Harmful garden fungi generally lurk in the soil, splashing their spores into the breeze and onto nearby plants when hit by pelting raindrops. Savvy gardeners fight fungi before they show themselves by spraying fungicide on dormant fruit trees, roses and other slumbering plants during dry winter days. But constant rains made dormant spraying difficult this year, while splashing a bumper crop of spores over trees, flowers and vegetables.
The results are now becoming apparent, with gardeners flooding into garden centers bearing samples of powdery cucumber plants, gnarled and twisted peach leaves, and rose foliage disfigured with rusty-red pustules. The dreaded early blight has also emerged in the form of desiccated brown streaks and blotches in stem and leaf that quickly reduce an infected plant to a blackened skeleton.
If caught early, infected plants can be successfully treated with minimally-toxic fungicide sprays containing copper, citric acid, beneficial bacteria or neem oil – all of which are allowed in organic agriculture. Overly-bushy or crowded plants can be thinned to encourage healthy air flow through the center of the plant.
But even if it’s too late to save this year’s plants, you can safeguard next year’s garden by picking up every scrap of infected plant material – leaves, branches and roots – and disposing of them in the trash or in a municipal green-waste bin. Do not toss them into your home compost pile, as the spores will hang around in the finished compost and eventually infest every inch of your garden. (Municipal compost systems get hot enough to kill pathogens, your home compost pile almost certainly does not.)
If possible, strip all infected leaves from fruit trees and rose bushes, and put them in the trash. Toward the end of the year, when deciduous plants have gone dormant, rake up all stray leaves and cover the ground with a couple of inches of clean shredded mulch. Wood-based soil conditioner available in bales at most garden centers is an excellent product for this use. Dense mulch will prevent the spore-laden soil from splashing onto plants when the rain falls.
Finally, spray the bare branches of dormant trees and shrubs with an organic fungicide, following the directions on the label.
In the vegetable garden, do not plant vulnerable plants in the same spot year after year if at all possible. If space is tight and fallowing a fungus-infected bed is not an option, try importing new sterile soil or using mulch to keep the spores down. And when choosing next year’s vegetables, look for disease-resistant varieties.
- Maria Gaura, UC Master Gardener
UCANR plant disease directory for vegetables and melons:
UCANR plant disease directory for fruit-bearing trees, berries and vines:
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