Left to right: A plant with no calcium applied; a plant treated with 800 ppm of calcium; and a plant treated with 1600 ppm of calcium. All three are shown 72 hours after being inoculated with Botrytis spores.
Photo courtesy of Jim Faust

Dr. Jim Faust, an associate professor at Clemson University, began researching calcium and its potential effectiveness in battling Botrytis seven years ago. At the time, he was working with funding from the American Floral Endowment (AFE) and focused on rooted cutting performance. He found that calcium helped improve the plants’ performance by making them more resilient.

Then, about four years ago, he began looking into petunia flower meltdown. It’s a problem many growers face when petunias rapidly deteriorate after being loaded onto carts and shipped to garden centers or other retailers. Again, Faust found that calcium was an effective tool for treating Botrytis.

“We thought, ‘Well, the calcium worked pretty well for the unrooted cuttings, let’s try it on the petunias,” he says.

During the past two years, Faust’s work with calcium has zeroed in on its effectiveness against Botrytis in the greenhouse. And, once again, testing showed the plants treated with calcium were more resistant to fungal issues. Like the other production challenges he’s addressed, Faust says it’s a widespread industry problem that needed attention.

“There are always challenges shipping cuttings around the world and figuring how we produce things that are more resilient,” he says. “Initially we tried a whole bunch of different products that all have the potential of being valuable, and calcium was one that continued to rise to the top.”

According to Faust, plants are more susceptible to Botrytis during shipping because the spores affect plants the most post-harvest in humid environments and when the plant material begins to decay.
Photo: Laura Watilo Blake

The research basics

Faust says his research — which he is currently carrying out alongside Clemson graduate student Katie Bennett — is largely centered on petunias. He also calls Botrytis “ubiquitous” because it makes itself readily available at times when growers and retailers want the plants to look their best.

“Any sort of decaying plant material has the potential to produce Botrytis spores. You can’t prevent that,” he says. “This is particularly aggressive in very humid environments. When we get the humidity up over, say, 93 percent, growth comes very aggressively, or if the leaves or flowers are wet. And that’s what happens in the post-harvest environment.”

To test calcium’s effectiveness in preventing Botrytis, Faust says he and Bennett inoculate petunia flowers in a humidity chamber, spray them with Botrytis and observe them over a 72-hour period.

“We create a perfect environment [for the botrytis to spread],” he says. “You see the plants are completely deteriorated if you don’t do something.”

The plants that are sprayed with calcium, Faust says, develop flowers that are more resistant to a fungal problem like Botrytis.

Outside data

In addition to his work at Clemson, Faust is part of a research network that further validates his research, the Floriculture Research Alliance. The network is made up of six universities and 40 to 50 greenhouse companies that obtain input from the businesses about what problems they are dealing with. University researchers like Faust then investigate the problems.

“It’s invaluable because we can only do so much in a research facility when we do our experiments,” he says. “We’re doing them on a few plants and a limited number of varieties. We don’t know what will happen in a real-life, large-scale commercial system. And [these growers] kind of have to do that experiment.”

With the calcium experiments done by commercial operations, Faust says their treatments typically take place on plants not as heavily affected by Botrytis as the plants he inoculated at Clemson. This setup also allows growers to take a concept Faust says has worked in his studies and apply it to their specific crops. Some members of the alliance, he says, are growing hundreds of different varieties and need to be sure a prospective treatment isn’t going to damage their plants. It’s also helped Faust determine what he thinks is the best spray schedule for calcium.

“The closer you spray to the plant [when it’s] being shipped the better,” he says. Faust recommends spraying plants weekly and notes that some growers mix calcium with a fungicide they are already applying.

More work to be done

Faust and Bennett are not done studying calcium yet. The AFE is funding Faust’s next round of research, which will focus on calcium treatments for cut roses. He’s also working on determining if silicone and calcium could be utilized in a potential treatment for greenhouse thrips; both projects are scheduled to begin this summer. Faust is conducting additional research to determine what kind of calcium is most effective in the greenhouse. Currently, he says that calcium chloride has proven to be a safe choice, but it is unclear if there is one calcium type that performs better than the rest.

“We don’t have that information yet,” he says. “Each formulation of calcium can potentially have a different amount of phytotoxicity. There are certainly some forms of calcium that are a little more dangerous to use because [they’re] more likely to cause damage than other forms. But so far, the calcium has always worked equal to or better than any fungicide we’ve tested.”

Outside of floriculture, Faust says both cannabis and produce growers have asked him about using calcium on their crops and he’s intrigued to learn what types of growers could benefit from using calcium.

“Botrytis is ubiquitous,” he says.