Beetle Borers
Prevent: Beetle borers are primarily found in outdoor gardens. Cleanliness and good habits will keep these pests out of greenhouses and indoor growrooms.
Identify: The beetle borer is the larvae of a large variety of beetles and a particularly nasty pest. These larvae leave entry holes at the base of stalks where they continue chewing through the stems of your plant. A brown trail of death will follow the path of a beetle borer, these pests cause severe enough damage to water transportation systems of plants everything around the trail dies. If the base of branches or heaven forbid the main stem of the plant are infected, death can quickly follow for everything outwards of the trail.
Note the entry hole on the left of the picture and subsequent trail to the location of the larvae
Eradicate
Repression: Keeping indoor grows clean is the only countermeasure.
Predators: The borer is a large enough tunneling insect that no effective predator has been identified. Predatory nematodes can help control grubs in the soil but this is a largely preventative measure and not a treatment.
Manual Removal: The best and virtually only way of controlling beetle borers. If damage is sited, follow the trail and cut the borer out of your plant. Oftentimes damage is already done when a beetle borer is located. If the branch or affected area does not bounce back quickly or is obviously done for, remove it with a clean cut from a knife or scissors.
Spray: The beetle borer lives inside the hardy stalks of your plant making sprays nearly useless. Bacillus papillae is a beetle specific fungal powder and can have limited success. If the beetle is in the main stem of your plant and you cannot get to it without endangering the life of your plant, injecting a product called rotenone directly into the stalk with a hypodermic syringe will kill the grub.