Count the number of mines on the undersides of the leaves. No treatment is needed for a find of zero to one mine per leaf. For second-generation monitoring, pick younger leaves rather than terminal leaves. Count incipient mines made by the second generation. If you find two or fewer mines per tree, treatment is not needed.
Pheromones are unreliable in the mid and late season for indicating whether sprays are needed.
In abandoned orchards, biological control of this pest is nearly 100 percent. At present, there is no apparent biological window when chemical control could be applied without serious effects on the parasites, though some pesticides applied at the prepink stage for control of tentiform leafminer eggs and adults have minimal effects on parasites. Low numbers of leafminers in the first generation do not guarantee that heavy infestations will not occur in the second and third generation. The need for control of first-generation leafminers can be determined at petal fall by counting the number of incipient mines on the udersurfaces of the leaves. The spotted tentiform leaf miner has demonstrated great proclivity for developing resistance to chemicals.