Tuesday, January 23, 2018

Beware the Pea Weevil this Growing Season!

Jesse Fulbright, MSU Liberty County Extension

There was a Montana Ag Alert sent out recently about the pea weevil.  This is not to be confused with the pea leaf weevil that we’ve been seeing for several years now.  Damage from this newer pest, the pea weevil, has been confirmed from the State Grain Lab in 2017.  While peas might not be the hot commodity they once were due to market prices, it is still important that we stay ahead of this pest and be aware of its potential in our region.

The pea weevil, or rather the larvae, feed inside the developing pea seed, leaving a circular exit hole and causing damage in the center of the pea.  Affected peas are unfit for human consumption, their seed germination rate decreases as well as the seed weight and yield, which in turn diminishes market value through dockage.  Let’s go back a step though to a stage we will typically see the pea weevil when scouting crops.  The pea weevil, similar to other weevils, is a small, gray-brown weevil flecked with light and dark irregular patches.  It can be surveyed in the field using a sweep net.  One weevil in 25 sweeps can result in a 10% infestation at harvest.  The threshold is considered to be two adults per 25 sweeps done in an 180 degree sweep.
Pea weevil damage to field peas.
The adult pea weevil overwinters as an adult and emerges about the time that peas are blooming.  Adults feed on flowers, leaves or pods, congregating on pea flowers at early bloom.  After mating the females will lays one to two eggs on the outside of the pea pod.  Larvae hatch within one to two weeks and burrow into the pod.  However, damage from the pest is most often discovered at the elevator. 

There are currently no pea weevil resistant varieties in the U.S.  From a cultural control standpoint, field sanitation can reduce infestations.  Sanitation measures include destroying crop residues, preventing shattering at harvest, eliminating volunteer plants and planting uninfested seed.  There are several chemical controls out there, including Carbaryl, Imidan, Malathion and Mustang Max.  Please read the individual pesticide labels for exact rates.  In regard to the pesticide label, please be aware of the preharvest interval.  These preharvest intervals can range from three to 21 days depending on the product.

I would encourage you to contact your local county Extension office if you have further questions about pea weevils, especially as we get closer to the growing season.

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