VEGETABLE CROPS. t> S."i 



Mildews. 

 Beans and peas and allied crops suffer attack by a number of fungi which 

 produce appearances known as Mildew. The most important of these are — 



(1) Damping-off Mildew, due to Pythium de Baryanum (Hee9e). 



(2) Downy Mildew, due to Peronospora vicioe I De Bary). 



(3) Downy Mildew, due to Phytophthora phaseoli (Thaxter). 



(4) Powdery Mildew, due to Erysiphe polygoni (D.C.). 

 Damping-off Mil'/' "\ — Smiling-, arc often affected with a disease known 



as Damping-off. The conditions which favour its development are a con- 

 siderable degree of warmth, abundant moisture, and a weakened condition 

 if the seedlings. It is common when plants are grown in a crowded condi- 

 tion. The fungus attacks the seedlings at or near the surface of the 

 ground, the stem shrinking and the plants falling over. Thinning out 

 seedlings, reducing the water supply, and allowing the free access of air and 

 sunshine will check the further development of the fungus. 



Downy Mildew due to Peronospora. — The fungus Peronospora vicia; (De 

 Bary) attacks the leaves of various leguminous plants, such as broad bean, 

 pea, vetch, melilotus, &c., producing felt-like patches of hyphae, which 

 become dense and whitish to greyish in colour. The hyphae produce many 

 branched conidiophores, and the spores, borne on the ends of the pointed 

 branches, rapidly spread the mildew in moist weather. When favourable 

 conditions change, the fungus produces a globular thick-walled resting 

 spore which can live from one season to another in any decaying parts of 

 the plant. The destruction of all plant refuse, the reduction of the moisture 

 on the plants by the access of sunshine, and the free circulation of air will 

 ■check the disease. Spray with Bordeaux mixture (6 — 4 — 100). 



Downy Mildew due to Phytophthora. — A downy mildew, similar to Late 

 •(or Irish) Blight of potatoes, but caused by another species, Phytophthora 

 phaseoli (Thaxter), causes destruction of Lima beans in some countries, 

 attacking young shoots, flower clusters, and leaves, causing them to become 

 ■dwarfed and distorted, and also forming a dense, woolly-white growth on 

 the pods. This does not occur in New South Wales, but might be intro- 

 duced at any time. The preventive measures used are: — The use of clean 

 seed, rotation of crops to get rid of the resting spore stage, destruction of 

 ■old plant parts, and spraying with dilute Bordeaux mixture (6 — 4 — 100). 



Powdery Mildew. — A powdery mildew, caused by the fungus Erysiphe 

 polygoni (D.C.), is a common disease that attacks over 300 species of 

 plants, including many of the Leguminosae, e.g., garden peas, beans, and 

 vetches. On peas in moist seasons it may form a dense, persistent myce- 

 lium, covering stems, leaves, and pods. When mildew attacks young plants 

 the crop is generally a total failure. The fungus produces spores in great 

 profusion, and in later periods develops it? perithecia (cases enclosing 

 asci which hold about two or three ascospores). This stage will carry the 

 fungus on till the next crop. The fungus may hibernate in the seed 

 derived from affected nods. Dusting with flowers . of sulphur and the 

 destruction of any dead vines or plants are recommended as methods of 

 ■control. 



Leaf Spot of French Bean. 



Leaf Spot is caused by the fungus Isariopsis griseola (Sace.). This 

 attacks the leaves, stems, and pods, producing brownish patches, and causes 

 the leaves to fall away. The spots become large and angular; they are 

 often limited by the veins. Bordeaux mixture (6 — 4 — 100) should be used 

 and affected plant refuse destroyed by fire. 



