Worms on Apple Trees: 10 Possible Suspects & Control Methods

Though your proud and beautiful apple tree may seem to be flourishing from your window, upon closer examination, the fruit appears quite small and in certain instances, distorted.

The culprit? Apple-hungry worms.

These critters and their offspring relish munching on apple tree foliage and living in the fruit, leading to things like premature fruit drop and a sad-looking harvest.

Don’t despair though — we’ll share our expert tips for dealing with 10 of the most common nuisances on your apple tree plus how to identify them and the unique damage each causes.

If you want to ensure your apple tree thrives, learning to spot common issues is important. Don’t miss my comprehensive guide, Apple Tree Diseases and Pests, to learn more today!

1. Codling Moth (Cydia pomonella)

A codling moth in larval form inside a fresh apple.

Adult codling moths are ½ to ¾ an inch long and brownish-black with mottled gray wings. The tip of each forewing has a coppery/bronze tinge.

The codling moth larvae are caterpillar-like with small white bodies and brown heads.

Damage Caused

  • Scarring on the apples.
  • Tunnels bored into fruit, often filled with golden-brown frass (a sawdust-like substance that’s actually larvae feces!).
  • Early fruit drop and dying fruit.

Prevention & Control Solutions

It’s difficult to detect the damage once the larvae have burrowed into the early-developing fruit from the base, so early detection and trapping are key to preventing females from laying eggs on the leaves and fruit undersides.

Entomologist Jeffrey Hahn at the University of Minnesota recommends the use of “delta” or “wing” moth traps.

These sticky wax-paper traps can be hung in trees around early May to bait male moths by giving off artificial female pheromones.

Another tip is to swiftly remove any infested fruit and clear the area of any fallen apples. Do this with healthy fallen apples after harvest too to prevent overwintering eggs.

2. Apple Maggot (Rhagoletis pomonella)

Several apple maggots feeding on a rotten apple.

Adult apple maggot flies are a little smaller than a housefly with a zigzag pattern of black stripes/bands on their wings and a pointed abdomen.

Maggot larvae are translucent and cream-yellow measuring approximately 7 millimeters long with two distinct black mouth hooks at the head.

Damage Caused

  • Dimpling, sunken areas on the apple skin.
  • Fruit becomes discolored and darkened, and bruise-like marks appear where maggots have sucked the nutrients.
  • Burrowed holes in the fruit.

Prevention & Control Solutions

Sticky traps like these are best for dealing with adult apple maggots, or you can create your own with a few home ingredients. Hang 2-6 traps per tree.

A spray of all-purpose insecticide around early spring is wise for general prevention, but as these maggot flies typically lay their eggs in growing fruit around June or July, a targeted spray of spinosad in June can be ideal as this is an especially potent toxin to fruit flies.

3. Oriental Fruit Moth (Grapholita molesta)

Adult moths are stone gray with dark gray mottled markings and ¼ inch wingspan. Oriental fruit moth larvae are ½ inch long with pinkish-white bodies with black heads.

Damage Caused

  • New twig growth begins to die back since first-generation larvae enter at the tip of a shoot and bore into the center, resulting in a wilted appearance.
  • Occasionally, these bugs feed on the side of the fruit instead of burrowing holes, so you may spot “gumming” marks and brown frass on the outer skin.

Prevention & Control Solutions

Research professor at Penn State Greg Krawczyk, Ph.D., suggests placing sex pheromone traps in your tree around early April and monitoring the traps throughout the season to assess the population and timing of the moths to determine when to start using a preventative insecticide.

4. Flatheaded Appletree Borer (Chrysobothris femorata)

Appletree borers have brown and white speckled bodies and resemble small beetles with their wide, flat heads. The borer larvae are pale yellow and worm-like with a large, swollen thorax.

Damage Caused

  • Leaves wilt, turn brown, and die off.
  • Adults take advantage of damaged bark and deposit their eggs in the exposed wood, later resulting in depressed/sunken areas of bark.
  • Bark appears wet and shiny in damaged areas, it may also ooze white liquid in injured spots.
  • Frass is packed tightly into bark cracks.
  • Left to fester, these pests can consume the inner cambium layer and sapwood ring beneath.

Prevention & Control Solutions

Infestations can be managed with an application of foliar insecticide shortly after blooming as this is when adult borers first emerge. Repeat the application in 3 weeks.

Larvae may also be controlled by applying a root drench with a systemic insecticide containing imidacloprid.

The best way to prevent these borer infestations is to reduce tree stress wherever possible.

Take care to prune cleanly without wounding the bark, reduce sun scald and drought stress, and maintain good fertilization and watering practices for your apple tree.

5. Leafrollers (Various Species)

A small, green leafroller in larval form on a leaf.

The most common leafroller species on apple trees are the fruit-tree and pandemis leafrollers — these are inch-long yellow-greenish caterpillars with black heads.

Damage Caused

  • Leafrollers begin sucking leaf sap before feeding entirely on the foliage. As they feed on leaves, the foliage begins to curl or roll up (hence their name), and you may spot a silken thread-like trail on the leaves.
  • They also feed on emerging flower buds, blossoms, and eventually the fruit, causing shallow holes and bronze-colored scars on the apple fruit.

Prevention & Control Solutions

Leafrollers are drawn to weeds, so keeping the base around your apple tree free clean and tidy is a great first defense.

