312 Q&A What is Fusarium Wilt? (And Why You Don't Want It!)

Show Transcript

312 TRANSCRIPT Q&A Controlling Fusarium Disease in the Garden

Farmer Fred  0:05

Welcome back to the Tuesday edition of the Garden Basics with Farmer Fred podcast. Unlike the Friday edition, we're dedicating the Tuesday podcast to answering your garden questions. Stay tuned to find out how you can get your garden question into the program. So come on, let's do this.

Farmer Fred

We like to answer your garden questions here on the Garden Basics podcast. We get a question from Linda. We don't know where Linda lives. Please, ladies and gentlemen, no matter how you get your questions into us, tell us where you're gardening, because that can really help us out in giving you an even better answer. So Linda asks, “We have Fusarium Wilt in our garden. We're putting in raised beds in April. What kind of barrier should go in at the bottom of the beds to prevent the wilt getting into the raised beds?”

Good question, Linda. Let's turn to a person who knows something about fusarium wilt in the garden. That would be Sacramento County Master Gardener Gail Pothour, who deals with it at the Fair Oaks Horticulture Center. Fusarium  is one of those diseases that once you got it, you got it.

Gail Pothour  1:12

Pretty much. I know it can stay in the soil, five, 7, or 10 years, a long time. So yeah, you've just got to kind of learn to live with it and manage it.

Farmer Fred  1:22

So let's let's talk a little bit about what Fusarium is and how you recognize it. There's a lot of good advice online from various universities about fusarium wilt. It's a very common disease from coast to coast. Susceptible crops that you'd grow in a home garden would include tomato, eggplant and pepper, but there are a lot more plants that are susceptible to fusarium wilt. In many situations the entire plant wilts, and turns yellow. Occasionally, the leaves will turn brown. Sometimes it's just half that turns yellow before it encompasses the entire plant. So the proper name for Fusarium. It's a fungus. It's called a Fusarium oxysporum and it infects solanaceous crops as well as some weeds too, such as pigweed, Mallow and crabgrass. The fungus can be introduced on infected transplants or spread via equipment, contaminated with the infested soil. Sometimes, even if you're buying it for a raised bed, it might come in that brand new soil that they're bringing to you. There are many varieties of host plants, though, with resistance to fusarium wilt. Building a raised bed is one strategy. So Gail, how do you think Fusarium got to the Fair Oaks Horticulture Center?

Gail Pothour  2:36

Good question. We first noticed it in  about 2013 or 2014. We had new raised beds built in 2012. And we had imported some topsoil/compost, put it in all the beds. We like to grow heirloom tomatoes, which typically aren't disease resistant, or at least you don't know if they are, and we started having issues  around 2015 or so I think. We actually pulled up a couple plants and took them in to the state lab. We bagged it up the way the state lab likes it ,took it into the state lab, which is the California Department of Food and Ag plant pathology center. And they confirmed that we had Fusarium oxysporum lycopersicum, which is the particular strain of fusarium that affects tomatoes. And we learned that it's host specific. So this strain only or species or whatever (isolate) you want to call it only affects tomatoes. And we had been noticing wilting and dying of the plants in several of the beds over the last couple of years. And so we determined it must have come in in our topsoil/compost planting mix. That's the only thing we can think of,  since it ended up in probably almost all the beds it came in and in the imported soil.

Farmer Fred  3:56

There are people listening to us right now going, “Oh, I'm glad I don't grow tomatoes. I won't get this fusarium problem.” Well, unfortunately, Fusarium Wilt effects, as I mentioned, many many plants. Susceptible woody ornamentals according to the University of California include trees such as the Mimosa tree, certain cacti like prickly pear and Saguro, date palms, and pyracantha. Herbaceous ornamental hosts include asters, carnations, chrysanthemums, cyclamen, daffodils, dahlias, freesias, and gladiolas. Other hosts include asparagus, beans, cabbage, cantaloupe, peas, and watermelon, besides tomato. So I would imagine there are other sections of the Fair Oaks Horticulture Center that may be dealing with fusarium as well.

