Orchid Sticky Sap: 3 Reasons Leaves are Covered in Dew

Your orchid is growing beautifully and has even bloomed. Yet, when you watered this week, you noticed that something wasn’t quite right with the leaves on your orchid. They were covered with a sticky, gooey substance that wasn’t supposed to be there. First, you have to identify where the sap is coming from to correctly fix this problem. In this article, you’ll learn the 3 main reasons orchid leaves become sticky.

The reasons orchid leaves become covered in sticky sap are 1) the blossoming flowers produce honeydew that drips on the top leaf, 2) excretions that are left behind by insects such as aphids, mealybugs, and scale, and 3) the natural tendency for the orchid to neutralize hydration pressure by releasing water which contains sucrose.
Sticky Sap on Orchid Leaves
Image Credit: "File:Prosthechea brassavolae GotBot 2015 003.jpg" by Averater is licensed under CC BY 3.0 
Prosthechea brassavolae  
Reasons for Sticky Leaves

1) natural honeydew

2) excretions that are left behind by insects

3)  neutralize hydration pressure

1. Sticky Orchid Leaves Caused by Honey Dew

Orchids naturally produce a sap called honeydew, happy sap, orchid nectar, or orchid sap. This is produced in higher quantities when the orchid is in bud or in bloom. The sap is highly nutritious and nurtures the newly formed plant tissue.

If you see no bugs on your orchid and the sap is on top of the leaf, then your orchid is well watered and growing perfectly. It’s a normal condition that you shouldn’t worry about.

If your orchid is in bud, look for sap that is being excreted from the blossom itself, or the pedicule (the attachment of the one blossom to a smaller branch) or the peduncle (a branch with several smaller pedicles attached to the flower spike).

In this condition, the sap that is dripping is normal and you just need to keep an eye out for cleaning the leaves properly. In this article, I explained 7 ways to clean orchid leaves that don’t harm them, so if this is what is causing your leaf to become sticky and gooey, be sure to read that article.

If not removed in a short period of time, this sap can open the door to future problems. The sap that sits on the orchid leaf will cause plant cell death on the outer layer of cells. All leaf cells breathe, even if the stomata are for the most part, on the bottom of the leaf.

The top of the leaf (and I’m mainly referring to the Phalaenopsis orchid, not other genera) is hydrorepelent. The waxy coating that gives the leaf it’s natural shine repels water. This is why misting is only effective if you point the mister to the bottom of the leaf and roots, and not at the top.

Yet if there is a thicker substance that sits for extended periods of time on the orchid leaf, there isn’t absorption of light nor adequate gas exchange. That changes the toxicity levels inside the plant cell and it can’t perform basic functions to survive, killing the top layer of cells.

This dead cell now is an open door for bacteria and viruses to enter the plant, traveling from dead cells to adjacent healthy cells. Soon, your leaf is seriously infected with bacteria. Bacteria by itself will kill the orchid if not treated, and I wrote an entire article about that which you can read here. It’s so serious that you need to act quickly to stop the spreading of Bacterial Brown Spots.

The other problem with leaving honeydew on the leaves is that the sugar in the sap is a pollinator-attractor. The high doses of sucrose attract other types of unwanted insects, like ants, bees, and other sugar-loving pests when outside. Inside orchids will also attract ants if given enough time. These pests will devour the leaves and newly formed buds since new plant tissue is more hydrated and has a higher nutrition value than older plant tissue.

The last problem with the honey dew left to evaporate by itself on top of your orchid leaf is that it doesn’t. It will sit there until the sugars in the honeydew attract fungus which feeds on sugar. This fungus creates a condition called sooty mold. Sooty mold will eventually kill the orchid, traveling from the tip of the orchid down to the stem.

2. Sticky Orchid Leaves Due to Insects and Pests

Some insects will secrete a sticky substance on your orchid leaf when they are feeding on plant tissue. This is a serious problem because the orchid can’t fight off those insects by itself. On the other hand, for some bacteria, the orchid can put up a good line of defense. But it doesn’t stand a chance against insects.

There is good news about the insects that are chewing on your orchid: the sap that they leave behind will not kill your orchid. It’s not the same as honeydew even though some “literature” (questionable literature) will call this sap honeydew as well. The sap left behind by insects are excrements, with low levels of sugar.

The bad news: the insects will kill your orchid. This “sap” left behind on the leaf will at most, cause sooty mold, mentioned above. But it’s not as sugary and harmful as the honeydew from the orchid itself.

Insects will chew your orchid to pieces and start on the next one in your collection, so they need to be treated with the pesticide of your preference. In this article, I explained the different types of pesticides and insecticides that can be used to get rid of each of these little sap-producing creatures.

Three main insects will leave behind a sappy substance on the leaf: aphids, mealybugs, and scale.  If you want to see pictures of the pests, I wrote an article about pests that inhabit sphagnum moss and this other article about pests that like to live in orchid bark. Both those are good places to get more information about each type of pest, and I included pictures in those articles.
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3. Sticky Sap on the Underside of the Orchid Leaf

What shouldn’t be normal is the sap on the underside of the leaf which looks like crystalized sugar. This usually happens when the plant absorbs too much water. The sap is an attempt to balance out the pressure caused by too much water inside the leaf. When the pressure is excessive for it to handle, little bubble-like blisters will form on the top side of the leaf, where the water “exploded” or stretched the plant sells to their maximum.

If this has happened to your orchid, this article about edema is a good place to start. In it, I explained why it happened and how to treat the leaf once edema in on it.

This isn’t a harmful situation, but you need to take a look at how much you are watering and if the water is allowed to exit the potting medium quickly. Orchids like to be wet, but not soggy.

Water will exit the bottom pores and because of the high sugar content in the orchid sap, the sugar will crystalize. You need to wipe the leaf carefully—let me emphasize that CAREFULLY—as to not hurt the pores on the leaf. A wet cloth will do the trick, and you don’t need to add any products. As long as the sugar comes off, your orchid will be fine.
Further Reading Suggestions:

Don't just take my word for what is written here. Continue researching other articles about the sap on orchid leaves, because everyone has a different point of view and unique techniques that work for them. Here are a few other articles from other websites if you'd like to continue your research:

The article  The Effects of Different Media, Sucrose Concentrations and Natural Additives on Plantlet Growth of Phalaenopsis Hybrid 'Pink' was published in the Brazilian archives of Biology and Technology goes over the different types of sugar and its effect on the Phalaenopsis orchid. It’s a bit technical but does a great job covering the bases.

Happy Cultivating!
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