One of the major insect threats to your asparagus plant is the asparagus beetle.There are two varieties of this insect pest: the common asparagus beetle and the spotted asparagus beetle.
Common and Spotted Asparagus Beetles
Both insects have oval-shaped bodies and are less than 1 inch long. The common asparagus beetle occurs more widely than the spotted variety. It also causes more damage to the asparagus plant.
The common variety has a bluish-black color with 6 cream colored spots on the back. The spotted beetle is reddish-orange in color with 12 black spots on the back. During the spring, both the adults and larvae feed on the plant spears, causing them to become brown and develop scars. It may also result in bending over of the spears to form a shepherd's crook.
In the summer, the beetles feed on the ferns, resulting in defoliation and reduced food supply to the crowns. This results in retarded plant growth. Proper development of roots is also hindered. Affected plants remain small in size and yield a much reduced crop quality. If you want to control the asparagus beetle organically, you may find the following suggestions helpful.
Handpicking the beetles is effective, although it may be time consuming since you need to be thorough when inspecting the plants. Check for beetles underneath the leaves as well as on the branches and stems. Once gathered, you can squash them or get rid of them.
Keep Your Garden Clean
Keeping your garden clean is the best prevention for the asparagus beetle. Till the soil regularly to disrupt hibernation. It is also helpful to get rid of garden waste and rubbish heaps where the beetles love to hide.
Companion planting is an effective strategy in controlling the beetles. Certain plants will repel the beetle. For instance, they prefer to avoid tomato plants, so it's a good idea to plant some tomatoes around your asparagus crop. They will repel the beetles and help protect your asparagus.
Introduce Beneficial Insects
Certain insects love to feed on the asparagus beetle and can have a beneficial impact when introduced in your garden. Encourage the presence of ladybugs and the chalchid wasp in your garden. You can get these from your home garden store. They make an excellent natural control agent to deal with the asparagus beetle.
Use an organic insect spray made of liquid garlic concentrate. Dilute with water and spray over your asparagus crop. The plants will absorb the garlic, which acts as a natural defense against asparagus beetles. The garlic spray will not alter the smell or flavor of the asparagus or other garden plants. It is effective and safe to use, as it contains no chemicals and is non-toxic.
Cut the shoots of your asparagus plants every 2 to 3 days to prevent the eggs from hatching. When consistently practised, it makes an effective control strategy in managing the beetles.
Use Netting and Row Covers
Young asparagus can be protected by covering them with a cheesecloth netting. You can also use row covers when the plants are still young, so that they're protected from the beetle menace.