Plant Disease Management Handbook

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California Poppy (Eschscholzia californica)

Cause The fungus-like microorganism Phytophthora cinnamomi has been reported and found frequently in Oregon. Waterlogged soils and warm temperatures favor P. cinnamomi. It survives unfavorable periods in soil and infected plant debris. Under favorable conditions, spores germinate and infect roots. After infection, the microorganism spreads mainly in the inner bark tissues of the root and stems.

Image related to Erica sp. (Heath)-Root Rot

These limbs have died back due to a Phytophthora root rot.

OSU Extension Plant Pathology Slide Set, 1991.

Leaves turn grayish and large portions have died back due to Phytophthora root rot.

OSU Plant Clinic Image, 2014.

Cause Nectria cinnabarina, a fungus. It is a common saprophyte on many plant species. The fungus colonizes bark, cambium, and sapwood of stems weakened by freezing, drought, mechanical injury, or other diseases.

The little dots on this branch are pinkish-red fruiting bodies of the fungus.

Photo by Iain MacSwann, 1962.

Image related to Elm (Ulmus spp.)-Nectria Canker

These stems are discolored and have perithecia.

Melodie Putnam, 2010.

Cause Ophiostoma ulmi (formerly Ceratocystis ulmi) and O. novo-ulmi, fungi with many subgroups. The first of two North American epidemics began in the 1920s with the introduction of a relatively non-aggressive subgroup, which reduced the native elm population. A second, more destructive epidemic began in the 1940s with the introduction of a more aggressive subgroup, which has been found in Oregon.

Image related to Elm (Ulmus spp.)-Dutch Elm Disease

It is important to scout for and quickly diagnose limb problems during the summer. Symptoms of this disease can occur very quickly.

OSU Extension Plant Pathology Slide Set, 1976.

Discolored cambium has been exposed using a pocket knife.

Photo by Jay W. Pscheidt, 1996.

Crown symptoms progress from the top of the tree down to lower limbs.

Jay W. Pscheidt, 2013.

Marginal leaf burn may be seen on leaves as the vascular system collapses.

Jay W. Pscheidt, 2013.

Trees can die rapidly during the spring and summer.

OSU Extension Plant Pathology Slide Set, 1977.

Many trees in an area can die from Dutch Elm Disease from root grafts and insect flights.

OSU Extension Plant Pathology Slide Set, 1975.

Elm logs saved for firewood contribute greatly to the DED problem. These logs had numerous bark beetle galleries and should not have been saved.

Photo by Jay W. Pscheidt.

Camperdown Elms are also susceptible and can die within a few months of infection.

Jay W. Pscheidt, 1990's.

Cause Wetwood is associated with bacteria including Enterobacter nimipressuralis, Bacillus megaterium, and Pseudomonas sp. Liquid accumulates in diseased tissue of the tree which is then colonized by the bacteria. Anaerobic growth of the bacteria produces gas inside the tree. The high gas pressure forces liquid out of the tree where it dries on the bark. A higher pH also can be detected in diseased tissue.

Image related to Elm (Ulmus spp.)-Bacterial Wetwood

Exudate originates from a torn branch wound.

Jay W. Pscheidt, 2013.

Active slime flux may be wet as shown here but can dry up and only look like the bark is stained.

Jay W. Pscheidt, 2013.

Note the staining of the trunk originating from the pruning cut.

Photo by Jay W. Pscheidt, 1996.

See:

Pepper (Capsicum spp.) - Verticillium Wilt

Image related to Eggplant (Solanum melongena)-Verticillium Wilt

Photo by Melodie Putnam, 1999.

2007 OSU Extension Plant Pathology Image

This is a cross section through the stem showing discolored dark vascular bundles.

Albert Paulus

Cause Phytophthora capsici, a fungus-like microorganism. This soil-inhabiting organism causes root rot in pepper and eggplant and is most active in moist, warm weather (75°F to 91°F). Disease is generally seen in the wettest areas of a field.

See:

Potato (Solanum tuberosum) - Late Blight

Tomato (Lycopersicon esculentum) - Late Blight

Chemical control

Cause Cercospora melongenae, a fungus that survives at least one year in infected plant debris or in soil. Wet leaves and a high relative humidity favor disease development.

Cause Colletotrichum coccodes (formerly C. atramentarium), a fungus that is saprophytic part of its life cycle and may survive from year to year in the soil and infected crop residues. Solanaceous crops and weeds are all hosts. Seed may also be infected. Free moisture and mild temperatures are conducive for disease with 68°F to 76°F being optimum for infection.