Post Frost Weed Control

So, it frosted.  In some areas, it was a hard frost with temperatures down in the 26 degree F range, and in others, plus/minus 30 degrees.  At this point in October, the question is: Is it a good idea to apply a post emergence herbicide to the lawn, considering the recent frost?  The answer?  It depends.


First, what’s the target?  If it’s spotted or prostrate spurge, puncturevine, vervain, purslane, prostrate knotweed, green foxtail, crabgrass, goosegrass, sandbur, mallow, black medic, common chickweed, shepherd’s purse or barnyardgrass, then it has either died on its own once the heat of summer took effect (winter annuals), or in the case of summer annuals, died with the frost.  These weeds do not need to be controlled.


crab seedhead

Large crabgrass

However, if the target is a perennial broadleaf weed such as plantain, dandelion, ground ivy or field bindweed, then it may be wise to make an application.  The key factor here is the degree of influence that the frost had.  If the leaves are soft and water-soaked in appearance, it’s unlikely that the herbicide application would have the desired effect, whereas if the leaves are green, stout and healthy appearing, then weed control is probable.


As with all applications, it’s wise to read and follow all label directions, especially ones related to wind speed, amount of product and water to use and protective clothing to wear.

John Fech
Horticulture Extension Educator at Nebraska Extension
John Fech is a horticulturist with the University of Nebraska-Lincoln and certified arborist with the International Society of Arboriculture. The author of 2 books and over 200 popular and trade journal articles, he focuses his time on teaching effective landscape maintenance techniques, water conservation, diagnosing turf and ornamental problems and encouraging effective bilingual communication in the green industry. He works extensively with the media to extend the message of landscape sustainability, making over 100 television and radio appearances each year.
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