By: Darcy Larum, Landscape Designer
Growing your own fruit can be very rewarding and save you money at the grocery store. If you notice skeletonized foliage on your pear or cherry trees, pear slugs could be the culprit. What are pear slugs? Continue reading to learn about pear slug pests, as well as tips for managing pear slugs.
Pear slugs, also known as cherry slugs, are not actually slugs at all. They are actually the larvae of the pear sawfly (Caliroa cerasi). This larvae has a slimy, olive green, slug-like appearance in their first four instars. In these earlier instars, pear slugs are somewhat tadpole shaped with larger rounded heads and tapered bottoms.
In their fifth instar, shortly before burrowing into the soil to form their cocoon, they take on a more caterpillar appearance with yellow to orange color and ten legs. They overwinter in cocoons below the soil surface and emerge in spring as adult pear sawflies. After mating, sawflies lay eggs, which look like small blisters on the upper sides of foliage. Their larvae, or pear slug pests, then feed on the upper sides of the foliage, avoiding the thick leaf veins.
It is believed that the pear sawfly is native to Europe but was brought to the United States unintentionally on plants during colonial times. While they do not bother peach trees, pear slug pests can infect other shrubs and trees, such as:
They produce two generations each year, with the first generation feeding on foliage in late spring to early summer, and the second, more destructive generation, feeding on foliage in in late summer to early fall.
Usually, pear slug pests are more of a cosmetic problem, leaving unsightly skeletonized leaves. However, in extreme infestations, they can cause major defoliation of trees, reduced fruit size, and reduced blooms in the year following infestation. Pear slug control is more important in an orchard setting where populations can quickly get out of hand than in a backyard with just a few fruit trees.
The first step in how to kill pear slugs is careful monitoring for their presence. Pear slug control methods will only work when these pests are present in their larval stage. Some common pear slug control methods are malathion, carbaryl, permethrin, insecticidal soaps, and neem oil.
If you prefer to avoid chemicals, soaps, and oils in the garden, pear slugs can also be blasted off foliage with a hose end sprayer.
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Read more about Pear Trees
The pear sawfly is a common pest in Iowa, attacking a wide variety of hosts. While it favors pear and cherry, it also attacks crabapple, apple, plum, hawthorn, cotoneaster, and mountain ash. The sawfly larvae damage these plants by feeding on the surface of the leaves, skeletonizing them, and leaving the network of veins.
The pear sawfly is one member of a group of insects sometimes called “slugs” because they superficially resemble true slugs. The bodies of these “slugs” are largest just behind the head and taper toward the tail end. The sawfly adult is a harmless wasp.
Sprinkle ordinary garden lime or magnesium lime around your plants and beds to build protective barriers.
The extremely water-absorbing effect should deter all slugs and snails.
Wind and water, however, quickly make the barrier ineffective.
This is why you should also sprinkle threatened plants or beds with a broad, thick ring of lime. A combination of lime and sawdust is possible.
You should ensure that there are no bridges or gaps, otherwise they will be exploited by hungry snails and slugs.
Since the deterrent effect is lost after contact with water, it needs to be spread again after rainfall.
Make sure that you do not overuse lime so that the pH value of the soil does not rise too much.
Some plants are susceptible to changes in pH levels.
When using lime, always wear gloves, respiratory protection, and goggles.
Only by taking these precautions can damage to health be avoided.
During application, the weather needs to be as calm as possible, so that the lime does not evaporate in all directions.
If you plan to use calcium cyanamide, make sure that it does not get on plant leaves or seeds because it will damage them.
You should also use it at least three or four weeks before sowing or planting, otherwise it will harm your seeds and plants.
Products must be stored in a safe place so that they are out of the reach of children and pets.
Pear sawfly (Caliroa cerasi) larvae are often called “Pear slugs."
The slug-like larvae are up to ¼” long and are found feeding on the upper surface of leaves in mid-July. The adult breeding stage of the insect is 1/5” long and is non-damaging to host plants.
Larvae feed on upper leaf surfaces, causing distinctive 'windowpane' damage. Heavy defoliation gives the tree a scorched appearance, and leaves many drop prematurely. Severe defoliation can adversely affect tree health.
Control by hand picking larvae or by washing them off with a forceful stream of water in mid/late July.
Pest description and crop damage Pear sawfly is a European insect now found in most areas of the U.S. It attacks both pear and cherry, and also is found on mountain ash, hawthorn, and ornamental Prunus spp. The adult is a glossy black about 0.2 inch long. The larva initially resembles a small slug, due to the olive green slime that covers the body and the fact that the head is wider than the rest of the body. Mature larvae are 0.37 inch long and orange-yellow. Larvae feed on the upper surface of leaves, skeletonizing them, the fruit surface may also be scarred when populations are very high. Heavy feeding causes leaf drop with reduction in vigor, yield and return bloom, particularly on young trees.
Biology and life history Pear sawfly overwinters as a pupa in a cocoon 2 to 3 inches deep in the soil. Adults emerge over an extended period in late April to May. The adult female inserts eggs into leaf tissue, and eggs hatch in 10 to 15 days. Larvae immediately begin to feed on the upper surface of the leaf. After 3 to 4 weeks, they drop to the soil to pupate. Second generation adults emerge in July, and larvae from this generation feed in August and September. Most larvae from this generation drop to the ground to overwinter.
Pest monitoring Watch trees for the slug-like larvae especially in August and September when large populations can build up.
Home orchardists: Individual larvae can be picked off, or they can be washed off with a strong stream of water.
Management-chemical control: HOME USE
Management-chemical control: COMMERCIAL USE
Usually controlled by regular spray programs but high populations can occur, particularly in organic pear orchards. Application of spinosad (some formulations are OMRI-listed for organic use) has been found to provide control.