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Home BYGL Bug Bytes April 24, 2008 SAWFLY LEAFMINERS FLY
SAWFLY LEAFMINERS FLY PDF Print E-mail
Based on plant phenology as well as GDD, the adults of four leafmining sawflies should be flying, or soon flying, in southern Ohio. Three of the sawflies are in the genus Fenusa. These include: ELM LEAFMINER (F. ulmi); EUROPEAN ALDER LEAFMINER (F. dohrnii); and BIRCH LEAFMINER (F. pusilla). The fourth sawfly is the HAWTHORN LEAFMINER (Profenusa canadensis). Larvae of these sawflies mine the leaf parenchyma producing large, blister‑like, reddish‑brown "blotch" mines. The mines usually extend from the leaf margin toward the midvein. The hawthorn and elm leafminers have one generation per year and the alder and birch leafminers have three generations.

For most insect pests, the occurrence of multiple generations usually means upwardly spiraling populations and ever increasing damage as the season progresses. However, for birch leafminer, the opposite is true. Larvae can only mine new leaves. So, most damage occurs in early spring when the first generation larvae mine the new, expanding leaves. After they finish feeding for the season, around 80% of the first generation larvae drop to the ground and remain as pre‑pupae until next spring. Control efforts should target the first generation since the second and third generations cause little damage, unless the tree is re‑foliating after leaves were stripped by some other problem such as gypsy moth.

Imidacloprid (e.g. Merit) has proven effective in controlling these sawfly leafminers when applied as a soil drench over the root zone in October or November. It is too late for soil applications made this spring to prevent all damage since it takes around 30 days for the insecticide to move into the plant in concentrations sufficient to provide control. However, a soil drench application made now will kill larvae in their developing mines. Foliar applications of pyrethroid insecticides may also provide some control, although all leafmining activity will not be suppressed where adults have already started laying eggs.

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Last Updated ( Thursday, 24 April 2008 17:47 )
 

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