In our article on Chemical Selection for Pests and Diseases, we discussed selecting the proper chemical treatment for the job – using an insecticide for an insect pest or miticide for mites, for example. In this article, I want to address a few often-made mistakes in treatments.
The very minute you see an insect or mite infestation, treat if fully and completely.
Many growers figure they can just “pick off” or squash a single critter, since “it’s not a huge infestation”. Unfortunately, the presence of a single pest is a “tip of the iceberg” scenario. If the conditions are right for one bug, chances are that there are more present, hidden from view, and they’re already reproducing.
It is usually inadvisable to apply fungicides to plants with root rot.
In the vast majority of cases, root rot is NOT caused by a pathogen, but by a cultural issue like letting the plant get too cold, or suffocating the roots by using a potting medium that is too dense for your conditions and watering habits. The fungal infection that follows is secondary, decomposing the necrotic tissues. The problem will not be cured by application of a fungicide; but the cultural deficiencies must be addressed. In fact, treating may actually exacerbate the cultural stress, as the old, dead tissues will remain in place, rather than being decomposed, releasing their nutrient stores, then washed away.
Do not use bactericides or fungicides if you see the tips of new growths die and turn black.
Again, the cause is likely cultural – a calcium deficiency – and the rot is secondary. Adjust your feeding regimen and move on. You may have lost those new growths, but more will follow and the infection is unlikely to affect otherwise healthy tissue.