Botrytis Blight: Gray Mold, Calcium Shields, and Building a Better Box
Blooms and Beyond — Season 1, Episode 10
Host: Dr. Ping Yu Guest: Dr. Jim Faust, Clemson University Producer: Rich Braman Duration: 48:51
Welcome & Introduction
Ping Yu: Hello everyone, welcome to the Blooms and Beyond podcast, a podcast that uncovers plant history, culture, and management through the lens of science. I’m your host Ping. How’s everyone doing today? I’m doing great because here I have a well-known researcher and a colleague of mine, Dr. James Faust, joining me today to talk about botrytis blight. James has years of research experience in floriculture physiology. In today’s episode, we’ll pick his brain on blight control on ornamental crops. So I don’t want to steal any more thunder from our speaker today. Let’s just jump right into it. Without further ado, here is my conversation with Dr. James Faust. I hope you enjoy it.
Meet Jim Faust: A Life in Floriculture
Ping Yu: Hi, Jim, welcome to the podcast. But first, let’s start off with the introduction. Can you tell our audience a little bit about who you are and what you do?
Jim Faust: I appreciate coming on your podcast today. I look forward to the discussion. Yeah, I’ve been in floriculture my whole career. I graduated from college in the 80s and got a job in the greenhouse and just fell in love with that and have never gotten away. So I’ve been at a few different universities and had grower jobs before that. And yeah, it’s been a good career so far.
Ping Yu: Yeah, because I remember I met you at one of the AFE, the National Floral Forum meeting a couple years ago back then when I was at grad school. And I also met your student, Melissa, at the same meeting. But what first sparked your interest in horticulture in general? Did you grow up as a nature kid or is this something that stumbled into this trajectory?
Jim Faust: Yeah, yeah. I think most people that get into horticulture have had some childhood experience. And I’m the same. My parents always had gardens. My dad had a vegetable garden and my mother always had flowers around the house. And she would actually go out in the front yard and, you know, disbud or deadhead petunias. And she would count how many petunias she would deadhead. And she was very proud of the fact that, you know, like every day she could go out there and take 200 flowers off. And yeah, so it was just kind of, I think all my siblings, I’m the only one who actually made a living growing plants, but we all have a passion for plants and gardening.
Ping Yu: Yeah, and speaking of the career, a lot of times we just had an episode on the potential or the opportunities in horticulture that never exist. People wouldn’t think of so many different job opportunities that even exist for horticulture. All they think about is just produce plants, but there are so many opportunities, hidden job opportunities within horticulture. But with all those plants that you have worked with, that you have exposed to, even with your family lineage with the plants.
Plant Spotlight: Poinsettias — A Fascinating Domestication Story
Ping Yu: Is there a plant that is your favorite plant?
Jim Faust: Yeah, you know, there’s no such thing as a bad plant, but, you know, I have a soft spot for poinsettias. You know, it’s kind of a very commercial crop that, you know, it’s beautiful, but I don’t think a lot of people are really passionate about it because it’s just kind of this commodity item. And yet it’s got to be one of the most interesting plants really in the world in the way it has really become domesticated. It has a storyline that is just unlike any other plant. A lot of intrigue, you know, it really wasn’t an important plant 200 years ago. And then, you know, Joel Poinsett brought the plant to the United States and it kind of caught on a little bit, but it wasn’t really until the 1900s, early 1900s, where it really became a commercial success and became really associated with Christmas. And anyway, that journey is fascinating to me. I’ve been working on a book for a number of years, trying to communicate that story. It’s hard finding time away from my day job to write a book. But I’m still hopeful that I can get this done before I retire. Because it’s just a fantastic story. It needs to be told.
Ping Yu: Yeah, yeah. And I think to begin with, right now, a lot of people were just thinking about poinsettia as those little tiny plants in the container that they were going to go buy during or before Christmas. But in reality, when it first started, when it was first discovered, it was actually a pretty big shrub right in the wild.
