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The Best Time to Use Roundup Weed Killer

By Keith Allen

Roundup is a Monsanto product containing glyphosate. Glyphosate is a broad-spectrum contact herbicide used to kill all plants with which it comes in contact. Various manufacturers make products utilizing glyphosate sometimes in conjunction with other herbicides and inert ingredients. Glyphosate-based herbicides are available in farm supply, garden and home improvement outlets. Always follow manufacturer’s instruction when using a herbicide.

Seasonal Use

Glyphosate-based herbicides work best when the plants it is applied to are actively growing. This occurs in the spring of the year when the plant breaks dormancy and in the fall as the plant stores energy for the winter. However, glyphosate is effective against plants anytime during the growing season, and it is often easier to find proper application conditions during the summer rather than spring or fall.

Temperature Ranges

Apply glyphosate herbicides such as Roundup when air temperatures range between 60 and 85 degrees. Spring and fall seasons are often too cool for effective application.

Atmospheric Conditions

Avoid windy conditions and times when rain is expected when applying Roundup. These conditions don’t affect the effectiveness of the herbicide but prevent the inadvertent transfer of the chemicals to non-intended plants surrounding the target plant. Because glyphosate kills all plants it comes in contact with, chemicals blown in the wind or washed off the leaves by rain can spread to other plants.

Chemical Information

Choose herbicides containing at least 41 percent glyphosate. A variety of manufacturers produce herbicides with at least this level including the most commonly known Monsanto product, Roundup. Some of the herbicides are formulated for specialty uses such as around ponds or aquatic vegetation.


About the Author


Keith Allen, a 1979 graduate of Valley City State College, has worked at a variety of jobs including computer operator, medical clinic manager, radio talk show host and potato sorter. For over five years he has worked as a newspaper reporter and historic researcher. His works have appeared in regional newspapers in North Dakota and in "North Dakota Horizons" and "Cowboys and Indians" magazines.