Citrus Thrips, Scirtothrips citri (Moulton), (Thysanoptera: Thripidae)            

Differentiating citrus thrips and flower thrips (PDF)

What is the optimal citrus thrips strategy for a grower or pest control advisor in 2001? 

First, one might consider re-reading the April 1999 issue of Citrograph (Schweizer and Morse 1999, a pdf copy is available below) that discusses our best guess regarding how citrus thrips population “pressure” will correlate with weather patterns prior to petal fall.
How weather affects citrus thrips populations, (PDF)

Secondly, frequent monitoring of citrus thrips levels on small fruit after petal fall is needed to assess citrus thrips levels (see UC guidelines for citrus thrips on citrus at http://www.ipm.ucdavis.edu/PMG/r107301711.html -- this includes current treatment recommendations). Depending on thrips severity, variety of citrus, and grove location, a chemical treatment may or may not be needed during a particular year. If a treatment is needed, timing of the treatment is critical (especially during hot weather, citrus thrips feeding stages develop very quickly and significant fruit scarring can occur within several days). A grower might consider modifying a weed sprayer for rapid response thrips control (Elmer et al. 1983, a pdf file is available below) – as soon as economic levels of citrus thrips are found on small fruit, a treatment should be applied.

Modifying a weedsprayer for citrus thrips control (PDF)

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  Sprayers used in study      
  Spray pattern of two sprayers

Navel oranges should be treated when immature citrus thrips are found on >5% of the fruit when less than 0.5 predatory mites are found per leaf.   The treatment threshold is raised to 10% fruit infestation with > 0.5 predaceous mites per leaf.  Both of these thresholds are doubled for Valencia oranges, because they are less susceptible to citrus thrips scarring.  In general, we don’t advise treating thrips on non-bearing citrus because several studies have shown that citrus thrips have minimal impact on tree growth. In addition, repeated treatments on young trees can rapidly lead to the development of resistance.

Choice of chemical will depend on how important conservation of natural enemies is (e.g., is Aphytis being released – in this case, Agri-Mek, Success, or Veratran are preferred), what other  pests require control (Agri-Mek will give some mite control; Baythroid, Cygon, and Success give varying levels of katydid control; Baythroid, Carzol, and Cygon give glassy-winged sharpshooter control), whether citrus thrips resistance has been seen in the grove being treated (Carzol, Cygon, and Baythroid resistances have been seen in some groves), cost of different materials, etc.  Growers should be careful not to depend on one pesticide season after season as that will select for resistance.  We can hope for low citrus thrips pressure in 2001, similar to what we generally saw in 2000, but for the near future, frequent monitoring of citrus thrips levels in each grove and advice from a knowledgeable pest control advisor is suggested.

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