THE PHYSIOLOGY OF CONVOLVULUS ARVENSIS (MORNING-GLORY OR BINDWEED) IN RELATION TO ITS CONTROL BY CHEMICAL SPRAYS

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Abstract
The persistent vegetative activity of the morning-glory is related to the large storage of starch in its roots. Early control methods, based on an attempt to deplete this starch reserve, have not proved practical. Killing of plants by arsenicals depends on penetration and distribution. Acid solutions are more effective than basic ones in penetrating cortical tissues in the morning-glory. Solutions between pH 3 and 9 do not cause rapid injury to tissues, the direct effect of their pH value being negligible. Plant buffers are active in neutralizing acid and alkaline sprays. Arsenic trioxide is soluble to a concentration of about M/20 at the pH of plant sap. Arsenic moves freely through the xylem of morning-glory plants. Cut shoots may take up enough M/20 As2O3 solution in 1 hr. to be completely killed. Injury appears only after a lapse of about 20 hrs. Eosin may enter cut stems and move toward the roots at a rate as high as 2.46 in. per sec. for 5 sec. The rate decreases as water deficit becomes satisfied. Water deficit, as indicated by the uptake of eosin solution, is correlated with soil moisture and transpiration. Prolonged exposure to the spray solution as by the condensation of dew or addition of water to the leaves greatly increases the depth of penetration of the arsenic. The hygroscopic properties of H2SO4 and its hardening effect upon tissues make it an effective ingredient of the spray solution. Maturity is an index of the proper time for spraying only as it is accompanied by water deficit. An examination of the pressure conditions in the xylem is a much more accurate test. The lethal concentrations of arsenic were 0.02% of the dry wt. in tops and 0.0003% in roots. As has been used with some success in the control of morning-glory but complete eradication is seldom accomplished by its use.

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