Image used with permission from Instagram user @bernygarden
One of the most challenging and frustrating parts of caring for succulents and echeveria is rot. Beginner collectors and experienced collectors alike experience rot at some point in caring for their plants.
Unfortunately, there is no standard protocol, much less agreed-upon information in the USA regarding how to treat rot in echeveria, so what I offer in the following blog post is a synthesis of knowledge about managing rot derived from over seven years of growing succulents professionally. In doing so, I hope that more customers and succulent growers in the USA can find success in caring for their plants.
So, what is rot? Bear with me, as we'll get slightly technical. But the details are important and worth noting!
Rot is a disease often caused by various pathogens, but in echeveria, it is predominately caused by TWO organisms. Fusarium oxysporum and Pectobacterium carotovorum aka Erwinia carotovorum. It may seem useless to differentiate between the two, but these two organisms are extremely different and cannot be treated the same.
Pectobacterium carotovorum, aka Erwinia carotovorum, is a small, single-cell, soil-dwelling bacterium known by growers and gardeners as Bacterial soft rot. You read that right. This is not a fungus. It's a bacteria! These little devils find their way into our beloved succulents through any entry point and secrete pectin-degrading and fiber-degrading enzymes that decompose components of plant cell walls. This is what leads to black leaves, collapsed rosettes, rotten mushy leaves, and other charming characteristics of bacterial soft rot.
Fusarium oxysporum is a soil-dwelling filamentous fungus referred to by growers and gardeners as stem rot or just rot. These guys are different from Pectobacteriumn because they are not bacteria but fungi! But just like our bacterial "friend," this fungus has an affinity for absolutely wrecking our plant babies.
"Well, how can I tell the difference when I see a sick plant, and why does it matter?" Oh, good one! The easiest way for us to determine which type of rot affects a plant is smell! If the rotting plant in question has a sweet, ripe, yeasty smell, it is likely bacterial soft rot since fusarium does not usually produce a strong foul odor when rotting plants.
Now, on to why we've made so much distinction between the two. We need to know which organism is infecting our plants so we can treat them correctly and prevent infection to our other babies! Generally, Fungicides only work on fungi and not on bacteria, while bactericides only work on bacteria and not fungicides. It would be a shame to stumble across a rotten plant, not know its bacterial soft rot, apply the wrong fungicide in the hopes it protects the rest of your plants, and continue to see plants suffer.
So now what?
The bad news is once a plant is infected with rot there's no cure except for trying to remove what healthy tissue remains. But, there are several excellent options for prophylactic management.
We can manage and kill rot by being rot-conscious in the garden, creating an environment unfavorable for the bacteria/fungus, and applying fungicides before any disease even gets a chance to kill our beauties.
Let's start with some tips on creating an environment unfavorable for bacteria/fungi.
- Provide plants with a well-ventilated, bright, sunny location.
- Reduce humidity (If indoors)
- Use coarse, fast-draining soil.
- Sterilize reusable pots, containers, and trays with bleach before the first or second use.
- Clean pruners or scissors with bleach often
- Eliminate the use of high NPK fertilizers as they weaken the cell wall in echeveria and allow easier entry of pathogens. For information on fertilizing, please read here.
Utilizing fungicides/bactericides preventatively is the next step in protecting your plants from rot.
Here, I'll include the products we use professionally, as well as our dosages and strategies. We've used countless products, tried countless dosages, and found the safest, easiest combination of products. All products names have been linked!
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1. Mancozeb (Dithane 45-M) is a broad-spectrum protectant fungicide/bactericide. (Treats Fusarium and Pectobacterium)
Mancozeb is an incredibly effective fungicide for succulents and is one of the most commonly used products by Korean succulent farmers and hobbyists. Mancozeb's multi-mode action makes resistance nearly impossible. Unlike most fungicides, Mancozeb protects succulents from Pectobacterium and Fusarium. While our professional experience confirms the efficacy of Mancozeb on Pectobacterium, studies like the following show that the fungicide may inhibit the organism better than antibiotics.
It can be applied as a foliar spray, but it leaves a heavy residue, so you may prefer to use it as a soil soak.
The optimal rate for our echeveria is 2 grams per liter or 7.5 grams per gallon when using the product in the link above.
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2. Thiophanate Methyl (Thiomyl) is another broad-spectrum fungicide. (Treats fusarium)
Thiomyl is another highly effective fungicide. So much so that it is recommended by the Korean Cactus and Succulent Plant Research Institute for the treatment of fusarium. Unfortunately, we have found succulents are sensitive to this fungicide (like they are to many) when sprayed on the foliage, so it MUST be applied using a soil soak. Applying this fungicide to the foliage can lead to chlorosis.
The optimal rate for our echeveria is 1.5 teaspoons per gallon when using the product in the link above.
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3. Copper Fungicide is our third broad-spectrum fungicide/bactericide. (Treats Fusarium and Pectobacterium)
Another great tool, especially for treating Pectobacterium. Can be sprayed on the foliage of succulents or soaked in the soil.
The optimal rate for our echeveria is 1.5 teaspoons per gallon when using the product in the link above.
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4. Bio-fungicide (Garden friendly bio fungicide) is a highly effective fungicide/bactericide. (Treats Fusarium and Pectobacterium)
This is an excellent alternative to chemical fungicides/bactericides. It uses a highly aggressive strain of good bacteria (Bacillus amyloliquefaciens strain D747) that out-competes other fungi and bacteria.
The optimal rate for our echeveria is two teaspoons per gallon when using the product in the link above.
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When applying fungicides, always wear proper PPE (gloves, mask, etc.) and always rotate products. Applying the same product continually will lead to resistant organisms. Fungicides/bactericides should be applied monthly or every fourteen days when conditions for disease are favorable. Always apply fungicides at dusk or when lighting is turned off.
While these are not the only fungicides available, they are the safest and most accessible for home gardeners and are products that have demonstrated great control in our greenhouses.
Hopefully this information will help succulent hobbyists keep their beloved plants safe and rot-free so we may continue to enjoy this hobby and the beautiful plants we grow.
-Chez
*The information on this website is for general informational purposes only*