CHE REFERENCE LIBRARY - ZetaTalk

CERTAIN ELEMENTS IN NURSERY PRACTICE 205red to dark brown, and a minute slightly elevated black areaappears iir the center of the spot.The spots are circular in outline and may be so numerousa.s to involve most of the leaf tissue. When the trees areseverely attacked the leaves turn yellow or brown, especiallythose of quince, and readily fa,ll. The disease also affects thetwigs to some extent. Leaf-blight may be distinguished fromthe septoria leaf-spot as the spots are smaller, more coloredwhen young, and somewhat more circular. The septoria spotsare apparent on the under surface of theleaf. In the nursery, septoria spot is generallyfound OH budded pears, while leafblightis commouer on quinces and pearseedlings (Fig. 21s).Crc17~~w. - The leaf-blight disease iswused by IfmY4Yl~ ~7Mfwl(rffl. Thc~ smalllhk specks previously ment ion~~d, wlklidevelop in the center’ of the aflkcted areasof the leaf, arc! the reproduc~tive hdies(acervuli) of the fungus. Kithin the FrcJ. 2tz.,,it,‘-““‘tacerxulus spores are developed, wll icli011 beir1.g discharged ar/’ carried by wind and rain to thefoliage. Uncler favorable condiths, with the presence ofmoistu**e, the spores germinate and produce new infections. Inthis way the fui~gus is propagated throughout the summer.Some of the spores 11xq’ live over winter on the diseased twigsand produce iitw infectious wh growth starts in spring ;but utj doubt ,thc greater proportion of infections in earl>spring is due to the sexual stage (peritliecia) of the parasite.The perithecia develop on the fallen leaves, and the nextspring discharge many spores which produce the first infectionsof the season.hr2.f rd. - Spraying with lime-sulfur solution 1 to 40, or‘dusting with a mixture of 95 parts finely ground sulfur and