Field Guide Pest Management Clover Leaf Weevil
Clover Leaf Weevil
CROPS IMPACTED: Alfalfa, clover, corn, wheat, timothy, snap bean
About the Clover Leaf Weevil
Reproduction and Life Cycle
The clover leaf weevil will overwinter as larvae by plant crowns in the soil. When they emerge in the beginning of spring, they immediately latch onto the host plant and begin eating the foliage. The larvae will usually spin their cocoons in the soil during April and May. This stage will last about 11 days when the adults emerge. These beetles are nocturnal and will only remain active for a short amount of time. When they are not feeding during the day, they hide from the sun in the plants crown. If it is a cloudy day, they may also feed at this time. The beetles will become active again in the fall to lay their eggs in old stems, on stalks or leaves. The eggs will hatch and then overwinter. However, sometimes eggs do not hatch in time; these weevils will overwinter as eggs and then hatch in the spring. Depending on climate, there can be 1 to 2 generations per year (2 generations typically occurring in milder climates).
Clover Leaf Weevil Identification and Habitat
The adult clover leaf weevil is a snout beetle that is 5 to 10mm in length and is covered in small scales that are yellow, brown, and gray in colour, giving it a spotted appearance. The eggs are oval, pale yellow in colour, and will darken to black as they mature. They are usually about 1mm in length. When the larvae hatch, they start off legless and are yellow-green in colour. They will mature to be about 12mm long, grub-like and will have a whiteish-pink line running lengthwise down their back with a dark line outlining each side. They have dark brown heads. The pupae are also yellow-green and about 6mm in length with an abdomen that is deep green in colour. The cocoon that encases it is straw coloured and can be as long as 10mm.
The clover leaf weevil can generally be found throughout North America where alfalfa or clover is grown. The larvae feed on the foliage of host plants, resulting in leaves looking ragged and skeletonized. Under large numbers, this pest can completely defoliate the plant. They will leave small holes and lopsided patches where they eat. They prefer weather that is cool and dry; therefore, in these conditions infestations tend to be the worse, especially during a late spring, as this weather does not promote good plant health. If the weather is humid and wet, most of the larvae end up dying by fungal disease. They can cause host plants to die; however, this is only if their populations are high. If growing conditions are good for the plant, it can usually recover quickly.
Clover Leaf Weevil Management and Control Methods
If you have an environment that promotes the growth of thriving crops, control of this pest will often become unnecessary and will also encourage fungus attacks on the larvae as this pest is highly susceptible to these diseases. Larvae spotted during the day are likely to be infected, turning a tan or brown colour. To help with this: have fertile fields, rotate your alfalfa or clover crops with grass crops frequently, and have good humus levels to help retain moisture. The economic threshold for the clover leaf weevil is at least 5 larvae per plant crown, or when 50% of the buds have been infected.
When clover leaf weevil populations are extreme and beyond the economic threshold, chemical control will be necessary for effective control. Some chemicals that have proven to have an effect on the clover leaf weevil is Matador/Silencer, Dicis 5EC, Malathion 500, Malathoin 85E (only effective on larvae), Imidan, and Lagon. Be sure to carefully read insecticide labels for cautions and proper application. Treatments later in March through to the beginning of April have shown to have the most effect on the larvae.
Latin / Alternative Clover Leaf Weevil Names