A Study of Meadow-Crop Diseases in New York 9 



TABLE 1. Determination of Diseased Area op Red-Clover Leaves Affected by 

 Macrosporium Sarcinaeforme 



* This last column of the table, which shows the percentage of total foliar area diseased, was calculated 

 by assuming the area of each dead leaf to be equal to the average area of the living leaves. Then the total 

 area of dead leaves is added to the total area in spots, this is divided by the total area of all leaves, and the 

 quotient ia expressed in a percentage. 



It may be argued that some leaves are killed by shading, but where no 

 leaf spots are present, fields show almost no dead leaves even though the 

 stand be exceedingly dense. Apparently, healthy clover leaves are very 

 resistant to shading. In the field concerned in the measurements, how- 

 ever, the stand was thin enough so that shading was reduced to a minimum. 



If the dead leaves and the dead spots in living leaves be charged against 

 the pathogene and considered a total loss to the grower, then he lost 

 approximately 36 per cent of the leaf material in that clover crop. Accord- 

 ing to Piper (1921:398), clover hay by weight consists of about 60 per 

 cent stems, 30 per cent leaves, and 10 per cent flower heads. If this be 

 true, then every ton contains 600 pounds of leaves. Since 36 per cent 

 of this is destroyed (table 1), approximately 216 pounds out of every ton 

 was lost from this field of red clover. This was a loss of material that 

 contains about three times as much protein as do the stems. It is true 

 that the leaf loss is not total since most of the dead material is present, 

 but this is counterbalanced on the other hand by (1) decreased growth 

 additions of stems, leaves, and flowers, (2) lowered quality, and (3) in- 

 creased shattering during harvest. For the purposes of this paper, there- 

 fore, the assumption is made that a clover leaf-spot disease of moderate 

 intensity reduces the leaf yield by a third, and this reduces the yield of the 

 entire crop by about 11 per cent. Since 45 per cent of diseased leaves, 

 an average for the moderate class, causes a total loss of 11 per cent, then 

 each per cent of diseased leaves causes a loss of 11/45, or 0.25 per cent, 

 in round numbers. 



This calculation probably tends to be more conservative than other- 

 wise. If the spots appear early in the life of the plant, they will cause 