Jim Faust: Yeah. Yeah, so it’s a plant that will get 12, 15 feet tall in its native location in Mexico. And so, you know, that was part of the domestication process really through the 1960s and 70s, where a lot of breeding really started in the U.S. and really took this plant that actually had been a successful cut flower in the early 1900s. But it really wasn’t a very good plant for greenhouse production because it was such a big plant. And then, of course, growth regulators came into existence in the 1950s, and so that helped. And then breeding helped to create more compact plants that just didn’t want to get, you know, six feet tall. And so that really allowed it to become a commercial success.
Ping Yu: And I think though people just get so used to poinsettia, seeing them every year, but there’s a lot of brilliant work behind the scenes that people keep bringing new varieties to the market, even though a normal consumer wouldn’t notice the difference. But there’s a lot of hard work behind the scenes, trying to bring new varieties to the market every year, right?
Jim Faust: You know, you’d be surprised. You know, there’s dozens and dozens of commercial varieties available. You know, if I just walk into a greenhouse with, you know, 36 different varieties of red, you’d like really can’t tell most of them apart. It’s, you know, the physical appearance of them is not that variable. It’s more the production traits that are the targets for breeders. Because really the consumer has in mind what the plant should look like, so you really can’t change that very much. You can get some different colors, but still, you know, if it’s not red, it doesn’t sell that well. We have orange and yellow and green poinsettias and they’re really pretty cool looking. But, you know, people are buying these things for gifts for a specific holiday. And so, you know, if it’s not red, it just doesn’t sell very well. So the breeders have really emphasized production characteristics. So that’d be something like heat tolerance. If a poinsettia variety is heat tolerant, then it’s much more easily produced in Georgia and South Carolina and Florida. And we have varieties that really can’t be grown in those states very well because of a lack of heat tolerance. So characteristics like that are really what breeders are looking for. So the consumer might not appreciate that there’s a lot of different poinsettia varieties out there.
Ping Yu: Yeah. Correct me if I’m wrong, but I think it would be the number one cut flower or floral crop in the United States that has been purchased by a consumer. If it’s not the orchids, it must be those two.
Jim Faust: Yeah. It’s orchids and poinsettias as potted flowering plants. Yeah. And of course, orchids has the advantage in that you can sell those 52 weeks out of the year. Poinsettia is really only sold for about four weeks out of the year. So that’s kind of impressive that you can be the leading potted plant with only basically a four to five week market.
What Is Botrytis Blight? The Disease Triangle
Ping Yu: Yeah, yeah, yeah. But every time when we mention your name, it normally ties closely to botrytis blight. And that’s basically, you have worked on this project specifically for botrytis blight control for years. But can you first start by telling us what is botrytis and what is the agent and how did you start the work on this in the first place?
Jim Faust: Sure. Yeah, I do not have a degree in plant pathology. And actually, I’ve never actually taken a plant pathology course in my life. But I think I have an honorary degree by now for the work that we’ve really been doing botrytis work now for eight years. And that really started with a discussion with — so we got involved with botrytis really eight years ago when I was discussing research topics with the board at the American Floral Endowment. And they had identified that botrytis and thrips were the two main industry issues that the endowment really needed to address with the research program. And I’m not a pathologist, but I have a pathologist colleague at Clemson, who’s actually a fruit pathologist. So he works with peaches and strawberries and with strawberries, botrytis is the major or one of the important pathogens. And so he was all on board to kind of be the scientific leader of the project, and then I would get the work done. And so we made a pretty good team and have been really working on botrytis for a number of years, and I think we’ve made some nice progress.
Ping Yu: Yeah, yeah, botrytis, you’re right. And one of the, I think, the biggest host plants for botrytis is the strawberry from the small fruit perspective. And what is the agent of the botrytis? We’re both not plant pathologists, but I have been working with plant pathogen scientists a little bit just what you did. But then you definitely have more experience on that. But can we talk a little bit about the agent and then move towards to some of the basics of plant pathology parts such as the disease triangle from that route?
Jim Faust: Sure. So, you know, we think of the disease as gray mold or botrytis blight, but the organism that causes the disease is Botrytis cinerea. And it’s a ubiquitous pathogen. It produces airborne spores that are probably in my office here today and in your office over there. You really can’t get away from it. It’s omnipresent. And so disease management is a challenge.
