MILDEWS 



197 



specimens come from the lilac, rose, or willow. These fungi do 

 not penetrate the host plant to any depth, but cover the leaves of 

 the host with the whitish threads of the mycelium. Hence they 

 may be killed by means of applications of some fungus-killing 

 fluid, as Bordeaux mixture. They obtain their food from the 

 outer layer of cells in the leaf of the host. Among the useful 

 plants preyed upon by this group of fungi are the plum, cherry, 

 and peach trees. The diseases known as black knot and peach 

 curl are caused by these fungi. 



Potato wart is another fungus disease which was introduced 

 into this country in 1911 and has now spread over the eastern 

 part of the United States. It attacks the potato tuber, so that 

 the disease may not be noticed until time to harvest the crop. 

 Since its spores may be dormant in soil for several years, the only 

 way to combat the pest is to rotate other crops on the field as 

 well as to destroy all infected tubers. 



GRAIN DESTROYED BY STEM RUST IN THIRTEEN YEARS 

 1915 to 1927, Inclusive 



State 



• 



Wheat 

 (Bushels) 



Oats 

 (Bushels) 



Barley 



and 



Rye 



(Bushels) 



Total 



All 



Grains 



(Bushels) 



Average 



Annual 



Stem Rust 



Losses 



All 

 Grains 

 (Dollars) 



Total 



Loss 1927 



All 



Grains 

 (Dollars) 



Colorado . 

 Illinois 

 Indiana . 

 Iowa . . 

 Michigan 

 Minnesota 

 Montana . 

 Nebraska 

 No. Dakota 

 Ohio . . 

 So. Dakota 

 Wisconsin 







2,469,000 



4,992,000 



2,974,000 



4,246,000 



6,487,000 



86,002,000 



14,863,000 



18,505,000 



202,316,000 



4,806,000 



76,209,000 



4,456,000 



176,000 

 50,156,000 



1,479,000 



33,761,000 



15,831,000 



50,345,000 



221,000 



3,922,000 

 14,788,000 



2,694,000 

 37,574,000 

 10,349,000 



541,000 



353,000 

 Trace 

 2,143,000 



453,000 

 3,498,000 

 Trace 



276,000 



4,606,000 



80,000 



4,170,000 



2,417,000 



3,186,000 



55,501,000 



4,453,000 



40,150,000 



22,771,000 



139,845,000 



15,084,000 



22,703,000 



221,800,000 



7,580,000 



117,953,000 



17,312,000 



$ 218,000 



2,275,000 



481,000 



1,580,000 



1,409,000 



11,742,000 



1,154,000 



2,437,000 



22,191,000 



562,000 



9,385,000 



1,109,000 



Trace 

 $ 8,707,000 

 Trace 

 729,000 

 765,000 

 18,592,000 

 Trace 

 Trace 

 19,075,000 

 247,000 

 9,297,000 

 375,000 



Total . ' . . . . 



428,325,000 



221,386,000 



18,627,000 



668,338,000 



54,543,000 



57,787,000 



These are official estimates of the Plant Disease Survey, Bureau of Plant Industry, United 

 States Department of Agriculture. The money value of the grain destroyed in the thirteen- 

 year period was $709,081,000, basing calculations on the farm prices for December 1 of each year 

 and disregarding any effect the reduced production, caused by rust, may have had on the 

 market price. Losses for 1927 are preliminary. 



