The Not-So-Sunny Sunflower Moth

Biodiversity, Butterflies & Moths, Pollinators

Over the last couple of years, our hort team began seeing black, disfigured masses at the centers of echinacea flowers. Puzzled, they researched the issue and discovered the cause—sunflower moth (Homoeosoma electellum) larvae inside the cone, eating the flowers from the inside out.

“It doesn’t look good, aesthetically,” says Andy Brand, Interim Director of Horticulture, “but more worryingly, other pollinators appear not to favor the disfigured flowers, and the plants won’t set seed.”

With multiple, overlapping generations throughout the growing season, the larvae are difficult to control. Adult sunflower moths lay eggs at the base of flowers found in the Asteraceae family—echinacea, sunflowers, black-eyed Susans, marigolds, cosmos, coreopsis, and asters—and larvae feed on pollen and florets before tunneling into seeds. Some larvae pupate in the flower heads, but most drop to the ground to pupate underground or beneath leaf litter.

“We started noticing the moth’s populations increasing over the past couple years,” Brand continues, “but they might have been here earlier. We’re growing more echinacea, so that means more food for them.”

Sunflower moth damage

On that note, he’s decided not to order more echinacea for next year because, unfortunately, there’s no effective, non-chemical control to stop the larvae from destroying the flowers. The horticulture team has been cutting and disposing the severely affected flowers, but nothing can be done about the caterpillars on the ground. “Echinacea is a super pollinator plant,” he explains, “and we need to accept some unsightly flowers in order to provide valuable resources for our insect friends.”

Gary Fish, Maine State Horticulturist, advises catching the caterpillars early and controlling the hatching larvae with Btk. Btk, or Bacillus thuringiensis kurstaki, is a bacteria naturally found in soil that, once ingested by pests, kills them. Btk will control leaf-eating (and flower-eating) caterpillars, but won’t affect insects that don’t eat the treated plants, so it’s the safest natural option to use to control pests without harming beneficial insects.

If applied early enough, Btk should keep the flowers from becoming deformed. However, it can do nothing to combat those pests in the soil; currently, there’s no known treatment for those at all. “We’re not sure how many generations occur in Maine, but it is critical to catch the first generation,” advises Fish, “so you need to scout the flower buds before they begin to open.” Problematically, no one is quite certain whether or not the sunflower moth is overwintering in Maine. Usually, it comes in on storms from the central plains where it’s a problem for sunflower farmers. Any evidence that it’s overwintering in Maine will be helpful information to have.

In an effort to ascertain more information, next season the Horticulture team will be monitoring the moth using pheromone traps to get a better understanding about the insect’s lifecycle and determine whether or not they really are enjoying our Maine winters.

The adult sunflower moth is buff-to-gray colored, less than a half-inch long, with an almost inch-long wingspan. The larvae, about 0.75 inches long, feature brown heads and alternating dark and light lines running lengthwise. Signs of feeding larvae include dark frass and webbing on flower heads. Too see images of the moth and learn more, visit the UMass Extension website