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.
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 mid-spring.
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.
Pesticides and Natural Enemy Releases
Not all registered pesticides are listed. The following are ranked by their IPM value, with the most effective and least harmful to natural enemies, honey bees, and the environment listed at the top of the table. When choosing a pesticide, consider information related to water and air quality, resistance management, and the pesticide's properties and application timing. Use PestManage to compare summarized management options for different pests in the same crop. Always carefully read the label of the product being used and take all necessary precautions when handling pesticides.
| Rank | Active ingredient | Example trade name | Group | Group Order | MoA 1 | Amount per acre | REI (hours) ‡ | PHI (days) ‡ | Comments | Selectivity 2 | Bees 3 | Predatory mites 4 | Predators 5 | Parasitoids 5 | Residue duration 6 | Leaching(fish) 7 | Adsorbed runoff(fish) 8 | Solution runoff(human) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Entrust # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
1.25–2 oz | 4 | 60 | Make applications only to asparagus fern... | narrow | low/high | moderate 13 | low/moderate | short to moderate 13 | very low | low | low | very low | low | 08/2019 | ||
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Success | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
4–6 fl oz | 4 | 60 | Make applications only to asparagus fern... | narrow | low/high | moderate 13 | low/moderate | short to moderate 13 | very low | low | low | very low | low | 08/2019 |
Legend
- ‡ a b Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
- # ↩ Acceptable for use on certified organic crops. Check with your certifier to confirm before application.
- 1 ↩ Group numbers for insecticides and miticides are assigned by the Insecticide Resistance Action Committee (IRAC). Insecticides with unknown modes of action are assigned mode-of-action group numbers (MoAs) that begin with UN. Rotate pesticides 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.
- 2 ↩ Range of insect and mite groups affected by a pesticide. Broad means the pesticide affects most groups of insects and mites; narrow means the pesticide affects only a few specific groups.
- 3 ↩ Risk of harm to honey bees. For more information, see Bee Precaution Pesticide Ratings.
- 4 ↩ Risk of harm to predatory mites. Toxicities are generally to western predatory mite, Galendromus occidentalis. Where differences have been measured in toxicity of the pesticide-resistant strain versus the native strain, these are listed as pesticide-resistant strain or native strain.
- 5 a b Risk of harm to parasitoids and general predators. Toxicities are averages of reported effects and should be used only as a general guide. Actual toxicity of a specific insecticide depends on factors including the application rate, environmental conditions, and the life stage and species of a parasitoid or predator.
- 6 ↩ Length of time residue affects natural enemies. Short means hours to days; moderate means days to 2 weeks; and long means many weeks or months.
- 7 ↩ Risk of harm to fish from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 8 ↩ Risk of harm to fish from adsorbed runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 9 ↩ Risk of harm to fish from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 10 ↩ Risk of harm to humans from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 11 ↩ Risk of harm to humans from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 12 ↩ Date information was last updated in the UC IPM Pest Management Guidelines.
- 13 a b c d Toxic to some natural enemies (lacewing and syrphid fly larvae, predatory beetles, and thrips) when sprayed and up to 5 to 7 days after.
UC IPM Pest Management Guidelines: Asparagus
UC ANR Publication 3435
E.T. Natwick (emeritus), UC Cooperative Extension Imperial County
B.J. Aegerter, UC Cooperative Extension San Joaquin County (European Asparagus Aphid)
Acknowledgement for Contributions to Invertebrates
R.J. Mullen, UC Cooperative Extension San Joaquin County
W.E. Chaney (emeritus), UC Cooperative Extension Monterey County
C.F. Fouche, UC Cooperative Extension San Joaquin County