Gail Pothour  4:42

Well, since the state lab had told us that this particular Fusarium oxysporum lycopersici its only host is tomatoes… They had assured us that the potatoes we wanted to plant the next year in that bed should not get it and they didn’t, as it turns out. And so my understanding, and I'm not a scientist, but that each of the oxysporum species, I guess you would call it (the proper term is “isolates”), are host specific so the fusarium that gets on  basil only gets on basil, or that gets on muskmelons only gets on muskmelons. And on okra only gets on okra. So it thankfully, is host specific, unlike verticillium wilt, which gets on almost everything. So that's one of the management techniques. If you know you have it in this particular area, and it's the one that gets on tomatoes, don't plant heirloom tomatoes. Only plant tomatoes that are resistant; or. plant something else there.

Farmer Fred  5:46

And the way to determine that is when you're buying tomato seeds on the packet, there may be some letters after the name of the variety. Letters like V, F, or N, or T, or a V for verticillium wilt, which can be difficult to distinguish between that and fusarium wilt. The F, of course,is fusarium, and N is for nematodes, which is a problem for a lot of people, the T is tobacco mosaic virus, and Alternaria, which is the A. They keep tacking on more and more letters to the ends of seed packets.

Gail Pothour  6:20

There’s a whole alphabet after that, yes. And some companies, I've noticed some seed companies have different abbreviations. Like for tobacco, tobacco mosaic virus would have a T, the other would have TMV. So they are a little bit different. You have to decipher it, I've learned.

Farmer Fred  6:37

And as I mentioned at the beginning, once you got it, you got it. a And unfortunately it spreads very easily. It can stick to your shoes if it's wet, muddy soil and move to another part of your yard. If you're working with shovels and trowels, and you still got some dirt on it that you've been working on in a Fusarium-infected bed, you could easily transfer the Fusarium spores to a different part of the bed or a different bed. So cleanliness helps a lot and being very careful about isolating it. And probably, too, once you find a Fusarium infected plant you should get rid of it.

Gail Pothour  7:14

Oh, yeah, because Fusarium will eventually kill the plant. Verticillium maybe not. But fusarium  will kill it. So get rid of it. Don't put it in your home compost, take out the roots and everything and throw it in the garbage. Because your home compost bin probably won't get hot enough to kill the pathogen. So yeah, just get rid of it. Because the fruit on the plant will be compromised. It doesn't have so much leaf cover. So it will get sunburned. And so the fruit itself will start looking bad. The state lab assures me that you could eat it, if as long as it’s not moldy or anything like that. I'm not sure I'd want to, because the fruit will look pretty bad because  it's wilting, and it's not getting the nutrients that it needs. So yeah, I just pull it up. Get rid of it.

Farmer Fred  8:05

Some of the suggestions for ridding yourself of fusarium. Well, one is - “soil replacement should be considered”. Well, that's kind of impractical, to say the least.

Gail Pothour  8:17

Our eight beds that are four feet by 20 feet long. That's a lot of soil that we'd have to replace.

Farmer Fred  8:23

Yeah. But the idea of building a raised bed has merit. A lot of universities do recommend that if you are dealing with fusarium. But how tall does that bed have to be for the roots not to touch any soil below that might have fusarium wilt?

Gail Pothour  8:41

Good question. I know with nematodes, they can move. Fusarium would not. And one of the management techniques for dealing with Fusarium is to go to raised beds, because if you plant in a saturated garden bed, there may be poor drainage or whatnot. But in a saturated bed, fusariium can spread a little easier. So raised beds is one of the management techniques. Now, how deep that bed needs to be. I wouldn't be able to speculate. But if Linda goes to building raised beds, I think that's a good start anyway.

Farmer Fred  9:13

Yeah. But I think before I build a raised bed, I would maybe spend this summer solarizing the soil with clear plastic that will be beneath the raised bed, just to mitigate some of the chances. It may not reduce the chances to zilch, but it might reduce the amount that's there.

Gail Pothour  9:34

I agree. Because soil solarization is also another management technique. If it heats up enough, you'll kill the pathogen, the soil borne pathogens, at least in the top several inches, six inches or whatever. That doesn't mean you're not going to have it a little deeper than that. But sure, I would start with the soil solarization and then cross your fingers and hope the soil you bring in isn’t contaminated with anything.

