234 NEBRASIvA STATE HORTICULTURAL SOCIETY. 



rust is the conspicuous stage in the "stem rust" of wheat. Some of the 

 other cultivated plants affected by rusts are the clovers and alfalfa, 

 beans and peas, beets, asparagus, plum and cherry, cottonwood and 

 willow, roses, carnations, and chrysanthemums. The cluster-cup stage 

 of many of the rusts produce fairly large, well-defined orange-colored 

 spots in many cases. This symptom is well illustrated in the well-known 

 "cedar rust" of apple leaves, and in the cluster-cup stage of the "crowned 

 rust" of oats on the leaves of the buckthorn. Deeper red or even purple- 

 colored spots or extended areas indicate the presence of a leaf parasite 

 in many cases. This is often noticed in the early stages of the shot- 

 hole diseases of the cherry or the peach, and is especially characteristic 

 in the bacterial blight of sorghum or Kafir corn. In the last mentioned 

 case the dark red or purple patches are generally somewhat elongated 

 and more or less irregular. The leaves of dandelion affected by rust 

 generally show a reddening of the whole leaf, while the under side of 

 blue-grass leaves affected with the powdery mildew frequently show 

 spots of a deep purple color. 



Definite brown areas, either small or somewhat extended, are quite 

 characteristic of spot diseases of either leaves or fruits. The leaf-spots 

 of apple, pear and plum are common diseases in this and adjoining 

 states. As a result of these troubles, the leaves begiti to drop and a 

 premature defoliation is the result, thus sending the tree into winter rest 

 with an insufficient supply of reserve food for the growth of the following 

 season. As a result of the leaf-spot, Ben Davis trees in Nebraska 

 are often defoliated when other varieties are in full foliage. The leaves 

 of tomato plants often show an abundance of small brown spots. As 

 these spots become more plentful the intervening areas turn yellowish, 

 the leaf begins to shrivel and curl and finally drops off. Many gardeners 

 do not recognize this behavior of tomato leaves as a symptom of disease, 

 since it is of such common occurrence. The early blight of potatoes is 

 characterized by brownish spots on the leaves that often show more or 

 less of a concentric zonation. As the fungus spreads the spots may 

 coalesce and thus the entire leaf will be killed. Sometimes the brownish 

 color is not confined to definite spots, but is more general as in the 

 diffuse form of apple-scab, which shows upon either the under or upper 

 surface of the leaves. The definite scab spots on the fruits or leaves 

 of apples, pears or peaches may be gray, brown, dark olive green, or 

 even almost black. More or less deep cracks or fissures often appear 

 in later stages of scab. Many other examples of a somewhat similar 

 character may be mentioned, as the leaf-spots of beets, watermelon, 

 maple, mulberry, chrysanthemum, rose, etc. Other troubles, such as 

 spray injury, or sun-scald, may be indicated by brownish discolorations, 

 but in the majority of cases this symptom indicates a fungus disease. 



The appearance of black spots upon stems or foliage is not an un- 

 common symptom of disease. One of the most striking cases of this 

 character is in the so-called "tar-spots" of our maples and willows. 



