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Thread: Hemp as Weed Control

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    Hemp as Weed Control

    D. P. West, Ph.D.
    Weed control is a recalcitrant issue in crops grown for organic certification. One approach is the prior use of a competitive crop. In his textbook, Modern Weed Control, A. S. Crafts cites as potential weed smothering crops: millet, Sudan grass, sweet clover, sunflower, rape, barley, rye, reed canary grass, crested wheatgrass, sorghums, buckwheat, soybeans, alfalfa, cowpeas, clovers, hemp, Jerusalem artichoke, and ensilage corn. Of these only one, hemp, can be taken seriously as an adequate weed controlling mechanism. The historical testimonials to hemp's ability to control weeds are numerous. For example:

    " is certain that hemp contributes more than any other crop
    towards repairing the damage done by its own growth through the
    return of the leaves to the soil, besides other matters while it is
    undergoing the process of retting. Hemp is an admirable weed
    killer and in flax countries is sometimes employed as a crop in
    rotation, to precede flax because it puts the soil in so good
    -Charles Dodge, Director, Office of Fiber Investigation, 1890.

    "There will be little trouble with weeds if the first crop is
    well destroyed by the spring plowing, for hemp generally occupies
    all the ground giving weeds but little chance to intrude....In proof of
    this, a North River farmer a few years ago made the statement that
    thistles heretofore had mastered him in a certain field, but after
    sowing it with hemp not a thistle survived, and while ridding his
    land of this pest the hemp yielded him nearly $60 per acre where
    previously nothing valuable could be produced."
    -C. Dodge, Hemp Culture, USDA Yearbook of Agriculture, 1895

    "Hemp prevents the growth of weeds and other vegetation
    which would be found on such soils in most other crops or after
    others are laid by, and its cultivation also seems to make the soil
    more uniform in character."
    -Lyster Dewey, The Hemp Industry in the United States, USDA
    Yearbook of Agriculture, 1901

    "Very few of the common weeds troublesome on the farm
    can survive the dense shade of a good crop of hemp...In one 4-
    acre field in Vernon County, Wis., where Canada thistles were very
    thick, fully 95 per cent of the thistles were killed...." Lyster Dewey,
    Hemp. USDA Yearbook of Agriculture, 1913.

    "Hemp has been demonstrated to be the best smother crop
    for assisting in the eradication of quack grass and Canada
    thistles....At Waupon in 1911 the hemp was grown on land badly
    infested with quack grass, and in spite of an unfavorable season a
    yield of 2,100 pounds of fiber to the acre was obtained and the quack
    grass was practically destroyed." -Andrew Wright, Wisconsin's
    Hemp Industry, 1918.

    "Hemp has been recommended as a weed control crop. Its dense,
    tall growth helps to kill out many common weeds. The
    noxious bindweed, a member of the morning glory family is checked
    to some extent by hemp."-B. B. Robinson, Hemp, USDA Agric Bull
    #1453, 1943

    "Among the species studied, the hemp species proved itself to be the
    best in fiber production. This plant was all the more interesting
    owing to its low fertilization requirements, and its ability to grow
    without being irrigated and without chemicals, whether it be for
    weed or pest control." Barriere, et al. 19941

    "Hemp grows quickly, soon covers the ground and chokes out
    the weeds. So weed control is not necessary." -Eddy A. A. de
    Maeyer. 19941

    In Holland, Lotz, et al. tested hemp's superior weed suppressing ability (Figure 1) against four other cropping situations in a controlled experimental setting. The target weed was yellow nutgrass (Cyperus esculentus), a weed also common in the US, which propagates by tubers and is difficult to control. The authors conclude, "...hemp was the most competitive crop in this study. Selecting this crop in a rotation will cause the strongest population reduction of C. esculentus on infested farmland. This control option of hemp against harmful weeds as C. esculentus is an attendant benefit of the introduction of hemp as a commercial crop."2

    1From papers delivered at the Conference on Alternative Oilseed and Fiber Crops for the Cool and Wet Regions of Europe, Wageningen, The Netherlands, April 7-8, 1994.

    2Lotz, L. A., P. R. M. W. Groeneveld, B. Habekotte, and H. van Oene. 1991. Reduction of growth and reproduction of Cyperus esculentus by specific crops. Weed Research

  2. #2

    Re: Hemp as Weed Control

    I just can't help but wonder how helpful Hemp is in the garden, in addition to being helpful to man.
    I wonder what it would be like if you planted hemp, in intervals in the fields what that would do for not only weed control, but pest control.