Farmer Fred  10:01

They also mentioned that - they being the University of California - say to avoid using undecayed organic amendments around host plants that may have fusarium. Avoid excess fertilization, especially with a nitrogen product such as urea, which is a quick acting nitrogen, which may promote development of even more fusarium wilt. And you want to keep mulch, other debris, and other plants away from the base of host plants of fusarium. Especially palms, because nearby plants and their management can wound the palm roots. And again, getting rid of the infected plants is an excellent idea. And we haven't yet talked about plant rotation, which is another strategy for controlling fusarium.

Gail Pothour  10:47

It is. actually. The  state lab, when they had given us their diagnosis, they had some recommendations for how to manage it. And soil solarization was one. Another is rotate your crops. Another one was disinfect everything, everything that comes in contact with the soil or the plant. So we found that during the first year or two, we were out there with Lysol wipes and bleach solutions, and we were disinfecting absolutely everything that touched the soil, which was very burdensome. I don't think home gardeners would do that. And over time, we pretty much stopped doing that cleanliness, that was quite so obsessive. We still tried to sanitize things, but that was a little bit overkill. And our farm advisor, Chuck Ingels, had said, why go to all that trouble, you're not going to get rid of it, it's a lot of work. Just be sure that you are cautious sanitizing things because it is easy to transfer into other beds. What we've decided to do is we'll take sanitation seriously, we'll do what we can, but we won't be obsessive about it. We solarize one bed each year. And the state lab also told us to get rid of the straw mulch that we used in each of our beds, which the first day or two we did that we just chucked it. we ripped it up and threw it away. Now we're not quite so diligent with that.  if we may take it out of the bed, we're solarizing and leave it in the other beds. But you know, it's a tough thing to manage. Chuck Ingels recommendation was be observant of sanitation. And probably the best management practice is to grow resistant plants.

Farmer Fred  12:31

Exactly. And Linda, about putting a barrier between the soil and the raised bed. I don't think you want to do that, for any number of reasons, not the least of which it would impede the flow of water from your raised bed. And you could end up with wetter soil, which could actually spread fusarium.

Gail Pothour  12:51

Yeah, I agree with that. I don't think I would put any kind of barrier, whether it's black plastic, landscape, fabric, whatever, I wouldn't put anything on the bottom. Now if she has gophers she may want to put down hardware cloth, but I wouldn't recommend putting down a barrier.

Farmer Fred  13:07

Yeah, hardware cloth is quarter inch or half inch mesh that would allow air and water to flow through. And yeah, if you do have a gopher issue, and you're building raised beds, not only do you want to cover the bottom, you want to bring the hardware cloth  up about halfway along the sides of all four sides of the raised bed, too. Because gophers are clever, they can find a way in.

Gail Pothour  13:25

That’s right. If it's laid flat, they will find a way to get into it. So yeah, bring it up on the inside of the bed and staple it or somehow affix it.

Farmer Fred  13:33

One question I had for Linda was, how do you know you have fusarium wilt in your garden?

Gail Pothour  13:39

That was my question too. Because you can't determine it on your own. I mean, you can  suspect it. What we do at the end of the growing season, when we take our tomatoes out, we will cut the plant at the soil line and look at the cross section. And generally with fusarium and verticillium, they kind of look like there'll be some browning inside. So that's your first clue. But you can't tell which it is, if it’s fusarium  or verticillium, or you don't know which race fusarium you have, or which strain.  We have the fusarium strain that affects only tomatoes so we can grow anything else in that bed and not worry about it. What does she know that she has? Is it truly a fusarium? Is it verticillium? And if it’s fusarium, which strain does she have?

Farmer Fred  14:26

One, two or three ? Yeah,  there's several.

Gail Pothour  14:31

And that's something only a soil lab could make that determination.

Farmer Fred  14:35

Exactly. And it's not a soil testing service either, that does that kind of work. It's an actual laboratory that you would have to go to. I was checking the three University soil testing sites that I usually recommend. The University of Massachusetts Amherst, Texas A&M and Colorado State. All three of them say we don't test for diseases. So that's why you have to go to a lab.

