Dealing With Fruit Tree Pests and Diseases

You and your family are going to be eating this fruit (and anything you spray on it), so choose your weapons accordingly. Stick with safe organic treatments, we have listed some here.


First we'll deal with the big pests because they are capable of doing so much damage so quickly. Deer can be fenced out. To keep cats from scratching the bark on young trees, wrap the trunk with temporary fencing. Birds are not usually a problem, but netting is available if you need it. Neighbors can be discouraged in various ways from helping themselves, but you're on your own there.

Spray it with some oil. Uh, what? In winter, before the new flower buds and leaves open, spray a light weight dormant oil on the bark. Spray it on the tree from all sides and directions. This will smother any eggs (they have to breathe, too) that the bad bugs have laid in the crevices. Don't make it easy for them, next year's bugs will have to come from somewhere else.   

The more insidious pests are the smaller ones. Treatment depends on which pest you will need to control. The best single preventive we have found for this part of northern coastal California is Spinosad, a bacteria (Saccharopolyspora spinosa) which affects the insect's nervous system after they ingest it. It is sprayed on the leaves and can be used to control fruit flies, caterpillars, leafminers, thrips, sawflies, spider mites, ants, and leaf beetle larvae. It will not harm sucking insects such as most predatory mites, ladybugs, or lacewings. Do not apply to areas where bees are actively foraging since it is very toxic to them while the material is in liquid form. It will not harm bees after it dries. Follow the directions on the label.

Spinosad is a soil bacteria which was first discovered underneath an abandoned rum distillery in the Caribbean. It's use is not limited to fruiting trees, it can also be used to control garden pests on plants such as squash, cabbage, beans, even ornamental plants such as roses. Apply it to the entire plant. It is fast-acting and odorless, non-toxic to humans and pets and can be used right up until the harvest. It kills caterpillars, so avoid using this product if you are trying to attract butterflies to your garden.


The most prevalent plant disease problems in this part of Northern California are scab, leaf blight, mold, mildew, rust and bacterial spot. The best single preventive treatment we have used is Serenade, another strain of bacteria (Bacillus subtilis) which forms a protective coating around all parts of the tree, discouraging the establishment of fungi. This product is available as a concentrate or as a ready-to-use form. Start applying this at the first sign of foliage and continue as needed. Follow the instructions on the label. Buy only what you need, the product is a living entity and has a definite shelf life.

It works by competing with the fungi and creating an environment which prevents them from getting started. It is best to use it before problems start. Similar to the above product, this can be used on other vegetable or ornamental plants as well, including lawns, and can also be used up until the harvest. It is also non-toxic to humans, pets and wildlife.

Another product which will assist you in keeping your plants healthy is the copper-based fungicide Liqui-Cop, a replacement for lime-sulfur spray and Bordeaux Mixture. This gives excellent control of common fungal diseases (such as peach leaf curl) on fruit, nut and citrus trees. Use this when the leaves fall to help eliminate many of the pathogens and prevent their return the following year. Make a  second spraying in the spring or late winter, just before the buds begin to swell. It can be mixed with a horticultural oil, allowing you to double your results with only one spraying.

Good housekeeping will go a very long way in keeping fruit trees healthy. Leaf diseases come back the next year because the spores will survive the winter in the ground. If diseased leaves fall off the tree and decompose on the ground, the spores will overwinter there and will infect next year's leaves. Remove diseased leaves and you break the cycle. After dormancy, sweep up all litter from underneath the trees and plants, and dispose of it, do not add it to the compost pile. Replace it with something useful (seaweed is good, we get that at the boat landings.)

The Gardener's Guide to Common Sense Pest Control.

If you have a home, an apartment, a garden, or a pet (or, in some cases, housemates or tenants), you've probably got pests. And if you want to control pests, there's no need to poison yourself. The science of pest control has given us potent but highly toxic chlorinated hydrocarbon pesticides. Not only are these products causing increasing hazards to our health, they are also spurring the rapid growth of insect resistance.

This book, first published in 1991 and updated in early 2013, focuses on designing a management program for pests. It is a reference for homeowners and home gardeners, a text for students, professional pest control personnel, maintenance workers and people who serve the public by selling pest control products. It provides solutions by placing emphasis on a decision-making process rather than a product-oriented solution. By reading about the problem and observing the circumstances of the problem, one can find the means to permanently modify the pest problem without resorting to hazardous scorched earth pesticide applications. This book is a highly recommended reader-friendly introduction to least-toxic Integrated Pest Management.

NEXT: Apple Ripening and Storage.