Preventing and Controlling Foliar Disease in the Garden - Ep. 195

Karin Velez [00:00:00]:
Foliar diseases in both vegetable and fruit plants can significantly impact our yield and the quality of that yield if left unmanaged. If you've ever had powdery mildew on your cucumbers or early blight in your tomatoes, you know exactly what I'm talking about. Even though the disease is affecting the leaves, the interruption of photosynthesis by the fungus affects the fruit development, and then the disease will jump from the leaves to the fruit, and then we've got a real mess on our hands. And sometimes, we can get one disease under control only to have another one swoop in and take out our plants before we even get any kind of harvest. This is especially true if you live in an area that is very humid, or if you have spring weather that bounces from warm and humid during the day to cool overnight with very little air movement and lots of rain. Warm temperatures, high humidity, lots of moisture, and prolonged leaf wetness are all the ideal conditions for fungal growth. Today on just grow something, we are going to cover the different ways that we can prevent fungal diseases from taking hold in our garden plants, what signs and symptoms to watch out for, which plants are most susceptible to fungal diseases, and which ones don't usually have much of a problem with them. There are lots of things that we can do as gardeners to prevent and minimize the occurrence of foliar diseases so that we can get the best yield possible from our plants.

Karin Velez [00:02:40]:
So let's start with the basic steps that we can take to reduce the occurrence of fungal diseases in the garden, and then we'll talk about what to look for when monitoring our plants for these diseases. The first consideration is site selection and possibly crop rotation. So you wanna choose a planting site with good air circulation and lots of sunlight exposure. That sunlight exposure is going to help in drying off those leaves and preventing some of those fungal diseases from taking hold. So you want to avoid planting susceptible crops in areas where foliar diseases have been prevalent in the previous seasons. And I know that this can be difficult, especially since we don't always have a wide area to choose from. If you only have one spot in your garden that is suitable or one spot in your yard that is suitable for a garden, then it's difficult to implement any type of a crop rotation plan. But if you can do that, that can help to break the disease cycles by planting different families of vegetables in each bed or each area, every year. Another way to help prevent some of these diseases is through healthy soil management. So if you can maintain the soil fertility and health through adding organic matter like compost, and using balanced amendments to help maintain that soil health, then that is going to promote vigorous plant growth, and that vigorous plant growth means stronger plants, which can improve that plant's resistance to those diseases. The next thing is proper plant spacing, and this is particularly tricky for somebody like me who really does a lot of intercropping and companion planting. It's fine for us to try to maximize the amount of plants that we can get in there, which is going to, minimize the amount of exposed soil that we have.

Karin Velez [00:04:33]:
But we want to avoid overcrowding the plants. This is can reduce the airflow around that foliage, and that just gives us a really favorable condition for disease development. So what I tend to do is follow the spacing recommendations for my plants that are either provided on the seed packets or on the plant labels or whatever, and I do that for each individual crop. But then when I'm looking to plant things in between or around those plants, I'm pairing taller plants with short ones and fast growing plants with slow growing ones so that they're not all occupying the same air space at the same time. So that example that I generally use, like planting tomatoes with lettuces, the tomatoes are taller, the lettuces grow lower, and therefore, they're not really sharing the same air space. So proper plant spacing is going to increase that airflow, which is gonna help us prevent some of these diseases. Another thing is water management. We really wanna try to water our plants at the base rather than overhead, because we're trying to minimize that leaf wetness, which encourages the spread of these foliar diseases.

Karin Velez [00:05:42]:
So if you can use drip irrigation or soaker hoses or somehow water at the soil level to keep the foliage dry, then the only moisture you're having to worry about is either high humidity or rainfall. If you do have to water overhead, then try to water early in the day to allow those leaves to dry before nightfall. The next thing is mulch. Come on. This wouldn't be one of my episodes if I wasn't talking about mulch. Right? You want to apply a layer of organic mulch, like straw or shredded leaves or whatever you're gonna use around the plants. This helps suppress weeds, which again, is going to reduce that humidity that's in and around that air space. Right? We don't want those extra plants in there.

Karin Velez [00:06:29]:
It's also gonna help to retain the soil moisture, so you are watering less frequently, which means there are less chances of the leaves getting wet. And it's also going to reduce the soil splashing up onto the foliage, either through rainfall or from watering. So basically, the mulch is gonna act like a barrier. It's gonna prevent those soil borne pathogens from splashing up onto the leaves when it rains or when we water. So once again, mulch is our friend. Now if you have had a problem with foliar diseases before, then you can choose to plant disease resistant varieties. There are varieties that are bred specifically for resistance to specific foliar diseases. So if you look in the seed catalog or if you look at the nursery label, it's going to tell you with these different codes or symbols that will indicate their resistance to common pathogens.

