Cutworms can eat the tips or sides of emerging spears causing them to grow crooked or die. Organic cutworm controls such as BT or parasitic nematodes can reduce damage.
Asparagus beetles chew on the fern, causing the stem to turn brown and reducing the yield the next year. Inspect the ferns throughout the season for insect feeding and fern dieback. Organic control options are limited. Hand pick the beetles from the plants in the morning when they are sluggish. Lady bugs and chalchid wasps will feed on beetle eggs and larvae. Some sites recommend dusting plants with bonemeal or rock phosphate which presumably would need to be reapplied after every rain.
Fusarium wilt is a disease is caused by one of several fungi of the fusarium species. Shoots begin to turn yellow, then a dingy brown and begin to wilt. Often pink and cottony looking or whitish strands will appear on the undersides of leaf scales on plants. Infected crowns may have a reddish brown appearance.
As the fungi penetrate plant roots they spread into the stems and leaves via the water conducting vessels in the plant. The vessels become plugged blocking the flow of moisture and causing wilt to occur. Fusarium wilt in asparagus plants favors temperatures between 75° and 80°especially weather that is wet. The disease is also spread by contaminated seeds, soil, plants and equipment and as such it often enters a new plant through the roots when transplanting. The fungi of fusarium wilt live on organic matter in the soil and so can be spread by anything that comes in contact with it.
Any plants, which show signs of infection, must be destroyed. No chemical control is available. Your best bet once plants become infected is to plant new plants the following year in soil that has not been infected and where asparagus has not been previously planted for a term of 2 to 4 years. If you choose to plant in infected soil, first fumigate the soil with meta-sodium two to three weeks prior to planting.
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