Avoid excessive vigor, which can be caused by excessive nitrogen fertilizer. For more information, see the fact sheet on Fire Blight. Insect Problems Aphids, Aphis pomi, Rhopalosiphum fitchii, Amphorophora crataegi . Several species of aphids frequently infest hawthorn. The rosy apple aphid, Dysaphis plantaginea , sometimes curls the leaves.
All species secrete honeydew which supports sooty mold fungus.
Sprays of ultrafine horticultural oil, insecticidal soap or malathion, which are among the compounds registered for use against this pest in Connecticut, will control these aphids. Several applications may be required to provide adequate protection. Imidacloprid, applied as a soil drench, will provide season-long systemic control. Consult the labels for dosage rates and safety precautions. Cankerworms , Alsophila pometaria and Paleacrita vernata Cankerworms feed on hawthorn foliage during the spring.