My outdoor marijuana garden took a serious hit because of some European corn borers. It is located in a non-urban, agricultural space. What these pests do is drill a small hole in the lower talk and then chow down all the way up to the top branches, where they eat any new growth. The only plants that made it did so because of some kind of corn borer predator. How can I stop these pests?
Borers are a lot like caterpillars (both in the Lepidoptera family), and can thus be treated in similar ways. You can stop borers from climbing up the stems with a barrier of sticky tape. They won’t be able to reach the upper stem and bore inside of it. You can also use Tanglefoot, a sticky, spreadable material that feels a lot like Vaseline. Insects can’t make it across these physical obstacles and small mammals don’t particularly like them either. You can find these at many nurseries or garden centers.
Bacillus thuringiensis (BT) is a bacterium that plagues insects in the Lepidoptera family along with moths and butterflies. When you locate the corn borer hole, you can spray some BT in with a dropper or straw. This is a 100% safe option for food crops. When borers ingest BT, they quit feeding and die shortly thereafter. They also secrete more BT so that a second wave of pests isn’t possible. It is harmless to humans, animals, and plants (aside from butterflies and moths) and maintains utility until it is physically washed off by rain or spray. You can find it at many nurseries under the brand name, Dipel. You can also find some on the internet.
Pyrethrum is a naturally-occurring insecticide created from plants like the chrysanthemum. You can find it in spray or powder form at many nurseries. It is quite potent and will eliminate caterpillars and borers effectively. It lasts for several days, but must be re-applied to reap the benefits. Warm-blooded animals show no ill effects when coming into contact with pyrethrum, but it is fatal for some fish, reptiles, and other invertebrates.