Water quality and herbicides

With the really dry conditions last year and earlier this year, the concentration of minerals in water used for spraying herbicides may have increased. If you are going to apply herbicides containing glyphosate, glyphosate/dicamba, diquat, bromoxynil, 2-4-D amine, sethoxydim, clethodim and tralkoxydim the quality of the water used can affect the outcome of the application. The water quality factors that are the main concern are cleanliness and mineral ion content.

Cleanliness refers to freedom from suspended silt and organic matter, both of which can reduce the activity of herbicides that contain bromoxynil, glyphosate/dicamba, paraquat and diquat. Only clear and clean water should be used for mixing these products. The same kind of inactivation can occur when these products are applied to plant surfaces that are covered with a layer of dust. Dust kicked up during the spray operation may also result in reduced control, especially directly behind the sprayer.

Many chemical elements can be dissolved in water but six major ions make up the dissolved material in most water. The dissolved chemical elements are present as ions which carry a positive or negative charge. Calcium, magnesium and sodium are positively charged (cations).

Sulphate, chloride and bicarbonate are negatively charged

(anions).

Water containing calcium and magnesium can reduce the effectiveness of glyphosate and 2,4-D amine. Calcium and magnesium levels are reported as calcium carbonate

(CACO3) equivalent in parts per million

(ppm) or grains per

US gallon. The value is called the hardness of the water.

For low rates of glyphosate, the maximum hardness in a water source should be 350 ppm

(20 grains/us gallon). For higher glyphosate rates, the maximum water hardness should be

700 ppm (40 grains/