How to combat gall mites on alder? - briefly
Prune and discard gall‑bearing twigs, then treat the remaining foliage with a horticultural oil or neem oil at the recommended concentration to kill the mites. Support natural predators such as lady beetles and keep the tree well‑watered and fertilized to reduce future infestations.
How to combat gall mites on alder? - in detail
Gall mites (Cecidophyopsis spp.) infest alder (Alnus spp.) by forming small, greenish to reddish galls on leaves, shoots, and young twigs. Infestations reduce photosynthetic capacity, stunt growth, and can predispose trees to secondary pathogens. Effective control requires a combination of cultural, biological, and chemical measures applied at appropriate times.
Cultural practices reduce mite populations by limiting favorable conditions. Remove and destroy all fallen leaves, twigs, and bark that show gall symptoms. Conduct a thorough pruning of heavily infested branches in late winter, before bud break, to eliminate overwintering sites. Maintain adequate spacing between trees to improve air circulation and lower humidity, which discourages mite development. Avoid excessive nitrogen fertilization, as rapid foliage growth creates more tissue for colonization.
Biological agents can suppress mite numbers without harming non‑target organisms. Predatory mites such as Amblyseius swirskii and Neoseiulus barkeri feed on gall mite eggs and nymphs; release them in early spring when mite activity resumes. Entomopathogenic fungi (e.g., Beauveria bassiana) applied as a foliar spray can infect mites, especially under moist conditions. Ensure applications follow label instructions for concentration and timing.
Chemical interventions are reserved for severe outbreaks. Select acaricides registered for use on hardwoods, such as sulfur dust, neem oil formulations, or synthetic miticides containing abamectin. Apply the first treatment at bud swell (stage 10–20 BBCH scale) when mites emerge from overwintering sites. A second application should follow two weeks later, targeting the peak of egg laying. Observe pre‑harvest intervals and re‑entry periods to protect workers and wildlife. Rotate active ingredients to prevent resistance development.
Monitoring is essential for timely action. Inspect leaves weekly from early spring through midsummer for the characteristic dome‑shaped galls and for the presence of mites on the undersides of foliage. Use a hand lens (10× magnification) to confirm infestations. Record the percentage of affected leaves; if more than 5 % of the canopy shows symptoms, initiate control measures.
Integrated management combines the above tactics: sanitation and pruning reduce initial inoculum, predators keep mite numbers low, and targeted acaricide applications eliminate outbreaks that exceed economic thresholds. Consistent implementation over several seasons typically restores tree vigor and prevents recurrence.