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Tuesday, September 22, 2015

Canary Island Date Palm Dying May Be Disease

Q. I had a mature canary palm in my back yard for about 10 years. This summer it became infected and died. I have a monthly service with a landscaping company and, despite their efforts, was to no avail. Do you suggest I plant another one or buy a different type of palm? It was in the center of our yard and served as a focal point to our landscaping.

A. Depending on why the palm became sick will determine if you can replant in the same hole. In California this palm is susceptible to a disease called Fusarium wilt which can contaminate the soil in the planting hole and prevent you from planting a new one in that spot. To my knowledge, this disease has not been reported on this palm in southern Nevada but your description fits.
            Older or lower leaves sometimes die before the newest leaves in the center begin to turn brown and die. In some cases leaves or fronds in the center of the canopy may die while the lower leaves appear healthy. And in even other cases, leaves on one side of the palm may brown while the other side remains green.
            Often, leaf fronds turn yellow before dying so it’s possible to confuse it with the chlorosis such as iron chlorosis or other micronutrients like manganese. The yellowing leaves may be confused with over watering symptoms. Infected palms frequently die in a couple of months or in some more rare cases die a slow death over several seasons.
            This disease can be spread on pruning tools such as chainsaws so it is important that these tools be sanitized properly between trees and between cuts if the tree is suspected of having this disease.
            Another point of entry for this disease is through the roots. If soils around this palm tree are kept excessively wet by watering daily or the soil does not drain very well, this could increase the chances of this disease.
            This disease can sit in the soil and remain active for 20 years or more so I would not recommend planting another Canary island date palm in that same hole. You would select plants that are more tolerant to this disease when planting in this area.

            You should also amend the soil for better drainage and make sure the planting hole drains properly before putting another plant in the same or near the same hole.

Here is a picture of what this disease may look like in Canary Island Date Palm

Here is some information from the University of California regarding this disease in Canary Island Date Palms


The fungus Fusarium oxysporum f. sp. canariensis causes Fusarium wilt, a lethal, vascular disease of Canary Island date palms (Phoenix canariensis). There are different forms of this fungus, and they typically are host-species specific. The form referred to as forma specialis canariensis causes disease only on Canary Island date palms. Other forms of this fungus cause wilts on other species in other parts of the world.
Identification and Damage
Symptoms usually appear in older or lower leaves before moving toward the center or newest leaves, although occasionally this fungus will affect mid-canopy leaves first. Leaves turn yellow then brown but remain hanging on the palm. Initially symptoms might affect the leaflets or pinnae on only one side of the leaf. Pinnae on the other side remain green, although they eventually also will turn brown and die. This pattern was once thought to be diagnostic for Fusarium wilt, but other diseases such as pink rot also can cause one-sided death of leaves. Pinnae death typically occurs first at the base then moves progressively toward the leaf tip, although this pattern sometimes is reversed.

Extensive discoloration along the petiole, the stalk connecting the leaf base to the leaf blade, is another common symptom of Fusarium wilt. External streaking is brown to black while internal, or vascular, discoloration is reddish brown to pinkish. Although incompletely understood, this pinkish discoloration might be a good diagnostic symptom of the disease.

Infected palms can die within a few months after symptoms appear, or they can linger for several years. Because wilt diseases decrease the ability of the host to take up water, palms with Fusarium wilt in cooler, more humid environments, such as near the coast, might show reduced disease severity and survive for many years. Infected palms in hotter, drier interior climates might show severe symptoms and die rapidly.
Because Fusarium wilt stresses palms, the opportunistic and mostly secondary disease pink rot frequently is present and can obscure or mask symptoms and hasten death. In fact, pink rot might kill a palm before Fusarium wilt runs its course.

In the landscape Fusarium wilt spreads frequently on pruning tools, especially chain saws. The pathogen enters cut petioles and, in extreme cases, the cut and exposed vascular tissue of severely pruned or skinned trunks. The pathogen can spread indirectly during pruning, because contaminated sawdust can drift as far as 100 feet.

The pathogen also can spread by entering the palm through its roots. Canary Island date palms tend to form a dense, extensive network of above-ground roots called pneumatophores, especially under excessively damp or wet conditions, which may facilitate pathogen entry.
Fusarium wilt can spread if people dispose of diseased palms or their seeds using a municipal yard-waste program that recycles debris into mulch. The pathogen can survive in the soil for at least 25 years.
Because no cure exists for Fusarium wilt and it is nearly 100 percent fatal, prevention and exclusion are critical to disease management. Obtain palms from a reliable source and avoid poorly drained soils and excessive irrigation that can increase the formation of above-ground roots. Keep the area around the base of the trunk free of plants, because they can damage above-ground roots, and avoid using municipal-yard waste as mulch on Canary Island date palms.

Also avoid or minimize pruning if possible. Frequently pruned palms are more likely to suffer from Fusarium wilt than those in an unmaintained setting. If you must prune, thoroughly clean all tools by vigorously brushing them to remove sawdust and other particles. Disinfect the equipment for 10 minutes in a 1:3 pine oil to water solution, or heat saw blades for at least 10 seconds per side with a handheld butane torch. Use manual pruning saws rather than chain saws whenever possible, because the latter are difficult if not impossible to clean and disinfect adequately. If you have extremely valuable palms, consider using a new saw for each tree, which you either could discard after one use or dedicate for future use on that one palm only. Avoid pruning palms in windy weather to minimize the spread of infected sawdust.

Because a Canary Island date palm with Fusarium wilt eventually will die, it is prudent to remove it as soon as feasible. To avoid spreading the pathogen, excavate the root ball and use a crane to remove the palm with its crown of leaves, trunk, and root ball still attached. Use plastic or wooden barriers to contain any cutting, grinding, digging, or other operations that can spread diseased plant parts. After bagging all debris, prepare removed palms for incineration or removal to a landfill; do not use a waste recycling program.

It is unwise to replant another Canary Island date palm at the same location where a diseased palm once grew, because remnants of infected roots can remain in the soil and transfer the pathogen to the newly planted palm. Removing the soil might not prevent the spread of disease either, because just one small piece of infected root is all that is necessary to infect a newly planted palm. Avoid replanting with any palm species, because host range susceptibility to this disease has not been fully established.

If you must plant a replacement palm, some species to consider include Mexican blue palm, San Jose hesper palm, Guadalupe palm, pindo palm (Butia capitata), queen palm (Syagrus romanzoffiana), and Mexican fan palm. If you want the Phoenix or date palm “look,” consider staminate (male) plants of the date palm (Phoenix dactylifera), because they are more robust than the pistillate (female) fruit-bearing plants and more closely imitate the larger, robust habit of Canary Island date palms.

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