I attended the International Plant Producers Society (IPPS) Southern Region meeting in Orlando, Florida, two weeks ago. I did a talk on fungus gnats, which I didn’t think went particularly well. The audience was great, but I didn’t perform. I dwelled too much on the relationships between fungus gnats and soil-borne diseases and ran out of time for the management section of the talk. That seems to be a common theme with my talks these days—poor budgeting of speaking time. I need to go to a speaking school, if there’s one, before my other scheduled talks ...

What I also didn’t do during the trip was go to SeaWorld or do the Orlando Slingshot, even though both attractions were only blocks away from the conference hotel. Never mind Disney World, which is a few miles away. Do I feel sorry for missing those attractions? No, not really.

What I didn’t miss was visiting another claim to fame for central Florida—I visited a few greenhouses and nurseries in the foliage plant capital with my colleague Ben Keyes of SePRO. We met with growers and talked about thrips, mealybugs, mites, bacterial and fungal leaf spots, propagation, water quality, and many other problems.

I didn’t just see problems; I saw some crops that I never expected to see, such as coffee and tea grown as potted plants. (My dad, who believed in crop diversification, grew tea for personal consumption and coffee as a cash crop on our family farm. Based on my experience growing and harvesting them, I don’t think coffee and tea trees do well in pots. But, hey, if the plants die, folks will have to buy more. At least they’ll have cute decorative pots for souvenirs in the end.) I also saw many nurseries that are doing a blooming business, which I’m glad.

I saw something interesting at one such expanding operation. There were several cultivars of sansevieria, or snake plant, grown from unrooted liners sourced from a South American country. Many of them had large water-soak lesions on the leaves. What’s causing these lesions?

Dealing with rust? No, not those under your car (or those in my joints)—rust the disease.

Janna Beckerman of Envu is telling us all about rust, with very nice photos to go with her article in the October issue of GrowerTalks. The rust species I deal with in my neck of the wood is mostly the heteroecious kind—that's the kind that infects different host plant species at different times, such as cedar-apple rust. So it’s great to learn about the autoecious kind that completes the entire life cycle on a single host species.

Obviously, success in managing rusts depends on careful timing of fungicides, which in turn depends on knowing the life cycle of the disease. That means you need to identify and know if you're dealing with the autoecious or the heteroecious kind.

Go HERE to read Janna’s article and learn about the conditions favorable to disease development and how to control rusts (without using WD-40).

The water-soaked lesion I showed y’all earlier is an early symptom of Anthracnose, caused by the fungal pathogen Colletotrichum sansevieriae. Below is another picture of a concentric ring, which is a more advanced symptom of the disease and an easier symptom to diagnose this disease, at least to a non-pathologist like me.

The black ring is formed by acervuli, which are the opened, saucer-shaped asexual fruiting bodies of the fungus. This ring is quite visible on the gray background, which is the diseased, sunken, desiccated leaf tissues. I also saw a brown ring, similar to the color of the water-soaked lesions, around some of the black-and-gray rings.

According to an article by Vanessa Campoverde and Aaron Palmateer, both of them at the University of Florida (UF) at the time, the disease diagnostic lab at UF’s Tropical Research & Education Center in Homestead, Florida, had started receiving infested samples since 2010. (Aaron is now with Harrell’s.) Through Koch’s Postulates, Vanessa and Aaron confirmed that Colletotrichum sansevieriae is the causal agent of Anthracnose of sansevieria in South Florida.

I checked the USDA Fungal Database and other resources online and found that this pathogen has been reported from Australia, China, Germany, India, Iran, Japan, Korea, Malaysia and the United States (Florida, Ohio and Tennessee). I suspect the disease’s distribution is likely wider than had been reported since not everyone identifies and reports diseases they find.  

What can you do about Anthracnose on sansevieria?

High humidity and overhead irrigation are favorable conditions for this disease. As anyone who spends any appreciative amount of time in Florida can testify, you can’t do much about humidity in Florida. Reducing humidity can be helpful in other places where sansevierias are grown in greenhouses.

Vanessa and Aaron recommended using microjet or drip irrigation, or irrigating during the early part of the day. Doing so keeps the foliage dry and denies favorable conditions for the pathogens to invade, establish and grow. Remove inoculum by removing and discarding any diseased leaves on and off the plants. Pruning should be done with constantly sanitized tools and under dry conditions.

Vanessa and Aaron also conducted trials to identify fungicides that are effective in managing this disease, both preventively and curatively. They identified preventive sprays of Pageant Intrinsic at 18 fl. oz. per 100 gal. (boscalid + pyraclostrobin; FRAC 7 + 11), Heritage at 6 fl. oz. per 100 gal. (azoxystrobin; 11), Concert at 28.5 fl. oz. per 100 gal. (propiconazole + chlorothalonil; 3 + M5), and Torque at 7 fl. oz. per 100 gal. (tebuconazole; 3) as the most effective options in reducing disease severity when compared to the inoculated control (see the graph below).


Efficacy of preventive fungicide treatment against Anthracnose on sansevieria. (Source: Vanessa Campoverde and Aaron Palmateer, Proceedings of the Florida State Horticultural Society 125: 359-360.)

It wasn’t clear how frequently Vanessa and Aaron sprayed. I would suggest re-application every seven to 14 days, depending on the label instructions. Also, remember to rotate your fungicide modes of action.

I also searched through Chase’s Digest that I’d kept because I remember Ann Chase wrote about her experience with Anthracnose on sansevieria at some point. Sure enough, Ann did a trial in 2024, where she sprayed four times at two-week intervals. In this trial, Orkestra Intrinsic at 10 fl. oz. per 100 gal. (fluxapyroxad + pyraclostrobin; 7 + 11) stood out as an effective fungicide, followed by Broadform at 4 fl. oz. per 100 gal. (fluopyram + trifloxystrobin; 7 + 11), Avelyo at 10 fl. oz. per 100 gal. (mefentrifluconazole; 3), and Concert II at 22 fl. oz. per 100 gal. (propiconazole + chlorothalonil; 3 + M5).

Looking at all the fungicides tested by Vanessa, Aaron and Ann, it seems to me that fungicides in FRAC groups 3 and 11 were consistently the winners against Anthracnose on sansevierias. Although not all active ingredients in these two FRAC groups were tested, I suspect some of them—such as mycobutanil, triflumizole and triticonazole—may provide decent preventive control against Anthracnose.  

Here's something that’s the most important takeaway from Vanessa and Aaron’s paper: curative sprays aren't effective at all, no matter what fungicide you use. So manage Anthracnose on sansevieria preventively, instead of curatively. That means you need to scout regularly immediately after potting the liners and spray as soon as the first symptom appears, instead of allowing the disease to spread and progress further. A preventive program is especially important if you bring in liners from a source that hasn’t always been clean or one that you aren’t familiar with.