Master Gardeners: the fall army-worm and your garden

September 15, 2021

This is Steve Rulison bringing you information on Shore friendly living and gardening from the Eastern Shore Master Gardeners and Virginia Cooperative Extension.  From my perch near the mouth of Occohannock Creek, I recorded 7-10ths of an inch of rain last week.

Today we will be sharing some information on the fall army-worm provided by Dr. Mike Goatley Jr., Dr. Tom Kuhar, and Dr. Alejandro Del Pozo, Extension Specialists from Virginia Tech. 

There are several caterpillars that attack lawns and ornamentals in Virginia over the primary growing season, and there is a distinction between the fall army-worm and the “common” army-worm. The common army-worm is found pretty much anywhere east of the Rocky Mountains and its cold tolerance allows this insect to persist essentially year-round in Virginia. Fall army-worm is a tropical moth native to warm climate areas of the western hemisphere. It cannot successfully overwinter in Virginia. However, fall army-worm moths are strong fliers, and populations can show up throughout the eastern United States in the late summer and fall months, sometimes in very high populations like we saw most recently in 2018 and again in 2021 in Virginia. Female fall army-worm moths can lay up to 10 egg masses (each with 100 – 200 eggs). So, huge densities of army-worms can build up from just a few egg laying moths in a field. This can completely destroy lawns. 

As its name implies, the fall army-worm is pretty predictable in terms of the timing of its appearance. Although the levels of pressure from this pest varies from year to year, it is anticipated that fall army-worm pressure peaks from mid-August to mid-September. Damage can be quick and severe when worms are present in large numbers, so having a control plan is often warranted. If damage is minimal, it is likely that you will have full recovery of the turf grass and in most cases applications of insecticides are not warranted. 

Insecticides recommended for control include most pyrethroids. Please note that control of large larvae is sometimes difficult with any insecticide. 

The fall army-worm is a fairly easy pest to control. Its appearance is quite predictable and very often does not require insecticide applications on your turf grasses. However, when present in large numbers and actively feeding, the damage to the turf grass can be severe, so be prepared to identify and treat this pest when needed.

For answers to Gardening questions and more, call your local Accomack or Northampton County Extension Office. Here on the Shore call either 678-7946 or 787-1361.

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