Farmers who aren't getting adequate kochia clontrol with 2,4-D may be overlooking a variable that has a strong bearing on the chemical's effectiveness. The sodium bicarbonate content in the water used could be a major factor.

John D. Nalewaja, professor with the crop and weed science department at NDSU, presented a paper on "Sodium Bicarbonate Antagonism of 2, 4-D"

Nalewaja says water used for herbicide application in North Dakota commonly contains 300 to 2000 parts per million of sodium bicarbonate, in addition to other salts. Sodium bicarbonate is sold in grocery stores and is more commonly known as baking soda.

"North Dakota is unique in that it has a higher amount of sodium bicarbonate in its water than other states," says Nalewja. "We often thought of 2.4-D, as a chemical that just didn't control kochia very well. But now we've learned that the control problem may result from the water being used."

Results of NDSU research, according to Nalewaja, indicated that sodium bicarbonate interfered with optimum control of kochia and other weeds by 2,4-D. The application dose of 2,4-D will help offset the effect sodium bicarbonate has on weed control. Using low spray volume also helped lto counter the effect of sodium bicarbonates.

Nalewaja says other minerals in the water or added to 2,4-D would either increase or decrease the effeetivenss of weed control. Calcium sulfate generally enhances 2,4-D control of kochia, while magnesium sulfate, sodium sulphate, and sodium chloride help decrease the effectiveness of 2,4-Don kochia.

Certain adjuvants, such as methylated sunflower oil (Sun-it) alone or in combination with 28 percent liquid nitrogen fertilizer helped overcome sodium bicarbonate effects. "Adjuvants would help but expense of application per acre would also be high," says Nalewaja. He adds that petroleum adjuvants weren't as effective as the sunflower oil adjuvant in overcoming sodium bicarbonate problems.

'Kochia is a hard weed to kill with 2,4-D in the first place, unlike mustard, which 2,4-D generally has succes in controlling." Nalewaja adds that using water with high amounts of sodium bicarbonate is just going to add to the difficulty of controlling kochia.

Nalewaja says farmers should test their water if sodium bicarbonate is suspected to interfere with adequate kochia control. "If sodium bicarbonate is a factor, farmers can increase the rate of application or switch to 2,4-D ester, which is oil soluble and provides better kochia control than 2,4-D amines, which are water soluble."

Since sodium bicarbonate is more likely to be found in ground water supplies rather than surface water, Nalewaja adds switching to another water source may be another option that could be considered.