The sap-feeding stage is composed of very small larvae that pierce plant cells and feed on sap. Damage caused by this insect consists entirely of leafmining. Each completed mine reduces the leaf's green tissue by about 5 percent. Sap-feeding mines are visible as light areas on the bottom of the leaf. The completed tissue-feeding mine buckles the leaf like a small tent and has white spots on the upper surface, hence the name spotted tentiform leafminer.
Excessive mining combined with drought is particularly destructive.
Because mines remain visible after the leafminer has emerged or been killed they must be opened to determine if they are active. Monitoring and management Studies in Massachusetts were conducted to correlate the number of leafminers per trap with the average number of mines per leaf. We recommend using one such trap for every 3 to 5 acres and, if cumulative prebloom captures from silver tip onward reach or exceed 12 adults per trap, applying an insecticide treatment against the adults. The trap should reduce the need to wait until first-generation mines appear before a leafminer spray decision can be accurately made. Endosulfan and Carzol have activity against adults.