Stem Borers

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These Borers can stunt a stem or kill a small plant

These Borers have been found in the stems of Strawberry leaves and the much larger main stems of Hollyhock and various other Plants and weeds. The Larvae appear to be identical and thrash their front ends around violently when disturbed. 

Some Borers attack roots, some attack stems, some bore through the bark of trees where they may girdle the Cambium layer causing the tree to die. Often there is a pile of sawdust or excrement below the access hole.

Normally, they cause very little crop damage, but a large invasion may lower the harvest noticeably. Pesticides are largely ineffective, since the Larvae are protected by their host plant. Preventive sprays meant for the egg-laying adults will also effect insects which are beneficial.

If you have a valued plant, and discover the Borer at an early stage, you may be able to limit damage by drilling a 1/8" hole about 2" above the hole made by the Larvae(away from the roots).

Then forcefully inject insecticide into this new hole with a squirt bottle or injection needle. The one shown is from a printer refill kit. Whatever you use will become contaminated by the insecticide and should be reserved for this purpose or disposed of properly.

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1- The leaves on this main stem have wilted from lack of moisture and nutrients because a Borer is living in the stem and preventing the upward flow. They are usually found between the hole and the tip, rather than on the root side of the hole.

Note the access hole indicated by the blue line; it may have been made by the ovipositor of the adult female insect, or by the Larvae which hatched and bored into the stem, or by the resident Larvae to get oxygen or remove its excrement. The leaves below the hole have access to nutrients and appear to be normal and healthy.
3- This photo shows the stem sliced in half exposing the larvae. 

4- The same Larvae eating the stem and also showing its excrement left behind it.
5- This stem with 9 leaves shows the destruction of borers called "Miners" inside the leaves.
6- Here the actual Miner can be seen inside the black circle, appearing as a black dot.
7- This Tomato has what appears to be the damage of a Miner. Borers have also been found inside Tomatoes!