xA-RizoNA Agricultural Experiment Station 413 



The third field, containing 10 acres, was in cotton in 1916 and 

 by midsummer the old rootstocks were destroyed by cultivation. 

 Numerous Johnson grass seedlings came up from seed introduced 

 by the irrigation water of July and August, 1916, and by the time 

 these plants had appeared the cotton was too large to admit of their 

 destruction by cultivation without serious injury to the crop. Be- 

 fore the freezing weather of fall numerous seedlings had formed 

 rootstocks. The land was plowed in January of this year and 

 seeded thickly to Tepary beans for green manuring pui-poses. Soon 

 after seeding to Tepary beans the weeds became quite troublesome 

 and when the green manure was plowed under early in June quite 

 large and vigorous rootstocks had been formed upon the Johnson 

 grass. These rootstocks sent out new plants which necessitated 

 some work with a weeder prior to planting to corn early in July 

 of this vear. By careful cultivation for the first few weeks aftv^r 

 the corn was planted the Johnson grass was again brought under 

 complete control. 



Considerable work with the weeder and cultivator held the 

 Johnson grass in check on the fourth field until it was planted to 

 corn early in July, 1916. Further cultivation destroyed the vigor of 

 the rootstocks by late summer of that year and since corn admits 

 of cultivation at a later date than cotton, seedlings introduced by 

 irrigating water were destroyed soon after their appearance. As a 

 result the land was very clean when planted to cotton in March, 

 1917, and has been kept free from Johnson grass without a great 

 deal more hoeing and cultivating than cotton ordinarily demands. 



With the appearance of spring the fifth field, which was fal- 

 lowed in 1916, disclosed a great number of fairly vigorous Johnson 

 grass rootstocks. The land was plowed in August, 1916, and seeded 

 to wheat in December. The luxuriant growth of .the grain pre- 

 vented the Johnson grass making much headway until after the 

 harvest in June. 1917. Due to shortage of labor and teams it was 

 impossible to plow this field immediately after the removal of the 

 grain, and by the end of June the Johnson grass was again appear- 

 ing in dangerous amounts. Plowing in August served materially 

 to restrict the growth of the weed, but the field is by no means 

 clean vet. 



The sixth field has been dry fallowed since August, 1915. By 

 June. 1916, the vigor of the Johnson grass rootstocks had been ma- 

 terially diminished, but a heavy rain early in September and acci- 

 dental leakage of irrigating water lent new energy to the weed and 



