BIOLOGY: Adults are active from May to September. They are 4 to 5 mm long. Females produce 30-130 eggs in their lifetime. Up to 5 eggs are deposited in the flower head of each knapweed plant. Larvae hatch in 3 days and then spend 4 weeks in the seed head before pupating. Pupation takes 1 week. Adults drop off of plants in September and overwinter in the soil.
DESTRUCTIVE STAGE: Larvae (feeding on seed head) and adult (leaf and seed feeding)
IMPACT TO HOST: Damage can reduce stands density and provide excellent control. L. minutus will be most effective when released with other knapweed biological control agents listed in this field guide.
REDISTRIBUTION: Adult L. minutus can be collected using a sweep net or by picking them off of plants in June and July. A typical release is 150-250 adult insects.
SPECIES OF KNAPWEED ATTACKED: Diffuse knapweed, spotted knapweed, squarrose knapweed.
BACKGROUND: Squarrose knapweed is a native plant of the eastern Mediterranean area. It is very competitive on rangelands. Knapweed releases chemical substance that reduces competing competition.
DESCRIPTION:This long-lived herbaceous weed has a simple taproot and grows 12 to 18 inches tall. The rosette and stems have deeply-lobed leaves. Flowers are rose to pink. It is often confused with diffuse knapweed, but differs in that the terminal spines on the flower bracts are curved outward and are not laterally toothed. Bloom occurs in the early to mid-summer.
CONTROL: Several biocontrol agents are available. Herbicides offer good to excellent control. Contact your state or county weed specialist for specific, updated information.