And so we think of disease management with any disease — we use the disease triangle as the kind of the model. And so there are three things that have to happen simultaneously in order for you to have a disease occur. And that is, one, you have to have the pathogen present. And like I mentioned, botrytis is always going to be present. It can be present in higher populations in some greenhouses, but it’s always present. So you really can’t exclude it. And exclusion is a means of control for some diseases, but not for botrytis.
The second corner of the disease triangle is that you have to have the right environment for that spore to germinate and grow. And botrytis requires — well, it has a broad array of temperatures that it grows under, but ideally around 65 to 70 is the ideal temperature. But you’ll even have botrytis becoming a big problem in a box of flowers that’s in a 40-degree cooler. So it takes longer at cool temperatures for it to grow, but it will grow at all temperatures. But high 60s, low 70s is kind of ideal. And you have to have high humidity and or a period where the leaves stay wet or the tissue stays wet for a long period of time. So that’s the conducive environment. And of course, in a greenhouse, we almost always have high humidity too.
So, you know, that is what makes it a bit challenging to control because you have the disease present, you have the organism present, you have the environment. And, you know, it’s kind of funny, I talk about this all the time and all of a sudden the third part of the triangle…
Host plant.
Oh, thank you. Oh, my gosh. Yep. So you have to have a susceptible host. And, of course, with flowers and greenhouses, almost all flowers are susceptible. So that’s a bit of a challenge. So you have a kind of a perfect storm in greenhouse environments. And that’s why it’s a problem in kind of every greenhouse on every crop, every floriculture crop.
Yeah, that’s why we never really get away from it. And we’ll never really solve the problem. It’s never going to go away. It’s not like some diseases where eventually you kind of eradicate them. It’s just always a problem.
Managing the Perfect Storm: Variety Selection, Detection, and Spread
Jim Faust: So the challenge you have is really to manage the situation, choosing varieties that have a bit more resistance. And that does work, but within every type of flower, there are going to be some really sensitive varieties. Like with roses, the red varieties are pretty good. They’re not that bad for resistance, but then you get some of the novel colors and then they’re really weak. And of course, you just can’t sell only red roses. So you end up having to grow these varieties that are a bit weaker.
So you just really can’t avoid having humid conditions in greenhouses. This leads us to really having to traditionally or conventional approaches, to do fungicide application on a preventative schedule. And of course, we learned from IPM management that we really don’t like to do preventative applications because you end up with a lot of fungicide being applied.
And some industries have approached this a little bit differently, like the strawberry industry in the Southeast has had a novel approach. They have basically, you can put a weather station into a field, and then that weather station measures when the environment is right for the spores to germinate, and actually then communicates to the grower electronically that now we’re under a period of high risk. And then the grower can time their applications of fungicides to the actual need rather than doing a preventative program. Like instead of spraying every week, you actually just spray on when there’s actually a high risk. So that can really reduce the number of applications of fungicides that one uses. Again, challenging in the greenhouse is that we’re almost always humid. It’s not like a field situation where if you have three weeks of no rain, then there’s very little risk. And so greenhouse is really more difficult.
Ping Yu: Yeah. Greenhouse basically created a perfect environment for botrytis or any given pathogen in there. The humidity is always there. And then the environment with the temperature is always there. Like you said, the temperature and high humidity in greenhouse almost perfectly serve the bubble for the pest to survive.
Host Range and Susceptible Crops
Ping Yu: But in terms of the host range, I know botrytis has a wide host range and roses are very susceptible. And can you name some of our flowers or ornamental plants that are pretty susceptible? I guess almost all those ornamental flowers or ornamental crops in greenhouse are somewhat susceptible to botrytis. But what is the most susceptible of the plant that you know of?
Jim Faust: Yeah, well, within a plant, even like a rose, which we know is highly susceptible, there’s different susceptibilities amongst the tissues. So like the leaves and the stems don’t get botrytis so badly, but the petals are really susceptible. And where we have trouble in greenhouse production tends to be in the spring, where you have bedding plant type flowers in the greenhouse. And then we have a week or two of cloudy, rainy weather, and it’s cool. And so the garden centers aren’t selling product, like sales are slow. And then the grower has a lot of flowering plants in the greenhouse that they’re having to hold and they can’t ship. And that’s when we tend to have big outbursts in production.
