Controlling Spider Mites and Aphids on Indoor Herbs
Answered by: Richters Staff
Question from: Anne Tayler
Posted: Before April 1998

I grow a number of herbs indoors year round, using grow lights and halogen lights. I have had good success with chives, basil, shiso, rosemary, dittany of crete, oregano, thyme, several sages, and jalapeno peppers.

Recently I was given another pepper plant which I did not inspect thoroughly enough and I am now waging a major battle with aphids and spider mites. I have tried misting with soap sprays every third day, but am only succeeding in damaging new growth.

Help! I have had to resort to hand-picking them, which is too time-consuming.

Dittany of crete and chives are rarely bothered by aphids so you may you may find that you can reduce sprayings on those.

If soap spray is damaging new growth it is either too strong or made from the wrong type of soap. Safer’s Insecticidal Soap is made with the potassium salts of fatty acids unlike other soaps which are made from sodium salts. Excess sodium can damage plants but potassium is an essential plant nutrient. If you are using a commercial soap insecticide make sure you use the correct dilution rate. If damage to leaves occurs using the recommended rate can then try reducing the dilution rate by 50%.

We find that spraying plants does not give adequate coverage, especially on the undersides of the leaves. Soap sprays rely on contact with the target pests. If the soap spray does not reach some of the bugs then they will come back. Soap sprays have no residual action like chemical sprays which is why repeated applications are necessary.

For small numbers of plants, dip the entire plant above the soil line in a pail filled with soap solution. Swish the plants around for 30 seconds or so to make sure no crevices remain untouched. Do this every three days to eliminate pests and continue for two weeks as a precaution against surviving eggs.

Both aphids and spider mites are susceptible to insecticidal soap so you can rely on soap provided the coverage is total.

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