Dave Shetlar and Joe Boggs reported that "blotch" mines produced by the HAWTHORN LEAFMINER (Profenusa canadensis) are now very evident in central and southwest Ohio, respectively. Joe Boggs also noted that HAWTHORN POD GALLS produced under the direction of a midge fly (Trishormomyia crataegifolia) are now almost fully expanded and turning from green to red in his part of the state.
Larvae of the leafmining sawflies live between the upper and lower leaf surfaces where they consume leaf parenchyma producing large, reddish-brown, blister-like blotch mines. The mines usually extend from the leaf margin toward the midvein and may be mistaken for freeze/frost damage. The sawfly has one generation per year and larvae appear to be relatively far along in their development meaning that most of the damage for this season has already occurred. Imidacloprid (e.g. Merit, Xytect, etc.) has proven effective in controlling this sawfly leafminer when applied as a soil drench in October or November.
Hawthorn pod galls arise from veins on the underside of the leaves of their namesake host. The elongated galls typically measure around 1/2-3/4" in length. Mature galls become crimson red and this coloration coupled with the gall's sometimes irregular surfaces gives rise to the alternate common name of HAWTHORN COCKSCOMB GALLS. Opening the hollow galls will reveal the tiny white, semi-transparent midge fly maggots that are responsible for directing plant gall formation. The galls do not disrupt vascular flow in the leaf veins, so infested leaves remain functional. Although the galls cause little harm to the health of the tree, heavily galled leaves become deformed and detract of the aesthetic value of infested trees.