CHE REFERENCE LIBRARY - Pole Shift Survival Information

CERTAIN ELEMENTS IN NURSERY PRACTICE 205
red to dark brown, and a minute slightly elevated black area
appears iir the center of the spot.
The spots are circular in outline and may be so numerous
a.s to involve most of the leaf tissue. When the trees are
severely attacked the leaves turn yellow or brown, especially
those of quince, and readily fa,ll. The disease also affects the
twigs to some extent. Leaf-blight may be distinguished from
the septoria leaf-spot as the spots are smaller, more colored
when young, and somewhat more circular. The septoria spots
are apparent on the under surface of the
leaf. In the nursery, septoria spot is generally
found OH budded pears, while leafblight
is commouer on quinces and pear
seedlings (Fig. 21s).
Crc17~~w. - The leaf-blight disease is
wused by IfmY4Yl~ ~7Mfwl(rffl. Thc~ small
lhk specks previously ment ion~~d, wlkli
develop in the center’ of the aflkcted areas
of the leaf, arc! the reproduc~tive hdies
(acervuli) of the fungus. Kithin the FrcJ. 2tz.,,it,‘-““‘t
acerxulus spores are developed, wll icli
011 beir1.g discharged ar/’ carried by wind and rain to the
foliage. Uncler favorable condiths, with the presence of
moistu**e, the spores germinate and produce new infections. In
this way the fui~gus is propagated throughout the summer.
Some of the spores 11xq’ live over winter on the diseased twigs
and 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 next
spring discharge many spores which produce the first infections
of 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