And again, almost every flower can get botrytis. Petunias and pansies would be some of the worst. But they can also be, you know, botrytis is also a post-harvest pathogen. So as is the case with roses and often with petunias, in the greenhouse, you might not see a lot of infection, but then you harvest those, put them in a box or put them on a truck. You know, that truck is, you know, plants around carts wrapped in saran. You deliver them and really over a 24-hour period, all the spores that are there germinate and start to grow. And you take those plants off the truck and the flowers are all melted down. So petunia flower meltdown is what we would call that, and it can occur pretty dramatically. Even though the plants in the greenhouse might look okay, they show up at the garden center in bad shape.
Detection and Spread
Ping Yu: Yeah, I think one of the ways that botrytis gets into the plant tissue is through the wound, especially for cut flowers. You’re already generating the wound for this pathogen to invade the plant. So it serves perfectly and makes them easier to get into the plant. But in greenhouse itself, before we’re not talking about cut flowers here at this moment, just in general for the greenhouse productions for ornamental plants, how does this pathogen spread in the greenhouse? Does it spread with wind and water splash or any other practices that will help them to spread widely within the greenhouse?
Jim Faust: Yes, spreading is entirely by air movement. And so, when tissue starts to die and decay, botrytis can grow on that tissue and then it has a bloom of gray mold, hence the common name. And then that mold can produce millions and billions of spores that then float around the greenhouse and land on other tissue and germinate. So sometimes if you have more air movement, you actually can spread the disease more. But really the issue is not the air itself. It’s that you have allowed plants in the greenhouse to get to the point of producing spores.
So this is why sanitation ends up being such a critical aspect of disease management. If you don’t let debris sit on the ground or on the floor or allow wounded plant tissue to remain on the plant itself, if you keep the facility clean, then you’ll minimize the number of spores that are being produced in the facility. You won’t eliminate them, but if you can reduce the amount of inoculum, then you certainly have less disease.
Early Signs and Scouting
Ping Yu: And so does the gray mold serve as the first sign of the invasion of the disease? What is the first sign of that? And where should people go detect the early signs before taking any actions?
Jim Faust: Sure. So the first signs are often a small lesion, a small spot that is often beige colored. And regardless of the flower petal color, the spots tend to be beige-like. And you can scout crops to look for spots where you, on denser plant canopies, especially when we hit these cool, wet periods of the year, you can actually have leaves down in the canopy that are rotting on, say, they’re wet on the soil surface. And so you start to disrupt or disturb that canopy and you’ll see spores floating around. So you can scout the canopy as a source of inoculum or scout the flowers in terms of looking for small spots.
Once those spots start to occur, then they spread and get bigger. Botrytis is a necrotroph, meaning it actually devours and kills the cells as it goes along. So as it infects tissue, it’s basically sucking out the goodies within the plant cells. And so as it does that, it kills that cell and goes to the next one. So you start out with a small lesion that gets bigger and bigger. And then if you have high humidity conditions, you will have sporulation and that lesion will put out this bloom of gray spores. And when you get to that point, then you’re kind of in trouble.
Ping Yu: Yeah, you know, a lot of times for pest or disease, the best strategy is to prevent them from happening so that you don’t have to deal with the big issue or the big trouble. But what happens, then sometimes if it’s too late, you have to lose the game by throwing them out and start over.
Biorationals vs. Traditional Chemicals
Ping Yu: In terms of once people detect the signs and symptoms of the disease, the next thing that they need to do is to take actions for management to manage this pest. And you briefly mentioned some of the traditional or the chemicals or chemistry that’s basically the go-to tools for a lot of growers to manage disease. But you have worked a lot of research on the biorational products to control the disease specifically. Can you tell us what is the difference between the traditional chemicals versus biorational products? And what are some of the commonly used biorational products for floriculture?
Jim Faust: Yeah. So if we go back, really, the first line of defense is always the environment. So if we can have a drier environment, that is always the best thing we can do. It’s just sometimes we can’t do that. So then the next line of defense traditionally has been chemical control. And we have chemicals that work — or fungicides that work really well against botrytis until botrytis develops resistance to those products.
