Pear slug on plum and pear trees – Wally Richards

Gardeners that have any cherry, pear or plum trees including the non-fruiting prunus types should check their trees for holes in the leaves. If found then it is likely you have a black slug like pest commonly called pear slug. You are likely to find these little black slugs on some of the leaves. They tend to be on the upper surface of the leaf rather than under the leaf. The pear slug larvae of the pear-leaf sawfly (Caliroa cerasi), also called the cherry slug, first appears from November onwards in a warm year. But it is usually the second generation which explodes in February and March

in warm years which does the most damage. The larvae rasp off the epidermis of
the leaves, resulting in the typical skeletonised effect, only the framework of
the leaves being left. In bad infestations where much of the foliage is damaged, often means a poorer crop next season.

The larvae are attacked by an ichneumon fly and predaceous bugs, but by that
time the damage has been done. Larvae which have been parasitised fail to drop
to the soil, where normal pear slugs hibernate over winter, so the numbers are
eventually reduced. But that is no help to a tree attacked right now.
Spiders, birds, preying mantis and other predators seem to dislike the slimy
slugs, and as the larvae are not caterpillars, so the caterpillar killers Bacillus
thuringiensis, or derris dust, are not useful. There is a simple answer and that is to make a mix of Liquid Copper and Raingard and spray the tree. The larvae are similar to slugs and snails who both hate the copper. When they come into contact with copper they dehydrate. If the trees are still bearing fruit then normal washing will remove the copper before  eating. If you are harvesting the fruit within 14 days of spraying then do not use the Raingard as it makes it harder to wash off the copper particles. Copper is not a good thing to eat and is a poison to us, but copper without Raingard washes off easily, there is no problem.

The pear-slug reacts to the Liquid Copper and falls out of the tree when it comes into contact with it. Higher  trees can be treated if necessary by setting the sprayer’s nozzle on jet and
firing the spray high over the tree, allowing it to drip down over the foliage.
While you are about it spray your tomato plants with the copper to protect against blights.

One comment on “Pear slug on plum and pear trees – Wally Richards

  1. scarlettui on said:

    thank you massive help they seem to be on my almond too

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