30 BULLETTX 1256, U. S. DEPARTMENT OF AGRICULTURE. 



symptoms. As far as known, it is rarely as serious as the two above- 

 mentioned diseases. This leaf-spot is undoubtedly the so-called 

 ordinary " rust " of Wisconsin, but on account of the fact that prac- 

 tically all leaf-spots, regardless of actual cause, are commonly re- 

 ferred to as " rust " by growers, the term " Wisconsin leaf-spot," for 

 want of a better name, is used at present to distinguish it from other 

 rust spots. So far as known, this disease is limited to Wisconsin, 

 where it is fairly common in some years, but occurs only rarely 

 to a damaging extent. 



The disease is in many respects similar to wild-fire, as far as 

 symptoms are concerned, except that these are less pronounced (PI. 

 VII, fig. 2). The bleached area or halo surrounding the center of 

 infection is usually much narrower than that characteristic of wild- 

 fire, spots. However, wild-fire spots also often appear without 

 marked halos surrounding them, and these are almost identical with 

 the Wisconsin leaf-spot. In such cases it is necessary usually to 

 resort to laboratory methods to distinguish the two. This can be 

 done readily, since wild-fire is caused by a white bacterium, whereas 

 a yellow bacterium causes Wisconsin leaf-spot. 



Wisconsin leaf-spot also makes its first appearance in the seed 

 beds, where tlie spots resemble those of black- fire in that they are 

 usually quite small and more or less angular. In the field the disease 

 is usually confined to the bottom leaves, only under exceptionally 

 favorable conditions spreading as high upon the plant as wild-fire or 

 black-fire. 



Cause. — Wisconsin leaf-spot is caused by an organism which has 

 been named Bacterium melleum. Aside from its yellow or honeylike 

 appearance on some culture media, it resembles the wild-fire and 

 black-fire organisms closely in shape and size. Wounding is es- 

 pecially favorable for infection. The spread and overwintering of 

 the organism are most probably the same as for wild-fire. 



Conditions favoring the disease. — The occurrence of the disease in 

 the seed bed has usually followed protracted periods of wet weather. 

 Its occurrence in the field is also dependent upon rainy weather, or 

 at least moisture and high humidity on and surrounding the leaves. 

 Storms no doubt favor the disease by spreading the germs and 

 wounding the leaves. 



Control. — Very little experimental work has been done aiming at 

 the control of this disease in particular. Where control measures 

 need to be practiced the same measures that were described for wild- 

 fire control will apply. 



FROG-EYE. 



Description. — This leaf-spot disease of tobacco is fairly common, 

 though not often serious, in the southern tobacco-growing districts, 

 but as far as known it is rare or does not occur in the northern dis- 

 tricts. The term "frog-eye" is unquestionably applied to various 

 leaf-spots similar in appearance but arising from different causes. 

 The description here applied, however, refers to one particular dis- 

 ease ordinarily recognized in literature as properly called frog-eye 

 because of the presence of the particular causal organism concerned. 

 This leaf-spot is characteristically located on the bottom leaves of 

 the plant, especially toward their maturity. More or less circular 

 brownish spots, with a grayish white area in the center, upon which 



