You can recognize insect damage easier than other kinds of leaf problems. Insects usually eat part of the leaf, or suck out the sap. They hide under the leaf, in the soil, or in the tips of the plants. Some of them are tiny, so it might help to have a magnifying glass when you look for them. The cures are as follows:
Pick off the bugs
Big ones like caterpillars can be picked off.
Little ones like mites and aphids can sometimes be washed off with water from a hose. If you’ve spotted just a few, this may be all you have to do.
Spray with an organic product
Bonide Oils and soaps will smother the insects and their eggs, and can work well. Spray early in the morning, when the leaf is not in full sun. And spray thoroughly! The entire plant, and under the leaves as well. The only bugs you’ll control are the ones that get coated.
Bonide Bacillus thuringiensis is a bacteria that you spray so the bug dies from the bacterial infection. It works well for worms and caterpillars. You’ll need to spray it several times, a few days apart, to get the best control
Bonide Captain Jack Dead Bug Brew® Contains Spinosad, a bacterial by-product. It works well on many kinds of worms as well as some small insects. Pyrethrins are from mum plants, and are sometimes called Pyrethrum. It is especially useful to control small insects.
Bonide Rose Rx 3 in 1® Insecticide, miticide and fungicide that can be used on roses, flowers, vegetables, fruits, herbs, houseplants, trees and shrubs.
Spray with a traditional chemical
Bonide Systemic products with Imidicloprid can be sprayed on plants or watered into the soil (depending on the label). The chemical goes into the plant, and when an insect takes a bite they also get the chemical. Very effective!
Bonide Eight® has the active ingredient of Permethrin, which is a synthetic chemical related to Pyrethrins. They last a lot longer and are very effective against a wide range of bugs, including aphids and Japanese Beetles.
Bonide Malathion is another old chemical (1950) that is still effective. It kills mostly small insects and can be used on flowers, fruits and vegetables.