Fungicide Resistance
So fungicide resistance is a real problem with botrytis because botrytis, it’s interesting in that it doesn’t have a sexual stage. So most organisms, you get mutation or changing of the — you get changes in the genetics when the offspring, when you have genes mixed between two parents, and then you have a unique offspring. With botrytis, it doesn’t have that sexual reproduction. It just reproduces asexually, and the way it then creates genetic uniqueness is by mutating, and it mutates very aggressively and continually.
And so when you apply a fungicide that has a very specific mode of action where it is interrupting one very critical biochemical process within the organism, it can work really well, it can keep the botrytis from growing. But one single gene mutation will allow the fungus to get around that mode of action. So even if only 1% of the mutated fungi has that mutation, then that mutated form, the successful form, the form that’s resistant to the fungicide, will produce the next generation of spores. And so with every application of a fungicide, you are selecting for resistance.
And when we really have a pretty limited number of products that work effectively for botrytis, growers have historically just sprayed the same thing again and again. And as a result, we have more and more resistance to those products. And so again, if you have no resistance, the fungicides we have are really, really good. The problem is, over time, there’s more and more resistance developed.
Categories of Biorationals
So that’s where we’ve been working on biorationals as an alternative. Really, the goal is not necessarily to not have chemical fungicide application, but to reduce the number of applications we’re making so that if we can space out our chemical applications more, then the chemicals we have will last longer. You know, if we just keep rotating the three or four products that work again and again, you’re going to have resistance. So if we can interrupt those rotations with other products, then you have less resistance to deal with.
So, biorationals is kind of an option. And by biorational, it’s kind of a vague term. It almost means anything that’s not a synthetic chemical. And so there’s a lot of different products that fall under that umbrella.
What people often think of as biological products would be what I would call biocontrol agents. Biocontrol agents are where you actually have a living organism that you’re applying. And so that’s like a specific type of biorational, but there’s really four or five different categories.
Biocontrol agents are probably the trickiest products to use because they actually have to live on the plant tissue to be effective. And that can be challenging for multiple reasons. One, you may have other chemicals on the plant that potentially kill the organism. And so they might not have compatibility with other things you’re spraying, or they can actually compete against each other in some cases. Or in the case of botrytis, you’re trying to get the biological organism to live on the foliage. And a lot of these biocontrol agents are really more happy in the soil. And so the aerial environment is a much harsher environment. It gets drier, it’s hotter, it’s sunnier. So for the biological control agents to actually colonize plant tissue is kind of difficult. And so our success with biocontrol agents is kind of limited. It’s not to say they don’t work. They can work, but it’s certainly a harder approach.
Some of the other options would be biofungicides, where you actually have a biologically based compound that is effective against fungal growth. And if you apply that, it’s kind of just like applying a fungicide. It just happens to be a biologically based fungicide. And so we have examples of that and they do work and don’t have to live — they’re not living organisms. They’re just compounds. They just happen to be basically biologically derived fungicides. And so those can work.
We have some plant extracts and we have essential oils, which are, again, plant-derived compounds that can be effective. Essential oils — our challenge has been phytotoxicity, where they can work pretty well, like things like thyme oil, but they also can be pretty damaging to plant tissue. So that’s one of the challenges.
A group of products we call systemic acquired resistance products, or SARs. And these actually are products that you would apply that then turn on the natural defense mechanisms within the plant. And these are tricky to use. The thinking is that you don’t immediately turn all these defense mechanism genes on immediately, so they can take a little bit of time to work. And then there’s also a cost. Like if a plant is expending energy to turn on these defense mechanisms, there’s an energy cost to that. And so that creates a challenge in that if you keep spraying these induced systemic resistance compounds, then the plant has to keep turning on these mechanisms of defense and that’s taking some of the energy away from the plant. So there’s a challenge. They can work, for sure, but management is challenging. There’s nothing easier than spraying a chemical. And it’s just like insects — it’s the same thing. It gets awfully complicated when we go to bio-based products. It’s not to say they can’t work, but it just is a challenge.
