The presence or absence of western flower thrips should be considered when growers make spider mite control decisions, say California researchers.

They point out that western flower thrips feed on spider mites and may be killed by chemicals targeting the mites.

They tested several miticides for spider mite control in spring and summer applications last year. Western flower thrips were plentiful in spring, but were essentially absent when summer treatments were made.

The researchers say several products currently unregistered for spider mite control in al-falfa gave excellent control in summertime treatments. They included Capture + Dimethoate 400, Zephyr + Trilogy, and three experimental compounds.

Results were quite different in spring testing, however. Three days after treatment, when western flower thrips were feeding on spider mites, many of the 22 treatments had more mites than untreated alfalfa. Exceptions were Capture + Dimethoate 400, Capture and two of the experimentals.

Two high-sulfur fertilizer treatments also had more mites than untreated alfalfa. The fertilizers probably repelled western flower thrips, say the researchers.