SA Graan September 2015

done by the ARC-Small Grain Institute. Much of the research done

is focussed on glyphosate, however, all herbicides are tested with

adjuvants to determine optimal efficacy. Many producers use poor

quality water for their spray mixtures.

Poor water quality is due to the presence of salts in the carrier water

and can be classified as hard water (simulated with CaCl

water) or

brackish water (NaHCO

water). Salts in the carrier water may de-

crease herbicide efficacy of certain herbicides (such as glyphosate),

as a result of poor absorption into the leaves.

A study was performed with three different water types (distilled,

hard and brackish water) and the influence it had on glyphosate ef-

ficacy (

Graph 1

). It was found that hard and brackish water antago-

nised glyphosate efficacy.

Only brackish water antagonised the efficacy significantly. The addi-

tion of ammonium sulphate (AMS) increased the percentage control

recorded in all three water types. The addition of AMS to the carrier

water in brackish water increased the percentage control signifi-

cantly from 52,68% to 94,19%.

The effect of iron in carrier water was also determined in studies

(

Graph 2

). The results clearly indicated that glyphosate efficacy de-

creased with an increase in the amount of iron in the carrier water.

The decrease in efficacy, however, was not significant. Some adju-

vants were tested to determine their ability to overcome antagonism

caused by iron. None of the adjuvants tested were successful and

more research is being done to address this problem.

Results from these studies clearly indicate that different salts in the

carrier water have an effect on the efficacy of glyphosate. This is also

true for most water soluble herbicides. However, there are excep-

tions of non-water soluble herbicides that are sensitive to salts in the

water. It is therefore recommended to always use clean water, as far

as possible.

Conclusion

Always read the label and know what you are getting. Remember

that not all AMS adjuvants are of the same quality. Make sure that

the product you have chosen has enough ammonium ions in it to

successfully transport the herbicide and overcome the salts in the

carrier water. Make use of high quality adjuvants and use them cor-

rectly to enhance herbicide activity. An increase in herbicide efficacy

will result in a positive return on the additional investment made.

For further information, contact Hestia Nienaber at 058 307 3420 or

deweth@arc.agric.za

Reference

De Villiers, B.L. 1998.

Adjuvant, acidification and

water quality influences on herbicides

. ARC-Small

Grain Institute.

Graph 1: Determining the influence of water type and AMS on a glyphosate formulation.

Graph 2: Determining the effect of iron on glyphosate efficacy.

September 2015