Calcium: The Nutrient Defense Against Botrytis
Jim Faust: So the last category being the one that we actually have worked on the most, and that would be using plant nutrients. And so, we’ve published a lot of work showing calcium is a very important plant nutrient that helps the plant be resistant to botrytis infection.
Why Calcium Matters
And so plants aren’t very good at accumulating calcium in the tissues, especially in flower petal tissue. Calcium levels are really, really low. Like they can be only 5% of the value of calcium that you would find in the leaf tissue on the same plant, like a petunia that has 1% calcium in the leaves will only have like 0.05% calcium in the petal. So it’s really low.
And so sometimes our only solution for that is to actually spray or dip susceptible tissues in calcium solutions in order to get the calcium where we want it to go. So calcium moves into the leaves fairly well because leaves bring a lot of water through them. The water gets evaporated or transpired and the calcium is left behind. But when you have a really rapidly developing organ like a flower, where it goes from a small bud to open flower in a matter of days, and that flower petal tissue doesn’t have stomata that transpire water through them. So you’re not pulling a lot of water into that flower petal. As a result, calcium’s not being pulled into that flower very well.
And in nature, this doesn’t seem to be so much of a problem because in nature, the flowers are pretty small compared to what we’ve done — horticultural breeders have bred everything to be bigger. Same thing with things like tomatoes. In nature, tomatoes are really small fruit. And you breed it to be giant and you start to have calcium deficiency issues because you just cannot move enough calcium into that tissue. And so you get blossom end rot.
And so once you have some necrotic tissue because of this localized calcium deficiency, then you give a place for botrytis to come in and grow. And so we have that problem with poinsettias. We call it bract edge burn, and really it’s calcium deficiency on the edge of the bract. And then you get little necrotic spots, and then the botrytis comes in and spreads rapidly.
So the lack of calcium is a challenge. But even on nice green tissue, we have found that if we can enhance the calcium concentration in that tissue, it becomes more resistant to botrytis infection. So what we think is primarily happening is, you know, calcium is a vital part of cell walls. And so as you strengthen those cell walls, what the botrytis is trying to do is send its mycelia, like its little arms and legs, or its roots, kind of down in through the cells. And it goes through the cell wall and sucks out the nutrients. And if you have a stronger cell wall, then the penetration of the fungus is not as good. So even if you get a small lesion, it doesn’t grow very well because the fungus is just not penetrating that stronger cell wall.
How Calcium Works
Ping Yu: So basically, to a certain extent the calcium is actually helping build a thicker cell wall to serve as a physical barrier for this pathogen to penetrate. But are there any other mechanisms that with the calcium that will actually help the disease control? Are there any other mechanisms that the calcium can serve besides the physical barrier?
Jim Faust: Yeah, and calcium is thought to be a signaling device of plant stress. And so, again, helps turn on defense mechanisms. So it’s not clear which, you know, there’s several potential modes of action for calcium. It’s really not entirely clear which is the most important. And it could be multiple things, too. But the key is having more calcium in the plant tissue.
Application Methods and Recommendations
Ping Yu: Which method of the application for the calcium is the most effective for botrytis control? Because you did so many different trials or research on this. Are there any way that you find the most effective and more importantly, cost effective?
Jim Faust: Yeah, so it depends on the crop. Like with cut flowers, we can dip the flowers into a calcium solution and that works really well. And probably the majority of roses that you would buy in the store these days have been dipped into a calcium solution before they were exported out of South America. So dipping works really well. And we’ve tested sprays on roses and they do work, just not as effective.
With the crops that a U.S. grower would be producing, you really can’t dip a tray of petunias. Like you can’t pick it up and — right, it just doesn’t work. So sprays are kind of what we have. And so what you see growers do is basically do a weekly spray as a preventative application. This actually started in the 90s when we had bract edge burn with poinsettia. The solution was just once you start getting color development on poinsettias, you just do a weekly spray of calcium.
And we’ve seen that that works pretty well with a lot of the spring crops that we grow. And so growers will tank mix calcium products with other sprays so that they’re not actually doing an additional spray, but if you’re already spraying a growth regulator or a pesticide, you can mix calcium into those spray applications and then try to get a weekly application on.
