CHAPTER IV. PLANT DISEASES 1/ 
In this report only losses attributable to specific parasites such 
as bacteria, fungi, viruses, and nematodes are estimated. Diseases 
resulting from nutritional disturbances are included only when cor-= 
rective measures are normally taken concurrently with control of 
diseases. 
Production statistics and losses to plants by diseases have been 
grouped by types of crops =— field crops, forage crops, fruit and nut 
crops, vegetable crops, and drug ane ornamental crops. Loss descrip- 
tions follow for each of the crops in the various groups. 
Field Crops 
Production statistics and estimated disease losses of the major 
cereal, sugar, tobacco, and fiber crops appear in Table 1. Estimates 
of losses to minor crops have not usually been made, as they would 
not contribute substantially to over-all agricultural losses, and on 
most of them less information is available. 
Barley 
The major diseases that attack barley in the United States, causing 
together an estimated annual loss of 5 percent of the crop, are loose 
and covered smuts, rust (stem and leaf), powdery mildew, the 
Helminthosporium diseases (net blotch, spot blotch, and especially 
stripe), sceb, scald, various foot rots, the bacterial diseases basal 
glume rot and bacterial blight, and virus diseases, The smuts cause 
the most consistent losses. The viruses are the latest to appear and 
cause serious damage. Smut, mildew, rust, and Helminthosporium are 
the most widely distributed. Scab, when it occurs, not only reduces 
the yield but also impairs the feeding value of the grain for certain 
classes of livestock. Transmission of the stripe-mosaic virus and 
loose smut within the seed from crop to crop increases the difficulty 
of control. Mild attacks of many of the diseases injure the quality 
(kernel plumpness) of the grain, thus lowering its value for use as 
malt. It is difficult to evaluate the quality losses, but in some 
years they are considerable, 
Corn 
Diseases reduce corn production in the United States by millions of 
bushels each year. The losses in individual fields often exceed 10 
1/7 Loss estimates for diseases transmitted by insects are included 
in this chapter instead of Chapter V. 
One. 
