The first killing frost may have brought an end to the growing season for some growers, but to many high tunnel and greenhouse vegetable growers the season is far from over. On some farms, high tunnel tomatoes are just starting to produce and in some area greenhouses the growers are continuing to lean and lower their indeterminate tomato plants in an effort to keep them producing through Thanksgiving.
While many growers believe that the first killing frost reduces the threat of insect pests in protected culture this assertion is not necessarily rooted in fact. In all actuality, high tunnels and greenhouses provide a rather attractive environment for pests as our days draw shorter and our nights get cooler.
In Central PA we have been receiving phone calls and requests for farm visits by vegetable growers who are noticing that the foliage and fruits of their tomato plants grown in protected culture are being fed upon by an often unseen enemy. Growers observing this damage are often reluctant to apply pesticides indiscriminately for fear of impacting the populations of beneficial insects and mites that they had introduced, managed and protected through the growing season.
On a recent trek out to an area tomato grower I observed the damage to the fruit and foliage of his greenhouse tomatoes. While the pest was not readily visible on the majority of the plants the size and consistency of the frass (excrement) that was deposited on the leaf was characteristic of a Lepidopteran pest like an armyworm. Armyworms by their very nature tend to hide during the day and feed at night. In the field they often conceal themselves between clods of soil or under the plastic mulch that surrounds the plant. Scouting in the early morning and evening is often necessary to detect and identify this pest in field and protected culture settings.
As I made my way through the greenhouse tomato planting I paid very close attention to damaged fruits that were partially obscured by the tomato foliage. Finally, the ”Eureka” moment took place and I detected a fruit where the lepidopteran culprit could be clearly seen. The pest in question was a yellow striped armyworm. Yellow striped armyworm are a common agronomic pest in our region with 3-4 generations observed in our state annually. The fourth generation typically is observed in the August to November period and is known to feed on the fruit and foliage of tomato plants.
Photo: Thomas Ford, Penn State
Yellow Striped Armyworm Management
Yellow striped armyworm can overwinter in the soil as pupae. In tomato greenhouses and high tunnels there is a possibility that overwintering pupae could mature and emerge from soil in the greenhouse as adults in the early spring resulting in significant plant injury to newly set spring tomato plants. Biocontrol of yellow striped armyworm can be accomplished through the release of generalist predators like the minute pirate bug and the bigeyed bug. If you are not utilizing biological control and are using conventional insecticides to manage yellow striped armyworm consider using registered formulations of insecticides containing: bifenthrin (Bifenture 2EC or Sniper), spinetoram (Radiant SC), spinosad (Entrust SC), and zeta-cypermthrin (Mustang Maxx). All of the listed controls for yellow striped armyworm are labeled for field use which means that they can be applied legally when the sides of the high tunnel are rolled up.
In addition, there are a very limited number of insecticides labeled for use in the greenhouse on food crops like tomatoes. As per the 2016 Mid-Atlantic Vegetable Guide, Pylon is the only registered insecticide listed for caterpillar pests other than Bacillus thuringiensis var aizawai ( Xentari and Agree) which is primarily effective on early instar caterpillars. The insecticide chlorfenapyr (Pylon) is labeled for use in greenhouses on tomato plants for managing caterpillars when the harvested fruits will exceed one inch in diameter (cannot be applied to cherry tomatoes).