Karin Velez [00:07:27]:
So if you say on there, it says resistant to t m v. This is a variety that is resistant to tobacco mosaic virus. So if you know there's a particular virus or a particular plant pathogen that you see commonly in your garden, then learn what the code is for that, and then you can look in the seed catalogs or on those nursery labels to find disease resistant varieties for that particular, disease that you're fighting. The next thing is sanitation. We wanna just practice good garden hygiene. That means removing all of the diseased plant debris as quickly as possible. So, getting them out of the garden. You also wanna avoid working in the garden when your foliage is wet because that's another really good way to spread the diseases from one plant to another.

Karin Velez [00:08:16]:
And then clean and disinfect all of your gardening tools, like your pruners or any garden stakes or anything else in between uses because we don't want the risk of spreading diseases from one plant to another or even one crop to another. If you have your tomatoes planted in one corner of the garden and you realize that you've got some foliar disease in there and you're in there pruning them back, And then you walk over into your potatoes, which are in the same plant family, and are, susceptible to the same diseases, but you haven't cleaned your pruning shears or even your gloves or your shoes in between, then you very well may have just carried that pathogen from your tomatoes into your potatoes, which maybe weren't already infected. So good good sanitation practices are key. You want to regularly inspect your plants for the signs of foliar diseases, and we'll talk kind of specifically here in a minute about what those signs and symptoms are. Just keep in mind that the earlier that you can detect these diseases, the faster you're gonna be able to intervene and help prevent the spread of that disease to your uninfected plants. And then proper pruning or even staking is going to help improve the airflow, and this is going to reduce the humidity around the foliage. Now sometimes sometimes this might seem like it's a futile process because if you live somewhere where it's really humid like I do I mean, I'm recording this right now, and it is 96% humidity out today. I'm not kidding.

Karin Velez [00:09:48]:
And so it might seem like, well, what is pruning gonna do for me? It's not gonna help reduce the actual humidity, but you would be surprised how much humidity really gets trapped in and around all of that foliage between the plants. So if you can prune some of that out to improve the airflow, and you know me, I don't prune just for pruning's sake, I I prune very little. But if you can do that, and then also remove and dispose of any infected leaves or branches really promptly, that is also gonna help prevent the spread of the disease. And then finally, you might consider using organic fungicides as a preventative measure or for controlling diseases when they do pop up. So, you know, copper based fungicides are good, sulfur, neem oil. There are even, like, bio pesticides that have beneficial microorganisms that will help. We'll talk a little bit more about that here in a minute, but you they're better used as a preventative rather than a control. But if you do see that you've gotten some diseases in there, then at least, you know, you have something that you can use to prevent it from spreading like wildfire to all of your other plants.

Karin Velez [00:11:04]:
Now, what should we be watching for? What signs and symptoms might indicate the presence of a problem, a foliar disease? This is gonna vary depending on the type of the disease that we're looking at and the specific plant species that's affected, but these are some common signs and symptoms to walk for watch for. The first one is leaf spots. So discolored spots or lesions on the leaves. These may vary in size, shape, or color depending on the type of the pathogen that's causing the disease. They can either be small dots, they can be irregular patches, they might be concentric rings, but if it looks like it doesn't belong there, it probably does not. The same thing goes with leaf discoloration. So you're gonna wanna watch for any yellowing, browning, or blackening. Now, of course, this could also be a symptom of a nutrient deficiency, but generally speaking, you know, it's it's gonna seem different when it is a disease.

Karin Velez [00:12:04]:
And this discoloration could be on the entire leaf, or it could be localized around little lesions or spots. So it's good to know, again, this is the importance of a soil test. If you know you don't have any deficiencies and you start to see this yellowing or browning of the leaves, then likely, you've got some sort of foliar disease going on. You also wanna look for leaf curling or distortion, so any abnormal curling or twisting or just really distorted leaves. Now sometimes this could be a symptom of herbicide damage, so if there's been any kind of herbicide spray in the area, that might be something that you're looking at. Also, like, environmental stress. So if the weather has changed dramatically in a very, very short period of time, That can stress the plants out, and it can also cause leaf curling or distortion of some sort. But if you had excluded both of those issues, then it's a pretty good sign that you have an infection of some sort of a pathogen.

