur on certain sweet corn varieties.
D.	BACILLUS THURINGIENSIS ssp. AIZAWAI#
	(various products)	Label rates	0
	MODE OF ACTION: A microbial (Group 11.B1)1 insecticide.
	COMMENTS: This material may be less effective than broad-spectrum insecticides, but it does not destroy natural enemies of corn earworm. Control is maximized by thorough coverage and by making applications when larvae are small.
E.	ESFENVALERATE*
	(Asana XL)	5.8–9.6 fl oz	Seed corn/Popcorn: 1
			Field: 21
	MODE OF ACTION: A pyrethroid (Group 3)1 insecticide.
	COMMENTS: Do not exceed 0.25 lb a.i./acre/season on field corn and seed corn or 0.5 lb a.i./acre/season on popcorn.
F.	PERMETHRIN*
	(Pounce) 3.2EC	4–8 oz	Sweet corn: 1
	MODE OF ACTION: A pyrethroid (Group 3)1 insecticide.
	COMMENTS: For field corn, popcorn, field corn grown for seed, and sweet corn. Apply before brown silk stage. Do not apply more than 1.2 lb a.i./acre/season.
	** Mix with sufficient water to obtain full coverage.   + Preharvest interval. Do not apply within this many days of harvest.   * Permit required from county agricultural commissioner for purchase or use.   # Acceptable for use on organically grown produce.   1 Modes of action are important in preventing the development of resistance to pesticides. Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode of action is assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/

PUBLICATION

UC IPM Pest Management Guidelines: Corn
UC ANR Publication 3443
Insects and Mites
L. D. Godfrey, Entomology, UC Davis
S. D. Wright, UC Cooperative Extension, Tulare County
C. G. Summers, Kearney Agricultural Center, Parlier
C. A. Frate, UC Cooperative Extension, Tulare County
Acknowledgement for contributions to the Insect and Mites section:
M. J. Jimenez, UC Cooperative Extension, Tulare Co.

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