Nontoxic Organic Pesticides for Apples

Copper

• According to Ohio State University, copper compounds work well against most apple fungus pests. They stay on the crop for a relatively long period, allowing growers to avoid repeated spraying. Avoid using large quantities of copper pesticides or spraying in cool, wet weather, as this increases the risk of copper damage to plant tissues. Common copper pesticides include copper sulfate --- bluestone or blue vitriol --- and copper sulfate with lime, or Bordeaux mixture.

Sulfur

• Sulfur pesticides, including lime-sulfur, work against powdery mildew, scab and other fungi, as well as some insects. Sulfur-containing pesticides have an unpleasant smell, similar to rotten eggs. When lime is present, the compound may also be caustic. Ohio State University recommends against using sulfur in weather above 80 degrees F. Sulfur kills beneficial insects and spiders. Only use it when other control methods fail. According to the University of Maine, lime-sulfur can be expensive. Microfine sulfur is usually a less expensive choice.

Microbes

• Certain bacteria, viruses and fungi control some insect pests in apples. Options include Bacillus thuringiensis, which controls caterpillar infestations; Beauveria bassiana, a fungal pesticide causing disease in weevils, thrips, aphids and other sucking insects; and Cydia pomonella, a granulovirus attacking codling moths. These pesticides have no residual effect, but may attack neutral or beneficial species related to the target pest insects.

Vegetable Derivatives

• Garlic and hot pepper extracts are common in home gardens for repelling animals and pest insects. According to Cornell University, these methods don't work well against most major apple pests, but may provide some repellent activity against birds, deer and other animals. These substances are low in toxicity, but require regular application of concentrated formulas.

Clay

• Spraying apple trees with kaolin clay results in an unattractive appearance but prevents insects from feeding and breeding. Kaolin clay is relatively inexpensive, and so nontoxic that it's used as a food additive. Kaolin is effective against plum circulio, lesser appleworm, codling moth, and a range of leafrollers and leafhoppers. It is unlikely to poison bees, but may harm some beneficial species after repeated application. Clay is messy and requires extensive cleaning after harvest.

Plant Toxins

• The neem tree produces substances that are naturally toxic to insects, but don't cause problems in humans or other animals when properly used. Neem oil controls aphids, leafhoppers and some leaf miners, but does poorly against beetles, scale insects and flies. It is toxic to bees until dry and can poison fish if allowed to escape into the waterways. Pyrethrin, derived from the pyrethroid daisy, works against European apple sawfly, apple maggot, aphids, leafhoppers, caterpillars and many other creatures. It degrades rapidly and requires frequent application. Synthetic pyrethroid pesticides are not safe under organic standards, although they were originally derived from this flower.