While mould is the bane of a weed grower's life there are, sadly, plenty of other pests which can damage your precious plants. Here are the top 5 and what to do about them.
Spider mites basically bite into and then suck the juice out of plants, which, if left
unchecked, will ultimately kill them. They like high temperatures and low humidity, so wetting leaves regularly can go a long way to discouraging them. Growers should still keep a constant look-out for small, white spots on leaves which are generally the first sign of a spider mite attack. In the early stages it may be possible to stop the attack by using an organic cure such as Neem Oil extract, but if this fails, or if the grower only picks it up at a later stage, the only real solution is to reach for a chemical product.
Some gardeners think of aphids as the technically-correct term for greenfly, but actually greenfly are just one particular kind of aphid. Not only do aphids suck sap, thus weakening the plant, they can also leave sticky deposits which can attract mould. While individual aphids are hard to spot, they tend to live in groups and thus can be more easily seen. The good news for outdoor growers is that there are plenty of other insects which see aphids as a tasty meal. For indoor growers or outdoor growers which still need a helping hand, there are both organic and chemical solutions available, but it's important to note that most of these need the plant to be completely sprayed in order for them to be effective.
Fungus gnat larvae attack plant roots and can cause a whole variety of problems. If your plants are looking poorly and you literally can't see why, there's a good chance fungus gnats are at work. There's also a good chance that you have been over-watering your plants and/or have poor air circulation and that rectifying this will solve the problem. If the top 2 or 3 centimetres of your soil is wet when watering is due, then you're giving too much water. Reduce it and see if this solves the problem, for a quicker fix, use air to dry out the top of the soil. For a really quick fix use a chemical treatment to stop the existing attack, but you will still need to sort out your plant-management issues or they'll be straight back.
Caterpillars may turn into beautiful butterflies, but you may not be thinking beautiful thoughts as they munch on your plants. How you deal with caterpillars depends on your point of view. You can remove them by hand and let them munch somewhere else (or be eaten) or you can use a pesticide. BT stops caterpillars from eating and thereby starves them to death, for those who find this on the cruel side Spinosad will kill them outright on contact and will also deal with other pests. Spinosad can be used in water as a preventative measure.
Slugs are pretty much caterpillars without any redeeming features. Stop slug attacks
by covering the base of your plants with something rough, like straw. The kind-hearted can remove any slugs by hand. The less kind hearted can use a beer trap to drawn them and the cold-hearted can kill them with salt.