Gail Pothour  15:01

Right. And a lot of publications will say check with your Cooperative Extension office  to have things tested. We have to send things to the California Department of Ag plant pathology lab. I don't know what's available in other areas and other states. Yeah, it's important to get a real test from lab scientists who know what they're doing, to tell you what you've got.

Farmer Fred  15:23

Yeah, and I'm sure whatever state you're in, you can reach your local Ag department, and they can give you advice about where to go to have your soil tested for fusarium. Just to make sure, we were talking about which race of fusarium you might have and which plants it might affect. The Missouri Botanical Garden pointed out something interesting. They have a very good page on fusarium and tomatoes. And they talk about sanitizing stakes and tomato cages at the end of the season. Because, if you recall, your stakes and tomato cages, they always have something clinging to them at the end of the season.

Gail Pothour  16:01

And that's what we did the first year, following  the state labs recommendation. We had mixed up a bleach solution, diluted bleach solution, and we're spraying  all the tomato cages and all the metal stakes. And we stopped using bamboo stakes, because they're hard to sanitize, and it was becoming burdensome. And knowing that we didn't know how much we were affecting fusarium areas, it's in there, but were we decreasing it? We still have it in all of our beds. Yes, I think we still do. And because I'm a kind of a science nerd, I have a compendium that's written by the American Phytopathological Society on tomatoes. And they say that under certain environmental conditions, the fusarium pathogen that gets on tomatoes can be shown to be airily disseminated. So not only can you move it around on your tools and your shoes and other infected plants, but if it's can be in the air, oh my gosh.

Farmer Fred  17:00

Yeah, I was reading that too. And  it's something else to consider. What's interesting, the Missouri Botanical Garden does talk about planting resistant varieties, and removing infected plants from the garden. But then it says, “For 4 years do not plant solanaceous plants in the area where the infection occurred. Tomato, potato, pepper and eggplant are all susceptible to the disease and may allow its survival year after year in the same planting area.” But as you've been pointing out, it depends on what race or strain (isolate) of fusarium you might have.

Gail Pothour  17:33

Or what species of it you have. Because as as the state lab told us, the oxysporum lycopersici, which is the one for tomato only gets on tomatoes. Eggplant has its own. It's oxysporum melongena. And pepper has a different one. So they assured me that yes, we can grow potatoes, which is in the same solanacea family, the following year you wouldn't have problems. So I think there's a little bit of conflicting information. I've read the same thing that they say don't grow anything in the tomato family for four or five years. And then other sources say it's fine. So I don't know. I guess just do the best you can.

Farmer Fred  18:13

This is all reminiscent of the first year of COVID.

Gail Pothour  18:17

Pretty much. One of the things I wanted to mention was, since this is a soil borne fungus, we thought okay, let's try growing heirloom tomatoes, which we love, in things that don't have soil. So grow it in a soilless potting mix in a container or a straw bale. We were doing straw bale gardening for a while. And wouldn't you know it? That year, we got plants in the straw bale that were wilting. And we got a plant in one of our wine barrels that was wilting. We took it to the state lab, they confirmed we had fuarium. And so my question was okay, this is a soil borne fungus. How do you get it in plants that aren't grown in soil? Because there was no soil in the straw bale or potting soil, which is a soilless mix in the wine barrel? Nobody could answer that question. So we thought okay, maybe we introduced it on some of our tools or because what what you do in a straw bale is you plant your plant and fill that hole in the straw bale with a better potting soil or compost. So okay, maybe we weren't good with sanitation. So the following year, we did the identical trial, the same plants. In the straw bale, new fresh bales. We were conscious of being sure that we disinfected our tools before we touch them. And it happened again. So that made me wonder about the aerial dissemination of the fungal spores or something. So I don't know. It’s a puzzle. Apparently resistant plants are the key.

Farmer Fred  19:47

I did find one source, the University of Minnesota, that pointed out fusarium wilt can be seed borne, but it is rare in commercial seed. So if you are in the habit of saving your own seed  to reuse, that might be how it's spreading, from year to year.

