Source: Ben Sale, available under creative commons license 2.0 creativecommons.org/licenses/by/2.0/legalcode
Description and life cycle
The adult moth is 1/8 inch long and brown with white transverse stripes margined with black. Eggs are 1/10 inch in diameter, oval, and creamy to transparent in color. They are laid on the undersides of the leaves and are more difficult to see on cultivars with hairy foliage. Full-grown larvae are yellowish and 1/8 inch long at maturity.
This leafminer overwinters as pupae in apple leaves on the orchard floor. Adults begin to emerge at the ½-inch green stage and continue activity through bloom. Females lay approximately 25 eggs singly on leaves. As they hatch in 6 to 10 days, young larvae chew a hole through the egg and into the leaf. They go through two developmental stages: sap-feeding and tissuefeeding. The sap-feeding stage is composed of very small larvae that pierce plant cells and feed on sap. The tissue-feeding stage has well-developed mouthparts and feeds on leaf tissue. A complete generation requires 35 to 55 days; there are three to four generations each year.
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. An effective trap for monitoring leafminer adults is a stickycoated, 8-by-12-inch red trap, slightly (about 135°) tent-shaped to allow for water runoff and hung at chest height in the interior of the apple tree canopy. 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 made accurately.
Control decisions for first generation can be based on sapfeeding mine counts. A procedure developed at Cornell University for determining threshold levels is as follows:
- During petal fall, select three fruit clusters from around the canopy of each tree sampled.
- Using a magnifier, count the sap-feeding mines on the undersides of the second, third, and fourth leaves in each cluster, counting leaves in the order they unfolded.
- After two trees have been sampled, begin comparing the accumulated total number of mines found with the limits for that number of trees.
- If the number of mines falls between the two values given, sample another tree. If the total is less than the lower limit, sampling is stopped and no treatment is required. If the total is greater than the upper limit, sampling is stopped and a treatment is recommended. If seven trees are sampled and the total number of mines is less than or equal to 63, no treatment is necessary.
For second brood, which begins to appear in early to mid-June, proceed as follows:
- Sampling should be done once, about 5 days after peak male moth catch (early July).
- Start at the orchard edge and, moving toward its center, sample every other tree until enough trees have been sampled. Select five mature terminal leaves from each tree, and count the sap-feeding mines on the undersides of those leaves using a magnifier.
- After 15 leaves have been examined, begin comparing the accumulated total number of mines found with the limits given in Table 2-7 for that number of leaves. If the number of mines falls between the two values given, take more leaf samples (five per tree), continuing to add the number of mines found to the running total while checking the chart again. If the total is less than the lower limit, sampling is stopped and no treatment is required. If the total is greater than the upper limit, sampling is stopped and a treatment is required.
Table 2-7. Counts of sap-feeding spotted tentiform leafminer mines to determine infestation status.
|First generation (petal fall)|
No. of trees
|Lower limit||Upper limit|
No. of trees
|Lower limit||Upper limit|
Specific chemical recommendations for home gardeners are in Fruit Production for the Home Gardener, and recommendations for commercial growers are in the Penn State Tree Fruit Production Guide.