Sunday, August 30, 2009

Johnson Grass

This tall grass is Johnson Grass, Sorghum halepense, which is legally defined as a noxious weed in Ohio. It is primarily a problem in crop fields where management techniques reduce competition from other plants. New colonies of Johnson Grass usually occur along the road from seed dropped by vehicles, especially farm equipment, contaminated by seed picked up at another location. Established prairies can often hold their own against Johnson Grass, but it’s best not to let a potential problem get started.

These open panicles are easy to spot atop the tall Johnson Grass plant. Many people think of my prairies as giant weed patches, so I aggressively try to eliminate plants like this that many people can positively identify as a weed. Normally I spray these plants early in the season before they can produce a flower head, but the threat of rain seemed to appear every time I could schedule time for this task.

Once these plants are tall enough to flower, spraying becomes an unsatisfactory method of control. Trying to spray such a tall plant results in a large kill radius and the loss of too many desirable plants in the surrounding area. My fall back strategy is to pull the plants. Pulling is not as effective as spraying because of the plant’s habit of spreading by way of rhizomes. Rhizomes left in the soil after the plant is pulled will survive and produce new plants. Fortunately I have been dealing with these plants for many years and am not working with established colonies. The young plants that I am pulling have not had a chance to produce many rhizomes and older plants are severely stressed when pulled.

These plants have been pulled before seed could begin to develop. Pulling plants that have already produced their crop of seeds results in those seeds being scattered even more than would have occurred if they had been left alone.

Not taking any chances that either early developing seed or hearty rhizomes are left in the field, I’ve carried the pulled plants and piled them in my garden. The organic material will help the soil and no seeds or plants will have a chance of surviving here. New Johnson Grass infestations will continue to occur along the road, so my involvement with this plant will never end.

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