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Kris Holmstrom – Plant and Pest Advisory
Many weather stations on the NEWA network except for typical colder sites in northern New
Jersey have surpassed 250 growing degree days (GDD) base 39˚F. 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. In recent years, initial feeding/egg laying scars have been
detected within a few days of local weather stations recording the 250 GDD threshold. Growers
who feel they may be impacted by this pest should check the accumulated GDD from local weather
stations. Growers in southern counties may reasonably assume there will be ALM activity in their
area soon, if not already happening. To determine GDD from local weather stations, the NEWA
website https://newa.cornell.edu/ is very helpful. From the NEWA home screen, select the nearest
weather station from drop down menu at the center of the page. Next, scroll down to “Weather
Tools” on the right side of the page, and select “DD Calculator”. Select your start date (1/01/24)
and end date as well as Degree Day Type (39 F) from the menu at the left of the page. The site will
automatically generate the accumulated GDD base 39F to the last day of your requested sample,
and then offer a forecast of accumulated GDD for the next week. If you should select 1˚C (34 F),
then the DD accumulation should be 350.
Growers should consider initiating the control method of their choice at this time, if any allium
crops are in the field. Affected crops include chives, scallions, garlic, onions and leeks. Look for
neat rows of white spots descending from the upper tips of allium leaves. Initial injury often occurs
on the tallest leaves. Under warmer, less breezy conditions, adults may be seen near the tips of
leaves. Perennial chive beds are often the first, and most heavily infested alliums of the spring
season, so this makes chives an ideal crop to confirm ALM adult activity.
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.