This past week, there were reports of increasing problems with clover root curculio infecting alfalfa in a couple of central Kentucky counties. Clover root curculio is an overlooked invasive pest from Europe that has been in the United States since the 1800s. This pest is often overlooked because the damage caused by the larvae occurs below ground and goes unnoticed until the damage becomes evident during droughty periods.  The injury caused by the larvae can result in substantial stand reduction. Fortunately in the past, problems have been localized and usually not at economic levels.

Clover root curculio emerges in early summer to feed on foliage for a few weeks before becoming inactive until fall. During warm periods in fall through spring, root curculio lays eggs around the crown of its hosts plants. These eggs begin to hatch in April, and the larvae feed initially on nodules. As larvae get larger, they feed on fibrous roots, then tap roots. Clover root curculio will feed on a wide range of legume species.

Unfortunately, there are no effective insecticides that can be used to control the larvae, either as a preventive measure or as a rescue treatment.  While there are insecticides for managing the adults, this stage does not cause economic damage, and controlling adults has not been shown to reduce subsequent larval infestation. Where insecticides have been used to control the adults, these pesticides have not been shown to provide economic returns as the adults emerge over an extended period during the summer. Management of clover root curculio relies on practices to reduce infestation and susceptibility of new plantings.

It is important to use a non-legume rotational crop following alfalfa, such as corn or grasses. Avoid new seedings immediately adjacent to older stands since adults can readily move to the new seeding. Particularly, avoid seeding fields near fields that are known to be infested. If practical, eliminate clovers and other legumes around field margins. Use spring seeding for new fields as these early plantings will be older and more tolerant of damage the following spring. Fall seedings will be less mature the following spring when larval feeding would begin and may suffer more damage.

If you suspect damage from the clover root curculio in new or existing alfalfa stands, contact your county agent and they can advise you on taking root samples and submitting them to the UK Disease Diagnostic Lab. Find the original post here.

~ Ric Bessin, UK Entomology Extension Specialist