Controlling Plant Pests Organically

Bugs are a fact of life. And the same wonderful scents that attract us to these wonderful herb plants also attract plant pests. While some plants like Tansy and Pennyroyal repel bugs, sooner or later you're probably going to encounter plant pests. Below is a list of common plants pests and easy ways to kill the little buggers. As an organic nursery, we use only organic insecticides on our plants. Since many of the herbs you grow are going to find their way to your dinner table, we recommend you use only organic insecticides too. These days, they are available at most garden centers. Organic controls include Insecticidal Soap*, Pyrethrum, Insecticidal Oils*, Bacillus thuringiensis, and Diatomaceous Earth. While isopropyl rubbing alcohol is not ‘organic' (we don't use it on our plants), it is relatively safe and very effective to daub on hard-bodied insects. You will usually need to reapply all controls a couple of times to kill the young insects hatching from existing eggs and break their lifecycle.

*Soaps can burn tender leaves. Apply in the evening, in the shade, and rinse off about 15 minutes later. Oils also can burn leaves but must be left on the plants to suffocate the insect, so leave the plants in the shade for a couple of days after treatment. Don't apply soaps or oils on extremely hot days.

Aphids: These are small, round, winged insects that suck plant juices. They usually congregate on new plant growth, where they shed their wings and stay to dine. They can be green, yellow, brown, orange or black. They're pretty easy to get rid of.
Control: Insecticidal Soap will kill them very effectively. Repeat about every five days to kill young aphids hatching from existing eggs on the plants.

Mealy Bugs: These are small, white, fluffy bugs that lodge in the nodes and bottom stems of plants. I hate these things. You can hand squish them, in which case they'll turn from white and fluffy to orange and gucky. They're generally not much of a problem outdoors because ladybugs love them. Inside they can be a real nuisance.
Control: They have a natural coating that repels Insecticidal Soap, so you need to either use an Insecticidal Oil to suffocate them, or daub them with rubbing alcohol on the end of a cotton swab. Reapply every week or so until you've broken their life cycle.

Scale: Not many herbs are prone to scale. These hard-bodied insects remain motionless on plant stems while sucking plant juices, so they're hard to notice. They are oval, tan, black or brown, and peal off easily. Don't be fooled by their immobility, they're sucking the life out of your plants.
Control: They have a hard coating that repels Insecticidal Soap, so you need to either use an Insecticidal Oil to suffocate them, or daub them with rubbing alcohol on the end of a cotton swab. Reapply every week to 10 days to break the life cycle.

White Fly: White flys are, well, white flys. They are slow flying, pure white insects that live under the leaves of plants, sucking the juices. Their telltale sign is the black sooty-mold they leave around their colonies, or long, glass-like fibers. They're especially partial to hibiscus bushes and citrus trees, but will sometimes attack basil.
Control: On tender-leafed plants like basil, try a hard stream of water first. This will disburse them. If they return, start with Insecticidal Soap, applying every 5 days, and rinsing it off about 15 minutes after applying. If that doesn't work, try Insecticidal Oil.

Slugs and Snails: Snails and slugs are mollusks that generally start eating leaves from the outer edge of the leaf. They usually do not begin chewing on the center of a leaf. Snails and slugs lay their eggs in soil, not on leaves, so young or mature snails and slugs crawl up the branches of the plant and start chewing the edges of the leaves. The telltale sign of snails and slugs is that they leave a shiny trail along their path from their ‘slime', which glistens in the sunlight. They are not a problem is areas with freezing winter climates.
Control: Avoid snail and slug bait. This is way too poisonous for the herb garden. Either collect them by hand at night, or sprinkle some Diatomaceous Earth over and around the plant. Also, copper snail barrier is very effective at keeping them off of plants.