Karin Velez [00:13:03]:
The same thing goes with wilting. If you've got excessive wilting or drooping or just stunted growth, this can be a sign of some sort of a foliar disease, but this might also be a root disease or a vascular pathogen. So that's gonna cause the plant to have problems for taking up, water or nutrients. So wilting or stunting is a little bit less definitive when it comes to foliar diseases, but it's still something to watch out for. And then you you also wanna watch for any kind of powdery or downy growth. So white, gray, or fuzzy growth on the surface of the leaves, or even on the stems or the fruit. This is characteristic of fungal diseases, like powdery mildew or downy mildew. Powdery mildew tends to be a bit more, like, white or or light gray.

Karin Velez [00:13:54]:
Downy mildew tends to be more grayish or in purplish patches, but they are both fungal diseases of the foliage. You also wanna watch out for any lesions or spots that look like they are wet or greasy. We call these water soaked lesions. This might be an indication of bacterial diseases. So bacterial spot or bacterial blight, will often present with these lesions. And then don't just check your leaves, but also check your fruit, because the fruit can also carry signs of diseases. You can have lesions, you can get this premature rotting or really weird discoloration or just deformities. And so fruit symptoms, I mean, these are gonna vary depending on the type of the disease and the stage of the infection.

Karin Velez [00:14:37]:
And, usually, you will have seen some sort of leaf or stem indicators before you see it on the fruit, but not necessarily if you don't know what you're looking for. So if you start to see any weird things going on with your fruit, then you can suspect that there's some sort of a foliar disease, and you can start looking at the foliage and on the stems to see if there are other signs or symptoms. You also wanna pay attention if you suddenly have your plants starting to drop their leaves, so premature defoliation. This can be a result of a severe foliar disease. I would hope at that point that you would have seen something else as an indicator, because, again, a sudden defoliation can be a indication of a severe environmental stress. So if we're watching closely and we're paying attention to anything that seems sort of out of the ordinary, we should see something happening before the leaves start to drop off. And then, again, there's just maybe a, like, general decline in the overall health of the plant. You may not be getting as much fruit off of it. You know, the the quality of that fruit might be reduced. The plant may just not seem to be growing very vigorously, indicated in there.

Karin Velez [00:17:04]:
So once a plant has become infected with a foliar disease, what can we do to sort of mitigate the damage and then potentially save that plant? If at all possible, you wanna isolate the infected plant to prevent the spread of that disease to other nearby plants that may not already be infected. And if you're a container gardener and you've got these in pots, this is a little bit easier to do. But if you have your plants all in raised planters or in in ground beds, it may be necessary to completely remove that entire plant. Now if it's just parts of plants or it's parts of multiple plants, then pruning is an option. You wanna remove and dispose of any of the infected leaves, the stems, or the branches, and make sure that you are sanitizing those pruning tools when you do that because you don't wanna go use it on another plant, and spread fungal spores or anything else to, other uninfected plants. You can also prune a little bit just to kind of help improve the airflow around the plant, and reduce that humidity to keep that that disease at bay if it's already infected. And then just make sure that you are removing all of that plant debris out of the garden area so that it's not gonna continue to spread.

Karin Velez [00:18:19]:
Once again, you know, at this point, if you see that you've got some foliar diseases, you wanna try to minimize the leaf wetness. So we wanna avoid the overwatering or the overhead watering, and use drip irrigation or soaker hoses, even if it means you stand out there with the hose at the soil line instead of automatically putting on your sprinklers, that's gonna help to prevent the spread. And we talked about organic fungicides as a preventative. You can also utilize these to sort of suppress the disease to allow it to or to prevent it from continuing to spread. So copper based fungicides, neem oil, these offer environmentally friendly alternatives to maybe using something that's synthetic. I have successfully used both baking soda and First Saturday lime, which is a filtrated filtrated a filtered, hydrated lime product. I have used these to combat many different fungal diseases. One of which that has worked really well on for me has been powdery mildew, and it works because we're changing the pH of the leaf surface.

Karin Velez [00:19:26]:
So it's making it more alkaline, which is a less hospitable environment for the fungus to survive. You can also create a milk spray. This is another alternative. You wanna dilute 1 part of whole milk with up to 9 parts of water. And then you use that as a spray twice per week on any plants that are showing signs of infection. Now it's not entirely clear why this works. Researchers think that the protein in the milk combined with sunlight acts as an antiseptic to fight powdery mildew. Although, from what I've researched, it seems to be better at prevention than cure, so using it before the plants show symptoms is probably best, especially if you know that you are prone to powdery mildew every year.

