Landscape - Leafminer Overwintering

The following is information on leafminer overwintering in the landscape.

Arborvitae, Boxwood and Holly leafminers all over-winter as live larvae within foliage tissue. Pale colored lines or blotches indicate the leafminer presence in evergreen leaves. Inspect mines for live larvae and physically remove infested leaves when populations are small. Heavily infested plants can be noted in your records and scheduled for treatment next season. If soil moisture is adequate, then a soil systemic (e.g. Merit) can be applied during the fall months.

Holly leafminer mines on leaf. Photo by Daniel Herms, The Ohio State University, Bugwood.org

Information from Steven K. Rettke, Ornamental IPM Program Associate in the September 17, 2009 edtion of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition, from Rutgers University http://njaes.rutgers.edu/pubs/plantandpestadvisory/2009/ln091709.pdf

Landscape and Nursery - Boxwood Leafminer

The following is information on boxwood leafminers. Adults should be emerging in the landscape at this time.

BOXWOOD LEAFMINER adults should be emerging from leaves during 192-796 [366 peak] GDD base 50. Adults are small orange-yellow to red and are gnat-like. They commonly attack Buxus microphylla and B. sempervivens but cultivars such as 'Handworthiensis', 'Pyramidalis' and 'Varder Valley' are reported to be resistant. Females mate and die shortly after ovipositing eggs into boxwood leaves. Eggs hatch after three weeks and yellowish larvae feed inside leaves, causing a blister-like blotch to form on leaf undersides. Infested leaves may be slightly discolored. There is only one generation per year and larvae overwinter inside leaves and pupate at 48-585 [204 peak] GDD base 50

There is little information known regarding natural enemies of the boxwood leafminer. A cultural control method is to remove infested leaves prior to pupation. Chemical controls may target either larvae or adults. Time products targeting adults to coincide with emergence (approx. at weigela bloom). Available products include abamectin, bifenthrin or other pyrethroids, carbaryl, imidacloprid, dinotefuran and novaluron. Casey and I conducted a trial evaluating fall soil injections of dinotefuran and imidacloprid to infested boxwoods. Dinotefuran provided about 70% control of boxwood leafminers by two weeks whereas midacloprid took more than three months to obtain about 65% control. Imidacloprid persisted in boxwood longer than dinotefuran treatments but imidacloprid also caused increases in boxwood spider mite populations. Our project did not investigate how a spring application of dinotefuran will affect spider mites.

Boxwood leafminer larvae feeding. Photo by Nancy Gregory, UD Plant Diagnostic Lab.

Information from Brian Kunkel, Extension IPM Specialist, UD.

Landscape and Nursery - Boxwood Leafminer

Watch for boxwood leafminer activity this time of year. The following is a short article on the subject from Rutgers University.

BOXWOOD LEAFMINER: This particular host specific pest is a good example of why it can still be important to monitor plants during the off-season. Although the single generation leafminer larvae have been in boxwoods leaves since May, their presence in new foliage is often not readily apparent until the fall. Most of the activity and feeding damage by the fly larvae are done during the fall and winter. Blister-like blotch mines are now just becoming noticeable on current season infested leaves. While most insect pests are winding down for the year, the boxwood leafminer is just heating up. When symptoms suggest their presence, “break the back” of the leaf and peal away the lower epidermis to detect the still clear and thin larvae (usually several are found in each leaf). As feeding continues through the fall months, the larvae develop into larger, yellow colored maggots. After a mid-winter resting stage the larvae begin feeding again in late winter. With heavy infestations, defoliation can occur in the spring. The various neonicotinoid class root systemics should provide outstanding, long lasting results against this pest. As long as good root uptake of the material is achieved, success is usually assured. Within a week, sufficiently lethal insecticide levels should be translocated up into the boxwood foliage if healthy roots and adequate soil moisture are present.

Blotch on boxwood leaf opened up to reveal the boxwood leafminer larvae. Photo from Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

Reprinted from "Landscape IPM Pest Notes" by Steven K. Rettke, Ornamental IPM Program Associate in the October 7, 2007 Edition of the Plant and Pest Adivsory, Landscape, Nursery and Turf Edition from Rutgers University.