Plant Health Update, May 2025 Summary

Published Jul. 2025|Id: EPP-25-35

By Jennifer Olson

This year, we had an extended period of rainy weather with moderate temperatures (50-85F). These conditions are highly favorable for leaf spot diseases, and we have seen an increase in sample volume of plants with leaf spot problems (Figure 1).

A close up view of a green leaf with small holes and red coloring around the holes.

Figure 1. Close-up of a hydrangea with a fungal leaf spot disease. Photo by Holly Dobbs, Rogers County Extension.

Leaf spot diseases may be serious in years with rainy spring weather, but are minor in years with less rain or warmer temperatures. Leaf spot diseases are best managed with a combination of cultural and chemical strategies which are outlined below.

Select plants that have resistance to leaf spot diseases.
Follow planting guidelines and ensure that plants are properly spaced. Overcrowded plants are more likely to develop leaf spot problems.
Ensure that plants have good air circulation. Prune plants to reduce crowding, as needed.
Remove spotted leaves and discard them in the trash.
Avoid overhead irrigation (sprinklers). When providing supplemental water, direct the water at the roots.
Use proper fertility. Plants that are over fertilized with nitrogen are more likely to develop leaf spot diseases.
Apply fungicides, if desired. When using fungicides, it is best to apply them when the disease level is low. The products will not cure leaves once they are already blemished. There are both organic and conventional fungicides for leaf spot diseases. Review and follow the label when mixing and applying chemicals.
If disease levels are high, consider replacing the plant with one that has increased resistance to the disease or another type of plant.

A summary of plant health problems from Oklahoma specialty crop growers (horticultural crops) is provided in Table 1. The volume of samples submitted to the lab has increased with the warmer weather.

Table 1. Summary of samples and diagnostic results for May 2025 from Oklahoma Specialty Crop Growers.

Table 1a. Samples that were submitted April 2025, but not complete until May 2025
Number	Host	County	Diagnosis/Identification	DD	M	C	MD	DS
1	Boxwood	Cherokee	Environmental/cultural problem		X	X	X	X
2	Falsecypress	Cherokee	Phytophthora blight		X	X	X	X
3	Fruit	Payne	Canker fungi and Pythium irregular		X	X	X	X
4	Geranium	Payne	False rust (Synchytrium sp.)		X		X	X
5	Italian Cypress	Garfield	Environmental stress, Opportunistic Fungi		X	X	X	X
6	Japanese Maple	Cherokee	Canker-Botryosphaeria seriata		X	X	X	X
7	Japanese Yew	Oklahoma	Branch decline		X	X	X	X
8	Magnolia	Alfalfa	Environmental stress	X
9	Oak	Oklahoma	Oak anthracnose, scales		X	X	X	X
10	Pecan	Tulsa	Pecan bunch disease		X		X	X
11	Pecan	Tulsa	Phytoplasma not detected		X		X	X
12	Pecan	Tulsa	Phytoplasma disease		X		X	X
13	Pecan	Tulsa	Phytoplasma not detected		X		X	X
14	Pecan	Tulsa	Pecan bunch disease		X		X	X
15	Viburnum	Cherokee	Botryosphaeria canker		X	X	X	X

