Forages: Alfalfa Weevil (Hypera
postica Gyll)
Pub 812: Field Crop Protection
Guide >
Chapter
3: Forages > Alfalfa Weevil
Field Crop Protection Guide 2011-2012, Order
2011-2012 publication
Table of Contents
- Description
- Integrated Pest Management Options
- cyhalothrin-lambda – Matador 120E
- cyhalothrin-lambda – Silencer 120 EC
- phosmet – Imidan 50 WP
- chlorantraniliprole - Coragen
- 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 there is 40% leaf-tip feeding, with
2 or 3 active weevils per stem and there is more than 7-10 days
to preferred harvest date, consider applying an insecticide. ("Leaf-tip
feeding" refers to the percent of plant tips showing obvious
signs of damage, which is not to be confused with the percent defoliation.)
- Less than 1 active larva per stem does not require action,
but continue to monitor the situation.
- Two larvae per stem requires action if the alfalfa is less
than 40 cm high.
- If there are more than 3 larvae, immediate action is required.
Second Cut: If damage was serious on first cut,
feeding may continue. Check early regrowth carefully for damage
and larvae.
Natural enemies are generally highly effective at controlling
this pest. For the 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.
| 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* |
3 (livestock foraging) |
| Comments |
For use in alfalfa only. Ground and aerial
application. Allow 7 days between treatments. Alfalfa seed
from treated crop is not to be used for production of alfalfa
sprouts for human consumption. Maximum 3 applications/yr.
Do not apply more than 1 application 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* |
3 (livestock foraging) |
| Comments |
For use in alfalfa only. Ground application only.
Allow 7 days between treatments. Alfalfa seed from
treated crop is not to be used for production of alfalfa sprouts
for human consumption. Maximum 3 applications/yr. 24-hr re-entry
period. |
| Active ingredient |
phosmet |
| Trade name |
Imidan 50 WP |
| Rate per hectare (product) |
2.25 kg per ha |
| Rate per acre (product) |
900 g per ac |
| PHI* |
7 |
| Comments |
For use in alfalfa only. Ground application only.
Do not apply during bloom. Maximum 3 applications/yr. Do not
apply more than 1 application per cutting. 5-day re-entry period. |
| Active ingredient |
chlorantraniliprole |
| Trade name |
Coragen |
| Rate per hectare (product) |
375-500 mL per ha |
| Rate per acre (product) |
151-202 mL per ac |
| PHI* |
0 |
| Comments |
Provides suppression only. For use in alfalfa only.
Ground application only. Begin applications when treatment
thresholds have been reached. Thorough coverage is important.
Use a minimum of 100 L/ha of water by ground. Maximum 1 application
per cutting. 12-hr re-entry period. |
Related links...