For severe infestations and once the leaves have already begun to roll up, a precise application of Monterey B.t (Bacillus thuringiensis) is a highly effective and organic method of killing leafrollers.

Additionally, you could lure lacewings to your garden (natural predators of leafrollers) by methods such as growing a diverse range of flowering plants.

6. Eastern Tent Caterpillar (Malacosoma americanum)

Eastern tent caterpillars grouped together in webbed tent.

Eastern tent caterpillars are hairy with blue or black bodies and a distinct orange or white stripe running down the back. Infestations are easy to spot as they create noticeable webs or “tents” in the forks of branches.

Damage Caused

  • The gray cotton candy-like webbing only affects the branches to which it is attached, and healthy apple trees can tolerate them, but larger “tents” obviously indicate larger numbers and potential damage.
  • Large caterpillar colonies can defoliate trees entirely, making trees vulnerable to disease and further pest infestations.

Prevention & Control Solutions

Wait for the caterpillars to return to their self-made tents when it rains or in the early/late hours of the day, and remove whole areas of webbing by hand — winding the webbing around a stick can be a good removal method.

Control small nests by spraying Monterey B.t. directly onto the tents and affected foliage.

7. Inchworms (Geometer spp.)

A single green inchworm on a tree leaf.

These inch-long skinny worms are smooth and hairless and are commonly light green but may be white or black with spot and stripe patterns running along their backs.

You can sometimes spot inchworms dangling from threads on twigs and leaves, twirling in the wind.

Damage Caused

  • Due to fierce appetites despite their size, they can leave large areas of defoliation.
  • Damage to leaf buds and flowers occurs, preventing or deforming fruit development.

Prevention & Control Solutions

Introducing beneficial natural inchworm predators to the garden such as ladybugs, lacewings, and songbirds can help to control numbers.

As for preventing infestations, you can remove them by hand as you find them and drop them in a bucket of soapy water.

Also, try to limit weeds beneath and around your apple tree as this will limit the food sources and breeding hideouts available to overwintering larvae.

8. Sawfly Larvae (Various Species)

A sawfly larva affixed to the bottom of a leaf rib.

The apple sawfly larvae are 4-5 millimeters long and caterpillar-like with a brownish-black head and thorax and a brown abdomen.

Winged adults have brown and white bodies but can also be green and orange or striped yellow and black.

Damage Caused

  • Fruit drop in early summer.
  • Tunneled holes in fruit that spill out with blackish-brown pellets (feces).
  • Wide elongated strips of bronze ribbon-like scarring winding around the apple skin.

Prevention & Control Solutions

Newly hatched larvae may be controlled with an application of the insecticide pyrethroid about a week after petal fall.

Also, pick off damaged apple fruit the minute you spot them, and clear fallen apples and other debris from the base around your tree to prevent larvae from pupating in the soil or nearby healthy fruit.

TIP: Plant cooking apple varieties like ‘Golden Delicious’ or ‘Pink Lady’ as these varieties are rarely affected by the sawfly.

9. Green Fruitworms (Various Species)

A green fruitworm, Amphipyra pyramidoides, on a leaf.

Similar in appearance to leafrollers but with thicker bodies, these small grub-like worms are over an inch long and sport cream to yellow bodies when young before maturing to bright green.

Damage Caused

  • Green fruitworms feed on the emerging flower buds, causing flower drop and early abortion of developing fruit.
  • Apples that do grow to maturity appear distorted with cork-like scarring.
  • Leaves may also appear chewed.

Prevention & Control Solutions

Besides compromising harvest quality, fruitworms are thankfully of little threat to the overall health of your tree, unlike the previously mentioned burrowing pests.

These can be removed by hand upon sighting or gently shaken off the leaves.

Large infestations can be managed with an application of Monterey B.t., first at the budding stage and again after petal fall. Small fruitworm numbers can be controlled by hanging sticky moth traps inside the tree’s canopy.

10. Weevil Larvae (Various Species)

An apple blossom weevil larva inside damaged flower.

Apple blossom weevils are roughly 8 millimeters long in larvae form with white to yellowish bodies and dark-brown heads.

You can identify adult weevils by their beetle-like form, black-brownish bodies, and long snouts.

Damage Caused

  • The larvae feed on flower buds, nipping at the base of the petals, causing the blossoms to cap (wither, turn brown, and cinch in on themselves).
  • As adults, these larvae feed on the underside of apple tree leaves.
  • Deformed fruit.

Prevention & Control Solutions

When infestations are light, weevil larvae can actually have a beneficial thinning effect for over-bearing fruit yields!

However, large numbers can devastate flower and fruit development.

If this is the case (significant areas of malformed fruit in one season), spray a broad-spectrum insecticide at bud burst the following season before widespread egg-laying can occur.

As for long-term prevention, clear debris and leaf litter at the base to stop the larvae from overwintering, and practice good care and nutrition practices in terms of good quality soil and appropriate fertilizer.

Conclusion

There are quite a few pests that can potentially ruin your glorious apple trees, but by recognizing each of the above nuisances, you can identify them before they can hatch the next generation of sap-sucking, fruit-boring nasties!

For infestations that get out of hand, there are thankfully many effective organic control methods such as introducing predatory insects, applying organic insecticide, and, of course, taking good general care of your apple tree.

Being able to spot problems on your apple tree before they turn into major issues is imperative. Keep learning about common apple tree problems by reading these articles next: