3i8 



Minnesota Plant Diseases. 



been reported from a greenhouse in this state where it de- 

 stroyed almost an entire winter crop of mint. 



The complete destruction of all diseased plants and espe- 

 cially all subterranean portions is necessary. (Fig. 209.) 



Asparagus rust (Puccinia asparagi DC). Of recent years 

 this rust of asparagus has become of great importance in the 

 eastern states and in California and will undoubtedly soon be of 

 equal importance in this state. In parts of eastern states aspar- 

 agus culture in whole districts has been ruined by this parasite. 

 The cluster-cup stage is produced on the asparagus plants in the 

 spring but is usually 

 not conspicuously 

 abundant. After 

 the crops have been 

 harvested, the sum- 

 mer spores appear as 

 brownish spots on -; 

 the stems of the^ ' 

 host plant. The 

 winter spores are 

 produced later in 

 long, black streaks 

 upon the stem. The 

 rapid spread of the 

 fungus and the tax 

 of the mycelium on 

 the nutrition of the 

 host, greatly enfeebles the plant and the crop of the following 

 season is seriously afifected. If no combative measures are 

 used, the fungus gains strength year by year and soon enforces 

 the abandonment of asparagus culture. The winter spores are 

 two-celled and germinate in the usual way in the following 

 spring. Several fungus parasites on the rust plant are known 

 but they do not apparently exercise sufificient destructive in- 

 fluence to be of assistance to the agriculturalist. 



This is a very serious disease and difficult to combat. It is 

 first of all necessary to remove all badly diseased plants and 

 to burn all infected plant remains in the fall. In badly diseased 

 districts this method will not alone suffice. Moreover, earlv 



I-'iG. 161. — Winter spores of the asparagus rust. Highly 

 magnified. Microphotograph by E. W. D. Holway. 



