68 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 



Plants that have large cankers or diseased areas on their 

 stems should be cut and burned. Those that show the disease on 

 only scattered branches need not be destroyed, but the diseased 

 branches should be removed and burned. Removal of all visible 

 infection in a branch is possible if this branch is cut off 18 inches 

 or more below the base of the external diseased area. Tools used 

 in removing a diseased branch should be treated with a disin- 

 fectant to prevent spread of the bacteria to other branches or 

 trees. All large wounds should be painted with a wound dressing, 

 as described under "Wound Treatment." Blossom blight and 

 twig blight infection can be prevented or reduced by applying 

 one or two sprays of copper sulfate, 4 pounds in 100 gallons of 

 water, at 2-week intervals before buds open. Spread of twig 

 blight during prolonged wet springs can be prevented by spray- 

 ing with streptomycin as recommended by the manufacturer. 

 The first spray should be applied as soon as twig blight appears 

 and additional sprays at 7-day intervals until July 15. 



OAK 



The oak is subject to several destructive diseases. Oak wilt 

 is the most destructive disease of oak in Illinois. 



Anthracnose. — This leaf disease, as caused by the fungus 

 Gnomonia veneta, affects both white oak and sycamore. On white 

 oak, anthracnose develops as irregular brown diseased areas 

 along the midribs and lateral veins of leaves (Fig. 64). In some 

 cases, the blades of most leaves of affected trees are killed, es- 

 pecially the blades of leaves on the lower branches. Dark brown 

 fruiting bodies (pustules) of the fungus appear on the diseased 

 areas of the leaves, especially on the midribs and veins. These 

 raised pustules or bumps can be seen with a hand lens and occa- 

 sionally with the naked eye. The fungus may spread from the 

 leaves into the twigs, where it produces cankers or causes twig 

 dieback. 



Control for anthracnose in oak includes burning of diseased 

 leaves and twigs and spraying of affected trees. Fallen leaves 

 and twigs should be gathered and burned in the autumn. When- 

 ever possible, diseased twigs should be removed and burned. 

 Spraying with organic mercury or Bordeaux mixture (copper 

 sulfate and hydrated lime) is recommended for the prevention 

 of leaf infection in the spring (Table 1). The first spray should 

 be applied when the leaves are about half grown. In wet springs, 

 a second spray should be applied 14 days later. Oak trees that 



