Pests Affecting a Sargent Crabapple

Sap-Sucking Insects

• Aphids, scale insects and mites suck vital juices from the leaves and tender new growth of Sargent crabapples. Feeding can cause stippling, distorted or stunted growth and, in severe infestations, some leaf death. Organic methods can controll all three types of insects. You can prune heavily infested areas to reduce the population. Since Sargent crabapples are small trees, you can try blasting the foliage with water from the garden hose to knock down aphids and mites. Once knocked to the ground, they cannot return to the crabapple. Repeat hosings every three or four days can significantly lessen the infestation. In severe cases, spraying the foliage thoroughly with ready-to-use horticultural oil kills the insects on the crabapple. Horticultural oil is less toxic than other products, but has no residual effect, so you may need to repeat the treatment every seven to 10 days until the insects are gone.

Ants

• Ants climbing in and out of a Sargent crabapple are a good indication that sap-sucking insects are infesting the plant. Sap-sucking insects excrete honeydew, a sweet, sticky substance that ants particularly enjoy eating. Ants will not hurt the plant, but they guard the sap-sucking insects, preventing natural predators from controlling the infestation. You can apply a sticky tape around the main stems of the crabapple, a few inches above the ground, to keep ants out of the plant. Commercially available ant baits placed near ant trails can also help control the ant population. The ants take the bait back to their nests to feed to other ants, killing them. With the ants gone, natural predators may control the infestation without human assistance.

Webworms and Bagworms

• These caterpillars spin cocoons or nests among the twigs and branches of Sargent crabapple plants. Often, you can see the caterpillars squirming around inside their silken homes. The "bags" and webs may have bits of plant debris inside.
  The fall webworm (Hyphantria cunea) spins its webs on the tips of the crabapple's branches. While not a lethal threat, fall webworm webs -- which can be as much as 3 feet across -- are unsightly. Eastern tent caterpillars (Malacosoma americanum) build their nests in the forks of the branches. These caterpillars leave their nest to feed on the crabapple's foliage.

  You can cut off and destroy branches with webs or nests. The caterpillars have many natural predators that may control the infestation once pruning reduces the population.

  Spraying the webs with Bacillus thuringiensis (Bt), a microbial insecticide, is an effective treatment when the larvae are young and small. In many states, you can use Bt even if fruit is present, as it does not contaminate the crabapples.

Japanese Beetles

• Members of the Coleoptera family, Japanese beetles have bright, metallic bodies and metallic-looking, copper colored wings. Beetles are 3/8-inch long and their soft, c-shaped larvae are 1/16th-inch long. The larvae, called grubs, inhabit the soil around plants and may damage roots with their feeding. Adults emerge from the soil between May and July, depending on the region, and begin feeding on crabapple foliage from the top down. Adult females lay eggs at different times, depositing them beneath the soil, then returning to feed on the tree before laying another set of eggs.

  Few natural predators eat Japanese beetles. If only a few beetles are on the tree, you can collect them by hand and drop them into a container of soapy water to kill them. Neem oil may be sprayed on the crabapple to kill the beetles. Ready-to-use Bacillus popillae, or milky spore disease, is available as a dust for applying to the soil around the crabapple. The disease kills the grubs that eat it. Bacillus popillae spreads in the soil and persists for many years, but does not harm beneficial insects.