Plant Disease Management Handbook

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Begonia - Nematode, Foliar

Cause Two types of wood decay occur in living trees: white rots and brown rots. The more common fungal white rots in hemlock are caused by Ganoderma applanatus (white mottled rot), Ganoderma oregonense (spongy white rot), Phellinus nigrolimitatus (white pocket rot), and Porodaedalea pini (red ring rot).

Ganoderma sp. conk sent in for identification.

OSU Plant Clinic, 2023.

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Fir, True (Abies spp.) - Drought Injury

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Holly (Ilex spp.) - Sooty Mold

Note Manage aphids that excrete honeydew.

Black fungal sooty mold growth all across this leaf.

Clebson Goncalves, 2025.

Insects on the underside of this leaf are responsible for the honeydew leading to sooty mold.

Clebson Goncalves, 2025.

Anything honeydew drips on gets covered with sooty mold including leaves, stems, branches, and nuts.

Clebson Goncalves, 2025.

Stem of 'Lewis' hazelnut with back sooty mold.

OSU Plant Clinic image, 2011.

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Rhododendron - Cutting Rots

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Gladiolus - Fusarium Yellows and Corm Rots

Split corm of Freesia
Split corm of Freesia

Corm rot of this 'Red Beauty' freesia yielded both Fusarium sp. and Pythium.

OSU Plant Clinic image, 2013.

Cause The fungus Neonectria neomacrospora can cause a canker and dieback on true fir. Host species in the PNW where the pathogen has been detected include native species, such as Abies procera (noble fir), A. grandis (grand fir), A. amabilis (Pacific silver fir), A. lasiocarpa (subalpine fir), A.

By H. Fukada and L. J. du Toit

See:

Freesia - Corm Rot

Note Both Rhizoctonia and Fusarium have been found on corm rot samples by the OSU Plant Clinic.

Crocosmia bulb cut half longitudinally
Crocosmia bulb cut half longitudinally

Root and basal plate rot on these 'Limpopo' crocosmia which yielded both Rhizoctonia and Fusarium (as well as bulb mites).

OSU Plant Clinic Image, 2016.

Root and corm rot of this 'George Davidson' crocosmia yielded Fusarium.

OSU Plant Clinic image, 2015.

Cause The fungus, Fusarium oxysporum f. sp. corianderii, causes wilt and root rot of cilantro and has been reported in California, India, and South America. This strain of Fusarium can survive many years in soil in the absence of a cilantro crop.