342 Diseases of Greenhouse Crops 



gus grows on the surface of the leaves in powdery 

 white patches. Affected leaves become pale and 

 drop off prematurely. The ascus stage of Micro- 

 sphera almi is rarely found on the freshly affected 

 foliage. It is, however, fairly abundant on the dead 

 and fallen leaves on the ground. The mildew may 

 be controlled in the same manner as for the rose 

 (see p. 323). 



Spot Disease 



Caused by Mycospherella pinodes (Berk, and 

 Blox.) Niesel. 



Symptoms. Although it is a dangerous enemy of 

 the garden pea, this disease has not attacked sweet 

 peas very often, especially where they are grown 

 under greenhouse conditions. The pycnidial stage 

 of the fungus is found on foliage of the garden pea 

 and of the sweet pea. The winter stage may be 

 foimd on dead leaves and vines of the sweet pea 

 and of the garden pea. 



The Organism. The pycnidia are brown, erum- 

 pent, globose, with thin walls. The spores are hya- 

 line, cylindrical, one septate and rounded at both 

 ends; they are guttulate only when young. The 

 perithecial stage was discovered by Stone. The 

 brown perithecia are found under the epidermis or 

 deeply sunken in the tissue of the spot. Their mouths 

 are elongated and beaklike. The asci are cylindri- 

 cal, while the ascospores are elliptical to ovate. Both 

 are two-celled hyaline bodies. Spraying with a 

 standard fimgicide may keep the disease in check. 



