Answer: Handpicking is a good strategy. Or you could use Permethrin. It is the oldest, and most common, of the pyrethroid insecticides. It is widely available and is sold under a large number of different brand names (Martin?s Vegetables Plus, Bonide Eight Vegetable, Fruit & Flower, and Hi-Yield Garden, Pet & Livestock Insect Control are three examples). Permethrin is labeled for use on many different vegetable crops and is effective against many beetle, bug, and caterpillar pests. Because it controls so many different insect pests and is labeled on most vegetables, this is probably one of the most useful insecticides for home vegetable gardeners to keep on hand.
In the fall, remove old asparagus ferns and garden debris where adult beetles overwinter to lessen the infestation in the spring. The beetles emerge from hibernation about the time asparagus shoots begin to grow. They lay small, dark brown eggs on the spears. The eggs hatch in one week and the tiny, dark sluglike larvae feed for two weeks until they drop to the ground and pupate. For a small planting, you can also try the following cultural controls. Asparagus beetle larvae are very poor climbers. If you spray the emerging spears every five days with a water spray and knock the larvae off the spears, they won't climb back up. Also, by picking the asparagus patch clean every three to five days and weeding out any volunteer plants, you can remove beetle eggs before they hatch, reducing the damage. If you still have a large adult population come summer, spray insecticidal soap or Permethrin to reduce the number of overwintering adults.
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