Forages: Alfalfa Weevil (Hypera postica Gyll)

Excerpt from Chapter 3, Field Crop Protection Guide, Order this publication

Table of Contents

1. Description
2. Integrated Pest Management Options
• cyhalothrin-lambda – Matador 120E
• cyhalothrin-lambda – Silencer 120 EC
• phosmet – Imidan 50 WP
3. Related links...

Description

The adult weevil is a brown snout beetle, about 5 mm long, with a dark brown stripe extending from the head down the centre of the back. Larvae are bright green with a black head, six legs and a distinctive white stripe down the centre of the back. At full size, they are about 8 mm long.

Image 1. Alfalfa weevil adults are about 8 mm long.
Note the dark stripe running along the back.

Image 2. Alfalfa weevil larvae feed on leaves,
causing skeletonization. Note: Larvae have black heads.

Do not confuse the alfalfa weevil larvae with the clover leaf weevil larvae, which are larger, have a light brown head instead of a black head and a white stripe edged with pink. Also, do not confuse alfalfa weevil larvae with predacious fly larvae, which have no head capsule and are legless.

Integrated Pest Management Options

First Cut: If 40% of the stems have feeding damage in the tips, cut and remove from fields as soon as possible. If this level of damage occurs in a week or more before optimum cutting time, spray may be necessary.

Second Cut: If damage was serious on first cut, feeding may continue. Check early regrowth carefully.

Natural enemies are generally highly effective at controlling this pest. For safety of these natural enemies, chemical control is not recommended unless pest population exceeds the action threshold. See OMAFRA Publication 811, Agronomy Guide for Field Crops, for more information on action thresholds.

Comments (Days to harvest, label precautions, etc.)
Alfalfa only. Ground and aerial application. Apply when larvae are small and populations are high. Maximum of 3 applications/yr, 1 may be by air. Allow 7 days between treatments. Do not apply within 3 days of livestock grazing. Alfalfa seed from treated crop is not to be used for production of alfalfa sprouts for human consumption. 24-hr re-entry period.

cyhalothrin-lambda – Silencer 120 EC

Comments (Days to harvest, label precautions, etc.)
Alfalfa only. Ground application only. Apply when larvae are small and populations are high. Maximum 3 applications/yr, 1 may be by air. Allow 7 days between treatments. Do not apply within 3 days of livestock grazing. Alfalfa seed from treated crop is not to be used for production of alfalfa sprouts for human consumption. 24-hr re-entry period.

Comments (Days to harvest, label precautions, etc.)
Alfalfa only. Ground application only. Do not apply during bloom. Only 1 application per cutting. 7 days to cutting or grazing.

Related links...

• Agronomy Guide for Field Crops - Publication 811
  • Forages: Alfalfa Weevil
• Insects
• Forages