Table 1b. Submitted May 2025
Number	Host	County	Diagnosis/Identification	DD	M	S	C	N	MD	DS	RS
1	African Violet	Carter	White flies	X
2	Apple	Okfuskee	Branch dieback, unidentified cause	X
3	Apple	Ottawa	Fire blight	X
4	Apple	Craig	Fire blight, Frog eye spot	X
5	Apple	Woods	Rust, Sapsucker injury, Schizophyllum commune	X
6	Apricot	Pottawatomie	Mechanical damage suspected	X
7	Arborvitae	Oklahoma	Wound canker, Environmental stress	X
8	Ash	Oklahoma	Blackheaded ash sawfly (Tethida barda)	X
9	Ash	Garfield	Ash rust, Puccinia sp.	X
10	Bald cypress	Carter	Environmental/cultural problem	X
11	Barberry	Cherokee	Rhizoctonia root and stem rot				X		X	X
12	Bermudagrass	Texas	Environmental stress	X
13	Bermudagrass	Oklahoma	Environmental/cultural problem	X
14	Bermudagrass	Blaine	Winterkill, Animal urine damage	X
15	Black raspberry	Payne	Cultural problem		X		X		X	X
16	Blackberry	Grady	Leaf spot fungus (transferred to researcher)		X		X		X	X
17	Burning bush	Cleveland	Nutritional deficiency		X
18	Cantaloupe	Wagoner	Suspected for bacterial fruit blotch		X		X		X	X
19	Chocolate Daisy	Carter	Spider mites	X
20	Coneflower	n/a	Aster yellows suspected	X
21	Crape myrtle	Oklahoma	Herbicide injury		X				X
22	Cypress	Oklahoma	Seiridium canker		X
23	Cypress	Blaine	Seiridium canker suspected	X
24	Cypress	Oklahoma	Seiridium canker suspected	X
25	Dahlia	Logan	Environmental stress, Opportunistic Fungi		X	X
26	Daylily	Cherokee	Distortion-suspected cold temperatures		X
27	Dianthus	Cleveland	Two-spotted spider mites		X
28	Eastern red cedar	Rogers	Branch dieback, wound injury suspected	X
29	Elm	Cleveland	Dutch elm disease		X		X
30	Elm	Oklahoma	Dutch elm disease		X		X
31	Elm	Oklahoma	Leaf spot-Botryosphaeria		X		X		X	X
32	Elm	Canadian	Native elm wilt-Dothiorella		X		X		X	X
33	Forsythia	Ottawa	Fungal root rot suspected	X
34	Fruit	Payne	No pathogen found		X		X		X	X
35	Fruit	Payne	Canker fungus, first report		X		X		X	X
36	Fruit	Payne	Canker fungus, first report		X		X		X	X
37	Fruit	Payne	Canker fungus, first report		X		X		X	X
38	Fruit	Payne	Spider mites and thrips damage		X
39	Fruit	Payne	Canker, root rot-Pythium		X		X		X	X
40	Fruit	Payne	Spider mites and thrips damage		X	X			X
41	Fruit	Payne	Fusarium root rot		X		X		X	X
42	Fruit	Payne	Phomopsis canker			X	X		X	X
43	Fruit	Payne	Botryosphaeria canker		X	X			X	X
44	Fruit	Grady	Leaf spot (Didymella)		X		X		X	X
45	Garden	Roger Mills	Root knot nematodes		X			X
46	Garden	Roger Mills	Nematode problem not found		X			X
47	Garden	Roger Mills	Root knot nematodes		X
48	Garden	Payne	Weevil/Billbug (Sphenophorus sp.)	X	X						X
49	Garden	Pontotoc	Slime mold	X
50	Grape	Oklahoma	Dark flower scarab beetle	X
51	Grape	Grady	Black rot	X
52	Green bean	Blaine	Insect damage suspected	X
53	Hackberry	Logan	Petiole gall, Herbicide injury			X
54	Hackberry	Canadian	Petiole and nipple galls, Borers		X		X		X	X
55	Holly	Cleveland	Mulberry whitefly		X
56	Holly	Cleveland	Armored scales		X
57	Hosta	Oklahoma	Cultural problem		X	X			X
58	Hydrangea	Cherokee	Bacterial leaf spot-Xanthomonas			X
59	Hydrangea	Garfield	Herbicide injury		X
60	Juniper	Jackson	Seiridium canker		X		X		X	X
61	Juniper	Beaver	Environmental stress	X
62	Landscape and garden	Garfield	Herbicide injury	X
63	Loblolly pine	Oklahoma	Dothistroma needle blight, insect damage		X		X	X	X	X
64	Magnolia	Oklahoma	Environmental stress, Opportunistic Fungi	X	X
65	Magnolia	Alfalfa	Environmental stress	X
66	Magnolia	Garfield	Environmental stress	X
67	Mahonia	Garfield	Herbicide injury		X
68	Maple	Payne	Root or trunk fungus suspected				X		X	X
69	Oak	Oklahoma	Canker fungi (Cytospora, Dothiorella, Diplodia)		X		X		X	X
70	Oak	Stephens	Bacterial wood	X
71	Oak	Payne	Environmental stress, Diatrypella		X		X		X	X
72	Oak	Stephens	Environmental stress	X
73	Oak	Oklahoma	Fuscoporia sp.				X		X	X

