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What is it?
Onion pea weevils are of the bruchus pisorum species and typically attack all varieties of edible peas. However, they also attack the bulbs of onion family plants such as garlic, leeks, shallots and of course, the common onion. Although pea weevil damage is not extremely common in onion family plants, when it does occur it can be devastating to the onion crop as once an onion plant has been infested with pea weevils the onion become inedible.
What does it look like?
Bruchus pisorum species onion pea weevils tend to by fat white grubs which grow to be approximately 1/5 inch long at their maximum size. Pea weevil grubs are extremely small and often you will not notice them, until the damage to your onion plants has already been done. Usually if you see them it is because you have sliced open an onion bulb. Onion pea weevils burrow in through the onion skin to the center of the onion bulb. It is there that they feed. Your onion plants may show signs of pea weevils infestation if you notice small, round burrow holes in them, or if the onion bulbs become hollow. Often the plants will turn yellow and begin to wilt. If this occurs they will eventually die as they are being weakened from the inside. Once an onion plant has been infested with onion pea weevils of the bruchus pisorum species they must be discarded and destroyed.
How does it manifest?
Onion pea weevils emerge from hibernation each spring as plants are beginning to emerge or bloom. Adult onion pea weevils are usually dark brownish beetles that are approximately 1/4 inch long and these mature beetles will often have lighter brown markings on their bodies. Pea weevil beetles can be seen both crawling around emerging onion plant growth and they also fly. Although adult onion pea weevil beetles do feed on the foliage of the plant, they do not actually make the onion inedible. It is when the fat white grubby pea weevil enters the onion bulb that the plant can no longer be used in the harvest. Adult pea weevil beetles can migrate up to 3 miles as they search for feeding grounds. Once they have established a good area to feed, adult female onion pea weevil beetles lay eggs on the developing foliage near the base of the plant. When the grubs hatch from these eggs they burrow into the soil and into the onion bulb where the pea weevils begin to feed with their dark brown heads. Typically onion pea weevils will feed for a period of eight weeks and then they pupate within the hollowed onion bulb. Approximately three weeks later the adult pea weevil beetles emerge and hibernate where they do not cause damage to plants until the following year. Fortunately, only one generation of onion pea weevils will do damge to your onion plants in a year.
What can you do about it?
Once you find damaged or onion pea weevil infested onion plants you will need to destroy and discard all infested onions as they are inedible. You can also spray plants with an insecticide containing rotenone in either a dust or a spray formulation. This helps to kill of mature onion pea weevil beetles before they can lay their eggs, as once eggs are laid it is too late to prevent injury to the onion plant. Additionally, spray repeat applications if you notice new signs of damage due to the vast migrating capabilities of these garden pests. Be sure that you carefully clear and destroy all fallen plant debris from the garden around your onion plants after harvesting the crop. You may also choose to plant onion family plants away from any pea plants to help cut down on pea weevil damage. However, if they run out of peas to feed on, no doubt the onion pea weevils will migrate in your garden, so it is good to know what signs to look for.
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