Allium Leaf Miner (ALM)
Many weather stations in southern and central counties have exceeded 250 growing degree days (GDD) base 39˚F within the past week. 39˚F is close to the lower developmental temperature (38.3˚ F) which our colleagues at Penn State recommend for predicting the first emergence of ALM adults. Last year, initial feeding/egg laying scars were detected within a few days of local weather stations recording the 250 GDD threshold. Limited inspections (Hunterdon, Morris counties) have not revealed scars yet, but feeding and egg laying is sure to come with the next series of warmer days. Growers in southern counties may reasonably assume there is ALM activity in their area currently.
Photo: Sabrina Tirpak. Allium leafminer oviposition scars on onion
Growers should consider initiating the control method of their choice at this time. Affected crops include chives, scallions, garlic, onions and leeks. Look for neat rows of white spots descending from the upper tips of allium leaves (see photo at left). Initial injury often occurs on the tallest leaves. Under warmer, less breezy conditions, adults may be seen near the tips of leaves (see photo of adult at lower right).
Floating row covers, kept on until this flight ends will help minimize access to plants. Insecticide applications targeting adults may be helpful as well, although frequency of applications is uncertain. Spinosyn materials (Radiant, Entrust (OMRI approved)), pyrethroids (Mustang Maxx, 
Warrior), neonicotinoids (Scorpion, Venom), the diamide Exirel (section 2ee recommendation) and the insect growth regulator Trigard are labeled for miner control.
Adult activity and observations of feeding will be reported on in the IPM Update as they occur. At this time, all growers should prepare to respond to the first adult generation. We will deploy yellow sticky cards and attempt to identify the end of the first flight so that growers know when the risk of infestation has abated.