So the form of calcium that we recommend, probably what we think is the best, would be calcium chloride. You can apply calcium in different forms. For example, you could do calcium nitrate. But we get better control in general with calcium chloride, and it’s also quite inexpensive. We like to get the calcium up to at least 500 parts per million, and if not, 1,000 parts per million. If you’re doing a weekly application, 500 is probably okay.
With calcium chloride applications, weekly preventative applications really do make sense because it’s just not very expensive to use. And you really want it on before the risk of botrytis is high. I know some growers that when they start — they know weak cloudy weather is coming up and risk of botrytis is going to be high. They make sure that they have preventative applications on the tissue because calcium is not mobilized in plants very well. So it really is like a surface coverage issue. You need to treat flowers as they’re opening up, basically, to protect them well. Having sprayed the foliage two weeks before doesn’t help you that much. So you have to kind of protect the tissue that is most susceptible. So that’s why just kind of mixing in calcium chloride into a tank mix can work quite well.
Ping Yu: And how many applications do you recommend them doing? Because do they start doing, like from the preventative perspective, I guess, they do the normal scouting for many of the pest and disease that they have for the greenhouse. And once they detected any potential symptoms or even before, like you said, they predict the weather is going to change and that will increase the likelihood of the disease and they’ll start application. And throughout the whole process, for instance, like the poinsettia perspective or other — or petunia, how many applications do they normally do on an average basis that you would recommend?
Jim Faust: Yeah. I mean, I know growers that just spray it every week. I mean, it’s just because I did a calculation once and it was like $2 per acre. There’s no real cost to the material itself. It’s the labor to do it. So if you just mix it in with other products that you’re spraying, then that would be very little additional cost. So why not just add that? So again, you always have to be, anytime you tank mix something, there are risks involved. So you do some trials internally. But for the most part, that has seemed to work pretty well.
If it was me, if it’s a dry time of year, you don’t need to be using it. I think most growers have a bit of a sense when they’re hitting a period where they’re at moderate to high risk, they have a lot of flowers in the greenhouse, it’s cloudy, wet weather coming up, cool weather. You’re getting condensation forming on the greenhouse and dripping on the plants at night. Those sorts of conditions are when it’s ripe for botrytis infection. And so you need to be prepared with your fungicide tools lined up, but also calcium as one of the tools in your chest.
Coverage and Spray Equipment
Ping Yu: And speaking of the coverage that you mentioned, to make it more effective, you have to cover basically the whole plant at the surface. Are there any specific spray or mechanism or machine that will help with the coverage? When spraying more, they’re just misting with the air blast, they just do their traditional spray and then hoping they’re going to cover the whole plant.
Jim Faust: Yeah. If you use a high-pressure sprayer that makes very fine particles, you’re going to get better distribution and better coverage. So we’ve even taken like a petunia flower and covered half of it up and sprayed half with calcium and the other half didn’t get calcium and then uncover it, spray it all with spores. And you see that the side of the flower that received the calcium spray doesn’t get botrytis, the other side does. So it really is a coverage issue. So your spray equipment, doing a very fine spray that is well distributed, that’s turbulent and covers the tissues quite well, is going to be better than just a real heavy spray that runs off.
Ping Yu: Yeah, because I was assuming that once they spray, especially with this disease and the calcium, you probably want them to apply them so that the chemical or the product would reach the backside of the flower or the leaves as well. So basically you wanted to cover the whole thing instead of just the surface or the canopy, but also the underside of the leaves, the abaxial leaf, right, so that you can have the whole plant covered with calcium to prevent it from getting the disease.
Current Research and Future Projects
Ping Yu: Yeah, and so what is the next excitement for your research and career?
Itersonilia on Aster Family Flowers
Jim Faust: Well, we’ve got several projects going on. We’re actually doing another pathology project that is kind of unique. It’s mostly aimed at flowers that are in the aster family. There’s a disease organism called Itersonilia. And it is causing some real problems with the cut flower growers of gerbera daisy and chrysanthemum. It also can infect China aster, sunflowers. So there are small spots on the petals that are partly noticeable in the greenhouse, but then you put those flowers into a box and ship them and those spots can grow substantially and make the flowers unsellable. So it’s an interesting organism because there’s only ever been like two or three papers ever published on it, so we don’t know very much about it. So we’ve been trying to understand what’s going on. It’s a type of fungi that usually doesn’t cause plant diseases. So it also makes it kind of unique. So that’s one project we’re working on.
