Oct. i, 1920 



Fusarium-Blight (Scab) of Wheat and Other Cereals 13 



force, as shown by the fact that they are driven around in the drop 

 with considerable velocity. It is rather evident, therefore, that rain 

 assists in the liberation of conidia from the pionnotes, and thus they are 

 carried down to the ground or transmitted from plant to plant as the 

 plants wave in the wind. 



Insects, no doubt, may also play some r61e in the dissemination of 

 Fusarium' conidia, but time did not permit a study of their importance. 



TIME OF NATURAL INFECTION 



The first blight infection in nature takes place during the latter part 

 of the blossoming period. It is, however, not the most severe one; the 

 secondary infections following shortly after the first being the ones that 

 are most destructive. 



Several wheat, rye, barley, and oat fields, all located within 4 miles 

 of Madison, Wis., were selected for experimental purposes during the 

 spring and' summer of 191 8 and were examined every other day, 

 beginning about one week before the period of blossoming of rye and 

 two weeks before the blossoming of wheat, barley, and oats. 



The following is a typical brief record of the observations on one of 

 the wheat fields : 



Station No. 2. Town of Burke, Wis. 



Field of Marquis wheat on corn ground. Field in level open country. Soil sandy 



loam. vStand good. . ' . „,, « 1 it. 



Tune 22 1918 Plants in blossom. No signs of blight infection. Throughout the 

 field there are numerous cornstalks with a great number of Gibberella saubinetn 

 perithecia with viable spores. ' , 



June 28, 1018. Wheat just passing blossoming stage. No signs of blight infection. 

 Ascospores in masses are oozing from Gibberella perithecia. 



July 7 , 1918. First indication of blight infection apparent. It consists of a water- 

 soaked spot on single spikelets, usually on single glumes. 



July 15, 1918. All suspected first infections have developed into distinct blighting 

 of the heads. 



Following the first infection there may be as many successive infec- 

 tions as weather conditions permit. 



This observation agrees with the results obtained with artificial inocu- 

 lations. Inoculation of plants before blossoming and following the 

 dough stage gave negative results. While the organism will attack 

 and penetrate the heads and the kernels in them during the latter part of 

 the dough stage and also after maturity, as demonstrated first by 

 Schaffnit (8) and later by Naumov (5), if there is abundant moisture and 

 warm weather, this can scarcely be spoken of as infection in the true 

 sense of the word. Wheat plants which were just heading out, others 

 which were just past blossoming, and a third lot which were in the late 

 dough stage were inoculated under exactly the same conditions, on the 

 same day, and with the same spore suspension. They gave the follow- 

 ing results: The first and third lots remained healthy during the first 



