Dutch elm disease in Illinois dutchelmdiseasei53cart Year: 1967 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 53 Fig. 1. The earliest visible symptoms of Dutch elm disease are the wilting, curling, and yel- lowing of leaves on one or a few branches. On this tree the wilted and curled leaves are evident on the branch at the left. wilt and die rapidly probably became infected during the previous growing season, at which time they would have shown no wilt symp- toms or only limited and relatively inconspicuous symptoms. Brown streaking develops in the sapwood of diseased branches. It appears most
Dutch elm disease in Illinois dutchelmdiseasei53cart Year: 1967 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 53 Fig. 1. The earliest visible symptoms of Dutch elm disease are the wilting, curling, and yel- lowing of leaves on one or a few branches. On this tree the wilted and curled leaves are evident on the branch at the left. wilt and die rapidly probably became infected during the previous growing season, at which time they would have shown no wilt symp- toms or only limited and relatively inconspicuous symptoms. Brown streaking develops in the sapwood of diseased branches. It appears mostly in the springwood of the current-season growth. In a cross-section of a branch, browning may appear as a series of dots in a single wood ring (Fig. 3) or the dots may be so abundant that the entire wood ring appears brown. In branches on which leaves wilt before summerwood is produced, the discoloration is usually conspicuous as fine streaks on the surface of the wood when the bark is carefully peeled from the diseased branch (Fig. 4). The outer sur- face of sapwood on trunks may also be brown (Fig. 5). The presence of brown discoloration in young sapwood is used in the field as a diagnostic symptom of Dutch elm disease. Although several wilt diseases of elm cause similar browning of young sap- wood, trees showing this discoloration in areas where Dutch elm disease occurs are most likely affected with Dutch elm disease. How- ever, if the presence of the fungus in the tree must be determined, it is necessary to make laboratory tests of specimens from the diseased tree. With these tests the organism involved is isolated and the spe- cific disease present is determined. However, in some instances the
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