The Sneaky Little Moth That Tried to Eat Us Out of House & Home

Paul Westervelt
It was another one of those industry news flashes about some new pest I’d never heard of that was a new problem on a crop we barely grew. I hadn’t seen symptoms and I forgot about it as quickly as I’d read about it. There’s always some new pest somewhere.

The next year, we saw a few mums (that crop we barely grow) wilt suddenly, but it wasn’t root rot … the stem was girdled at the base. It was only a handful of plants in an already small crop, so we took a picture of the larva to be identified and banished the affected plants to Mount Phooey (the dump pile).

An entomologist identified it as European Pepper Moth (EPM), but it was late in the year and everything we read said our normal winter temps should kill them. I don’t think we saw it the next year. Operation “Sneak Up On Us” was underway.

In the fall of 2015, we saw a few older Verbena bonariensis Lollipop brown suddenly in the middle of the crop. Then the stems of a few upright sedums collapsed. Then the heuchera looked a little weird and the monarda intended for sale the following year didn’t bulk up the way I expected. They all had EPM. The more we looked around, the more we found. We stopped selling and started investigating. Here are some of the more useful things we’ve learned:

• Adults kick up pretty easily while walking crops, but only fly a short distance before landing under a leaf or on the shady side of a pot. At night, however, they can travel long distances. A University of Florida bulletin says they can travel upwards of 62 miles (100 km).

• Several articles we read said normal winter temps should kill them, but that hasn’t proven true in our case. There’s a theory that even if normal cold temps should kill them, that the heat generated from the dump pile may allow those living on the edges of the pile to overwinter and repopulate our production areas. We think we have a permanent population now. Because they’re strong nighttime fliers, our on-site dump pile can’t be far enough away. And just last week (Week 9), a larva was found on a penstemon that spent the (not-so-cold) winter in a covered, but unheated, hoop house.

• It’s easy to overlook. Unless you look closely, it looks like a zillion other little brown moths. Water traps with pheromone were recommended to monitor adult populations, but they didn’t work for us. Finding almost nothing, we thought we were managing the population—and maybe we were. Or maybe our overhead irrigation washed them out before we checked traps each day or something else entirely. What I do know is when our resident bug nut, Lindsay Day, switched to delta traps with sticky cards and pheromone, we saw impressive numbers of adults overnight in houses where we had only seen one or two a week in the water traps.

• Monitoring larval populations can be disheartening because they have a very wide host range. The only herbaceous perennials we’ve not found them on are hypericum and perovskia. They’ve been especially problematic on chrysanthemums, Verbena bonariensis, Eupatorium rugosum, heuchera and heucherella. EPM larvae make a telltale webbing where the crown of the plant touches the soil and they like wet places, so checking the wettest plants in a block first (like those in a low spot) can speed up scouting. That said, we still found them on delosperma and upright sedums, which we run pretty dry.

• They’re relatively easy to kill if you can get the chemical to the larva, but that can be tricky, too. The larvae that feed on the crown at night burrow into the soil during the day. A dense canopy of foliage can further reduce the effectiveness of sprays. And on some plants, like upright sedums, we’ve seen EPM bore into stems, making them very difficult to control. We’ve found success with acephate as a drench and we’re experimenting with Mainspring this spring.

I sure wish I threw those first few mums in the trash rather than the dump pile. GT 

Paul Westervelt is Annual & Perennial Production Manager for Saunders Brothers, Inc. in Piney River, Virginia.