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Symptoms develop in spring and early summer.  As vessels become blocked, leaves turn dull green, bronze, or tan.

                 

Wilt appears from the top of the tree downward.

                 

On red oaks, leaves typically fall very rapidly.

                 

Red oaks are killed rapidly while white oaks are often able to tolerate infection indefinitely.  Here, an apparently healthy bur oak grows next to a dying red oak.

 

In white oaks, tyloses form rapidly, and extensively.  As a result, the fungus is contained and does not spread.

 

More tyloses.

 

White oaks form root grafts much less frequently than red oaks, and this might also help to explain why they are less susceptible to C. fagacearum.

 

In hardwood forests, oak wilt pockets begin with the death of a small number of trees.

 

The fungus spreads to neighboring trees.

 

The pocket grows as the fungus spreads from tree to tree. Oak wilt pockets can reach sizes of several hectares in the lake states. Pockets are smaller in the east.

           

 

Combined DBH (in.)	(Inter-tree distance in ft.) Loamy Sand	(Inter-tree distance in ft.) Sandy
2	3.1	3.9
4	6.2	7.8
6	9.3	11.6
8	12.4	15.5
10	15.4	19.4
12	18.5	23.3
14	21.6	27.2
16	24.7	31.0
18	27.8	34.9
20	30.9	38.8
22	34.0	42.7
24	37.1	46.6
26	40.2	50.4
28	43.2	54.3
30	46.3	58.2
32	49.4	62.1
34	52.5	66.0
36	55.6	69.8
38	58.7	73.7
40	61.8	77.6
42	64.9	81.5
44	68.0	85.4
46	71.1	89.3
48	74.1	93.1

 

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