Gail Pothour  20:04

Could be. They said that the commercial seed companies, they have standards that will kind of prevent that. And in fact, we had sent the seeds, they were brand new seeds that I had purchased for the straw bales. We sent them to UC Davis to their seed lab, to make sure they weren't contaminated. And they were fine. Yeah, it's a puzzle.

Farmer Fred  20:27

Yeah. A lot of these are outlets the average home gardener just wouldn't have access to. And the best thing you can do is to try to be careful.

Gail Pothour  20:39

Right? Yeah. And you're taking your chances. And one thing that we've learned because we now have nematodes, at least in a couple of our beds, even if you plant tomato varieties that are resistant to fusarium and verticillium, they need to have the nematode resistance as well, because if you have nematodes, the nematodes will make wounds on the roots, and that's where the fungal infection will creep in. So even ones that are resistant, if the disease pressure is high enough for if you have nematodes that can override the resistance.

Farmer Fred  21:11

One recommendation I have given to people who think that if they have fusarium on their tomato plants is, you're gonna yank the plant out anyway. Make a cut at the main stem and take a look at that core. is it a cream colored or is it dark? If it's dark, chances are it probably has fusarium. But that can be a confusing thing, because some sources talk about doing a little slice off the side of the main stem.

Gail Pothour  21:41

Kinda like you're whittling?

Farmer Fred  21:45

Yeah. Like like you're whittling. And if you see some dark, red or brown, discolored vascular tissue, well, that could be fusarium. Well, it could also be verticillium. Right?

Gail Pothour  21:55

That's why it's important to have it tested and find out exactly what you have. Because even though the management is pretty much the same for both verticillium and fusarium, because verticillium gets on so many plants, I mean, they virtually would get on almost all vegetables, I think. the fusarium are host specific. So while you don't want fusarium, at least if it's the strain  that gets on peppers or the one that gets on cantaloupes,  you'll know which ones to not plant there, you can plant something else and it shouldn't get it.

Farmer Fred  22:31

There are a lot of controls we've talked about for controlling, but really not eliminating, but controlling fusarium. And don't forget the weeds that might be in your garden as well, Because weeds can serve as hosts of the spores of fusarium.

Gail Pothour  22:47

Yeah, fuarium spores would overwinter on the weeds, but won't affect the weed. The weed won't get fusarium, but the spores overwinter on it. Yeah, so weeds can be a real problem as far as keeping the spores in the surrounding soil and then they'll contaminate  your plants the next season.

Farmer Fred  23:05

We talked about not using high nitrogen fertilizers or excessive nitrogen. That can encourage the disease. Another thing, too, is if you have very acidic soil, you could have fusarium run amok. So for acidic soils, the University of Minnesota recommends raising the soil pH to seven to help control the disease.

Gail Pothour  23:28

One more reason that it's important to even do a soil test with those soil test kit that you do it yourself, to test your pH. Because not only is that important for the plant's ability to take up the nutrients, but you're right, if it's too acidic, then your fusarium might rear its ugly head.

Farmer Fred  23:47

Fusarium is a fatal disease to a plant. If you see the plant wilt, the leaves turn yellow and the yellowing probably won't be uniform. If the entire plant soon wilts and turns yellow, pull out the plant, put it in the trash, don't compost it, just get rid of it. And be very careful working with that soil. Now getting back to Linda's question about the raised bed. Obviously, putting anything on the bottom really won't work. So we come back to the question of  how high should that raised bed be to avoid the roots of the plants getting down through to the existing soil below that might have the fusarium. And I mean, just off the top of my head, I'd probably say at least 16 inches.

Gail Pothour  24:31

Yeah, I would say 12 inches would be the minimum. I like to go 18 inches, all my beds and the ones that the Horticulture Center are 18 inches high. I don't have any idea how far those fusarium spores can be down in the soil. So I don't know how high the raised beds  need to be, but I'd say the higher the better. And as we get  get a little bit older, you like to have higher beds, you don't have to bend over so much. I know from experience.

Farmer Fred  24:59

Yeah. I've known that for 30 years now. Or actually 40 years. Right? But fusarium wilt is just one of many things we can live with. We can work around it, there are plants that are resistant to it, varieties that are resistant to it, rotate your crops, practice common sense about cleaning your tools. Don't bring in suspicious soil, whatever you do.

