Wednesday, July 29, 2015

Phymatotrichum root rot appearing in Southern New Mexico

A composite photo of a pear tree. The tree on the left is showing leaves that are turning yellow and brown. The tree on the right is the same tree seven days later with dark brown dead leaves.
Pear tree infected with Phymatotrichopsis omnivora
(these two photos were taken one week apart)
(Photo: NMSU-PDC)
A microscope photo of the characteristic cross-shaped fungus strands
Characteristic cruciform (cross-shaped) hyphae of
Phymatotrichopsis omnivora (Photo: NMSU-PDC)
Featured Diagnosis: Phymatotrichum root rot. This disease is also commonly known as Texas root rot or cotton root rot. It is caused by the soil-borne fungus Phymatotrichopsis omnivora. The fungus has an extremely wide host range that affects more than 2,300 species of dicotyledonous (broad-leafed plants). This disease produces very distinctive symptoms on plants and characteristic fungal structures which make diagnosis relatively easy (assuming the plant specimens evaluate contain the appropriate material). The most noticeable symptom on plants is rapid death of the crown with leaves remaining attached to the plant. Although the plant may have been infected for some time, symptoms appear quickly making it seem as if the plants died in a matter of days! The fungus produces fungal strands on roots which produce characteristic cruciform (cross-shaped) hyphae. Observation of cruciform hyphae under the microscope is a confirmation of the disease. The fungus is VERY LIMITED geographically to parts of the Southwestern United States and Mexico. Even within its geographical boundaries, the fungus is spotty in occurrence. The pathogen may be so isolated that it is only found in small areas; areas small enough that only one or a few plants are affected. It may also be found in larger areas where many plants may be affected. It is found only at elevations below 5,000 feet. In New Mexico, the disease has been found only in the southern part of the state (see map).

If you are concerned that you may have a plant with this disease, please contact your local county extension agent for assistance in submitting specimens for diagnosis.

Read on for more information on pecan diseases

Map of New Mexico showing the locations where Phymatotrichum has been found
New Mexico Counties were Phymatotrichum
root rot has been confirmed since 1993
Large tan fungal spore mat on the ground
Spore mat on Phymatotrichopsis omnivora
on the soil (Photo: R. B. Hine,
University of Arizona)

Cotton field with a large patch of dead plants
Phymatotrichum root rot on cotton
(Photo: NMSU-PDC)
A composite photo of fungal strands on roots; the photo on the left shows a strand on a cotton root and the photo on the right shows a strand on a pecan root.
Fungal strands of Phymatotrichopsis omnivora
on a cotton root (left) and a pecan root (right)
(Photos: NMSU-PDC, left; and R. B. Hine,
University of Arizona, right)

A composite photo showing two dead pecan trees
Phymatotrichum root rot on pecan trees
(Photos: NMSU-PDC)

Two men digging up a dead pistachio tree
Phymatotrichum root rot on a pistachio
tree (Photo: NMSU-PDC)

A composite photo showing a dying tree with a close up of the branches. The insert photo shows a microscopic image of the fungal hyphae (strand).
Phymatotrichum root rot on Chinese pistache (left); Close up of leaves clinging to the branches (right);
Fungal strand from the roots of this tree (insert). (Photos: NMSU-PDC)

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