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Editor’s Note: This installment of the biweekly column by Cache County Agent Jake Hadfield was co-written by Extension horticulture assistant Emma Feuz

Fall can be a great time to use herbicides and kill some weeds. In fact it is more effective to spray some of our local noxious weeds in the fall before the first frost than it is to spray them in early spring. Here are some great reminders about herbicide damage, how to avoid it, and how to use herbicides safely:

Chemical usage on a landscape can be a tricky but useful endeavor. Herbicides can do great things for weed prevention; however, they can cause major plant damage if applied incorrectly. Fortunately, Utah State University Extension offers guidance on how to safely and effectively use herbicides.

There are many different chemical options to use. As a general rule, always read the product label before applying any chemical to a landscape. The label will have instructions on how much and how to apply the herbicide.

Plants can be exposed to chemicals in a few different ways. Using 2,4-D or Dicamba when the temperature is above 80F may result in the liquid volitizing and spreading through the air. This can cause plant problems in much of the surrounding area in addition to the application site.

Some herbicides remain active in the soil. These products can leech into other root systems as water carries the herbicides through the soil beyond just the application zone. Run-off treated soil can also be a problem. Often, both of these problems can occur in the same area.

Plant injury can happen if the chemical is misapplied, if either the concentration or the timing is wrong. Herbicide contaminated material, such as compost or fertilizer, left around susceptible plants can also cause damage.

Different chemicals cause different plant damage. Dicamba and 2,4-D affected plants exhibit abnormal growth with yellowing or browning leaves. Dicamba is especially dangerous around trees. Glyphosate simply causes plants to yellow or brown and eventually die. All soil sterilants are slow acting but can kill plants for years to come.

Corrective measures must be taken immediately if chemicals are used on an undesired area. Start by washing the area completely and putting down a layer of activated charcoal at a depth of six inches. Besides these options, have patience. Some plants might show symptoms of herbicide for a season but will recover in time.

Please stop by the Utah State Extension office or call at (435) 752-6263 if you have any questions regarding herbicide use.

Reference: Herbicide Injury. Integrated Pest Management. Utah State University Extension.

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