258 Diseases of Truck Crops 



DISEASES OF THE HOREHOUND {Marrubium 



vulgare) 



Powdery Mildew 



Caused by Erysiphe galeopsidis D. C. 



Powdery mildew is characterized by powdery 

 white patches on the leaves and stems. The trouble 

 is not known to occur in the United States. 



Leaf Spot 



Caused by Diplodia herbarum (Corda) Lev. 



The spots are roundish to irregular, numerous, 

 brownish to dark in color. The disease attacks the 

 older leaves, causing them to drop off prematurely. 



DISEASE OF THE MINT 



Rust, see Balm, p. 256. 



DISEASE OF THE PEPPERMINT (Mentha 



pepenta) 



Peppermint is a very hardy plant. With the ex- 

 ception of Rust (see Balm, p. 256), it is practically 

 free from attacks of fungus diseases. The same is 

 also true for the spearmint, Mentha viridis, which is 

 known to be attacked by the same rust diseases as 

 the balm and all the other Labiatae. As far as we 

 know the weeds in this family are not carriers of 

 diseases which concern the trucker. 



