Language

Google Translate Disclaimer

A number of pages on the Government of Saskatchewan's website have been professionally translated in French. These translations are identified by a yellow box in the right or left rail that resembles the link below. The home page for French-language content on this site can be found at:

Renseignements en Français

Where an official translation is not available, Google™ Translate can be used. Google™ Translate is a free online language translation service that can translate text and web pages into different languages. Translations are made available to increase access to Government of Saskatchewan content for populations whose first language is not English.

Software-based translations do not approach the fluency of a native speaker or possess the skill of a professional translator. The translation should not be considered exact, and may include incorrect or offensive language. The Government of Saskatchewan does not warrant the accuracy, reliability or timeliness of any information translated by this system. Some files or items cannot be translated, including graphs, photos and other file formats such as portable document formats (PDFs).

Any person or entities that rely on information obtained from the system does so at his or her own risk. Government of Saskatchewan is not responsible for any damage or issues that may possibly result from using translated website content. If you have any questions about Google™ Translate, please visit: Google™ Translate FAQs.

Is it Ever Too Dry to Spray?

By Sherri Roberts, PAg, Crops Extension Specialist, Weyburn

July 2022

Optimum uptake and movement of glyphosate into foxtail barley roots occur at temperatures above 10 C.
Optimum uptake and movement of glyphosate into foxtail barley roots occur at temperatures above 10 C.

With the late start to the season in the southeast part of the province, spraying for weeds will be the norm as we come into July. Is it ever too hot to spray crop protection aides? The answer to that question depends on the product and what weed you are targeting. While the ideal air temperature for applying most post-emergence herbicides is between 15 C and 26 C, there are several factors that need to be considered.

In order to work well, herbicides need to be taken up by the plant. Knowing the optimum temperature ranges for both the target weeds and the herbicides being used is paramount for successful weed control.

Common Lamb’s-quarters respond to high temperatures by developing a thick wax layer on the leaf surface to decrease their water transpiration losses.
Common Lamb’s-quarters respond to high temperatures by developing a thick wax layer on the leaf surface to decrease their water transpiration losses.

Weeds will respond to high temperatures by producing a thicker wax layer or increased density of hairs on the leaf surface. This natural defense mechanism creates a barrier to effective herbicide absorption. Heat stress will also result in smaller, more erect leaves and shorter stems, which reduces the total surface area for herbicide coverage. Grassy weeds will also roll their leaves and broadleaf weeds will droop.

High temperatures increase the loss of volatile herbicides. 2,4-D ester or dicamba will rapidly volatilize (gas off) at temperatures above 27 C, increasing the risk of drift damage to nearby sensitive crops. Evening cooling after a very hot, calm day can result in the accumulation of volatile herbicides under inversion layers that may flow across landscapes and impact sensitive neighbouring crops over a large area, larger than drift from windy conditions.

Dicamba drift on potatoes.
Dicamba drift on potatoes.

Humidity should also be considered when spraying as it can impact herbicide performance in two ways. First, high humidity allows fine droplets to remain suspended for longer periods, giving them more opportunity to move off target and cause injury to neighbouring crops. Second, crops can be more susceptible to injury from herbicides when high relative humidity is combined with high temperatures, since this combination of conditions means plants invest less in cuticle layers on leaves and leave their stomata open, enhancing herbicide penetration into the leaf and translocation within the weed as well as within the crop.

The efficacy of glyphosate and diquat decreased significantly in the presence of dust on wild mustard (Asadi-Sabzi, 2020).
The efficacy of glyphosate and diquat decreased significantly
in the presence of dust on wild mustard (Asadi-Sabzi, 2020).

We need your feedback to improve saskatchewan.ca. Help us improve