Extension and Ag Research News


Dakota Gardener: The biggest threat to our gardens

Herbicide misuse can cause problems for lawns, gardens and trees.

By Tom Kalb, Horticulturist
NDSU Extension

What’s the biggest threat to gardens today in the Dakotas?

It is herbicide misuse. Nothing else comes close.  

Gardeners send me over 1,000 photos of sick plants every summer. The most common photos are of tomato and potato vines that are mysteriously twisted and curled. In many cases, nearby tree leaves are stretched and cupped.

These symptoms are caused by herbicide injury. Today’s herbicides are much more powerful and persistent than ever.

Lawn clippings may be toxic to garden plants. In the past, we could use lawn clippings as mulch in our gardens three mowings after the last herbicide application. This may no longer be the case. Read the label of your dandelion killer. In many cases, it will recommend not using lawn clippings as mulch in your garden – ever. That’s because today’s herbicides are more persistent in the environment.

Compost may be toxic to garden plants. Twelve years ago, I went to my city landfill and received truckloads of compost that were free of herbicides. This is no longer the case. People are dropping off lawn clippings treated with long-lasting and sometimes restricted-use herbicides that can persist for several years after composting. It is risky to use the compost from a city landfill in a garden today.

Manure may be toxic to garden plants. If a cow eats herbicide-treated hay, the herbicide does not decompose while the hay is digested inside the cow. The manure from this cow contains herbicide and may be toxic to garden plants for years.

Herbicide drift may be toxic to garden plants. Herbicides used on fields can drift to our landscapes and cause damage. I see trees with cupped leaves every day.

The misuse of herbicides by gardeners is another concern. Sometimes homeowners spray at rates higher than what is recommended on the label. The mentality that more herbicide works better than recommended rates is false. Excessive herbicide rates will kill weeds, but they will also damage our lawns, gardens and trees.

Some homeowners have access to restricted-use herbicides designed for use in crop and hay production. These agricultural herbicides will kill weeds in home lawns, but they may also damage the lawn and surrounding plants and trees.

What can be done?

More than ever, it is critical that we read and follow the directions on the label. I implore you: Just do it! Follow the recommended rates. Use only herbicides that are registered for use on your lawn and garden.

Be careful where you get your manure or compost. Contact me for simple tests available to see if your manure or compost is safe to use.

Spray judiciously. The most effective time to kill lawn weeds is in mid-September. Most lawns are healthy and attractive with a single application of herbicide per year.

Whenever you spray, and it should not be often, reduce the risk of spray drift. The wind should be less than 5 mph. Avoid foggy and perfectly calm times where pesticide spray can persist in the air. Use a heavy droplet, not a fine mist while spraying. Avoid temperatures in the upper 80s or warmer. Spray only when necessary.

A dandelion is not a symbol of failure. To the contrary, it is not natural or healthy to have a weed-free lawn.

For more information about gardening, contact your local NDSU Extension agent. Find the Extension office for your county at www.ndsu.edu/agriculture/extension/county-extension-offices.

NDSU Agriculture Communication – July 3, 2024

Source: Tom Kalb, 701-877-2585, tom.kalb@ndsu.edu

Editor: Elizabeth Cronin, 701-231-7006, elizabeth.cronin@ndsu.edu

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