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Glyphosate drift causing damage in Arkansas rice fields

Early planted rice results in the highest yields, but we sometimes struggle to get from early planting to this time of year. This year is no exception. Cool, wet temperatures caused slow rice growth and resulted in herbicide injury in Arkansas fields.

In addition, I have received almost no grass control calls this year. Command performance has been excellent to almost too good in some fields. Combinations of Command followed by other herbicides such as various propanil formulations and tank mixtures have at times singed the rice a bit. This damage is somewhat normal. I do think, however, there have been a few more dead plants from Command injury than I have seen in the past.

I received several calls about and have looked at numerous fields with Newpath injury to the Clearfield hybrid rice varieties XL8 and XP730 this year. This injury is much more severe than anything we have seen in previous years in the research plots which were sprayed under ideal conditions.

Injury has ranged from dead plants to stunted plants with yellow or chlorotic leaves.

In these fields is a higher-than-normal occurrence of dead plants next to injured plants next to relatively healthy plants. The hybrids have an amazing ability to tiller out, which may result in better-than-expected yields on some of these fields.

I have been recommending an application of ammonium sulfate and/or DAP and a flush on the injured fields. So far, this strategy seems to be working, but we do not have a lot of hard data on this program.

The call now dominating my cell phone is glyphosate drift. When you add this drift on top of the other situations discussed above, the damage in many fields seems more severe than it has been for the past couple of years.

Typical glyphosate drift symptoms to seedling rice include chlorotic (yellow to white) leaves, dead leaves, and delayed growth. Severity of injury depends on the amount of drift that has occurred.

Glyphosate drift in combination with other rice ailments, such as salt damage on levees, typically results in seedling rice plant death. My recommendation for nursing glyphosate-damaged rice back to health is the same as for Newpath injury.

Typically I worry about glyphosate drift on rice at two times during the year. One is already past for most rice — the one- to four-leaf stage. Little rice is particularly sensitive to damage from glyphosate (see picture).

Rice does not have a stage where it is safe from drift glyphosate, but little damage is typically reported once rice begins tillering and prior to panicle initiation or “green ring.” Damage during this time is typically limited to a few yellow or chlorotic leaves. This is also the recommended time to apply 2,4-D to rice.

The other stage and the one that can be the most economically damaging to rice production is from just after panicle initiation to just prior to heading. This damage often goes undetected until the rice seed heads emerge or fail to completely emerge. Again, the severity of this damage depends on timing and rate of drift.

Often, the rice panicle will get stuck trying to emerge from the sheath and not emerge at all, or if the head does emerge, it will be malformed. These malformations can range from blank seed heads with no grain at all to seed that has a characteristic hook or “beaked” appearance.

In addition, shortened flag leaves are typically observed from drift at this timing. This damage usually results in a very significant impact on rice yields.

As we move into mid-post glyphosate treatment timings on Roundup Ready soybeans and cotton, please take care if you are anywhere near a rice field. Our research has shown that damage can result from rates as low as 0.1 quart of 4 pounds-per-gallon glyphosate or 2.2 ounces per acre of Roundup WeatherMax. In other words, it does not take much to injure rice. So, be careful out there!

Bob Scott is an associate professor and Extension weed specialist with the University of Arkansas.

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