Description of the Pest
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.
Damage
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.
Management
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.
Organically Acceptable Methods
Weed management in and around the field and sprays of the Entrust formulation of spinosad are acceptable for use in organically managed fields.
| Common name | Amount per acre** | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used. | ||||
| A. | SPINOSAD | |||
| (Entrust)# | 1.25–2 oz | 4 | 60 | |
| (Success) | 4–6 fl oz | 4 | 60 | |
| MODE-OF-ACTION GROUP NUMBER1: 5 | ||||
| COMMENTS: Make applications only to asparagus ferns. Do not apply more than 0.28 lb a.i./acre/crop. Check with organic certifier to determine which products are organically acceptable. | ||||
| ** | See label for dilution rates. |
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest. |
| 1 | Rotate insecticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee). |
| # | Acceptable for use on organically grown produce. |