Involvement of Soilborne Phytophthora Species in Northeast Illinois Rapid Oak Decline and the Effect of Site Factors on the Disease

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Figure 1.
Locations of the 18 study sites in the Chicago region with rapidly declining trees. Numbers refer to Table 3.
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Figure 2.
Depth of the perched water table on soils with good and poor drainage, and daily rainfall, during the spring months of 2022. Measurement calendar dates were 2022 April 10, 15, and 29, May 17, June 7 and 28, and July 13.
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Figure 3.
Soil water content in the upper 20 cm on soils with good and poor drainage, and daily rainfall, during the spring months of 2022. On poorly drained sites, soil moisture content was consistently above field capacity (horizontal dashed line) even after the water table had receded to as much as 25 cm below the surface (Table 2). Measurement calendar dates were 2022 April 10, 15, and 29, May 17, June 7 and 28, and July 13.

Table 1.

Soil series, slope, and drainage class of soils occurring on sites with rapidly declining oaks (Natural Resources Conservation Service [NRCS] 2024).

Table 3.

ELISA test results from the 18 oak decline survey sites.

Site #	Site character	Soil series	# Tested	# Positive
1	Park-like	Grays	7	4
2	Park-like	Ozaukee, Ashkum	8	6
3	Park-like	Ozaukee, Beecher	10	10
4	Residential	Nappanee	3	3
5	Residential	Ozaukee	1	1
6	Natural	Ozaukee	3	3
7	Park-like	Zurich	1	0
8	Park-like	Zurich	4	4
9	Park-like	Del Rey	3	3
10	Park-like	Ozaukee, Kane	5	5
11	Residential	Urban land	6	5
12	Park-like	Fox	2	1
13	Park-like	Ashkum	3	3
14	Park-like	Ozaukee	2	1
15	Park-like	Ozaukee	4	4
16	Park-like	Ozaukee	5	5
17	Park-like	Beecher, Blount	9	7
18	Park-like	Ozaukee	11	11
Total			87	76
			% Positive	87%