Corn: Armyworm (TRUE - Pseudaletia unipuncta, FALL - Spodoptera frugiperda)

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Pub 812: Field Crop Protection Guide > Chapter 1: Corn > Armyworm (True and Fall)

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Field Crop Protection Guide 2011-2012, Order 2011-2012 publication

Table of Contents

1. Description
2. Integrated Pest Management Options

• chlorantraniliprole - Coragen
• carbaryl - Sevin XLR Plus
• cyhalothrin-lambda - Matador 120 E, Silencer 120 EC

3. Related links...
   

Description

True armyworms, full grown, are 4-cm (1 1/2-in.) dull-green to brown larvae that can be easily confused with other caterpillars, including variegated cutworm and fall armyworm. Two distinguishing features that true armyworm possess are white-bordered stripes running laterally along the body and dark diagonal bands at the top of each abdominal proleg. The head is yellow-brown with a network of dark brown lines creating a pattern. The adult sand-coloured moth has distinctive white spots on the centre of each forewing.

Image 1. True armyworm larvae have black bands at the top of each proleg and the lighter brown head.

Full-grown fall armyworms are 4 cm (1 1/2 in.) long, varying in colour from light tan or green to near-black. Three white, thin stripes run down the back with one thicker, yellow band with red spots running along the side, just above the legs of the larvae. Scattered along the body are black spots called tubercles that have spines coming from them.

Image 2. Fall armyworm larva damage on corn ear. Larvae leave entry holes on the exterior of ear. Note head is black wih a white, inverted "Y" on the front.

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Integrated Pest Management Options

Late-planted corn is most susceptible to leaf and whorl feeding by armyworm.

True armyworm: Insecticide may be warranted in seedling corn if there are two or more unparasitized larvae per seedling and feeding damage exceeds 10%. In corn past the 6-leaf stage, if 50% of the plants are showing damage are are infested with larvae smaller than 2.5 cm, insecticide treatment may be warranted.

Fall armyworm: Insecticide may be warranted if 50% of the plants are infested with unparasitized larvae smaller than 2.5 cm. However, damage is usually not economical unless infestations are high, and feeding is concentrated on the undeveloped tassels.

If larvae have white eggs attached to them, they are parasitized and may not need treatment. If larvae are 2.0 cm or larger, chemical control will not work well and is not recommended. Once the larvae are in the corn ear, insecticides cannot provide control.

Active ingredient	chlorantraniliprole
Trade name	Coragen
Rate per hectare (product)	250-375 mL per ha
Rate per acre (product)	101-151 mL per ac
PHI*	14 (field corn) 1 (seed corn)
Comments	Apply to foliage when rain is not expected in the nest 24-hr. Use a minimum of 100 L/ha of water. Maximum 4 applications/yr. 12-hr re-entry period.

 

Active ingredient	Carbaryl
Trade name	Sevin XLR Plus
Rate per hectare (product)	2.5-4.0 L per ha
Rate per acre (product)	1.0-1.6 L per ac
PHI*	1
Comments	For larvae in whorls and foliage, treat entire plant. Repeat as necessary. Follow label precautions regarding honeybees.

 

Active ingredient	cyhalothrin-lambda
Trade name	Matador 120 E
Rate per hectare (product)	83 mL per ha
Rate per acre (product)	34 mL per ac
PHI*	14(silage) 21(field & seed)
Comments	Ground and aerial application. For best results, apply in the early morning, before temperatures rise, or during the evening. Use 100-200 L water/ha for ground application, 10-40 L water/ha for aerial application. Spray no later than 10 days after egg hatch. Maximum 3 applications/yr. Do not apply more than 2 applications of 83 mL/ha by air. 24-hr re-entry period.

 

Active ingredient	cyhalothrin-lambda
Trade name	Silencer 120 EC
Rate per hectare (product)	83 mL per ha
Rate per acre (product)	34 mL per ac
PHI*	14(silage) 21(field & seed)
Comments	Ground and aerial application. For best results, apply in the early morning, before temperatures rise, or during the evening. Use 100-200 L water/ha for ground application, 10-40 L water/ha for aerial application. Spray no later than 10 days after egg hatch. Maximum 3 applications/yr. Do not apply more than 2 applications of 83 mL/ha by air. 24-hr re-entry period.

 

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Related links...

• Agronomy Guide for Field Crops - Publication 811
  • Corn: True Armyworm
  • Corn: Fall Armyworm
• Insect
• Corn