Thursday, August 7, 2008

Disease Prevention

These are, for the most part, general measures designed for the overall health of the Orchard. Occasionally additional measures may be useful for a specific Pest that has gotten out of control. The objective is to have an overall strategy that maintains a healthy ecosystem for plants, critters, and people,and encourages beneficials. It's called IPM (Integrated Pest Management). The point of the Newsletter is to help you keep your trees healthy and vigorous by good cultural methods, so they can resist disease with a minimum of additional intervention. 
A - "Keeping it Simple!"
Make sure the Team has done a good job on the "Clean-up," and check for any "mummies" left on the tree. Remove any residual leaves and hose off the tree using a pressure-spray nozzle. It's beneficial to see that all dead leaves are removed from the tree, and raked up. For the Apple Trees; cut a 3 inch wide strip from a corrugated cardboard box, and wrap it tightly around the trunk (so the little tubes are vertical), just below the first branch (or about a foot and a half above the ground). Remove the band on December 1st, put it in the garbage pail (not for garden composting). 
* If there has been a severe infestation of soft bodied insects or scale a "Horticultural Oil" can be sprayed during the Christmas Vacation period, when children are away, and when the Tree is dormant. 
B - "More in Depth"
OK -  The Corrugated Cardboard band will catch Codling Moth Larvae as they travel down to the ground to pupate. Removal in early December should catch some of the larvae in the little corrugations. Best to burn, or dispose of these with trash. This will help reduce the Codling Moth population in the coming season, although, if you had a heavy infestation we'll have more suggestions for Winter and Spring.
Obviously-diseased shoots and branches can be Pruned out when the tree has gone dormant and you're removing residual leaves. (The tree begins going Dormant when at the ends of the twigs the tiny leaves have been replaced by a tight Leaf Bud. This is where growth will be initiated in the spring               
* Spraying of pesticides (organic or chemical) should only be done if there is evidence of disease uncontrolled by the physical and mechanical techniques. There is always the risk of upsetting the natural balance by injuring the beneficial insects and microbials.  When appropriate however, spray strategies can be used. 

If you're concerned about the level of disease in some trees, call your County Master Gardener office and request a visit from one of the Master Gardeners. The School holiday weekends and holiday weeks during November, December, and January are the best times to use preventive sprays (like Horticultural Oil), and to deal with a School Orchard disease problem.
C - "Why is that ?" 
Many insects and pests (soft bodied insects, scale, etc.) over-winter in the crotch of branches, in the bark, and even  in the bud tips.  Although dormant, they need  to respire (breathe). The Oil will smother them if the coverage has been complete. Horticultural Oil may also be called "Narrow-range" or "Superior" Oil. This technique, is relatively safe and has minimal adverse environmental impact. AdditionallyIt's important to realize that most control measures are only effective at certain stages of a pests life cycle. Oil is most effective during dormancy, at other times the effect may be negligible.
For Deciduous Trees, spraying in the Dormant season has many benefits: The days are cooler and moister, when sprays are less phytotoxic (harmful to plants).  The elements of the tree most likely to suffer damage (leaves, blossoms, new shoots etc.) are safely out of the way. Bees, and other pollinators are relatively safe.

For School Orchards that have Citrus trees, Columbus Day weekend would be a safe time to use Horticultural Oil spray. You don't want to do it any later in the year, and be  sure that the trees are well watered before any spray operation. If they have been a problem; this treatment will help control Scale, Aphid, White Fly and other soft bodied insects that overwinter in the tree.

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