Johnson Grass Control 



(Sorghum halepcnsc) 



INTRODUCTION 



For several years the need for data on the control of Johnson grass 

 in the irrigated valleys of Southern Arizona has been manifest. An 

 excellent opportunity for experimental work in the eradication of this 

 weed under average farm conditions was offered when the Agricultural 

 Experiment Station began to operate the Salt River Valley Farm near 

 Mesa. Half of this tract of land was infested with a perfect stand of 

 Johnson grass and about 40% of the other half of the farm was very 

 heavily seeded to the weed. 



As is well known, Johnson grass at an intermediate stage in its 

 growth sends out a fleshy rootstock in which is a considerable quantity 

 of stored up substances, capable of supplying new plants formed at the 

 nodes of this rootstock. As a result, if the above-ground part of the 

 plant is destroyed, food materials stored in the rootstock are capable 

 of producing nev^ foliage, v^hich, after it again has made a slight 

 growth, is maintained by its fibrous roots and by the nutritive pro- 

 cesses which are carried on in the leaves and stems. Since the growth 

 of all of the higher plants is dependent upon plant foods derived from 

 two sources ; first, the soil solution through roots, and second, from 

 the air by means of synthetic processes carried on in leaves and stems 

 and assisted by sunlight; and since neither is sufficient in itself to 

 maintain the life of the plant, the destruction of Johnson grass may 

 be accomplished by cutting off one of these sources of supply, thus 

 forcing the stored up substances in the rootstocks to maintain the 

 plant, continuing this process until the reserves in the rootstocks are 

 exhausted. Two means of thus disturbing the normal processes of 

 Johnson grass plants were chosen ; the destruction of the stems and 

 leaves by cultivation, and by close-grazing with livestock. For the 

 latter method sheep were selected.* 



♦Acknowledgements. — The writer desires to state that the experimental work 

 leading to this publication was planned by Professor John F. Nicholson prior to his 

 departure in February, 1917, the program being carried out and the publication 

 written by himself. 



