How to Manage Pests
UC Pest Management Guidelines
Thrips are small, slender insects with mouthparts developed primarily for sucking and rasping. The adults measure about 0.04 inch (1 mm) in length and have two pairs of narrow wings that are fringed with hairs. Immature thrips are wingless, whitish to yellowish in color. Adults emerge continuously throughout the warm months. Adults and immatures may be found in asparagus ferns at any time during the summer and fall when ferns are growing. Eggs are deposited in plant tissue and hatching occurs in about 5 days during the summer months; the immature stages take about 5 to 7 days to complete development.
Thrips are most noticeable and of greatest concern on young seedling plants but can severely damage mature ferns of asparagus. Their feeding will make the plants look ragged, cause the ferns to turn yellowish gray, and can cause the cladophylls (branchlets) to drop. Thrips remove moisture from the fern, causing a shortening and twisting of the cladophylls as well as some twisting of the stalks. This results in a loss of crop vigor and even the death of the tops of small seedlings.
Thrips tend to be a problem mainly from April to June in the Delta area when surrounding crops and weeds begin to dry, causing thrips to seek more succulent vegetation. Thrips attack all plantings of asparagus but are particularly injurious to asparagus crown nurseries, direct-seeded new plantings, seedling transplanted fields, and new 1-year-old crown plantings because these plantings are in fern when the thrips are immigrating in from surrounding fields in midspring.
In the Imperial Valley, bean thrips attacks ferns during summer and can cause severe damage, even in mature stands. Further, the stress of losing foliage during summer makes the crops more susceptible to attack from Fusarium sp.
Good weed management in the asparagus field and surrounding crops and areas is an important aspect of managing thrips. Monitor young plantings in mid-spring for thrips when the fern is present and flowering. Treat if needle drop is observed.
UC IPM Pest Management Guidelines: Asparagus