Home & Garden: Rain appreciated by plant pests (how to deal with mildew, snails & slugs)
Free Press Gardening Columnist
The wet weather we have been having has been great for our lawns and gardens, with most plants experiencing a growth spurt. This is especially true when rains are accompanied by lighting due to the plant-available nitrogen produced when a huge energy surge from lightning passes through the air. Plants require nitrogen to form chlorophyll making nitrogen essential for photosynthesis. Nitrogen also is necessary for the formation of plant and animal proteins, as well as DNA and RNA.
You and I get our nitrogen from the plant and animal tissue we consume, but plants get their nitrogen from the soil in either the nitrate or ammonium form. Even with the abundance of nitrogen in the air (78 percent), the chemical form cannot be used by plants. Atmospheric nitrogen (N2) is combined with oxygen to form a nitrate, and lightning provides the energy necessary to accomplish this process. Nitrates formed by lightning dissolve in the rain, ending up in the soil where it can be utilized by plants. The nitrate formation process is the reason our lawns typically grow faster and look healthier after a lighting storm.
The rains are also appreciated by some plant pests to include powdery mildew and snails and slugs. Powdery mildew requires high humidity and cool temperatures to infect our roses, marigolds, lilacs, and other plants.
Many plants are presently infected with powdery mildew due to our current weather conditions. As the weather gets hotter and dryer, few new infections of powdery mildew will occur; but the plants already infected will continue to be damaged by this fungus. There are a number of great products on the market that can help reduce damage. Propaconazole is a synthetic product, which provides great control. Neem oil, products containing potassium bicarbonate, and several other more natural products also work well in the control of this disease.
Slugs and snails are especially benefited by wet weather. The brown garden snail has really enjoyed our damp conditions as evidenced by the damage this invertebrate caused to the hosta (in the photograph I took the other day). The damage snails cause is unlike the type of damage caused by any other pest. Thus, it’s easy to identify even when you can’t find the snails responsible. If you enjoy escargot this is the snail to use.
I would suggest using an iron phosphate granule scattered around my most susceptible plants to rid the area of snails. Products containing iron phosphate are available at more garden centers. There are other products on the market more effective in controlling slugs and snails; but some, like metaldehyde, are deadly on dogs, horses, and other mammals. Consequently I would avoid using any product containing this active ingredient. When looking for a product to use for snails, slugs, powdery mildew or any other plant problem, be sure to read the list of active ingredients. Do an online search for the active ingredients and always select the least toxic product available.
Free Press columnist Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu, 970-778-7866 or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.
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