Caterpillars: These are the larval stage of any butterfly or moth, and are found throughout the U.S. in many different forms, and all of them feed on plants. Caterpillars usually begin chewing on a leaf in the center, or away from the edge of the leaf. The adult butterfly or moth usually lays its eggs on the leaf surface (or sometimes the bloom). As the egg on the leaf hatches, the tiny caterpillar comes out and immediately begins eating the leaf. They don't crawl to the edge of the leaf to begin eating. These holes start out as tiny pinholes, and as the caterpillar grows, become increasingly larger. The telltale sign of caterpillars: They leave their waste in the form of small black or green ‘pellets', which collect on the leaves below where they are residing and eating.
Control: Firstly, let us state that if there were no caterpillars, there would be no beautiful butterflies. No monarchs, no swallowtails, etc. Tolerating a few caterpillars in the garden is part of encouraging nature, and that is what gardening is all about. However, when we have an infestation of ‘bad' caterpillars devouring our basil before we have a chance to, it's time to dispose of them on that particular plant. The best and safest means of doing so is by using a naturally-occurring soil bacteria called Bacillus thuringiensis, or Bt, a very specific organic insecticide. It affects only leaf-eating cutworms, and does no harm to ladybugs and their larva, lacewings and their larvae, spiders, the wasps and hornets that devour caterpillars, or humans. You simply spray a liquid form of Bt on the leaves of a plant, and when the caterpillars come to dine the next time, they ingest the Bt which proliferates in their intestines and paralyzes their digestive systems. The caterpillars quickly starve to death.

Thrips: Thrips are brown or tan, about one-eighth of an inch long. They're very narrow, appearing the shape of a tiny alligator. They're hard to see with the naked eye, but their damage is very clear. Thrips chew the top surface of leaves, leaving a striped, tan dead layer of leaf behind. The damage can appear as ‘white spots' on leaves, or a lacy or skeletal appearance on the leaves.
Control: Insecticidal Soap will kill thrips very effectively. Repeat about every three days to kill young thrips hatching from existing eggs on the plants.

Spider Mites: These are most common on indoor plants, and they can do serious damage. They are very hard to see with the naked eye. Spider mites leave a yellow, stippled-effect on the leaves, like tiny yellow spots. Spider mites may appear as tiny brown, green or red specks on leaves. They often leave a white webbing on the leaf surface. To confirm spider mite infestation, hold the leaf over a piece of white paper and sharply rap leaf. If you see small specks running around the paper, go directly to Control below.
Control: Spray the entire plant and the surface of the soil with Insecticidal Soap. Reapply every 4 days, for about two weeks.

Fungus Gnats: These tiny, black, flying insects are a real nuisance. Although usually only a problem on indoor plants, they are the bane of the nursery industry. They live on the soil surface and do little plant damage if any, but left unchecked on indoor plants, you'll soon be spitting them out of your mouth as you walk through the house! Pugh!
Control: Fungus gnats are easily controlled with Insecticidal Soap. Spray the soil surface well, and let completely dry out between spraying. Too-frequent watering of plants exacerbates a fungus gnat infestation. Water your inside plants well, and let the soil surface dry out between waterings. Sometimes removing the top quarter inch of soil and replacing it with fresh soil will remove all of the gnats and their larva.

Ants: If you have ants crawling on your plants, you've probably got some bug problems that need to be addressed. Ants themselves do not harm your plants, and are sometimes there just to collect nectar. However, ants are little ‘farmers' that help several other bad bugs harm you plants. Ants like to farm aphids, white fly, scale, and mealy bug, which then pass ‘honeydew', a euphemism for their excrement, which is highly nutritious for the ant colony. The ants stroke the backs of the aphids with their antenna, and the aphids reward the ants with honeydew. As good farmers, the ants protect these bad bugs from their natural predators, attacking ladybug and lacewing larva coming to eat the aphids. Ants also carry aphids to the tender and most succulent new growth of plants.
Control: To control ants, spray them with Insecticidal Soap. Spray the bugs they are farming with one of the above controls. Follow the ant trails as far as you can to discourage them from returning.