Time to kill barley cover crops in onion

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

With the recent rains and cool weather, barley interplanted with onions has been growing rapidly. The barley is planted to protect the young onions from wind and water erosion. Barley should be sprayed with a graminicide (Fusilade, Poast, Select, or a generic) at a sufficient rate to kill it at the appropriate time. Normally that is when the barley reaches about five to six inches in height and the onions are in the 1-leaf stage.

This year, with very dry conditions in April, most of the onions and barley were planted earlier than normal. Barley did not grow very rapidly because of the lack of moisture. Now the barley is expanding rapidly. The objective in killing the barley is to avoid crop competition (and thus crop thinning) while still maintaining some erosion control. Onion plant death normally is a result of desiccation through loss of soil moisture to the barley. With recent rains, this is not as serious a threat as in some years, so growers have some flexibility concerning their graminicide application.

Onions are not affected by the active ingredients in the graminicides, but can be burned or killed by the combination of the herbicide plus crop oil concentrate (COC) or nonionic surfactant (NIS), especially if they are in the flag (cotyledon) stage or have been exposed to freezing temperatures for several hours. To avoid crop injury under these conditions, wait until the first true leaf is two to three inches high, and do not spray until onions resume growth after a hard frost. Then apply sufficient graminicide to kill the barley, which is often higher than the lowest rate. Check labels for guidance, or contact me for advice at .(JavaScript must be enabled to view this email address).

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