Page 4 



BETTER FRUIT 



March, ip20 



On tender twig growth scab first ap- 

 pears in the characteristic sooty spots, 

 but persists over winter and eventually 

 causes the bark to become ruptured, so 

 that after a year or two the younger 

 branches seem to be covered with small 

 irregularly circular shaped and blister- 

 like cankers. As the brancli grows 

 older these roughened areas slough off' 

 and healthy bark is formed over the in- 

 jury. Twig infection is not as prevalent 

 as llie other types, but is likely to be 

 foun<l in neglected orchards. It is im- 

 portant chiefly as a source of infection 

 for fruit and foliage. 



The Fungus Causing the Disease — 

 The fungus causing the disease is close- 

 ly related to the well known apple scab 

 fungus, but it is a different species. It 

 persists over winter not only on the 



FiciRF. 2 l.:rlc iiifictioii of scab on a Bartlett 



pear and injury caused by the syneta leaf 



beetle. Ttie elongated spots were produced 



by the beetle. 



pearance, black or olive green in color. 

 In size the spots range from mere 

 specks to areas that may cover the en- 

 tire side of a young pear, while two or 

 more spots may coalesce and increase 

 the extent of the affected area. When 

 very young pears are affected they may 

 drop before they become one-half inch 

 in diameter. The fungus causing the 

 disease grows just beneath the cuticle, 

 which becomes ruptured, exposing the 

 epidermis, which is rendered corky on 

 exposure, thus forming a roughened 

 spot. Its effect is strictly local at first 

 and causes no discoloration or harden- 

 ing of the flesh beneath; but as the pear 

 grows the scab injury restricts the ex- 

 pansion of the fruit and causes it to be- 

 come distorted in shape, a most objec- 

 tionable feature. If the normal growth 

 of the fruit is greatly distorted, cracks 

 may be formed which extend halfway 

 around the pear and almost to the core. 



The infection of buds and blossoms 

 on unsprayed trees is frequently severe 

 and often results in a great reduction 

 of the crop. Scab on the buds and 

 blossoms is exhibited as dark, velvety, 

 and sooty-appearing spots, much the 

 same as on the young fruits, and infec- 

 tion may occur on any of the more ex- 

 posed flower parts. Infection of the 

 flower stalk is almost certain to prevent 

 the fruit from setting. 



Foliage infection frequently is not 

 recognized by the orchardist, but it is 

 one of the most serious manifestations 

 of the disease. Infection occurs chief- 

 ly on the under side of the leaves and is 

 exhibited as a dark olivaceous colored 

 spot, similar to scab on the fruit. When 

 many infections occur on a leaf it may 

 become somewhat curled and deformed, 

 and frequently it drops prematurely. If 

 the defoliation is severe the tree is un- 

 able to function normally and can not 

 store up the food requisite for the pro- 

 duction of fruit buds and the mainte- 

 nance of its own vitality; hence, the 

 succeeding crop may be greatly affected. 

 Foliage infection is also important as a 

 means of carrying over the disease from 

 year to year. 



able. These "summer spores" thus rap- 

 idly reproduced serve as a constant 

 source of infection throughout the sea- 

 son, and the fungus becomes estab- 

 lished. Spores matured on the twig 

 cankers cause infection in the same 

 manner or may be washed on to the 

 fruit and foliage during rains. 



The period of greatest infection is 

 from the time the first buds appear until 

 about a month after blossoming, or un- 

 til sunmier weather is encountered. The 

 cool, wet weather which usually prevails 

 during this period constitutes the most 

 favorable climatic condition for the 

 growth and dissemination of the fun- 

 gus, while the new pear growth is very 

 tender, permitting scab infection to be 

 easily established. Hot, dry weather is 

 very unfavorable to scab and it does 

 not thrive after the period of spring 

 rains, but if a period of wet weather is 

 encountered later in the season new in- 

 fections will be formed. If infection 

 occurs when the fruit is about mature, 

 small scab spots are produced, but no 

 distortion occurs. (Figure 2.) Fre- 

 quently at this time the fungous growth 

 occurs around the margins of earlier 

 scab spots, so that these roughened 

 areas are often seen surrounded by a 

 fresh ring of dark velvety scab growth. 



Treatment — In the treatment of pear 

 scab it is important to dispose of all 

 possible sources of infection, and to 

 this end twig cankers, if present, should 

 be removed in pruning and the infected 

 wood burned. Some disposition should 

 also be made of fallen leaves, which 

 harbor the fungus over winter and 

 which are the most important source 

 of early spring infection. It is im- 

 practicable to rake and burn them, and 



Figure 3 — Power dusting machine in operation 



showing how the trees should be covered 



with dust. 



twigs but also on the fallen leaves. In- 

 fected leaves remaining on the ground 

 over winter permit the fungus to com- 

 plete a stage in its life history. In the 

 spring, at about the time the buds on 

 the pear trees are breaking, "winter 

 spores" are matured from the old scab 

 spots on the fallen leaves. These 

 spores are wafted about by the wind 

 and lodge on the tender buds and foli- 

 age, and if the moisture which is neces- 

 sary for their germination is present 

 infection proceeds and a new scab spot 

 is formed. This new scab spot produces 

 "summer spores" with great rapidity, 

 mature spores being formed within two 

 weeks if weather conditions are favor- 



FiouKE 4 — A Bartlett pe.nr twig, showing the 



condition of the buds at the time when the first 



scab spray or "delayed dormant" spray 



should be applied. 



