The control program for Persea Mite that we follow begins early, when the infestation is very low. When pest mites are found on 10% of the leaves, we begin distributing the predatory mite Galendromus helveolus. This allows the predators to become established before pest numbers grow to overwhelming levels.
We then monitor the growth of the pest and predator populations to determine if further treatment is necessary. To do this we count the pest mites (see Counting Method) on the leaves, not the number of spots. This is because the spots are permanent; once formed they remain on the leaf forever and thus don't represent the number of pests which caused them.
If pest levels reach 50 to 100 mites per leaf, we usually spray the trees with 15 gallons of a narrow-range 415 oil in 85 gallons of water by helicopter. This reduces the pest numbers dramatically. It also kills some of the predators, but, since the predators have had time to spread through the trees, any pockets of pest that survive will be likely to have some predators as well. These remaining predators will usually control the pest for the rest of the season without further treatment.
If you are scouting your own grove and the infestation has reached 50 to 100 mites per leaf when you make your first count, it is probably too late to put out the predators. An oil spray would be the strategy most likely to keep the trees healthy and avoid economic loss. If there is still a month or two of warm weather, a predator release after the oil application may prevent the need for a second oil spray.