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Webspinning mites can produce copious amounts of webbing.

Monitor Spider Mites—Fruit Development

From May through August, monitor for mites at least weekly. If the orchard has problem areas such as trees along roads or water-stressed trees, monitor every few days once mite densities start to increase.

Before July 1, focus monitoring on hot spots, the areas that develop mites first. These are often dusty or water-stressed areas of the orchard. Once the mite threshold has been reached in these areas, sample the remainder of the orchard to determine if a spot treatment is sufficient or if the entire orchard requires treatment.

After July 1, monitor the whole orchard, dividing it into sampling areas that could be treated separately.

How to monitor spider mites:

  1. Within each sampling area, sample a minimum of 5 trees. Select 15 leaves from each tree, randomly picking leaves from both the inside and outside of the canopy as you walk around it.
  2. Examine both sides of each leaf using a hand lens, looking for:
    • Spider mites and eggs
    • Western predatory mites and eggs
    • Sixspotted thrips
    • Other predators
  3. Count the number of leaves on each tree with pest mites or their eggs, and the number of leaves with predators, then note on the spider mite monitoring form (113 KB, PDF). Do not count individual mites or predators.
  4. As you move from tree to tree, keep a running total of leaves with mites. Once you have sampled 5 trees, compare your total to the numbers in the "Don't Treat" and "Treat" columns on the monitoring form.
  5. If your numbers are:
    • The same or less than the "Don't Treat" column, you can stop sampling.
    • As much or more than in the "Treat" column, stop sampling and treat.
    • In between, continue sampling until a decision can be reached.

Be sure to take into consideration the presence or absence of predators as noted on the form.

Important links

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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Agriculture and Natural Resources, University of California

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