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Crop Advisor’s Casebook: tank mix-up

Last June, while driving past his silage barley field, John noticed distinct strips forming in his crop. When he stopped to investigate further, he saw the barley plants inside the strips were healthier looking and taller by a foot than those in the surrounding areas, which were paler in colour and tinged with yellow. He thought the herbicide I recommended had caused an injury to his crop.

“The herbicide you recommended has severely damaged my silage barley,” he told me over the phone that same day. I had recommended a Group 1 herbicide to take care of his wild oats and grassy weeds, and an appropriate tank-mix partner for broadleaf weed control. His sprayer operator had applied the herbicide tank-mix three weeks earlier.

I traveled to John’s farm in Cardston, Alta., that afternoon to see the strips for myself. There were six in total; the plants inside the strips were a height of 24 to 26 inches, while the surrounding plants were 12 to 14 inches tall. The weeds inside the strips were taller too, especially the grassy ones. John told me all of the barley plants had been the same height before the herbicide application.

By measuring the distance between the recent tracks in the field and using the sprayer width, we confirmed the strips in John’s field were areas the sprayer had missed.

The rest of the field appeared to have suffered an herbicide injury, but I did not believe the Group 1 herbicide and tank-mix partner for broadleaf control I recommended could have caused the damage because they were completely safe for use on barley.

Upon further inspection of the sprayed areas of the field, I found the level of control on the targeted weed species was less than expected. In particular, the annual grass weed Persian darnel as well as some broadleaf weed species had escaped control. Meanwhile, it appeared other grassy weeds that I did not expect, such as downy brome, were being controlled.

Further examination and comparison of sprayer records, acres treated, product purchased, and planned use of product per acre confirmed what had caused the damage to the crop. The sprayer operator had not added the correct tank-mix partner to the Group 1 herbicide. The sprayer operator added a Group 2 herbicide that targets wild oats and some broadleaf weeds, but was not a registered tank-mix partner with the Group 1 herbicide, and acted antagonistically to the Group 1, diminishing its efficacy and reducing its control on the Persian darnel.

The Group 2 herbicide was also not registered or recommended for use on barley, and had injured the crop after its application. This was also the reason why the downy brome was controlled — it was a targeted weed species of the Group 2 herbicide.

John thought the sprayer operator may not have read or understood the instructions for herbicide application on this field. Unfortunately, the operator also had not understood the agronomic implications of spraying that particular Group 2 herbicide on barley or the effects of mixing it with the Group 1.

To avoid such a mix-up in the future, I recommended stronger training for John’s sprayer operators in order to increase their knowledge of products and tank-mix partners. I also suggested that he make resource information readily available by listing contact numbers at mixing sites and placing more crop protection guides in key locations. Additional organization when storing products, whereby products intended for each field are stored together and not on a mixed pallet, would also decrease tank-mix errors.

John’s strong fertility plan, as well as the half-inch of rain that fell on the crop the day after the herbicide application, enabled the barley plants to grow and still produce sizeable heads. At harvest, John had a substantial grain yield, despite the injury early on. †

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