Chills & fever: Aftermath of SW Florida’s cold winter tells tales in palm damage

Christmas palms damaged by cold exhibited foliar browning, as well as stem breakage, when the cold weakened fronds turned black and broke off.

Bob Shafer/Special to the Daily News

Christmas palms damaged by cold exhibited foliar browning, as well as stem breakage, when the cold weakened fronds turned black and broke off.

Our postcard view of Jamaican Tall coconuts down Broad Avenue may be missing some palms due to the earlier cold damage.

Doug Caldwell/Special to the Daily News

Our postcard view of Jamaican Tall coconuts down Broad Avenue may be missing some palms due to the earlier cold damage.

Ixoras started to leaf out about two weeks ago. That means it is easier to tell which twigs are dead, so pruning is easier.

Then there are the crotons. I have a list of cold tolerant croton varieties, but I was surprised to see such differences in one species. More on that later.

I am getting many calls on coconut palms, one of our quintessential tropical species. Remember these are truly topical, as are the arecas. Neither fared well at all with our prolonged cold winter. However, I’m surprised that the Bismarckia palms didn’t discolor like they have in the past when we had some cold winter nights. Typical horticulture: Just when you thought you knew what would happen, it doesn’t always go that way.

Coconut and Christmas palms are continuing to spiral into brown droopy fronds and some coconut palms are losing their heads. Here is a fertilizer maintenance reminder: The University of Florida palm researchers are seeing a positive response with palms which were fertilized before the cold hit. The recommended fertilizer, an 8-2-12-4 (N-P-K-Mg) with 100 percent of the N, K and Mg sources as controlled-release forms, as opposed to quick release, which equals highly soluble fertilizer sources.

The UF palms were fertilized four times per year with 15 pounds of fertilizer per 1000 square feet. Over a three year-period the percent necrosis was 2 to 6 times greater with unfertilized palms. This year there was 32 percent canopy necrosis with the fertilized, but 68 percent necrosis with the unfertilized group. There was a strong correlation with the K (potassium) content of the foliage and damage. The palms with greater K had significantly less damage. I’m including earlier recommendations from Feb. 12 column, following, as a reminder to be patient and wait.

Christmas palms are experiencing a unique symptom, that as Stephen Brown, Lee County UF-IFAS Extension agent, reports, “The fronds of Christmas palms are broken deep inside the canopy where the fronds come together in a bundle and before they are fully emerged. The fronds are otherwise green.” This cold-damage injury is vulnerable to an anthracnose disease, but it is secondary and the palms seem to recover without extra attention.

New information comes from palm researchers Monica L. Elliott and Timothy K. Broschat at the UF Research and Education Center in Fort Lauderdale, in a report that released this summary on January 31, 2010 (slight modifications are my own) on palms and cold weather.

First, be wary of salespeople strongly recommending palm treatments at this time, they say. Any treatments are of unknown value and probably not needed, especially trunk injections.

“Trying to grow tropical palms in sub-tropical and temperate climates means cold damage is inevitable. This year’s cold weather is not atypical for Florida. For example, in the late 1970s and early 1980s, a series of hard freezes destroyed much of the citrus industry located north of Orlando, which is why that industry pushed south to Immokalee. During that same time period, severe freeze damage occurred on palms throughout the state,” according to their report. “The only difference between then and now is that there are a lot more palms planted in communities that did not even exist in the early 1980s. So, for many people, this is their first experience with severe cold damage.”

This paper is in response to your many questions about cold damage on palms and expands upon some themes outlined in the EDIS document “Treating Cold Damaged Palms.”

As described in the EDIS document “Cold Protection of Ornamental Plants” (/edis.ifas.ufl.edu/mg025), tropical and sub-tropical plants can be damaged at temperatures above freezing. Furthermore, while some years we experience only one cold event the entire winter season, in other years, such as the current one, we may have an extended cold season. If trunk damage is observed externally due to a freeze, it is likely that there is substantial internal damage to the vascular and structural trunk tissue. These palms should be removed because they can pose a structural hazard.

All new leaves of a palm develop from the apical meristem (bud), so the primary tissue that needs to be protected is the apical meristem. Since leaf bases provide insulating protection to the apical meristem, this is one reason to not overtrim palms at any time of the year. Furthermore, good fertilization practices, including routine applications of 8-2-12-4Mg (100 percent slow-release N, K and Mg), have been shown to greatly enhance cold tolerance.

Copper fungicides (not copper nutrients) are recommended as an attempt — not a guarantee — to protect the apical meristem and developing leaves from secondary microorganisms that may attack damaged spear leaf tissue. There is no research to confirm if this is effective or not. The recommendation is based on what has been observed regarding cold damage to palms and our knowledge of fungicides.

Please note that copper fungicides are contact fungicides and not systemic fungicides, so you must have complete coverage of the target tissue to be effective – in this case, the base of the spear leaf and the bud. Also, please read the label and be cautious of staining concrete surfaces. Be sure to wear required eye and face protection equipment as copper can cause severe irritation and eye injury.

If the spear leaf does rot and can be easily pulled from the bud, it should be removed immediately, followed by a copper fungicide spray or drench of the bud region, which is now exposed. It is important to use a copper fungicide and not a copper nutrient solution.

The normal recommendation is to apply the copper fungicides no more than twice because of the possibility of copper phytotoxicity. If it is believed that more chemical protection of the bud is needed after the copper fungicides have been applied, a broad-spectrum contact fungicide may be beneficial.

You will not know if the bud has survived until new growth emerges, which may be 4 to 7 months later. Hence, the need for patience! The new growth may be severely malformed or damaged, but the emergence of any living leaf tissue is a sign the palm is alive.

If you replace coconut palms, it may be wise to go with a Maypan coconut, which seems more cold-tolerant than the Green Malayan, according to both Karen Burns at Palmco Nursery and Julie at Soaring Eagle Nursery both on Pine Island.

Remember to make your palm population a diverse one: Use different cultivars or better yet different species such as a combination of foxtails and royals or try sagisis palm (Heterospathe elata), Sentry palm (Howea forsteriana) or piccabeen palm (A. cunninghamiana).

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Doug Caldwell, Ph.D., is the commercial landscape horticulture extension agent and landscape entomologist with the University of Florida Collier County Extension Service. E-mail dougbug@ufl.edu; phone, 353-4244 x203.

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