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 whe...