V, LOSSES FROM SMUT 



Onion smut has caused — and is now causing — great losses to the onion growers 

 because : 



1. Many acres of land best suited for the growing of onions have had to be 

 turned to the growing of other crops because the land was so impregnated with smut 

 that a good crop of onions could no longer be grown. 



2. It costs just as much to tend a crop where smut has reduced the stand as it 

 does to tend a full stand but the returns are less. The diminished yield frequently 

 leaves no margin between cost of production and the selling price. 



3. The price of chemical, special apparatus and extra labor for application of 

 chemical, where preventive measures are used, must be added to the production 

 cost. 



The Plant Disease Survey of the United States Department of Agriculture 

 (32:210) estimated the loss from this disease in the United States in 1918 at 754,000 

 bushels. In individual fields in Massachusetts losses may vary from to nearly 

 100 per cent. 



At attempt to calculate the losses in dollars would be conditioned by so many 

 modifying factors that it would necessarily be the merest guess and no such attempt 

 will be made by the writers. It is, b}^ all odds, the most important disease of onions 

 occurring in America, and time or money spent in controlling it is well worth while. 



SYMPTOMS 



The first signs of smut appear on the young seedlings within two or three weeks 

 after the seed are planted. In fact, the very first recognizable indication of disease 

 has been observed here (1:131) within ten days from the date of planting. The 

 cotyledon (or seed leaf) wliich is the first part to appear above the ground is marked 

 by a slight cUstortion and swelling instead of being perfectly straight as is the case 

 with a healthy plant. A few days later, when one holds the plant up to the light 

 and looks through it, he sees a dense black, opaque, elongated area (or several of 

 such) inside the seed leaf. Many of these weakened plants "damp off" and fall at 

 this stage. Even if they do not damp oli they gradually shrivel and die if the attack 

 is severe. If one crushes these dead cotyledons he finds them filled Mith a black 

 powder (spores). The heaviest loss in an infested field is during this cotyledon 

 stage; the grower notices that his rows become thinner day by daj^, until only a 

 fraction of the seedlings which came up remain standing. If, however, the initial 

 attack was not very severe the plants do not die in the cotyledon stage but the 

 successive leaves develop and in many cases are perfectly healthy, the disease having 

 been sloughed off with the cotyledon. But usually smut will appear as long dark 

 streaks in each of the succeeding leaves. Such plants remain stimted and the leaves 

 are short, brittle, and distorted (Fig. lA). They continue to die in various stages 

 of development throughout the summer. Very few of them develop bulbs of any 

 size. Even if they continue to live until time of harvesting, they are never stored 

 because in the last stages they develop "bottom rot" and are thrown out. As the 

 diseased plants grow larger, the black smut pustules (or lesions) also increase in size. 

 They may be several inches long or extend throughout the entire length of the leaf. 

 As the leaf becomes old and dried these lesions spht open and the spores fall out 

 (Fig. lA). Frequently they rupture to the inside of the hollow leaf. On the bulb 

 itself, the pustules are raised and appear gray as one looks at the black mass through 

 the white covering of the scales (Fig. IB). When the outer scales die the black 

 spores fall out into the soil (Fig. 1). The appearance of a row of diseased onions as 

 compared with a row of healthy onions is shown in Fig. 2. 



THE CAUSE OF SMUT 



Smut is produced by the growth inside the tissues of the onion of a parasitic 

 fungus of the order Ustilaginales. The spores of this fungus were first distinguished 

 and figured by Taylor in 1872 (43:193 and Fig. 29), but the first accurate description 

 is by W. G. Farlow of Harvard University in 1876 (14:175). C. C. Frost of Brattle- 

 boro, Vt., had previously examined it and found that it belonged to the smut genus, 



