Alfalfa weevil populations continue to develop, as we get closer to taking first cutting. Alfalfa weevil populations vary across the state, but when scouting, larger larvae are becoming more common with some developing into the pupa stage inside their cocoons.
County educators across the state continue to report scouting numbers in Table 1. Overall weevil numbers are lower than last week, but there are still fields that are hovering around the recommended action threshold. Much of the noticeable decrease in alfalfa weevil numbers this past week can be attributed to control efforts taken across the state.
Table 1: County alfalfa weevil scouting reports for April 27 – May 3
|
County |
Alfalfa Height (inches) |
Larvae Count per Stem |
|
Defiance |
14 |
0.9 |
|
Defiance |
11 |
0.5 |
|
Defiance |
12.5 |
0.3 |
|
Holmes |
13.5 |
0.4 |
|
Madison |
19.8 |
0.5 |
|
Mercer |
24 |
0 |
|
Mercer |
23 |
0 |
|
Miami |
12 |
1.8 |
|
Putnam |
19 |
1.2 |
|
Ross |
15 |
0.2 |
|
Ross |
13 |
0.3 |
|
Ross |
16 |
0 |
|
Wayne |
14 |
0.3 |
Table 2. Alfalfa Weevil Threshold Recommendations
|
Stand Height (Inches) |
Indication of Problem (% Tip Feeding) |
Problem Confirmation (Larvae per Stem) |
Recommended Action |
|
6 |
25 |
1 |
Recheck in a week |
|
9 |
50 |
>1 |
Spray |
|
12 |
75 |
>2 |
Spray |
|
16 |
100 |
>4 |
Harvest early |
Across the state we are seeing more sprayer tracks in fields or hearing of plane applications as control actions are taken. As we get closer first cutting there are a few extra considerations to make. As always, it is a good idea to scout to ensure that control is necessary. For a scouting refresher this ~4 minute video “Alfalfa Weevil Scouting” is a quick and easy resource.
If a pesticide application is warranted, consult the pesticide label to make sure the application is completed effectively. As we get closer to first cutting in some portions of the state, it is very important to make sure any harvest restrictions associated with a pesticide application are considered.
If you are harvesting a field with an alfalfa weevil infestation, it is recommended that you scout the field a few days after harvest to make sure the alfalfa weevil population is still not active. If the alfalfa weevil population persists, they can do significant damage to the second cutting since the alfalfa regrowth can’t support excess feeding pressure without a yield impact.