Watch for early spring pests as temperatures warm

Updated Feb 22, 2024
Critters like weevils can prove to be an early pest in the spring.Critters like weevils can prove to be an early pest in the spring.

As the earth slowly warms and wakes up dormant plants, it also awakens hungry insects. As the days begin to warm up, you'll likely start to notice an increase in the number of pests around your clients' properties. 

Some of the early spring insects to be on the lookout for include:

Honeylocust plant bug

Honeylocust plant bugs (Gleditsia tricanthos) can be found throughout the eastern United States and anywhere honeylocust trees are growing. Its eggs begin to hatch just after honeylocust buds begin to break in early spring. When the eggs hatch in late April, the nymphs feed on the foliage, causing the most damage.

Photo: Utah State University ExtensionPhoto: Utah State University Extension

They crawl into unfolding leaves and inject toxic salvia during their feedings. Leaf stunting, distortion and chlorosis are common. Extreme infestations can result in complete defoliation of the tree, but tree death rarely occurs.

Avoid planting susceptible cultivars like yellow-leafed ‘Sunburst.’ It has been found that green-leafed varieties such as ‘Shademaster’ and ‘Skyline’ are more resistant. For non-chemical treatment, landscapers can opt to use high-pressure water sprays to knock nymphs off the leaves.

Conventional insecticides should be sprayed seven to 10 days after the buds break in spring. This method can be ineffective at times as the insects can migrate to untreated areas.

Iris borers  

Iris borer caterpillars (Macronoctua onusta) are troublesome pests for irises. They overwinter on old iris leaves and plant debris and then hatch as tiny pinkish caterpillars. The caterpillars chew tiny holes and tunnel through the inside of the iris leaves, making their way to the rhizome.

Photo: University of Wisconsin ExtensionPhoto: University of Wisconsin Extension

Infested irises feature tan or water-soaked streaks. By mid summer the caterpillar will have reached the rhizome, leaving the plant open to bacterial soft rot. To stop the infestation, check for chewing damage or streaks. If caught early enough, the insect can be crushed inside the leaf or just remove the infected leaf entirely.

Applying acephate or spinosad when the eggs are just hatching can also prevent iris borers from being a problem. For a non-chemical method there have been some successes using beneficial nematodes to kill the caterpillars, but they need a moist environment to be effective. Siberian irises are also noted to be more tolerant to attacks.

Eastern tent caterpillar

The eastern tent caterpillar (Malacosoma americanum) can be easily spotted with its noticeable nests found in the forks of trees. It prefers to plague cherry, crabapple and apple trees but has been known to infest other ornamental shrubs and shade trees. They overwinter as an egg mass on twigs and begin to hatch when cherry leaves start to bud.

Photo: Katja Schulz/FlickrPhoto: Katja Schulz/Flickr

Their silken tents are considered unsightly and the caterpillars frequently eat all of the leaves on a tree, weakening it, but rarely killing it. Infested trees will generally grow a new crop of leaves.

Eastern tent caterpillars are the prey of many birds and other insects and many more die from unfavorable weather. If nature is too slow, you can prune small twigs that have egg masses on them from December to March before they hatch. Insecticides should be applied in April around and on the nests, preferably in the early morning when the caterpillars are inside the nest.

White pine weevils

White pine weevils (Pissodes strobi) become active early after the first few warm spring days and can kill the terminal leader of eastern white pines, Colorado blue, Norway and Serbian spruces, and occasionally Douglas firs.

Photo: USDA Forest ServicePhoto: USDA Forest Service

The adults will spend the winter in the litter near host trees and then begin to scale its host mid-March through April. Females will mate and deposit one to five eggs in feeding wounds. A single female may lay up to 100 eggs in a terminal over the span of a few weeks.

Once the eggs hatch, the larvae feed inside the terminal under the bark causing the current year’s growth to wilt, droop and eventually die. Other laterals may bend to take over as the terminal and this results in a permanently crooked tree.

Signs of an early infestation are resin droplets on the leader in early spring. Insecticide can be applied from late March to April when the droplets are noticed. Adults can also be captured in Tedders traps, which attract adults with alcohol and turpentine, but this must be done before the adults become active.

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