The good news is that those tiny mites hanging out on the underside of your honeylocust (Gleditsia triacanthos) are not going to bring the whole tree down. Spider mites (Platytetranychus multidigitali) commonly congregate on these trees, feeding on the leaves' undersides, and causing them to turn bronze and fall. Consistent infestations might slow growth, but your tree will survive. More good news --- you can handle the spider mites without resorting to dangerous pesticides that you don't want to use around your children. In fact, good old-fashioned water plays a key role in keeping spider mites away.
1 Water your honeylocust tree consistently, especially when the weather is hot. Irrigation helps diminish the spider mite population and minimize damage. Trees suffering from drought are more likely to be infested. When you water the honeylocust, if conditions are dusty, wash off the tree. Not only do dusty conditions harbor more spider mites, but forceful spraying of the tree's leaves can wash them off.
2 Protect populations of beneficial insects that control spider mites by avoiding broad spectrum pesticides. Spider mites begin to thrive in July if their natural predators, such as sixspotted thrips (Scolothrips sexmaculatus) and the spider mite destroyer lady beetle (Stethorus picipes), have succumbed to pesticides often applied to trees in the spring. Predatory bugs can keep spider mites under control.
3 Use horticultural and plant-based oils, such as canola, cottonseed or neem to get rid of spider mites. Do not use the oils when the temperature exceeds 90 degrees Fahrenheit or when your honey locust tree is showing signs of water stress. Apply the oil with a sprayer, and completely coat as much of the tree as you can, paying special attention to the underside of leaves.
4 Clear all fallen leaves and debris immediately in the fall to get rid of spider mites and prevent them from overwintering near your honeylocust tree. Then apply a dormant season oil to as much of the tree's trunk and branches as you can. Spider mites could be overwintering anywhere in the tree.