Start controlling next years disease problems now
August 30, 2011
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Taking steps this fall to clean up your garden and fruit plantings can help to deter some problems next year. The different diseases we contend with carry over from year to year in different ways. Some, such as downy and powdery mildew, are the snowbird type that can only overwinter in warmer temperatures where there is green plant matter to survive on. For these, we actually have to wait for weather systems to deliver the spores to our area each summer before they infest our plants. So other than using disease resistant varieties or fungicides, there is little we can do to prevent a problem next year.
There are also the homebody type diseases that are content to hunker down and spend the winter months here. For some, such as verticillium or fusarium, very little shelter is needed at all as they can simply survive in the soil for years. These are tough ones that we have to rely on resistant varieties and long-term rotations (at least three to five years without a host crop) for control.
However, the ones we can take advantage of are the ones that need a somewhat temporary shelter, such as plant debris that has not yet fully decomposed, to survive on through the winter. Black rot on grapes is one of these where the overwintering shelters are the raisin-like fruit that drop to the ground. For apple scab it is the infested leaves that litter the ground. For both of these, imagine tiny cannons on the plant matter that shoot the spores into the air next spring. If we can remove or incorporate these bits of plant matter into the soil to spoil the cannons shot, it will help with next years control efforts. With grapes this can mean raking up any fallen fruit and disposing of it away from the growing area or raking them into the soil to bury them. For apple scab, rake up and burn or dispose of the leaves. Brown lot of peaches is another one that if we get rid of the overwintering structure, which are mummies that hang on the trees, it can help reduce the infestation next year.
Still other diseases, like early blight, overwinter on plant matter with the spores being windblown or rain splashed onto the plants the following year. Fall plowing to bury and encourage decomposition as well as using a three to four year rotation away from tomatoes or potatoes can help. Also use mulch next spring to prevent the soil from splashing onto the leaves.
If you had fire blight on your apples, crabapples, or pears this year, you will also have cankers on the trunk and branches for the disease to carry over so removing infested branches or twigs will help. And if you had peach leaf curl on peaches, youll need to apply a fungicide such as lime sulfur during the dormant season (either late fall or early spring) to reduce the number of spores that carryover on the bark of the tree.
These efforts will not control all diseases by any means. But they will help. Anytime we can remove or destroy an overwintering structure, it gives us a leg up on next years disease control efforts.
