210 



this area spreads eastward so as to include the Rock River valley, the 

 tributaries of the Illinois, and the watershed of Lake Michigan. 



Losses from this disease are probably greater than is ordinarily sus- 

 pected. Estimates of crop reductions for the years 1918-1923, inclusive, 

 and reproduced in Table 35, vary from a trace to 2 per cent. When 

 definite estimates have been made they have ranged from 33,000 to 199,- 

 000 bushels, and from $61,000 to $208,000 in valuation. 



The seriousness of black-rot infection is indicated by an examination, 

 made in 1922, of 22 orchards distributed among 18 counties and includ- 

 ing 54 acres. Of the trees 91.2 per cent were infected, and the notes in- 

 dictate that 27.3 per cent of the leaves and 0.92 per cent of the fruits were 

 diseased. 



To keep black rot under control it is necessary to cut out and burn 

 all dead wood in the trees, to cut out all cankers with sterile tools, to keep 

 fallen fruit picked up, and to apply an extra spray of Bordeaux in late 

 July or early August. 



Blister Canker 



Caused by NiDiunnlaria discrcta Tul. 



Blister canker, also known as "Illinois canker" and as "nail-head," 

 is one of Illinois' serious apple diseases. It was first reported in the state 

 by Hasselbring in 1902. Since that time the disease appears to have 

 been increasing and spreading steadily. This has been especially true 

 because of the large proportion of Ben Davis apples grown; for this 

 variety, more than any other, is susceptible to attack. Besides Ben Davis, 

 Delicious, Gano, and Willow Twig are especially susceptible. 



As usually seen in its advanced stages the blister canker is character- 

 ized by a covering of dead bark, often loose and shredding, through which 

 project warts having the appearance of heads of nails driven into the tree. 



The distribution of blister canker in Illinois is shown on Map 4?. It 

 reaches from the southern tip of the state, where infections have been 

 found in Massac and Pope counties, to the northern boundary, where in- 

 fections have been seen in Lake, McHenry, and Boone counties. The 

 disease is known to be present in Ofi of the 102 counties of the state, and 

 in practically all of the important apple-growing counties. As we know 

 it at present, the disease occupies a range of territory including, in south- 

 ern Illinois, the tributaries of the Wabash and Ohio rivers and, in the 

 extreme southwest, those of the Mississippi. Northward the disease is 

 wide-spread in the valley of the Mississippi and Illinois rivers. 



Injury by this disease results in the death of the wood. Girdling 

 eventually occurs, and all the twigs or branches beyond the girdle die. 

 Or, if the canker is on the main trunk, the whole tree dies. 



Crop losses from blister canker are large, and the disease is especial- 

 ly serious, because the damage done to a tree in one season can not be 

 repaired but continues to cause losses season after season. Anderson' 



' .\nilpison. H. W. Disea-ses of Illinoi.s Fruits. 111. Acf. Kxper. Sta. Circ, 241: 

 .31. 1020. 



