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Research Bulletin (Iowa Agriculture and Home Economics Experiment Station)

Abstract

Sodium chlorate has proved the most effective herbicide for the eradication of leafy spurge. The following formula is effective when applied as a spray: Sodium chlorate, 1 pound; animal glue, 4 grams; sulfuric acid, 3 cubic centimeters; water, 1 gallon.

The best kill was obtained when the chlorate solution was sprayed on actively growing plants in full foliage.

In northwestern Iowa, sodium chlorate sprayed on the aerial parts has given better and more consistent results than when applied dry, directly to the soil.

The highest percentage of kill of leafy spurge through sodium chlorate was produced when the spray was applied the latter part of May or when the plant was about to come into blossom. The second spray, applied the latter part of August or before killing frost, usually completed the eradication of leafy spurge.

Sodium chlorate has proved more effective in killing leafy spurge when treated in small grain or millet than where growing alone.

Leafy spurge was eliminated in a large pasture by spraying with sodium chlorate, the first application being made the latter part of May and the second the latter part of August.

Pound for pound, the old Atlacide on the market in 1930-33 apparently was not as effective in killing leafy spurge as sodium chlorate.

Dilute sulfuric acid and C.-K. (creosote-kerosene) killed the tops of leafy spurge with little injury to the roots.

Heavy applications of ammonium thiocyanate may prove valuable as a herbicide for leafy spurge.

Potassium chlorate was about as effective in eradicating leafy spurge as sodium chlorate. Residual soil effect was greater for potassium chlorate than for sodium chlorate.

To insure complete elimination of leafy spurge by spraying with sodium chlorate, 2 years are necessary. Two applications the first year will destroy most of the spurge. Remaining plants must be given two treatments the second year.

Kainite, a fertilizer, will exterminate leafy spurge when heavy applications are made.

Applications of well rotted manure (3 tons to the square rod) were effective against leafy spurge. Straw had no effect.

Plowing leafy spurge deeply (7-8 inches) in the fall and again in the spring materially reduced the amount of leafy spurge.

Millet, sorghum and soybeans drilled in heavily about the middle of June after the ground had been plowed and fallowed proved to be good crops for infested areas of leafy spurge. Reduction in leafy spurge population is greater if the land is plowed the preceding fall and again the following spring, and cultivated until the smother crop is planted.

Fallowing for 2 years, by cultivating 30 times each year from June 1 until Oct. 1, completely destroyed leafy spurge.

A program of eradication with growing competitive crops may be shortened by giving leafy spurge one application of sodium chlorate the previous fall, shortly before killing frost.

Leafy spurge population in corn was not reduced by four cultivations. Surface cultivation in corn following regular cultivation did not prove to be an effective procedure in eradicating leafy spurge.

Alfalfa did not compete successfully with leafy spurge.

Alfalfa was tolerant to sodium chlorate and may be used on ground where the leafy spurge has been killed with sodium chlorate or Atlacide. Barley was sensitive to sodium chlorate in the soil; soybeans are less tolerant than barley or oats.

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