September thorn

Systematic position. The September thorn (lat. Ennomos autumnaria) belongs to the order Lepidoptera, family Geometridae. It is a moth species recognized in agricultural and forestry contexts for its potential to cause defoliation in various deciduous woody plants across its temperate range.

Host plants and damage. This pest is a generalist feeder. It attacks a wide range of deciduous trees, including birch, lime, alder, and willow, as well as significant fruit crops like apple, pear, and cherry. The larvae feed on the foliage; early instars create small holes, while older larvae consume entire leaf surfaces, leaving only the midribs, which stresses the host tree significantly.

Biology and life cycle. The species completes one generation per year. It overwinters in the egg stage, with eggs attached to the bark of host branches. Larvae hatch in the spring, coinciding with leaf bud break. They feed throughout the spring and early summer before pupating in leaf folds or bark crevices. Adult moths typically emerge in late summer and autumn for mating and oviposition.

Impact on crops. Economic damage is most severe during outbreak years. Widespread defoliation significantly reduces the tree's photosynthetic capacity, leading to reduced growth, lower fruit yields, and compromised tree health. Repeated attacks over consecutive seasons can leave trees highly susceptible to drought and secondary pathogens.

Control measures. Integrated Pest Management (IPM) is essential for controlling this pest. Recommended practices include:

• Monitoring of larval emergence to determine the necessity of insecticide application.
• Application of selective biological insecticides such as Bacillus thuringiensis.
• Use of trap bands on tree trunks to monitor or capture migrating larvae.
• Encouraging natural predators, including insectivorous birds and parasitic wasps, within the orchard ecosystem.