Out in the cold: Frost and post-emergent herbicide application
Temperatures are continuing to drop across the state and frost events are imminent.
Elders agronomist Logan Smith, who services the eastern wheatbelt of Western Australia, explains the risks and considerations for post-emergent herbicide applications.
During frost events or periods of extreme cold, moisture in the cells of the leaves, stems and shoots can freeze, causing tissue death. This means plants can’t carry out their basic functions and are not considered to be ‘actively growing’. It’s only when they thaw out that they are once again growing and are stress free.
Herbicide sprayed during these conditions is not likely to be taken up by the target weeds, significantly reducing the chemical’s efficacy. As stipulated on many herbicide labels, applications should only be made to ‘actively growing’ plants to ensure efficacy.
The severity and length of the frost will also have an impact on application timing. The general rule of thumb is to wait 24 hours before frost, 24 hours after a frost and 48 hours following two consecutive events. If an application is made during these conditions, then results are expected to vary.
Particular care should be taken when spraying populations that are considered or known to be susceptible to certain groups of herbicides. Such an example is Clethodim, which is a grass-selective herbicide belonging to the group A’s (inhibitors of acetyl co-enzyme A carboxylase) used for controlling and suppressing annual ryegrass. It’s advised when using this product to only apply to small ryegrass plants that are planted in good growing conditions.
Incorrect use of herbicides can increase the level of resistance which can influence future management and business decisions.
Elders offers a range of crop protection products.
For more information about protecting your crop from frost contact your local Elders agronomist.