Ford Says: Command Injury

Ford Says: A phenomenon observed more than usual this year is very defined (and often severe) injury patterns in some fields from clomazone or Command. While it is not uncommon to see old levee patterns, planter patterns, wheel track patterns, tillage patterns, and some soil residual herbicide applications, some of these with clomazone this year seem much more pronounced than usual. The more I have walked in these, the more I have figured out what I don’t know. When you see one row in a drill pattern that is much better or worse than the others, something is obviously different about that unit. It could be depth or other settings. Then, about the time you think the pattern is consistent, it may change to a different row, set of rows, or randomly present in an area effect. The green row in the center of this photo was in every drill pattern. However, there was an outside unit resulting in a green row going one direction and a nearly dead row side by side on the return pass. How does one explain that? Also, there is no chance it was a spray pattern, as it was sprayed perpendicular to the drill rows. Passing it off as a seeding depth/compaction problem is easy. There is an obvious relationship. In the fields where I have dug up plants, the most severe injury seemed to be where seeds were shallower, although the depth differences were not huge.

In some cases where seed was very shallow, compaction also worsened. However, compaction problems do not typically line up with drill patterns all the way across a field. Does that mean shallow planting or compact soil results in more Clomazone injury? I’m not ready to go there yet. One obvious conclusion is that some final tillage passes (whether made previously or at planting) may not result in the best uniformity. Another is that the drill, or the way it is being operated, is resulting in a lack of uniformity across row units. I have seen several fields on the same farm with these patterns, often planted in a similar time frame. Therefore, environmental conditions are obviously playing a role. Some of these fields had 10 or more inches of rainfall in one event; generally, it has been cold and wet.

Lots of folks, including me, are pontificating profusely about these patterns. As a weed scientist, who at one time did lots of research with Command on rice, I cannot get my head around the severity difference in the injury from one drill row to the next. How can a quarter-inch difference in seeding depth mean the difference between zero injury in one row and dead rice in the row beside it? In addition, the fields I have looked at were sprayed with 8-to-10-ounce rates. How can one possibly kill rice at any seeding depth or compaction level with these rates? We did all our Command research back in the day with one- and two-pint rates in every seeding and application method we could think of, and it never killed rice. However, we are planting much earlier now, conditions tend to be colder and wetter, drills are different, tillage tools and methods are different, and varieties are different compared to when much of the research was conducted. Therefore, environmental conditions are a research opportunity here, and my university counterparts are aware of it and on it.

Any farmers or consultants who have seen this in their fields and have their observations and theories are welcome to share these.

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