MSU researchers advise on protecting fruit from moths during spring

As trees bloom across Montana, many backyard apple and pear growers wonder when they should spray their trees to avoid having worms in their fruit when harvest comes. Montana State University specialists with MSU Extension and the College of Agriculture work to answer that question annually, based on temperature and pest emergence.

The worm most frequently found in fruit like apples or pears is the larvae of the codling moth, a common pest across the state. Because moths are cold-blooded, their life cycle from egg to adult is influenced by environmental temperatures. To accurately gauge when producers should implement control methods, researchers use models or traps baited with pheromones to determine where the moths are in their life cycle and extrapolate when they may become a threat to fruit.

“When trees start to bloom, folks get excited about protecting their fruit,” says Katrina Mendrey, orchard program manager at MSU’s Western Agricultural Research Center in Corvallis. “But spraying insecticides during bloom not only doesn’t control the target pest, it harms bees and, hence, reduces fruit pollination.” 

Mendrey advises that growers be patient and wait for temperatures to rise until moths reach the appropriate life stage for various controls to work. Those controls include wrapping and bagging fruit as well as conventional pesticide spraying.

Scientists at the WARC and MSU Extension monitor temperatures and moth emergence in several areas across the state, including the Flathead, Gallatin, Clark Fork, Missoula and Bitterroot valleys. As more data become available, they will post information about when to apply chemical controls, as well as various ways to reduce the number of worms in your apples, online at agresearch.montana.edu/warc.

Additionally, WARC hopes to work with local garden centers and nurseries selling chemical products to advise growers on accurate timing and use of controls while also protecting important pollinators. 

“As with any pest, growers must use several different tools for preventing damage. Spraying alone is never the answer,” says Mendrey. She said bagging whole trees or individual fruit may be an important option for backyard growers hoping to grow a few pristine apples for fresh eating. The WARC has conducted trials for two years exploring the potential for bagging fruit and will be building on this research in the coming months using whole tree bagging methods.

To find out more about Montana orchards, growing apples in Montana and codling moth control, visit www.mtapples.org/grow.