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Agronomic Crops Network

Ohio State University Extension


Statewide Alfalfa Weevil Population Update #1

Alfalfa weevil is a pest that develops and causes increasing levels of damage in alfalfa as growing degree days (GDD) accumulate. Most of southern Ohio is within the range of GDD for peak alfalfa weevil activity and as seen in the table below there is significant activity in northern countries that have not peaked yet.

The following table indicates the average alfalfa height and alfalfa weevil population for the couple of fields scouted in each county for the week of April 16th-22nd.


Alfalfa Height (inches)

Larvae Count per Stem










All of the sample fields scouted this past week are below the threshold requiring a control method, with the southern Ohio sample fields in Ross County being the closest to that control threshold.

Alfalfa weevil scouting is very easy and helps guide decisions on harvest timing and insecticide usage, to maximize forage yield and quality. There are many great resources to get started, reference the article written earlier this year “Scouting Early Alfalfa Weevil Activity” and this forage team video “Alfalfa Weevil Scouting”. Alfalfa weevil control is determined by the average larvae per alfalfa stem and the maturity of the alfalfa stand. If control thresholds are met, options for control are an early harvest of insecticide usage. Both methods of control require timely decision making and the best way to do that is to know the levels of alfalfa weevil in your fields.

Additional Authors: Ryan Slaughter

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.