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Friday, July 29, 2016

Removing Nutgrass by Excavating Soil May Not Work

Q. We have a large garden in an area that used to be underwater. The soil is dark, has very small particles, and it clumps like clay. It also has nutgrass. We have tried several way to get rid of the nutgrass and so far, none have been successful. The soil needs amendment and we are wondering if digging up the weedy surface and disposing of it and replacing it with compost and topsoil would fix the problems, or if there is a better solution.
Nutgrass with its "nut" attached to the roots.

Nutgrass with its triangular stems because it is a sedge, not a grass.

A. Underwater? You are opening up a whole new area of horticulture that should be called scuba gardening. Yes, nutgrass is an important weed in rice paddies. Very difficult to control. I'm sure you have done your homework. They produce a nut like swollen stem that will generate new plants if it is separated from the mother plant. 

So when you pull, hoe, burn or apply pesticides the tops die but the nuts regenerate new plants. Weed killers like Roundup and dandelion killer kill the tops but not the nuts. You do all these things and nutgrass comes back with two or three times the population. 

Solid research has shown that you can exhaust these knots and nutgrass if you are diligent. The technique is to continually remove the tops at the time when they have exhausted most of the nut but not yet have rebuilt it. 

Timing of the removal of the top is critical. The most effective stage to do this is when the top of the plant has produced four leaves. If you wait longer than this, the plant begins rebuilding new nuts. If you remove them sooner than this than the nuts have not been fully exhausted. You will start to see a decrease in the population the first year you attempt this. Every year the population of plants will get smaller and smaller. 

Use anything that either burns or removes the tops. Your other option is to remove the soil to a depth that captures all of the nuts. This would be a minimum of 12 inches followed by removal of the tops of any of the nuts that remain to exhaust the mother plants.

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