How to Beat Garden Diseases

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The outbreak of plant disease in the garden is almost as inevitable as stink bugs and Japanese beetles. However, there are several tactics that gardeners can execute to slow the spread of diseases and reduce the introduction of new diseases. Integrated pest management (IPM) for garden diseases can be summarized in three general recommendations: 1. Minimize the presence of the pathogen, 2. Reduce the presence of vulnerable hosts, 3. Eliminate the favorable environment for disease development.

Keep garden-disease-inducing pathogen populations low by pruning out diseased leaves, removing disease damaged fruit, and eliminating garden residue at the end of season. Diseased plant tissue allows pathogens to spread through spores and other survival structures. If you leave this residue in your garden some of those pathogens will be able to survive in the soil for many years. Don’t put diseased plant tissue in the compost pile. Many of the fungal spores and survival structures can survive home garden composting and spread to the rest of your garden when you add compost to the beds. Bury it deep in a pit, burn it, or throw it in the trash. Clean your pruners and other garden tools with a bleach solution. If you visit a friend’s garden be sure to clean the bottom of your boots. Be careful not to introduce contaminated soil through the sharing of tools and equipment. Tillers can spread nematodes, weed seeds, and some very challenging soil borne disease pathogens – be sure to power wash any such equipment before putting them into your garden beds. Mulching is another key strategy to eliminate pathogen presence on your plants. Many fungal diseases spread when rain or overhead irrigation causes soil to splash onto plants. Mulching will slow down the spread of diseases like early blight by covering soil and preventing splash dispersal of the fungal spores.

Your garden plants will be much more resistant to disease spread if they are growing in optimal conditions. Good soil fertility can be achieved by taking a soil test (call the Cooperative Extension office for help on this) and following recommendations for lime and fertilizer additions. Over-fertilization will increase disease incidence. Adequate watering is also critical. Too much water can be worse than too little so don’t overdo it and utilize raised beds for adequate drainage. Finally, choose resistant varieties if you are suffering from certain soil borne diseases. Many heirloom varieties provide delicious fruit but do not have the disease resistance enjoyed by newer varieties.

Finally, one of the best disease management considerations involves taking away favorable environments. For many of the fungal diseases that cut summer harvests short that means reducing the time of leaf wetness. When your tomato plants get wet from a rain or overhead watering fungal spores on the leaf surface germinate and begin growing into the leaf. If that leaf wetness lasts for several hours fungal organisms can become established inside the leaf. Water your plants at the base and minimize leaf wetness. Tie up tomatoes, cucumbers, pole beans and other vine veggies to maximize ventilation around the leaves. Planting in full sun will also reduce leaf wetness. Keep up on proper pruning so that air can make it into the plant’s canopy. Don’t overplant the garden. Overly dense plantings have higher leaf humidity and greater fungal disease pressures.

Garden diseases can be managed if you follow these considerations. Contact the Cooperative Extension service (828-465-8240) if you would like more information on success in the garden. Come out to our Advanced Gardener library presentations, try a gardening workshop, speak with a Master Gardener, or just stop by our office in Newton.