Gail Pothour  25:26

And you know what else I'd forgotten, there are grafted tomato plants. And I don't know if there's other grafted plants, but look in seed catalogs or whatnot, or maybe even nurseries. There are tomato varieties that they graft onto a rootstock that is fusarium resistant. We actually tried that, oh, golly, maybe six or eight years ago, we purchased an heirloom variety. And then we purchased from the same company the same heirloom variety that was grafted onto rootstock that was resistant. It was quite a bit more expensive. There pricey. And we grew them side by side. Interestingly enough, the one that was grafted is the one that died. But so we don't really know what happened. Maybe our disease pressure was so high that it affected the rootstock, I don't know. But that is one way as you can get grafted tomato variety that's been grafted on to a resistant root stock. Just be aware it is a little more expensive. And also I know some people have said, well, if it's a fungal infection, can't I just spray some fungal thing, a fungicide? But there are no fungicides available to home gardeners for fusarium. So yes, not an option.

Farmer Fred  26:38

So we go to other integrated pest management strategies. Some good advice from the Missouri Botanical Garden, again, about planting resistant varieties, remove infected plants from the garden, avoid over application of high nitrogen fertilizers, avoid activity in wet plantings, sanitizing tools, stakes, cages, and maybe not plant that same variety again and go for resistant varieties.

Gail Pothour  27:03

Well, that's what we've learned. And this is what our farm advisors, recommend. Their recommendation  was, just don't throw heirlooms in those beds, if we want to do them, do them in a container or whatever. So we have stuck with hybrids that have the VFN after their name, we tried to get the ones that have more than one F. So one F is race number one, two F’s are races one and two, and then three F's is one, two and three. We don't know which race we have of fusarium, because eight, nine years ago, when the state lab did the test, they didn't have the capability of determining which race it was, whether it was one, two or three. They could tell which species it was, but not which race. I don't know if they can do that now. So just to be on the safe side, we tried to get hybrid tomatoes that have V, FFF, and N after them.

Farmer Fred  27:52

By the way, if you are planting in containers, and you have other places in the yard that have fusarium, you’ll want to clean your containers thoroughly before you plant them because soil sticks to the sides.

Gail Pothour  28:07

That's right. So sanitation not only on your tools, but on containers. If you're growing your own transplants, be sure if you’re reusing containers that they've been sterilized. Get good quality potting soil or a soilless mix.

Farmer Fred  28:23

Well, have we killed it off?

Gail Pothour  28:24

I think so.

Farmer Fred  28:27

As much as we could. It's a control. It's not a cure.

Gail Pothour  28:32

We just have to learn to live with it.

Farmer Fred  28:34

Yeah, exactly. And there's plenty of other things you can grow, other varieties to grow. And like you say, if you have this hard head about growing that particular heirloom, do it in a nice new container with nice new soil. All right, Gail Pothour,  Sacramento County Master Gardener, who much to her chagrin works with fusarium on a daily basis. Gail, thanks so much for your help here.

Gail Pothour  29:00

You're welcome Fred.

Farmer Fred  29:09

Want to leave us a garden question? You'll find a link at Gardenbasics.net. Also, when you click on any episode at Gardenbasics.net, you're going to find a link to Speakpipe. You'll find it in the show notes. And when you bring up SpeakPipe on your computer or smartphone, you can leave us an audio question without making a phone call. You can go to Speakpipe directly at speakpipe.com/garden basics . You want to call or text us? We have that number posted at Gardenbasics.net . It's 916-292-8964, 916-292-8964. Email? Sure, we like email, send it along with your pictures to Fred at farmerfred.com. Or again, go to gardenbasics.netand get that link. And if you send us a question, be sure to tell us where you're gardening, because all gardening is local. Find it all at Gardenbasics.net .

Farmer Fred

Garden Basics with Farmer Fred comes out every Tuesday and Friday and it's brought to you by Smart Pots and Dave Wilson Nursery. Garden Basics. It's available wherever podcasts are handed out. For more information about the podcast, visit our website, gardenbasics.net and that's where you can find out about the free Garden Basics newsletter on Substack,  “Beyond the Basics”. And thank you so much for listening.