May 4, 2016 3 min read

An invasive pest new to the United States was discovered for the first time on a farm in Lancaster County and has spread to at least four other counties, including Chester, Dauphin, Delaware and Lehigh.

According to a report from the state Department of Agriculture, the pest, known as allium leafminer Phytomyza gymnostoma, infects crops like onions, leeks, garlic, chives, shallots and green onions. Previous research suggests the pest can be more damaging in organic, noncommercial farms or homeowner gardens.

“For our farmers, an infection of this pest could mean a loss in production of allium crops. And for our consumers, this could result in a lack of availability of these crops for consumption,” said Agriculture Secretary Russell Redding. “As we are warning residents of this new invasive species, the allium leafminer, know that there is no risk to public health.”

Covering early onion, chive and garlic plants, prior to the emergence of adults, and keeping plants covered during spring emergence can minimize crop exposure to the pest. For fall allium crops like leeks, the department recommends delaying planting starts until after mid-May to reduce infestation rates.

Leafminers are likely transported with commercial cargo or in passenger baggage.

Adult leafminers are about three millimeters long and appear to be gray or black flies with a distinctive yellow or orange patch. The eggs appear white, about 0.5 millimeters long and slightly curved. The larvae are white, cream or yellow and up to eight millimeters long.

Adults appear in late winter into spring with females laying eggs on the base of stems. Emerging larvae mine downward, feeding on the bulbs, which results in softening of the plant parts, increasing susceptibility to bacterial and fungal infections. The leaves of infected plants appear wavy, curled and distorted with a row of white dots.

Surveys are ongoing to determine if any other areas of the state have positive detections.

Anyone who thinks they have observed damage or a life stage of the allium leafminer should contact a plant inspector in the regional Department of Agriculture office or Penn State Cooperative Extension. Citizens are urged not to transport any crops suspected of infection, as doing so will greatly increase the risk of spread of the pest.

Adult specimens in counties outside of those listed can also be turned into the department’s entomology lab or to the Penn State County Extension Office for identification. Adult specimen can be placed in alcohol or hand sanitizer in a leak-proof container. A sample submission form can be located on the Department of Agriculture’s website at www.agriculture.pa.gov. The Penn State County Extension office website is www.agsci.psu.edu.

People can take photos and submit them to Badbug@pa.gov. They also can call the Bad Bug Hotline at 866-253-7189 with details of the sighting and contact information.