Vegetable Weevils

Adult and larval vegetable weevils are primarily night feeders.

Vegetable weevil (Clemson University - USDA Cooperative Extension Slide Series , Bugwood.org) CC BY 3.0

Before we dive into the world of weevils, let me explain that there is some confusion about vegetable weevils. There are actually two species in question: Listroderes difficilis Germain is the true vegetable weevil, native to South America and now found globally. The other vegetable weevil, Listroderes costirostris, is currently only found in California and western Arizona. Of course, that may change as these garden pests take advantage of our changing climate and increased global trade.
 
For the sake of our discussion today, we are talking about the true vegetable weevil, though the information is just as relevant to both species. Either way, if you know what to look for, you will be better able to prevent problems from getting worse.
 
Vegetable weevil damage
 
Your first clue of a vegetable weevil problem may be plants cut off at ground level. Adult weevils often girdle stems close to the ground. You will also see feeding holes in leaves. Those holes start out small and round, but eventually expand into larger, irregularly shaped holes.

Vegetable weevil larva feeding on tobacco (R.J. Reynolds Tobacco Company, Bugwood.org) CC BY 3.0

While they can fly, they almost never do, so crop damage is usually first seen around the edge of a garden.
 
These pests feed on the buds, leaves, and roots of several garden crops, including beans, beets, cabbage, carrots, cauliflower, collards, lettuce, mustard, onions, potatoes, radish, spinach, Swiss chard, tomatoes, and turnips. As they feed, they create places where other pests and diseases can take hold.
 
Vegetable weevil description
 
Vegetable weevils look very similar to carrot weevils. They are small (0.38 inch/1cm), bristly, tan to grayish brown snout beetles with elbowed antennae. If you look closely, you may see a V-shaped spot on their wingtips, though that marking can fade over time.
 
[One easy way to catch many insects for a closer look is with a loop of packing tape wrapped around your fingers, the same way you collect pet hair off that favorite sweater. Insects have not evolved a defense against packing tape, and it gives you a relatively clear view without the hassle of trying to chase your specimen around with a magnifying glass.]
 
Vegetable weevil larvae start out as pale, C-shaped grubs with dark heads. As they feed, they turn green and stretch out. They are about the same size as the adults. Eggs are yellowish white and often laid on plant stems.
 
Vegetable weevil lifecycle
 
Vegetable weevils are parthenogenetic, which means females reproduce without assistance from males. According to the Virginia Cooperative Extension, “males are not known for this species.”
 
Some of those lady vegetable weevils can live for two years. They overwinter in plant debris and weeds. In summer, as temperatures rise, they lay low in the weeds in a behavior known as aestivation.
 
Vegetable weevils often hide in the soil, so raking the soil after harvest exposes eggs to predators. [My hens always loved it when I gave them a freshly harvested bed to play in!]

Vegetable weevil management
 
The best way to deal with vegetable weevils is with diatomaceous earth (DE). This ultra-fine powder blocks the air holes in a weevil’s exoskeleton. Apparently, they don’t like it on their feet, either.
 
Since they rarely fly, you can often keep these pests off young plants with row covers. Crop rotation, neem oil and other insecticidal soaps, sticky barriers, spinosad, and a bevy of birds and beneficial predators will also help you keep vegetable weevils from doing too much damage in your garden, but diatomaceous earth is your best bet.
 
Did you know that startled vegetable weevils play dead, falling from the host plant when disturbed? Now you know.