Gardening Help FAQs

Here are answers to some of the most common questions we receive about garden plants. You will find concise information on general gardening techniques as well as plant selection and care. For detailed information on specific plant pests and problems refer to our Common Garden Pests and Problems page.

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Horticulture Questions and Answers

How do I use copper or sulfur for pest control?

Chemicals derived from mineral-bearing sources, like copper and sulphur, have been used for centuries to control garden diseases and some insects. The Greek poet, Homer, described the "pest-averting sulphur" 3000 years ago. Sulphur can be used as a dust, wettable powder, liquid or paste. Its primary use is to control powdery mildew, leaf blights, fruit rots, apple scab and certain rusts. It is also useful in controlling thrips, spider mites and psyllids. Sulphur is usually listed for use on tomatoes, peas, potatoes, beans, and many fruit crops. It is most effective when used during cool weather, as sulphur can cause injury to foliage in high temperatures. Sulphur is also incompatible with other pesticides. It should not be used on plants within 20-30 days of applying spray oils, as sulphur will react with the oil to create phytotoxicity. Sulphur is non-toxic to mammals, but it may irritate eyes and skin. Precaution should be taken to not inhale any dust, which can damage the lungs, and eye protection should always be used.

Copper is also a naturally-occuring element. Combined with lime, it is known and sold as Bordeaux mixture. Bordeaux mixture is primarily used as a fungicide to control anthracnose, downy mildew, bacterial leaf spot, cankers and blights, but can also be used to repel many insects. It is commonly used on vegetables, tree fruits and nut crops. Bordeaux mixture, like sulphur, can be phytotoxic to plants. If applied during wet, cool weather, it can burn leaves or cause russeting of the fruit. Follow mixing directions carefully and avoid direct contact with the solution.Copper compounds can also be toxic to fish and other aquatic animals.