You know, I was going to end this series with the last post before it occurred to me to address houseplant afflictions. Bet you’re sorry it did.
Anyway, pests and diseases – well, what’s the difference? Both are caused by other organisms attacking the plant. In practical terms, plant diseases are caused by microorganisms (bacteria, viruses, fungi) and pests are, well, pests – you can see them with the naked eye (assuming you have reasonable vision), at least at some stage in their life cycles. Some people might count nutritional deficiencies as diseases as well: scurvy in humans, for example, is a Vitamin C deficiency. For plants, that’s more of a problem with the soil and fertiliser, so I won’t go into it here.
I can’t possibly talk about every single disease or pest that could affect every single houseplant – I certainly don’t know about every single houseplant, much less everything that attacks them. Even if I did, that would fill an entire set of books. I’ll just go into the ones that are most common on houseplants here. Much of it also applies in greenhouses.
Pests and diseases indoors can sometimes seem to be much more of a problem because of the isolated nature of the environment. Outdoors, many of these things are controlled to a manageable extent by natural predators or simply the living conditions; indoors, those factors are not present. Annoyingly, they are often brought into the house when you bring the plants inside for overwintering; they may not be apparent because they were kept under control by outdoor factors and then suddenly they boom into a problem. Some of them spend part of their life cycles in the soil and remain hidden there for a time.
As is usual, prevention is better than cure. When you start thinking of bringing the plants inside, take a good look at them for signs of anything wrong. If you find diseases, prune off the affected plant parts and if possible burn them. A good drench of insecticidal soap or solution is a good idea, but it must reach every single part of the stems and leaves and it won’t reach things hiding in the soil. A hard pruning (which is a good idea for a lot of plants at this point) can make this a lot easier. If a plant is due for repotting and a complete soil change, think about doing so now.
Prevention also depends on keeping plants healthy in other respects: plants that are weak, overwatered, underwatered, overfed, underfed, or otherwise not given conditions to their liking, are more susceptible to pests and diseases. Just like humans, really.
Even if you do all you can, don’t beat yourself up if later something bad does show up. Pretty much all of the common pests and diseases have stages that are very difficult to see or find, much less eradicate.
Once you do recognise something amiss, try to isolate the plant while you treat it so as to minimise the likelihood of the problem spreading. On the other hand, by the time you notice it, the problem probably already has spread…