Plant Disease Management Handbook

See:

Greenhouse Plants, Ornamental - Impatiens Necrotic Spot

Symptoms Leaves, especially the youngest ones, may become strap-like or narrower than normal.

See:

Peony (Paeonia spp.) - Stem Rot

Petunia (Petunia spp.) - Stem Rot

Note the sclerotia begining to form within the mycelial masses along this stem.

Photo by Stacey Fischer.

Cause Several fungi including Septoria tageticola, Alternaria sp., and Cercospora sp. Although there are no published reports of finding these fungi in the Pacific Northwest, the OSU Plant Clinic has found Alternaria leaf spot. Cultivars of the African marigold (T. erecta) are susceptible to S.

See:

Petunia (Petunia spp.) - Damping-off

Aster - Wilt

See:

Petunia (Petunia spp.) - Damping-off

Alternaria was found in the small, ground line lesions girdling these seedlings. Wound normally expect organisms such as Rhizoctonia in this case.

OSU Plant Clinic Image, 2018.

See:

Greenhouse Plants, Ornamental - Gray Mold

Image related to Marigold (Tagetes spp.)-Botrytis Blight

Flower petals become water soaked and brown and may show the gray sporulation of the fungus.

Jay W. Pscheidt, 2013.

The gray fuzz characteristic of this disease consists of spores of the fungus.

Jay W. Pscheidt, 2013.

See:

Pansy (Viola spp.) - Thielaviopsis Root Rot (Black Root Rot)

See:

Verticillium Wilt in the Pacific Northwest

Branch dieback and death in vine maple (left), black maple (center) and Norway maple (right) caused by Verticillium wilt.

Photos courtesy of Jerry E. Weiland (USDA-ARS).

Sugar maple with Verticillium wilt.

Jerry Weiland (USDA-ARS)

Red maple with Verticillium wilt.

Jerry Weiland (USDA-ARS)

Vascular discoloration of vine maple (bottom right) caused by Verticillium wilt. Note how the discoloration occurs along the direction of the grain and appears as a circular or semicircular pattern in cross section.

Jerry Weiland (USDA-ARS)

A cross section of the stem will show vascular discoloration in rings or arcs as can be seen in the stem on the right.

Jay W, Pscheidt, 2008.

Vascular discoloration of sugar maple caused by Verticillium wilt. Note how the discoloration occurs along the direction of the grain.

Jerry Weiland (USDA-ARS)

Cause Rhytisma punctatum, a fungus. The disease is common on bigleaf maple on the Pacific Coast and also attacks many other species, particularly silver, mountain, and striped maple. The fungus overwinters in stroma on fallen leaves. Leaf areas with stroma do not decompose as fast as areas that are not infected. Infection occurs as spores are ejected from these overwintered leaves during rainy periods in the spring.

Numerous tar spots can show up on leaves in the fall.

Jay W. Pscheidt, 2018.

Image related to Maple (Acer spp.)-Tar Spots

Note the large leaf spots on these big leaf maples.

Photo by Iain MacSwann, 1980.

The stroma of the fungus can easily been seen in the center of the lesions.

OSU Plant Clinic Collection, 2011.

The green island effect is easily seen on this detached maple leaf. The effect is thought to be due to the production of cytokinins by the fungus.

Jay W. Pscheidt, 2018.

Cause Phyllactinia marissallii, a fungus that attacks only maple. Sawadaea bicornis has been found in all states on bigleaf and Norway maple. It is suspected that this fungus was introduced into North American sometime before 1938 from Europe. S. tulansnei has been found in Idaho and Oregon on Norway maple.

Note the white patches on these leaves.

Jay W. Pscheidt, 2020.

White colonies of this fungus can cover the leaf surface.

Photo by Jay W. Pscheidt, 1999.

Image related to Maple (Acer spp.)-Powdery Mildew

Norway maple in nursery with powdery mildew.

Robin Rosetta, 2006.

Sawadaea sp. of powdery mildew on Acer macrophyllum (bigleaf maple) on the BC Lower Mainland.

Janice Elmhirst, 2012.