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Alfalfa Plant Bug in Asparagus

An unusual new pest appeared in Asparagus fields in Southwestern Ontario in 2007 and again in 2008. Alfalfa plant bugs (APB) have piercing and sucking mouthparts. As they feed they inject a toxic substance into the plant, causing the spears to become shriveled and distorted. Severely affected spears fail to elongate and dry up at the soil surface. APB damage is similar to the symptoms caused by phytophthora infections; however APB populations tend to become active in warm, dry conditions. Phytophthora is more common in cool, wet conditions and on heavier soils.

Alfalfa Plant Bug Nymph(photo credit: Scott Bauer, U.S. Agricultural Research Service)

The alfalfa plant bug is in the lygus bug family. The tarnished plant bug is another common lygus bug pest. The alfalfa plant bug feeds on a wide range of crops and weeds including alfalfa, beans, canola, strawberries, chickweed, dandelion, red clover, red root pigweed, lamb's quarters, plantain, golden rod, and asters. While both the adults and the nymphs will feed on asparagus, it is the sudden influx of nymphs into a field that seems to cause the most damage.

APB feeding can have a significant impact on harvest quality and yields during cutting. Initial sampling undertaken in 2007 & 2008 indicates that this pest may also act as a vector of fungal root pathogens such as fusarium, rhizoctonia and possibly phytophthora. It is possible that spores from the soil enter the wounds caused by APB feeding. Once infected with a root pathogen the crop often continues to decline over time, impacting the longevity of the crop.

Alfalfa Plant Bug Damaged Spears (photo credit: Scott Bauer, U.S. Agricultural Research Service)

Alfalfa plant bugs over-winter as adults in hedgerows and plant debris. They emerge in mid-April to late May and begin to feed and lay eggs. Winter annual and perennial weeds will offer attractive over-wintering and early season feeding sites for these pests. The eggs are laid on the stems/petioles of host plants. Approximately ten days later the nymphs emerge. They have been seen feeding in asparagus as the temperatures heat up in mid-to-late June.

Monitor fields at least once a week or whenever there is a sudden change in the crop's growing conditions. Instruct pickers to report any unusual pest activity in the field. Alfalfa plant bugs appear to be easily managed with insecticides commonly used for asparagus beetle control. Repeat applications may be necessary if new migrations of nymphs enter the field.