Plant Disease Management Handbook

See:

Greenhouse Plants, Ornamental - Black Root Rot

See:

Greenhouse Plants, Ornamental - Pythium Seed Rot, Damping-off, and Root Rot

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Poinsettia (Euphorbia pulcherrima) - Bacterial Leaf Spot

Cause This fungal disease, caused by Alternaria alternata, has not been formally reported from the Pacific Northwest but has been found on a few samples sent to the OSU Plant Clinic. The disease is favored by prolonged cool, moist conditions and low nitrogen fertility. Older leaves are particularly susceptible if they are senescing. The fungus survives on dead leaves on the soil surface and spores are spread by air currents.

Cause Sclerotium cepivorum (teleomorph: Stromatinia cepivora), a fungus. Enough sclerotia from an initially high population may survive 20 to 30 years or more in soil without the presence of an Allium host to incite unacceptable levels of disease in the next Allium crop. Only Allium spp. such as onion, leek, and shallot are attacked.

Cause Puccinia allii on garlic, onion and wild Allium species. This fungus has caused major epidemics in California and losses in Arizona and Oregon. California isolates did not infect leek, shallot or elephant garlic. However, P. allii in Europe is extremely damaging on leek.

Cause Manganese toxicity due to low pH, especially below 5.

Symptoms Cloves have a loose internal structure, and internal tissues are discolored. The exterior of infected bulbs is white when compared to healthy bulbs.

Cultural control

Cause Ditylenchus dipsaci, several strains of which are known to be in Oregon. The only known hosts for the garlic strain belong to the onion family: garlic, onion, leek, and chive. However, it also attacks Shasta pea, parsley, celery, nightshade, and salsify.

Cause Botrytis porri and B. aclada (formerly B. alliiaclada), fungi. Both fungi are found in western Oregon but only B. porri is found on garlic east of the Cascade Range. These pathogens survive the winter on dead plant parts in soil, as sclerotia, and on infected bulbs. Infection occurs through neck tissue or through wounds in bulbs.

See:

Garlic (Allium sativum) - Neck Rot (Gray Mold)

Cause Botrytis squamosa, a fungus that is a problem only late in the season under high humidity, excessive rain, or irrigation. Does not occur in central or eastern Oregon.