Table 1b. Submitted May 2025 (Continued)
Number	Host	County	Diagnosis/Identification	DD	M	S	C	N	MD	DS	O
74	Oak	Pontotoc	Oak anthracnose	X
75	Oak	Pontotoc	Sapsucker damage, Branch dieback	X
76	Oak	Payne	Root injury, Phytophthora root rot suspected	X
77	Oak	Oklahoma	Iron chlorosis	X
78	Oak	Mayes	Bot canker; Wood decal fungus (Order Xylariales)				X		X	X
79	Oak	Logan	Kermes scale	X
80	Oak	Seminole	Branch dieback, lichens	X
81	Oak	Jackson	Iron chlorosis	X
82	Oak	Creek	Oak decline	X
83	Oak	Oklahoma	Ganoderma root rot suspected	X
84	Oak	Beaver	Environmental stress	X
85	Panicle Hydrangea	Oklahoma	Suspected cold temperature injury		X	X
86	Peach	Murray	Insect and mechanical damage	X
87	Peach	Pontotoc	Bacterial leaf spot	X
88	Peach	Pontotoc	Suspected white spring moth	X
89	Peach	Okfuskee	Shot hole, Insect damage	X
90	Peach	Le Flore	Insect damage	X
91	Pear	Grady	Slime mold	X
92	Pear	Cherokee	Canker disease (Various fungi)		X	X	X		X	X
93	Pecan	Marshall	Decline (Diaporthe sp.)		X		X		X	X
94	Pecan	Marshall	Fusarium root rot		X		X		X	X
95	Pecan	Marshall	Fusarium and Pythium root rots		X		X		X	X
96	Pecan	Marshall	No plant parasitic nematodes					X	X
97	Pecan	Marshall	Decline (Diaporthe sp.)		X		X		X	X
98	Peony	Cleveland	Nutritional deficiency		X				X
99	Peony	Cleveland	Nutritional deficiency		X				X
100	Peony	Cleveland	Nutritional deficiency		X				X
101	Peony	Cleveland	Nutritional deficiency		X				X
102	Peony	Cleveland	Nutritional deficiency		X				X
103	Phlox	Garfield	Mechanical injury		X
104	Pin oak	Payne	Phlebiopsis sp. (P. crassa suspected)		X				X	X
105	Pin Oak	Payne	Hypoxylon (Biscogniauxia) canker		X		X		X	X
106	Pine	Pontotoc	Diplodia tip blight, Sapsucker damage	X
107	Pine	Beaver	Environmental stress, root problem suspected	X
108	Pine	Beaver	Diplodia tip blight	X
109	Plant Identification	Stephens	Vetch	X
110	Potato	Pontotoc	Early blight suspected	X
111	Red oak	Mayes	Lecanium scale, Leaf miner, Stress		X
112	Redbud	Pottawatomie	Environmental stress	X
113	Redbud	Grady	Cercospora leaf spot suspected	X
114	Rose	Tulsa	Rose rosette disease		X				X
115	Rose	Tulsa	Rose rosette disease		X				X
116	Rose	Payne	Cane borer			X
117	Rudbeckia	n/a	Septoria leaf spot suspected	X
118	Sedum	Logan	Leaf spot-Septoria suspected	X
119	Shasta daisy	Logan	Environmental stress	X
120	Spruce	Oklahoma	Branch dieback (unidentified agent)	X
121	Strawberry	Tulsa	Rhizoctonia crown rot, Charcoal rot		X		X		X	X
122	Strawberry	Tulsa	Pythium root rot		X			X	X	X	X
123	Sweet gum	Lincoln	Decline-Botryosphaeria dothidea, Peniophora sp.				X		X	X
124	Sycamore	Payne	Sycamore anthracnose		X
125	Sycamore	Major	Sycamore anthracnose	X
126	Sycamore	n/a	Cladoptosis, surface roots	X
127	Sycamore	Garfield	Environmental stress	X
128	Sycamore	Garfield	Cladoptosis, environmental stress		X
129	Sycamore	Payne	Phomopsis canker		X		X		X	X
130	Sycamore	Wagoner	Herbicide injury	X
131	Sycamore	Grady	Sycamore anthracnose	X
132	Tomato	Ottawa	Cutworms suspected	X
133	Tomato	Stephens	Spider mites, herbicide injury	X
134	Tomato	Craig	Herbicide injury	X
135	Tomato	Garfield	Thrips, Herbicide injury		X	X
136	Tomato	n/a	Nutrient deficiency suspected	X
137	Tomato, Pumpkin	n/a	Edema, cultural problem	X
138	Tree	Blaine	Bark loss, undetermined cause	X
139	Variegated liriope	Cherokee	Fusarium crown rot		X		X		X	X
140	Verbena	Cleveland	Spider mites, Thrips		X
141	Virginia pine	Tulsa	Needle blight (Mycosphaerella)		X		X		X	X
142	Weed ID-turf	Major	Field bindweed	X
143	Weeping Alaska cypress	Payne	Seiridium canker		X		X
144	White gaura	Payne	Fasciation (abiotic); Leaf spot		X				X
145	Wisteria	Craig	Aphids	X
146	Zucchini	Stephens	Herbicide injury	X

Table 1c. Key for Diagnostic Testing Methods
Key	Diagnostics Method
DD	Digital Diagnosis
M	Microscopy
S	Serological tests
C	Culture analysis
N	Nematode analysis
MD	Molecular diagnostic methods
DS	DNA sequencing
RS	Referral to specialist
O	Other diagnostic tests

Fire blight has been a significant problem this spring and symptoms may be present on apples, pears and related hosts. For information about fire blight, review this newsletter article.

At this time of the year, fire blight is managed by removing blighted shoots. It is best to cut at least 12 inches into healthy wood to remove the pathogen. After each cut, clean hand pruning tools with a disinfectant (ie. Lysol spray, 10% household bleach solution). Pruning for the purpose of removing diseased plant tissue can be done at any time of the year, but it is best to prune when the plant is dry and dry weather is expected for a few days.

In some cases, fire blight can be difficult to remove by pruning. In Figure 2, fire blight has killed the branch on the left side of the pear tree. The limb should be removed by pruning as soon as possible, but the bacteria may have already infected the trunk. This tree is in my own landscape, and the limb has now been removed. The best approach is to “wait and see” if my pruning effort is successful. The tree will likely decline over the next few years. In preparation, I am shopping for a new fruit tree to install in another area of the landscape this fall. (One that is resistant to fire blight.)

A small tree with a damaged branch with brown leaves.

Figure 2. Fire blight, a bacterial disease, has caused the limb on the left side of this pear tree to die.

Look for additional plant health updates from the PDIDL throughout 2025. If you have suggestions for future topics, please contact jen.olson@okstate.edu or call the PDIDL at (405) 744-9961.

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