The Biscayne Times

May 31st
Don’t Spray Those Spores PDF Print E-mail
Written by Jeff Shimonski, BT Contributor   
January 2019

Let your ferns and palms age naturally

WPix_YourGarden_1-19hy are those leaves yellow, you may ask? Is the plant drying out, is it diseased, and do we need to spray it with a broad-spectrum pesticide that will kill lots of things? These are questions that I field on a regular basis.

Take a look at the photo that accompanies this article. It’s of a bird’s nest fern -- well, really, an Asplenium nidus that I grew from a spore. The yellow leaves at the base of the plant are obvious. Is this a disease or water issue? No.

It may be difficult to see, but the undersides of all the leaves, including the green leaves, all have brown “lines” fanning out in V-shaped patterns. These are the spores. If you tap the leaves, you may see a brown dust falling. These are the spores being dispersed, and this is how ferns reproduce. They don’t produce flowers and seeds like other plants.

When the leaf is older and all its spores have been released, it will begin to deteriorate, or senesce. It will start to yellow and eventually turn brown and brittle. The leaf will then be dead. But while the leaf is yellowing, the plant will be “pulling” nutrients out of the leaf to send to other parts. This is why the leaf yellows -- the green chlorophyll and other stuff are first removed. And this is why foliage should be left on the plant until it begins to brown.

I often get calls from property owners who’ve had landscapers spray their ferns with foliar fertilizer and pesticide to “save” the plants from the yellowing foliage, yet in most cases the yellowing was due to natural senescence, rather than a disease or nutrient issue. It was obvious they’d been “upsold” and that the landscapers either didn’t know or didn’t care. This is also a common issue with staghorn ferns.

Palms do something similar. While they don’t produce spores (they reproduce from seed), the yellowing, or senescence, of the lower foliage can happen rapidly. Most palms in highly manicured landscapes are way over-pruned, which causes other issues, but I also hear from property owners who’ve been told to “spray” their palms because of yellowing lower foliage.

While it’s often true that insects or spider mites might be found on the yellowing foliage -- the mobilized nutrients moving out of the dying leaf into other parts of the palm are in a more available and soluble form, and are more nutrient-rich and digestible -- spraying and fertilizing are a waste of both time and money. Usually all that’s accomplished is that they’ve wiped out of the beneficial predators of the insects and spider mites that were feeding on the leaves.

Some multi-trunked palm species like Caryota and Arenga have individual trunks that gradually die after they’ve produced flowers and fruit, while the other non-blooming trunks carry on and remain healthy. When a landscaper tells you to apply pesticides, fungicides, or fertilizer to the multi-trunked palm on your property that has a yellowing trunk, find out what’s really going on first. Identify the species, and question the person who suggested blasting the chemicals.

By the way, spider mites aren’t insects, and the pesticides normally applied to insect populations will not control them. Acaricides or miticides should be used instead. Make sure that the people applying the chemicals properly identify the target and apply the proper chemicals.

There’s a balance, a tolerable insect and spider mite load that plants can sustain, and of course, at the same time you’ll be maintaining insect predators in your landscape. If you follow this course, when an insect population gets out of hand, you’ll already have the predators nearby that can respond and begin to build up their populations and control your insect or spider mite issue.

The other day someone came to me to ask what was going on with his highly sprayed and fertilized lawn. The lawn is beautiful -- you know, with that unreal green color -- but there are “spots” on the lawn. I asked the owner what the professional landscape team had recommended. They’d said that the yellowing of the grass was caused by a fungus and they were going to spray a fungicide.

Now, I happen to drive by that lawn several days a week, and I noticed that there were areas where the lawn was drying out in the afternoon. I knew those areas would yellow since the grass was wilting, and that there was a good chance that chinch bugs would move in. That’s exactly what happened. Instead of adjusting their irrigation system, the owners paid to have the lawn sprayed. Go figure.


Jeff Shimonski is an ISA-certified arborist municipal specialist, retired director of horticulture at Parrot Jungle and Jungle Island, and principal of Tropical Designs of Florida. Contact him at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .


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