The Proper Temperature to Apply Roundup Weed Killer

Temperature

• According to the Iowa State University Extension, the general rule for using any herbicide such as Roundup is to take into account the active growth period of the targeted weed and also the desired plants around which the weed is growing. The proper time for applying glyphosate-based herbicide such as Roundup is when temperatures are between 65 to 85 degrees F, suggests the Prairie Grains Magazine.

Effects of Sun

• Glyphosate efficacy also increases during high humidity, and chemical activity remains unaffected during periods of sunlight. The good time of day to apply Roundup is anywhere between 10:00 a.m. and 4:00 p.m. As opposed to certain other herbicides, glyphosate does not produce fumes or vapors when applied during periods of full sun.

Water Solubility

• The active ingredient in Roundup, glyphosate, is highly soluble in water. Don't spray wet plants or plants that are covered with dew as this will reduce efficacy of the chemical. Also avoid treating plants with Roundup when rain is expected within six hours of application. Disregard any label recommendations that cite rain-fast advantages, warns the Prairie Grains Magazine.

Use Suggestions

• Roundup is a systemic herbicide that moves through the plants as it takes effect. Avoid using the chemical on drought-stressed plants as the lack of water in the plant will slow down chemical translocation through the plant. Plants that have already been treated with another chemical are likely to be resistant to Roundup. Since the chemical is nonselective in nature, it will harm all plants that it contacts. Avoid spraying on very windy days to minimize drift to non-target areas.