Forages: Alfalfa Snout Beetle

Excerpt from Agronomy Guide for Field Crops (Chapter 5)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Description
2. Life History
3. Damage
4. Scouting Technique
5. Action Thresholds
6. Management Strategies
7. Updates on Forages: Alfalfa Snout Beetle
8. Related links...

Description

The adult is a flightless, dark grey weevil approximately 12 mm in length. Larvae are small, white and legless with a light-reddish-brown head and can be found in the soil, feeding on or in the roots.

Plate 89. Alfalfa snout beetle adults are approximately 12 mm long and cannot fly.

Plate 90. Alfalfa snout beetle larvae girdle the taproot or gouge its surface, leaving deep spiral grooves. Larvae are white and legless and have a reddish-brown head.

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Life History

The snout beetle has a 2-year cycle. Adults emerge from their overwintering sites in April, feed on new alfalfa shoots and migrate into new fields to lay eggs. Adults may walk short distances or may be carried longer distances via the transportation of soil, gravel, hay, farm machinery and waterways. All the adults are female. The eggs soon hatch and begin feeding on the main and side roots of the host plant. The total life cycle requires a span of 2 years.

Damage

This potentially serious pest of forage crops was discovered in Eastern Ontario near Prescott and Brockville. The larvae girdle the taproot or gouge its surface leaving deep spiral grooves. Severely injured plants may appear yellow and leafless in the fall. Adults feed on leaves and stems causing only marginal damage. Damage is most evident in late summer and early fall.

Scouting Technique

Early-season scouting for beetle migration should be done in infested counties of Eastern Ontario. Later in the season, wilted plants should be dug and checked for damage and the presence of larvae. Alfalfa snout beetle has a wide range of hosts. Although it finds alfalfa to be the most attractive crop, larvae of the insect may attack all species of clover, grape and strawberry. They sometimes even feed on weeds, especially ones with fleshy roots such as wild carrot and dandelion.

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Action Thresholds

None available.

Management Strategies

Rotation of alfalfa with non-host crops breaks the cycle and decreases the population of snout beetle significantly. Non-host crops include corn, small grain cereals and soybeans. In heavily infested fields, it is recommended that the rotation crops be grown for at least 2 years to reduce the insect population dramatically.

To minimize the chance of transporting this pest, all farm machinery should be cleaned thoroughly before being moved from an infested field. First-cut hay from infested fields should be stored for at least 2 months before it is shipped. There are restrictions on the transportation of hay, straw, soil and compost material from infested fields. If you suspect you have this pest, consult the provincial field crop entomologist or forage specialist.

Updates on Forages: Alfalfa Snout Beetle

• Field Crop Protection Guide - Publication 812
  • Forages: Alfalfa Snout Beetle

Related links...

• Insects
• Forages

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