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. Treatments later in the season for European asparagus aphid control thrips.

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/Acre**	P.H.I.+
(trade name)			(days)
When choosing a pesticide, consider information relating to water quality and impact on natural enemies and honey bees.
A.	DISULFOTON*
	(Di-Syston) 8EC	1 pt	30
	MODE OF ACTION: An organophosphate (Group 1B)1 insecticide.
	COMMENTS: Apply to fern stage of asparagus when thrips infestation appears. Do not exceed 3 applications/year. Use allowed under 24(c) supplemental label.
B.	SPINOSAD
	(Entrust)#	1.25–2 oz	60
	(Success)	4–6 fl oz	60
	MODE OF ACTION: A microbial (Group 5)1 insecticide.
	COMMENTS: Make applications only to asparagus ferns. Do not apply more than 0.28 lb a.i./acre/crop.
C.	PYRETHRIN AND ROTENONE
	(Pyrellin E.C.)	1–2 pt	0
	MODE OF ACTION: A botanical (Group 3)1 and a synergist (Group 21) insecticide.
	COMMENTS: Apply in intervals of 7 days or less and repeat as necessary. Not as effective as other materials.
** See label for dilution rates. + Preharvest interval. Do not apply within this many days of harvest. * Permit required from county agricultural commissioner for purchase or use. 1 Modes of action are important in preventing the development of resistance to pesticides. Rotate chemicals 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. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode of action is assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

PUBLICATION

UC IPM Pest Management Guidelines: Asparagus
UC ANR Publication 3435
Insects
W. E. Chaney, UC Cooperative Extension, Monterey Co.
E. T. Natwick, UC Cooperative Extension, Imperial Co.
C. B. Fouche, UC Cooperative Extension, San Joaquin Co.
Acknowledgment for contributions to the insects section:
R. J. Mullen, UC Cooperative Extension, San Joaquin Co.

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