Alfalfa Pest Management

Alfalfa Pest Management

Sampling Guidelines

Pest

Sampling Method

Growth Stage: Mid- March to First Cutting
Alfalfa weevil Minimum of 30 stems per field collected in a W-pattern, place stems top first in bucket, measure stem height and count the number of larvae per stem
Pea aphid  Collect a minimum of 30 stems per field and  count the number of aphids and beneficial insects present per stem ( e.g. lady beetles and syrphid fly larvae )
Growth Stage: After First Cutting (mid-May) to September
Alfalfa weevil – only for 2 weeks after first cutting Minimum of 30 stems/crowns per field in a W-pattern, place stems top first in bucket and count the number of larvae per stem/crown
Potato leafhopper Ten sweeps in ten locations – plants should be dry
Blister Beetle 10 sweeps in ten locations<
Garden webworm and other defoliators Estimate defoliation in 10 location

Alfalfa Insect Thresholds

Pest March – April May – early June mid June – mid Sept.
Alfalfa weevil 0-11 in. – 0.7 per stem12 in. – 1.0 per stem

13-15 in. – 1.5 per stem

16 in. – 2.0 per stem

17-18 in. – 2.5 per stem

0-11 in. – 0.7 per stem12 in. – 1.0 per stem

13-15 in. – 1.5 per stem

16 in. – 2.0 per stem

17-18 in. – 2.5 per stem

after 1st cutting – 2 per crown

 
Pea aphid <10 in. – 50 per stem>10 in. – 100 per stem

1 or more beneficials per 50 aphids should provide control

<10 in. – 50 per stem>10 in. – 100 per stem

1 or more beneficials per 50 aphids should provide control

 
Potato leafhopper   3 in. or less – 20 per 100 sweeps4-6 in. – 50 per 100 sweeps

7-11 in. – 100 per 100 sweeps

12 in. or more – 150 per 100 sweeps

3 in. or less – 20 per 100 sweeps4-6 in. – 50 per 100 sweeps

7-11 in. – 100 per 100 sweeps

12 in. or more – 150 per 100 sweeps

Garden webworm / general defoliators     25-30% of tips damaged
Blister beetles     1 per sweep