How To Spot Common Apple Tree Pests Before They Take Over

In the hopes of crunching into homegrown produce or experimenting with heirloom varieties, many homeowners grow apple trees in their backyard. But because pests quickly overwhelm apple trees, more often than not, all their effort and investment reduces to zilch. So, to shield you and your trees from such a terrible fate, we caught up with Emma Grace Crumbley, an entomologist with Mosquito Squad Plus, for an exclusive interview. What follows is her ready solution about spotting common apple tree pests and their management.

Starting with apple maggots, Crumbley says, "Apple fly maggots infest fruit when adult female flies lay their eggs under the apple skin. As larvae grow inside the apple, they eat the fruit and bruise the crops." So, how can you spot their damage? "Look for these warning signs: brown, soft, rotted fruit still on trees; small puncture holes across apple skin; brown, linear trails carved in apple fruit," she suggests. In addition, you may find "maggots in fruit, falling from the tree, and crawling on the ground underneath" as well as "small adult flies with black zigzag markings on translucent wings"— usually between July and September.

Plum curculios behave similarly with the beetles, drilling crescent-shaped holes into developing fruits for egg laying. After hatching, their larvae feed on the fruit down to its core. For them, Crumbley advises watching for signs like "fruit dropping prematurely and puncture holes across apple skin [which] are often surrounded by a brown circle of discoloration." You'll also find grubs actively feeding during spring.

In her exclusive House Digest interview, Crumbley further elaborates on the modus operandi of codling moths. "Codling moth eggs are laid on the surface of fruits, and after larvae hatch, they burrow into the fruit itself. Mature larvae will eat their way back out before dropping to the ground to pupate." To spot their damage, she suggests scanning for "many large holes across the fruit surrounded by brown bruising." Also, "gold or orange frass (insect droppings – small pellets) are sometimes found near the exit holes on the fruit surface," she adds. Rarely, you may find their white larvae inside the fruit. "Small brown moths with wings tucked in at rest, resembling small dead leaves" may also be present.

"Other apple tree pests can include pests that attack the fruit and tree directly, like spotted lanternflies or Japanese beetles, or secondary pests that are attracted to the rotting fruit, like ants and rodents," Crumbley explains. "In any case, the most significant warning sign for an apple tree pest is seeing the pest itself." Assuming you either notice the pest or its ensuing damage, what's the mitigation strategy? "Remove and dispose of infested fruit," advises Crumbley. "Putting up sticky traps to catch flying adults" should help, too. Additionally, "connect with your state's extension agency for guidance on chemical applications and further assistance." However, if despite taking these measures "you still notice damage or find bugs in your apples, it's time to call a professional," she advises.

Seeing as chemical treatments are a necessary evil to prevent further pest damage, what is the best time of year to spray fruit trees? "After the blossoms have finished blooming and dropped their petals but before the fruit has begun to grow," elaborates Crumbley in her exclusive House Digest interview. The reason? "After the flowers fall off, pollinators will no longer visit the tree to interact with blossoms, so the likelihood of accidentally hurting pollinators with insecticide application decreases." But would it work on apple maggots and plum curculios that depend on fruiting before making a show? Acknowledging the difficulty, Crumbley admits, "The timing can be tricky here, but depending on your region, the type of tree, and the severity of the infestation, post-bloom pre-fruit is an ideal time to apply treatment."

Elaborating further, she adds, "Other times to [treat] fruit trees is during the dormant season, usually after the fruit has been harvested and the leaves have defoliated. During this time, the trees are slowing down and conserving energy for the cold season, and pests are also slowing down to diapause or overwinter." However, she adds a qualifier. "Depending on the infestation and treatment level needed, trees may suffer from phytotoxicity if they still have leaves or buds that become exposed to chemical treatments." Rounding it off, "Document the type of pest and time of season it was found and create a prevention plan," directs Crumbley. Also, "keep the area around and under trees neatly kept and well managed to remove pest harborage sites and discourage overwintering near trees."