CHE REFERENCE LIBRARY - ZetaTalk

196 THE NURSERY-MANUALga.11 infections call be reduced by using a root and cion of approximatelythe same size and by wrapping the grafts carefully.APPLE- AXD ~UPSC,~B. - The scab diseases exist apparentlyin every country where apples and pears are grown commercially.In the nursery, the pearscabis usually of importanceonly on the FlemishBeauty buds. The applescabis most destructivein the nursery on the varietiesMcIntosh, Transcendentand Martha.Lkmipt~ion .-The leavesand the fruit and sometimesthe twigs are affected.The disease appears onthe leaves as olivaceousto dark brown or nearlyblack spots (Fig. 212).There is a tendency forthe lesions to extend alongthe veins of the leaf, makingthem irregular in ap-FIQ. 212. Scab on apple leaves. pearance.Cmcsc. - The scablesions are caused by the fungi Tk~Wia ilLceqlraZis and V~turiapyrinn, which produce a large number of spores in the spots.The spores are disseminated by wind and rain and are responsiblefor the new infections which occur throughout the summer.On the diseased leaves that fall to the ground in autumn,special fruiting bodies (perithecia) of the fungi are producedand by this means the organism lives over winter. In springthe perithecia produce spores which attack the new foliage.