Western tentiform leafminer (Phyllonorycter elmaella)
Pest description and crop damage Adult moths are about 0.12 inch long. The wings are held rooflike over the body and are golden bronze with white bands. The larvae vary in appearance depending on their age, as they progress through five instars. Young larvae are legless and cream-colored. Older instars have legs and are cylindrical in shape, cream-colored and about 0.125 inch long. Mature larvae are yellow and about 0.167 inch long. The larvae feed within the leaf tissue creating dead discolored areas on leaves. If feeding is extensive, fruit quality and yield may be affected.
Biology and life history This insect overwinters as pupae in leaf litter. The adults emerge early in the season and lay eggs on the undersides of leaves around the pink stage of flower bud development. Eggs are flat and translucent. The first three larval instars feed on spongy soft tissue inside the leaves, creating blotches visible only on the undersurface of the leaves. By early- to mid-May larvae begin to feed on the upper surface of the leaf beneath the epidermis, spinning silken webs to tie the mine together, giving it the characteristic "tentiform" appearance. Larvae of the first generation then pupate in the leaf. There are three to four overlapping generations per year.
Sampling and thresholds An average of three eggs per leaf is the proposed action threshold.
A small parasitic wasp, Pnigalio flavipes, provides sufficient control that insecticides may not be required. Leafminer problems may be induced by loss of biological control due to broad spectrum insecticides.
Management-chemical control: HOME USE
Stages 3-4: Prepink & tight cluster sprays
If required, sprays should be timed after the eggs of a generation have hatched, but before tissue-feeding larvae are observed.
- azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
- carbaryl -Highly toxic to bees.
- gamma-cyhalothrin-Highly toxic to bees.
- imidacloprid-Soil drenches may have residual activity in woody plants lasting for 12 or more months. If short-term management is the goal, consider other approaches. Highly toxic to bees.
- kaolin-Applied as a spray to leaves, stems, and fruit, it acts as a repellant to target pests. Some formulations are OMRI-listed for organic use.
- lambda-cyhalothrin-Highly toxic to bees.
- permethrin-Highly toxic to bees.
- pyrethrins (often as a mix with other ingredients) -Highly toxic to bees. Some formulations are OMRI-listed for organic use.
- spinosad-Highly toxic to bees. Some formulations are OMRI-listed for organic use.
- zeta-cypermethrin-Highly toxic to bees.
Management-chemical control: COMMERCIAL USE
Stages 3-4: Prepink & tight cluster sprays
Treatment at this timing may create mite problems. It is best to wait until the second generation appears before making a decision to spray.
- abamectin (Abamex) at 10 to 20 fl oz/a in up to 100 gal water per application. For best effect apply against egg and early sap feeder stages of first and second generation. Do not apply during bloom. Do not apply more than two applications per growing season. Best used early in the season (before June 15); control after that may be unsatisfactory. Do not use within 14 days before or after Captan. Use with an adjuvant. May cause russeting on light-skinned varieties (e.g., 'Golden Delicious'). REI 12 hr. [Group 6]
- acetamiprid (Assail 70WP) at 1.1 oz/a in up to 100 gal water per application. Do not make more than 4 applications per year or exceed 13.5 oz/a per growing season. REI 12 hr. [Group 4A]
- pyriproxyfen (Esteem 35WP) at 3 to 5 oz/a in up to 100 gal water per application. Provides suppression when applied as part of a season-long program. Do not exceed two applications per growing season. REI 12 hr.. [Group 7C]
- spinetoram (Delegate WG) at 4.5 to 7 oz/a in up to 100 gal water per application. Do not exceed four applications per growing season. REI 4 hr. [Group 5]
- spinosad (Success) at 4 to 10 fl oz/a in up to 100 gal water per application. Do not apply more than 3 applications or 29 fl oz/a per season. May act slowly. REI 4 hr. [Group 5]
- spinosad (Entrust 80WP) at 2 to 3 oz /a in up to 100 gal water per application. Do not exceed 9 oz /a per season. REI 4 hr. [Group 5] larvicidal] OMRI-listed for organic use.