Specialists from the State Forest Service and the Latvian State Forest Research Institute “Silava” are warning of an outbreak of leaf-eating pests – winter moths – in birch stands. Currently, birches with sparse foliage or even completely devoid of leaves can be observed in several locations across Latgale.

Surveys of damaged birch stands in the Līvāni, Jēkabpils, Preiļi, and Rēzekne municipalities have confirmed the presence of several species of winter moths. The dominant pest is the northern winter moth (Operophtera fagata). This pest has been observed alongside several other species, including the winter moth (Operophtera brumata), the mottled umber (Erannis defoliaria), and the autumnal moth (Epirrita autumnata).

Many tree species can serve as host plants for winter moths, including fruit trees and even bilberries and cranberries. All of these pests share a similar developmental cycle. At present, the voracious larvae are nearly fully grown and will soon head to the forest floor to pupate. Only in late autumn – September, October, and even November – will the moths emerge to lay eggs in the bark crevices of birch (and other) trees. Female winter moths, though they are moths, are wingless and move by crawling. The males have fully developed wings and search for females by flying. Newly hatched larvae typically spread to new stands; by releasing a fine thread that acts as a sail, they are carried by the wind for kilometres.

Previously healthy birches, even after complete defoliation, will regenerate their canopy as early as the summer – in June or July. Deciduous trees usually compensate well for even complete loss of foliage; however, in cases of repeated defoliation, individual trees may die. Generally, economic losses are limited to a reduction in timber increment.

If these pests are observed in orchards, the damage can be significant. In such cases, it is necessary to place sticky bands on fruit tree trunks in autumn – in September or October – at a height of about 50 cm above the ground. Since the females are flightless, they will be trapped in these sticky bands while trying to reach the tree canopies, preventing the development of the next generation the following spring. If these pests are observed in orchards in large numbers, it is possible to use bacterial plant protection products (preparations containing Bacillus thuringiensis) or even chemical insecticides, although it should be noted that such plant protection products are not environmentally friendly.