By Blake Jackson
The Allium leafminer (ALM) is an invasive insect that targets plants in the Allium family, such as onions, leeks, chives, and garlic. Adult flies puncture leaves to lay eggs, and as the larvae develop, they consume leaf tissue and burrow into bulbs. This feeding can stunt plant growth and render both leaves and bulbs unappetizing.
ALM was first identified in Pennsylvania in 2015, specifically in Lancaster County, and has since spread to neighboring states. It is now believed to be widespread across Pennsylvania.
Gardeners and farmers can monitor for ALM by checking onions, including wild varieties, for small puncture marks along the leaves, indicating where the adult flies have deposited eggs.
Garlic growers can take proactive steps to protect their crops. Planting garlic later in the season helps reduce the risk of fall infestation.
Penn State Extension Horticultural Educator Tim Elkner recommends planting garlic as late as possible in the fall, so the plants develop only a few inches before winter.
In southeastern Pennsylvania, this means planting around November 1, while in colder areas, planting can be delayed by about two weeks such as mid-October instead of early October.
Although late fall planting helps avoid the fall flight of ALM, it does not prevent spring infestations. In the spring, a new generation of leafminers will seek host plants to lay eggs. Covering garlic crops with a floating row cover in early spring provides effective protection. By planting late in the fall, gardeners reduce the need for multiple row cover applications.
For the most accurate timing to apply row covers and monitor ALM activity, growers should consult the Penn State Extension website for current updates.
Photo Credit: gettyimages-gimbanjang
Categories: Pennsylvania, General