Karin Velez [00:20:12]:
And you'll need to play around with the dilution to find out what works best in your garden. So basically, all of our garden plants are susceptible to some sort of a foliar disease, but there are several of them that are more susceptible. And the first one on that list is absolutely tomatoes. They are highly susceptible to various foliar diseases. We're talking early blight, late blight, septoria leaf spot, and bacterial spots. We get early blight in our area every single year, and it is very quickly followed up by septoria leaf spot. So these diseases can cause leaf spotting, wilting, and fruit rot, and you may not get any kind of a harvest at all if you leave it unmanaged. So I have learned to make sure that as soon as I get my plants put into the garden, then I start treating with a copper fungicide right away, on the schedule according to the manufacturer's directions, because it's the only way that I can prevent this from happening.

Karin Velez [00:21:16]:
It doesn't matter how far apart I plant the tomato plants. If you're planting them outside in Missouri, you are gonna get some sort of an early blight or something. So, yes. Tomatoes definitely up on the the list. Right behind tomatoes is potatoes because, obviously, they're in the same plant, plant family. And so potatoes are also prone to early blight and late blight. They've also got, another one, common scab, which is, also affected, also affects potatoes. This can affect both the foliage and the tubers.

Karin Velez [00:21:51]:
So if it's got the disease, and you do manage to get a harvest, not only is it going to reduce the quality of those potatoes that you're harvesting, but it's also gonna shorten their storage life. So if you see something growing in your potatoes as far as a foliar disease is concerned, try to get it under control quickly as possible. Next on the list is cucurbits. Anything in the cucurbitaceae family, so cucumbers, squash, pumpkins, melons, These are all susceptible to powdery mildew, downy mildew, and bacterial wilt. Now that last one, bacterial wilt, is spread by both the striped and the spotted cucumber beetle. So if those are prevalent in your area, your best bet is to try to exclude those pests from your cucurbits crops. These diseases can cause leaf yellowing, wilting, and premature fruit rot, and I will tell you I have seen it with the cucumbers specifically when we start to get the cucumber beetles popping around not long after we see those guys in the plants, then we will start to see signs of that bacterial wilt because that is what they are so good at spreading. So, if you can prevent those bugs from getting in, those insects from getting in there, then it's gonna help prevent that.

Karin Velez [00:23:07]:
Pepper plants are vulnerable to foliar diseases like, bacterial spot, bacterial leaf spot, and powdery mildew. I have not seen as much of a problem in the peppers as I have, for instance, like, in my tomatoes. And I think part of this is because we tend to plant the peppers in the area where they are going to get the most amount of sun. Because peppers really like a hot growing season, then I usually put them in the areas that get the most amount of sunlight. And so I think this helps to keep that foliage dry. The only problem with that is that peppers can also be susceptible to sun scald. And so I just make sure when I'm planting pepper plants that they're sort of holding hands. The leaves are always sort of touching each other.

Karin Velez [00:23:53]:
They're touching the plant that's next to it, and that helps to sort of shade each other when it comes to the fruit, which sounds a little counterintuitive when we're trying to make sure we have proper spacing, but it's never been a problem. And they always tend to stay dry. I very, very rarely will ever have problems with my peppers. So if you have seen problems in yours, then maybe try putting them in an area that gets a little bit more sunlight than the rest of your garden. Apple trees are also susceptible to foliar diseases. We're looking at apple scab, powdery mildew, and cedar apple rust. Cedar apple rust is one that actually is spread by cedar and juniper plants or trees. These diseases can cause leaf lesions, premature defoliation, and fruit blemishes, which can actually, you know, destroy the fruit to the point where it's it's not able to be eaten.

Karin Velez [00:24:42]:
Grape vines are also prone to powdery mildew, downy mildew, and black rot. So it's gonna affect the leaves, the shoots, and the fruit clusters. So you very well may not get any kind of a harvest out of them at all. Lettuce. Lettuce is one that if you've got a foliar disease, you likely aren't gonna get any harvest at all. So we're talking about all these other crops. If they get a foliar disease, but we can manage it, well, then at least we can get some sort of a harvest because they're producing a fruit or a vegetable of some sort. But with lettuces, that is the harvestable crop.

