Marin Master Gardeners
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Marin Master Gardeners

Marin IJ Articles

Deal with garden’s pests and diseases now

January 26, 2109
Dot Zanotti Ingels

I am writing this column while watching the rain pour and the wind blow with gusto. I can see my apple, peach and pear trees. The leaves are gone and the beautiful structure of each tree is in full view. I like this time of year for so many cozy reasons and one of them is less demand for garden work. It is easy to be lured into thinking there is nothing to do but, in fact, a bit of effort now can lead to fewer problems later in the year. The best time to manage problems of pests and diseases from the past year is before the precious plant buds that hold the promise of yummy treats to come break open.

The most common insect pests and diseases we receive questions about at the UC Marin Master Gardener help desk are codling moth, fire blight and leaf curl. The three problems are caused by three different vectors.

Leaf curl

Leaf curl is caused by a fungus and is seen on nectarine and peach trees. The fungus spores overwinter underneath bud scales and other protected spots. Leaf curl shows up as distorted, reddened, puckered and curled leaves that are visible in spring. The leaves fall off and fruit production is reduced if the disease is severe.

Fire blight

Fire blight is caused by bacteria and is found here mostly on pear and apple trees. Fire blight infections overwinter in the wood and, in spring, the bacterial ooze is spread by bees and rain. Common symptoms of the disease start with brown spots and shrivel on leaves. Stem and blossoms can rapidly expand as the blight clogs the water-conducting vascular system of the host and causes areas of dead and discolored tissue.

Codling moth

Codling moth is an insect. Codling moth has the greatest potential for damage of any apple pest, yet it can be effectively controlled with properly timed treatments. It causes two types of fruit damage: stings and deep entries. Stings are entries where larvae bore into the flesh a short distance before dying. Deep entries occur when moth larvae penetrate the fruit skin, bore to the core, and feed in the seed cavity. Larvae may enter through the sides, stem end or calyx end of the fruit. One or more holes plugged with frass (poop) on the fruit’s surface are a characteristic sign of codling moth infestation, but calyx entries are difficult to detect without cutting the fruit.

Dormant treatments

In fruit trees, yearly applications of a dormant treatment are the key to successful pest management. Dormant spraying is a generic term for any spray applied to leafless deciduous trees during fall, winter and early spring. Some dormant sprays are applied to control over-wintering insects, while others are used to prevent disease infection.

In Marin, dormant sprays are applied from late November until the latter part of February or until you observe the beginning of the bloom. The dormant spray is the most important because it is the least disruptive to beneficial insects and the environment and is easy to apply.

Dormant season applications of specially refined oils (often called insecticidal or horticultural oils) are effective against many insects common to most deciduous fruit trees. They work by smothering the insects. Dormant season applications of copper or a synthetic fungicide are used to limit infection and prevent the spread of bacterial and fungal diseases like fire blight and leaf curl. For diseases with long infection periods like fire blight, it may be necessary to make several applications to protect new emerging shoots and flowers, especially during rainy spring weather.

Spraying is super easy to do yourself. Thorough application and coverage is essential for successful treatment of problems. The oils and fungicide can be mixed and applied together. Wear protective gear (goggles, mask, long sleeves and long pants). Pump sprayers are the best way to evenly and thoroughly apply the material. Trees should be hydrated and do not spray in heavy fog, rain or freeze.

Check with your nursery for help in selecting the best products for you and the best timing of application for your variety. Get your trees protected and wait for the wonderful fruits of your labors.

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