Indiana Alfalfa Growers Should Look For Weevils
Purdue University entomologists are advising alfalfa growers to spend time looking for alfalfa weevils. They say alfalfa fields in southern and central Indiana need to be inspected immediately for weevil tip feeding and skeletonization of leaves.
Alfalfa Weevils Numerous In Missouri
Alfalfa weevils have increased to threatening levels in central and northern Missouri, according a University of Missouri extension entomologist. "Alfalfa weevil larvae are two to three times the economic threshold in many fields," says Wayne Bailey. Last week, 100% of plants were showing signs of foliar damage in the central part of the state.
The economic threshold is one larva per alfalfa stem with 30% of plants showing signs of feeding damage, according to Bailey. Most larvae in fields surveyed by MU extension specialists last week were in early growth stages and damage was limited to the upper whorl of leaflets. However, damage will increase as weevils mature.
"Problems can quickly develop and result in substantial loss of forage yield and quality," Bailey says. Larvae grow rapidly in warm temperatures and increasingly feed on leaves. So scout fields to determine weevil numbers. Applying a foliar rescue insecticide is the most common control strategy. Other options include early harvesting, grazing and biological control.
"This season, early harvest may be a viable option as alfalfa plants have grown rapidly with the cool, wet conditions this spring." But alfalfa must be within seven to 10 days of the normal harvest stage, Bailey warns. Be sure to monitor fields afterward.
If alfalfa plants are 6-8” tall, and weevil numbers are at the economic threshold, management-intensive grazing may reduce weevil larvae by 90% – as long as most spring-laid eggs have hatched, Bailey says. But grazing wet fields can cause hoof damage, and watch for bloat. Graze only the upper two-thirds of the alfalfa so it can recover for the next cutting.
A fungus or parasites can sometimes be used to kill weevil larvae, but not this year because of the high weevil populations.
Contact Bailey at 573-864-9905.
Alfalfa And Clover Leaf Weevils In Nebraska
The University of Nebraska is alerting the state’s alfalfa growers to be on the lookout for feeding damage from alfalfa and clover leaf weevil larvae. Insect development has been delayed in Nebraska due to below-average temperatures, but as temperatures start to climb, the insects may be getting to work. Temperatures and conditions in southern Nebraska indicate that some feeding may be observed as tiny pinholes on the leaves of the upper part of the stem.
The weevils feed on first-cutting alfalfa as larvae and also consume regrowth after first cutting as adults and sometimes as larvae. Research in northeastern Nebraska has shown that clover leaf weevil feeding doesn’t reduce first-cutting yield, but alfalfa weevil feeding can cause severe losses to its yield and quality.