225 



The known occurrence of leaf blight in Illinois is shown on Map 

 71. It has been found in 56 counties widely distributed over the state. 



Loss from this disease is difficult to estimate, but it was less than 1 

 per cent in 1923 and about 1 per cent in 1923. The field notes for 1923 

 indicate that of the plum trees examined in 9 counties 100 per cent were 

 afTected, each tree having more than 90 per cent of its leaves spotted by 

 this disease. 



Control of leaf blight is obtained by the use of the usual sprays, 

 though in this case the addition of lead arsenate to the lime-sulfur in- 

 creases its effectiveness, while a further addition of iron sulfate (1^4 

 pounds to 50 gallons of spray) lessens the injury to the foliage. 



Bl,ACK-KN0T 



Caused by Dibotryoii morbosum (Schw.) T. & S. 



Unique among the diseases of stone fruits is the black-knot of plum, 

 in that it is wholly confined to the woody part of the tree, and the injury 

 which it causes is permanent. 



It first appears on young branches, where it causes knots up to six 

 inches in length and half an inch in diameter. The knots are usually on 

 but one side of the twig, though they often completely encircle it. They 

 are at first greenish and quite soft but later become black and hard. 



The history of black-knot in Illinois, so far as known, dates from 

 the year 188", when it was found at Edgewood, Efifingham county. In 

 1898 it was reported from Clark county, in 1899 from Marion and Stark 

 counties, in 1900 from Cook and Madison counties, and in 1903 from 

 Edgar countj'. The majority of these early collections were presumably 

 from nurseries, as they are among the collections of the State Nursery 

 Inspector. In 1911 Burrill reportefl the disease in Champaign, Clark, 

 and Montgomery counties, with the notation that it was serious locally. 

 In 191.3 he added Bond, Coles, and Crawford counties to the list, saying 

 that black-knot was common in the last two. 



The distribution of black-knot as known at the present time is shown 

 on Map ?2. It is known to occur in only 21 counties, few of which are 

 in the northern part of the state. 



The best protection against the losses which black-knot causes, lies 

 in the use of resistant varieties, among which the Wild Gocse is pre- 

 eminent. With other varieties constant watchfulness is necessary to in- 

 sure cutting out all knots as soon as they are recognized. Badly affected 

 trees are beyond hope and had better be cut down at once. Spraying is 

 not effective. 



Scab 



Caused by Cladosporium carpophilum Thuem. 



Pliuii .scab is apparently of rare occurrence in Illinois. L'p to the 

 ]jresent tinie it has been found in only three counties along the northern 



