Oleander Knot - Olive Knot

Fig 1. Young galls on young branch http://www.australianolives.com.au/archives/olive%20knot%20photos/young-galls.jpg"	Fig 2. Young gall on twig http://www.australianolives.com.au/archives/olive%20knot%20photos/galltwig.jpg
Fig 3. Galls on main trunk around pruning wounds http://www.australianolives.com.au/archives/olive%20knot%20photos/gall-trunk.jpg	Fig 4. Older gall http://www.australianolives.com.au/archives/olive%20knot%20photos/older-gall.jpg
Figures from the Australian Olive Association Website

Oleander Knot - Olive Knot

Oleander knot is caused by Pseudomonas syringae pv. savastanoi. Bacteria survive the winter in infected plants. They also exist as epiphytes (on the surface) of the bark and leaves of trees. Rainy periods with temperatures around 72-77慚 are optimum for infection. The bacterium enters plants via wounds, natural openings, mechanical means such as pruning, and frost damage. Water splash and pruning tools are the most common local methods of dispersal as well as purchasing infected plant material. Leaf injury immediately prior to or proceeding infection causes the greatest symptoms. The bacterium cannot enter the plant by its own means.

Signs and Symptoms

Cream/white, small, rough growths are produced on all above-ground plant parts but not underground. These growths (galls) become larger, up to one inch in diameter, and black with age. Infected stems show signs of cankers with deep fissures in them. Bacteria may ooze from the galls or cankers.

Plant Health Management

Purchase gall-free plants
Remove diseased areas: Prune plants several inches below the galls and place trimmed areas into a container or bag for disposal. Treat open wounds with 10% bleach and dip pruning tools in bleach after EACH cut to prevent further spread.
Water management: Since bacteria are dispersed by water, avoid watering shortly after pruning. It is best to prune in the dry seasons for this reason where feasible.
Remove entire plant if too large to prune effectively.

References

Jones, Ronald K. and D. Michael Benson. 2001. Diseases of woody ornamentals and trees in nurseries. American Phytopathological Society, APS Press, St. Paul, MN. pg. 251-252.
Olsen, Mary. 1999. Diseases of urban plants in Arizona. Cooperative Extension, University of Arizona, Tucson, AZ. pg. 19-20.

Useful Links

University of Arizona

Australian Olive Association

Highlighted Area

Galls are formed by the bacteria synthesizing indoleacetic acid (IAA), a growth regulator, for tissue proliferation

Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was researched and drafted by: Jennifer Fleer, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided link directly to the Australian Olive Association web site

Questions, Comments, Complaints and Complements?

This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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