By John Kochanowski
UCCE / El Dorado County Master Gardener
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We can feel the hint of winter in the air and leaves are falling from your trees. Once the leaves are off the trees, it is time to protect them from next year’s pests and problems.
Late fall and winter is the time to spray your trees to protect them from bacterial invasions like fire blight and the bacterial blasts that affected many trees this year. Spraying trees in the dormant season with horticultural oil kills over-wintering eggs of the fruit tree leaf roller, gypsy moth, tent caterpillars and other caterpillars that spend the cold season in the bark. It also controls scale and the over-wintering eggs of mites and aphids.
If you noticed leaf curl on your fruit trees, the time to prevent next year’s reoccurrence is in December or early January. A single treatment of fixed copper or preferably, a Bordeaux mixture will often be sufficient. If we have another late, wet spring an additional application would be advised before bud break in spring.
Bordeaux mixture has been used for decades as an effective fungicide and bactericide to control diseases of tree fruits, nuts and vine fruits. It is best applied in dormant season. Application to leaves can cause yellowing and loss of the leaves.
A Bordeaux mixture is preferred to fixed copper because it will adhere better in wet weather. The downside to Bordeaux and most sprays is you must wear appropriate protective gear, and take care near house paint and ornamentals. The spray will leave a blue residue and is corrosive. Eye and skin protection is mandatory. You will find complete instructions on the Bordeaux mixture in Pest Notes Publication No. 7481. This publication and others like it can be downloaded at no charge from the University of California Statewide Integrated Pest Management Program (IPM) Website at ipm.ucdavis.edu in the homes, gardens, landscapes and turfs section.
While there are many Bordeaux mixtures, a 10-10-100 mixture works well for many plant diseases. Just like fertilizer, the numbers represent pounds of material in the mixture. The first number is pounds of copper sulfate, the second pounds of hydrated lime, and the last, the gallons of water used. In our quantities, this means a gallon of water contains 3 1/3 tablespoons of copper sulfate and 10 tablespoons of hydrated lime.
In non-commercial quantities, it is easiest to prepare stock solutions of the lime and copper sulfate. Mix 1 pound of copper sulfate and a gallon of water in a plastic bucket. This solution can then be stored indefinitely in a clearly labeled glass bottle. Do the same with a pound of fresh hydrated lime and a gallon of water. Let stand at least two hours before use. When you are ready to spray, put 2 gallons of water in a plastic bucket and add a quart of each solution while stirring with a wooden paddle. Continue stirring for several minutes after adding the solutions.
Powdered copper sulfate or bluestone dissolves easily because of its fine texture. It is better for a Bordeaux mixture than lump copper sulfate. Keep it dry. If it gets wet it will lump and be difficult to work with and will clog your spray equipment. You can use hydrated lime or slaked lime. Hydrated lime is easier to work with. It should be fresh, as exposure to air carbonates it. Since it is a dust, be sure to wear eye protection and a good dust mask. You will need your lungs for a long time, so buy the more expensive dust mask for maximum protection. It will be thicker and can be found at the better building supply outlets.
You should not spray when it is windy, or when humidity will be over 90 percent for 48 hours. Some plants are sensitive, so check the label. Wear long sleeved protective clothing and goggles when spraying. You can buy disposable plastic lined coveralls that will protect your skin from exposure to the corrosive and coloring effects of the spray. You do not want to end up looking like a member of the Blue Man Group.
Your first dormant application should be made after the rains start to assure that the trees are not water stressed. If you irrigate your trees, you do not have to worry about this. Do not apply if the temperature is below freezing or if it is foggy. Do not spray your citrus trees since they do not go dormant.
For tree size applications, it is best to buy a pressurized spray tank. I prefer a 1 gallon tank because I need to use a ladder to reach some of my taller trees and I would rather carry 8 pounds up a ladder than 16 pounds. I fill three tanks at once and then can spray all of my trees. Read and follow the instructions for your sprayer. You will be using a corrosive product, so don’t have an accidental discharge of material. Imagine your spouse or mother cautioning you to be careful. Pick a calm day with no imminent rain. Thoroughly spray the bark. Be sure to constantly shake the sprayer to keep the mixture in solution and to prevent clogging. Bordeaux mixture is highly corrosive, so thoroughly rinse equipment three times after use.
For a mixture that will remain on the tree for the entire rainy season, combine 1 ½ quarts of the solution with 2 gallons of water. At bud break in spring, or on plants that may be sensitive, use 1 pint of the solution with 2 gallons of water.
Remember that after bud break, the bacteria are already established, so the time for prevention is while the leaves are off the tree and before you see those buds starting to open. This seems like a lot of work, but you will be rewarded next spring with healthier trees and more fruit.
On Saturday, Nov. 13, UCCE Master Gardeners will present a free class on “African Violets and Other House Plants.” The class will cover how to plant and care for the many varieties of African violets and other house plant selections. The class starts at 9 a.m. and will be held in the Bethell-Delfino Agriculture Building at 311 Fair Lane in Placerville.
Master Gardeners are available to answer home gardening questions Tuesday through Friday, 9 a.m. to noon, by calling 530-621-5512. Walk-ins are welcome. The office is located at 311 Fair Lane in Placerville. For more information about our public education classes and activities, go to the Master Gardener Website at HYPERLINK “http://ceeldorado.ucdavis.edu/Master_Gardener/” or ceeldorado.ucdavis.edu/Master_Gardener/.
If you are interested in becoming a Master Gardener, read the information and download an application from our Website or pick one up at our office. The deadline to submit applications is next Monday, Nov.15.