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New Biofungicides Pit Bacteria Against Garden Fungi

March 21, 2023 New York Times, Science Times, D5 announced the discovery of compounds made by bacteria that kill pathogenic fungi in both plants and animals by riddling them with holes. It has proven effective against Botrytis cinera, or gray mold, and against Candida albicans, a fungus that cam infect the human body.

            The Times story was about the naming of the new compounds keanumycins, after an actor who has held “many iconic roles in which he is extremely efficient in ‘inactivating’ his enemies, Keanu Reeves. (Mr. Reeves says he thinks the naming is “pretty cool,” though he thinks it might have been more appropriate to name the compounds after John Wick, the killer he plays in a recent film.) While the article contains no information to suggest that keanumycins are available in any commercial product at present, there has been much research in the area of biofungicides recently. However, some new products do protect plants against gray mold.

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The strawberry on the left is so badly infected with Botrytis, or gray mold, that it will never enlarge or ripen.

            This disease is common in humid locations, such as in a greenhouse or near the coast in and near San Francisco. You may have seen it on strawberry fruits, where it makes a very obvious gray mass. It also grows on leaves and flowers of susceptible plants such as tomato, rose, German primrose, and painted tongue (Salpoglossis). I used to tell gardeners that their best defense against the disease was to pick off all traces of infected plant material before it could spread spores. This is still excellent advice that you should act upon whether or not you have another tactic. You can also select plants for a humid garden that have smooth or waxy leaves and fruit that is not soft. (This is easy unless you have your heart set on growing tomatoes, roses, or strawberries.)

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Botrytis shows itself as colored spots on the petals of roses. To reduce its spread, pick up all fallen rose petals and deadhead spent roses. 

            However, you may also want to try products currently available that promise to kill Botrytis cinerea. The ones I know of contain the soil bacterium Bacillis amyloliquifasciens D747. One formulation that contains it is sold as Revitalize. You can get it as a concentrate or in a ready-to-use spray bottle. It can also be used as a soil drench to control a number of diseases that start there. Also on the label of products containing this bacterium are anthracnose, bacterial leaf blights, black spot of roses, various leaf spots, and powdery mildew. Those diseases are controlled by the product. Only suppression, not control, are promised for downy mildew, early blight, fire blight, and scab. In all cases, it is best to apply the product before the disease shows up or in its very early stages.

            The main point is that a considerable amount of research is taking place in the area of biofungicides, some that has resulted in products already on the market, others in the pipeline. So, it is a good idea to start studying the offerings of your local, environmentally responsible garden center and reading the labels. You will already be pleasantly surprised, and more, even better surprises are likely to come soon.