Karin Velez [00:25:16]:
So if you had downy mildew, or lettuce leaf spot, or lettuce drop, then you're getting leaf discoloration, you're getting wilting, you're getting rotting, and so we don't get any kind of a a harvest at all out of those. So if you have experienced any type of a foliar disease in your lettuces, my suggestion is to, a, make sure that you have a good organic mulch that's going over top of the soil because since lettuce is closer to the ground, you are more prone to get those fungal spores splashing up from the soil and onto the leaf surface. So if you can prevent that by providing a barrier, my favorite is straw. I use straw underneath my lettuce all the time. It's a it does a great job at exclusion, of those those foliar diseases. But then also try to plant them a little further apart from each other so that they get that airflow. And then finally, citrus trees are also vulnerable to foliar diseases. We're talking about citrus canker, citrus greening, and citrus black spot.

Karin Velez [00:26:15]:
So these diseases can cause leaf lesions, premature defoliation, and fruit deformities. So, of course, no plant is entirely immune to foliar diseases, but there are some fruit and vegetable plants that have a greater resistance or tolerance, at least, to these issues compared to others. So our alliums, garlic and onions, they are known for having a relatively high resistance to foliar diseases. Onions, specifically the ones that have really strong necks and are really good for long term storage. They also tend to be less susceptible to things like, you know, downy mildew and and bacterial rots. You just wanna make sure that your garlic and your onions are planted somewhere where they're gonna have proper soil drainage. Carrots are also generally less prone to these types of diseases. You the one thing with carrots is trying to maintain the weed management, so that helps to sort of give them a little bit more of that airflow.

Karin Velez [00:27:12]:
Asparagus is relatively resistant, however, you wanna make sure that it is in a well drained soil. They don't do well with constantly wet soil, and that can actually promote Fusarium crown rot. So if you've got poorly drained soil or an overcrowded asparagus bed, it's it's ideal to amend that bed and to thin out those plantings a little bit. Peas are generally less susceptible also to foliar diseases, and I have never seen a foliar disease like a powdery mildew or anything in my sugar snap peas, and I plant those peas fairly close together. Like, they're a really thick stand once they come up, and I've never had a problem even when we have the super high humidity that we've got right now. Beans can be hit or mess, though. I have seen some foliar diseases. As the season goes on with pole varieties of of beans, because, obviously, we're harvesting off of those longer, you know, you plant them early on and they go all the way through till frost.

Karin Velez [00:28:19]:
But I have not really noticed as much of a problem in my bush beans. And I think it's probably because the bush beans are in the the garden for a shorter amount of time than the pole beans are. If you think about it, bush beans, you're only gonna harvest them for about a 2 to 3 week window, and then they're done, and you're pulling them out of the garden. So even if a disease like bean rust or anthracnose gets a hold of your bush beans, it's less likely to affect your crop as much because it is sort of a short term crop, and then you're gonna get that out and replace it with something else. So if you have experienced problems with foliar diseases in your pole beans, then maybe try planting some bush beans instead. Sweet potatoes are another one that are less prone to, foliar diseases. Part of this, I think, is because they also appreciate a whole lot of sun. They are another crop that really like a long, hot growing season.

Karin Velez [00:29:17]:
And so I tend to put them places where they're gonna get the maximum amount of the sun. And so I think that dries the leaves off a little bit better. But you just wanna make sure that you're planting them at the right depth and maintaining that that soil moisture, or you're managing that soil moisture. They're another one that doesn't like to be wet all the time. And then finally, rhubarb also is also known for a relatively high resistance. You just wanna make sure if it does catch something like the rhubarb leaf spot, that you are cutting off the infected foliage and getting that out of the garden. I have had an entire crop of tomato plants completely wiped out in a matter of weeks from foliar diseases. So trust me when I say, if you can keep an eye on your plants early on and use as many preventative measures as possible to keep those diseases at bay, then you're gonna be better off for it.

Karin Velez [00:31:14]:
Provide good air circulation, give them the most sun that you can without giving them too much. Avoid allowing the foliage to remain excessively wet or wet for long periods of time, and then monitor your plants for signs and symptoms so that you can remove infected leaves or even whole plants if necessary to prevent disease from spreading to your other plants. If this has been a problem for you in the past, I highly recommend planting resistant cultivars to hedge your bets so that if a disease does hit, the plant is more likely to survive it and produce a decent harvest.