Building a Better Box for Unrooted Cuttings
We are working with unrooted cutting suppliers. And so these are the growers in Mexico and Central America that ship poinsettia cuttings, impatiens, petunia cuttings, and trying to build a better package to ship the cuttings in. So we have post-harvest related issues with cuttings in that there’s not a lot of temperature control during shipment. And as a consequence, cutting performance can be sometimes poor. You can get too cold, you can get too warm, you can get ethylene damage.
And so the idea is if we can build a box that actually is more breathable so that gases like ethylene can’t accumulate and cause problems, because we’ve done some nice work this past semester showing what concentrations of ethylene really start to cause damage and how those concentrations are actually pretty common in commercial shipping boxes. And so we’re trying to see if we can build a better box. So that’s been an active project.
Post-Harvest of Domestic Cut Flowers: Dahlia and Zinnia
We also have a project on post-harvest of domestically produced cut flowers. So this would be species that U.S. growers, especially cut flower growers, are producing that are not being produced in the international market. So we have been working a lot with zinnia and with dahlia, trying to improve the post-harvest longevity of those crops.
So dahlia has a really terrible post-harvest. Like they can die in two or three days. And so that kind of makes it only useful for events. Like you can’t really sell it as a cut flower because most of them don’t last a week, which is kind of what you hope a cut flower will last.
And then zinnias — well, the other thing that happens with the domestic market is most growers are cutting and then immediately selling the next day. And they’re not really storing product for very long. And what would be ideal is if we know that we could store flowers for even if it’s two, three, four days, then you could cut multiple days in a week and have more flowers available for your farmer’s market on the weekend, for example. So storage is really useful as long as you still have good vase life.
And so with zinnia, we’re looking at how to store them better because you can’t store them below 50 degrees because you get chilling injury. And so what we’ve learned with zinnia actually has been kind of interesting is that if you actually look on a zinnia flower, if you turn it upside down, you’ll notice it actually is green on the underside of the petals. The top side of the petals is yellow or orange or red or something, but the underside is greenish. And those petals actually have stomata on the undersides. And so I assume the green is chlorophyll and the petals are actually doing some photosynthesis.
And so what we’ve been able to show is you can harvest zinnia, and if you put them in buckets, like really high density buckets in an office somewhere — in the low 60s would be ideal, like an air-conditioned office. But if you put light on them, like with some cheap LEDs, you can light them. The light intensity would be like about 100 foot candles or 20 micromoles per square meter per second. So it’s not real bright. So it’s very doable. But if you put light on those flowers while you’re storing them, they actually still have a very good vase life.
If you store them in the dark, they don’t store well at all. Like the vase life goes quite badly. But if you store them in light, they actually seem to continue to, I’m guessing, produce sugars and photosynthesize because they’re doing photosynthesis. So they still manage to produce some food to survive. And so you can have a bucket, like a five-gallon bucket stuffed full of flowers and you don’t really need the leaves per se because there aren’t many leaves on them and you can’t see the leaves in a bucket anyway. It’s just the flowers that are exposed to the light, but those flowers seem to be doing sufficient levels of photosynthesis to improve their vase life. So that’s been really cool.
Wrap-Up and Resources
Ping Yu: I want to thank James for taking time out of his busy schedule to talk with us today. And I have put all those resources and links in the show notes so that you can find more information on all the work that he did. Besides that, I’ve also added the additional resources that AFE provides through the AFE Thrips and Botrytis Research Library. You can find more information on thrips and botrytis research, control, and other resources. So I will add all those links through the show notes so you can find all the information and resources on this topic.
Credits and Closing
Ping Yu: This episode in our first season is made possible through an educational grant from the American Floral Endowment, whose research priorities helped shape the topics that are featured. To learn more about AFE and access their research and educational resources, visit their website at endowment.org.
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Transcript produced for Blooms and Beyond / UGA Center for Urban Agriculture Support: American Floral Endowment Educational Grant