Frost Damage And Herbicide Plans — To Spray or Not to Spray?

Late frosts developed through parts of the country raise this question regarding post-emerge herbicide applications:

What effect does frost have on herbicide performance?

The short answer: it depends.

Herbicides perform best on actively growing weeds, so weeds damaged by frost will have decreased sensitivity. [content_block id=2498 slug=inline-banner-left-side

If you are targeting small summer annuals (2 or less true leaves), I suspect effective control can still be achieved. If summer annuals are bigger and showing clear signs of frost damage, it probably would be best to delay applications until new growth is present.

Foliage of winter annuals and many perennials generally is hardier than that of summer annuals, thus these weeds are less likely to be damaged by frost.

If shoots of these plants appear to have escaped significant frost damage, there probably is no need to hold off on herbicide applications. Research has shown improved control of certain perennials when herbicides were applied after frost, but that research was conducted in the fall.

Make sure sufficient spring growth is present on perennials to allow transport of the herbicide to vegetative reproductive structures.

In situations with an established crop, closely consider whether the crop was damaged by frost. Any stress from frost will reduce the ability of the crop to tolerate the herbicide and could result in herbicide injury.

If weeds are still small and not threatening the crop, delaying applications for 5 to 7 days will reduce the risk of crop injury.

Source URL: https://crops.extension.iastate.edu/blog/bob-hartzler/spray-or-not-spray