Prevent next season’s diseases now Next gardening season

By David Sprague

OSU Ext. master gardener volunteer

Well, the temperatures dropped fast the past week and this year’s gardening season is almost over.

Before you lock up the garden shed for the winter and go inside to read seed catalogs for next season, here are some things to do to help prevent diseases from getting started in the garden next season.

Prune your trees and shrubs. Pruning in the late fall and winter is recommended for most deciduous trees and shrubs, except those that bloom in early spring. Disease pathogens are less active in cold temperatures and less likely to be transmitted during pruning. Proper pruning includes removing all dead and crossing branches as these can be sites where disease can gain a foothold next spring. Prune woody plants to open up their center to allow more airflow and sunlight to reach inside the canopy of the plant next year.

It is very important to prune oak trees only in cold weather to reduce the risk of oak wilt. The oak wilt fungus can be spread by sap beetles. These beetles, which are active during warm weather, are attracted to the sap from a pruning wound. If you limit pruning of oak trees to colder weather, when the sap beetles are not active, you can do your part to prevent this means of disease transmission. Oak wilt is also transmitted via connected roots from infected trees to healthy trees. However, unlike the sap beetle, there is little a homeowner can do to prevent this method of disease transmission.

If your roses showed signs of black spot (circular black spots on leaves) get ahead of it for next year by pruning out all the diseased canes now and raking up and destroying all fallen leaves. The canes should be pruned back several inches into the good wood.

If you grew potatoes this year, be sure to get all left over tubers out of the garden. These tubers can be a place for the late blight fungus to overwinter and be ready to cause disease next year. Late blight is a serious disease and is most famously known for causing the Irish potato famine in the 1840s. The late blight fungus cannot survive freezing temperatures. So you can leave the tubers on top of the ground to freeze or bag them and throw them away. Late blight can also infect tomatoes. Don’t put any tomato plants you suspect of having this disease (or any other disease) into the compost pile. The heat generated in the compost pile might not be high enough to kill the pathogen, but could be enough to keep the pathogen alive over the winter. Bag up diseased plants and throw them away.

Also, it’s not too late for a general fall cleanup. This includes cutting, pulling out plant debris and raking vegetable and perennial beds. Continue watering perennials, especially evergreens, until the ground freezes.

And while looking through seed catalogs for next year’s garden plants, choose varieties that are listed as disease-resistant. Disease-resistant does not mean the plant won’t get the disease, but if it does, the disease should be milder and more manageable. For more information on preventing diseases, go to:

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