May 30, 2015

1 - Sprouts from roots of a dead cottonwood tree will stop growing once the food reserves in the roots are depleted.

Yard and Garden May 30, 2015

Q.

We had a 30-40 year old cottonwood tree on our property. Several years ago it became diseased and unfortunately we were not able to correct the issues and she died. About 6 months ago we had it removed and stump ground. About 2 months ago our yard started to spout growth from the root system of the tree that has spread nearly 50 yards from the site of the cottonwood. The more we mow or even rip them out from the root, the faster the growth grows.

My question is pretty simple but I do not know if the answer is. How do we remove or kill the roots? We have a sprinkler system so I ca not rotor till the entire yard. Is there something that I can apply or spray? I have not watered the grass at all and still they grow.

-Jason R.

A.

The cottonwood tree sprouts from the roots grow in response to the removal of the large tree. That is their survival mechanism for dealing with their flood plain habitat. As an old tree washes away, the roots left behind sprout to fill the void left by the old tree. These sprouts draw nourishment from the roots of the old tree until they develop their own root system. This is what you are noticing as the compensatory regrowth and the reason you want to kill the roots.

A systemic herbicide applied to the sprouts that will translocate into the root system can be used to speed the death of the roots, but that will take time. Such chemicals do not kill the whole root system. Cutting the sprouts at or below ground level each time they sprout (within a couple of weeks of their appearance) will also work, though it may take a little longer. The principle behind each of these methods is to allow the sprout to grow, extracting stored food from the root, and then to remove the sprout and the food it extracted to ultimately deplete the food stores in the root. The length of time to accomplish this depends on the size of the root and the stored food reserves. In time, with cutting of the sprouts, decomposing fungi will enter the old roots if these fungi are not already there. The food reserves in the roots will be depleted even faster as the fungi consume the dying roots. Anything you do to encourage the fungal growth - providing moisture and nitrogen fertilizer for the lawn will enhance the depletion of the root food reserves. If you allow a sprout from the roots to remain too long before removing it, the sprout will begin storing food in the roots underground. This will allow the roots to support development of sprouts for a longer period of time.

Persistence is the best "herbicide" whether you use chemical controls or physical removal of the sprouts. Frequent removal of the sprouts during the growing season will ultimately (within one to two years) result in success.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

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