Garden Talk: Plant Diseases And Mid-Summer Gardening

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• Experts: Heavy Rains Mean Plant Diseases Will Flourish

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  Even when people take good care of their plants, nature doesn’t always cooperate. June was a particularly rainy month and that means conditions are ripe for plant diseases to develop and thrive.

  Brian Hudelson, the director of the University of Wisconsin-Madison Plant Disease Diagnostic Clinic, said that he is seeing a lot of fungal leaf spots.

  “A lot of the rain came at a time when the trees were beginning to leaf out,” he said. “That’s a critical time for a lot of fungal infections to occur.”

  Root rot is also an issue when heavy rains make the ground saturated.

  “The way that root rots function is that they destroy root tissue,” said Hudelson. “So, the plant can’t take up water, and that leads to wilting above ground.”

  In addition to wilting, another symptom of root rot can be discoloration, which means that root rot can easily be mistaken for a fertility problem. When dieback sets in, that indicates that the problem is not with fertility, but with rot.

  When those symptoms are present, Hudelson said to check the roots: If there is rot present, there will be browning and discoloration of the roots.

  Ironically, the first reaction of gardeners when they see the wilting and discoloration is to water more, Lis Friemoth said. Previously a horticulturalist for Walworth County, Friemoth is now the owner of The Garden Hoe concierge horticulture services.

  More water, said Friemoth, isn’t what the plant needs. Instead, it only encourages the rot.

  “The root rot pathogens are doing a little happy dance in the soil because they really tend to do much, much better when we have wet soil condition,” said Friemoth.

  Good drainage is key to avoiding and reducing root rot. Making sure that water can pass through potted plants or container gardens is important, and in landscaping, adding organic matter is always a good idea. Hudelson said this will encourage “better flow of the moisture through the soil.”

  Treatment for root rot is possible, but usually not by a homeowner. Friemoth said that identification of the specific pathogen is key and that means extensive testing and diagnostic work. In addition, Hudelson said that for home gardeners, most herbaceous plants aren’t worth treating. He said that by the time it is detected, the disease is beyond treatment or would be costly to cure.

  Woody ornamentals usually represent more of an investment, both financially and emotionally. For those, Hudelson said, “If you catch the disease early, you can have a professional come in and make fungicide treatments.”

  He emphasized though that in this case as well, correct identification of the pathogen is critical for successful treatment.

  “The chemical controls are very specific in their range,” he said, “and if you don’t get a proper diagnosis, you can spend a lot of money … and you don’t get control.”

  Preventing these diseases can help a gardener avoid dealing with them in the first place. Hudelson said that good garden clean-up in the fall is one great preventative measure

  “A lot of the disease-causing organisms are going to survive in that old plant debris that’s left over,” he said. “If you don’t remove that from your yard, those organisms are going to … produce spores that are going to reinfect your plants next year.”

  Proper spacing between plants can also help to limit the spread of disease. Disease-causing organisms generally like moisture, and closely spaced plants retain dampness more than plants that have more air circulation around them.

  Finally, carefully and thoroughly disinfecting tools and clothing is important, too. Cleaning between plantings and before using tools on multiple plants is critical. Friemoth said that she has many large bottles of rubbing alcohol in her car, shed, and other locations in the garden. She said she either wipes blades of tools with it, or she dilutes it in a bucket as a wash.

  “It gets dumped on everything,” she said.

  Taking all possible precautions to prevent diseases makes sense with unpredictable weather, but gardeners will inevitably have to roll with the punches.

  “Mother Nature is still going to slap us upside the head and say, ‘Guess, what? We’re not going to stop raining even though you did everything right,’” said Friemoth.