Anyone else have basil downy mildew issues?

[mattie g]

This is the third year I've been growing basil, and this time around I decided I was going to make a lot of pesto (in addition to other fresh uses and for drying), so I have six plants in the ground and one in a container. I half expected I might have downy mildew problems again, but I was shocked when it started showing up on one of my in-ground plants about two or three weeks ago. I have gotten to late-July or August before it shows up, but this year it came quite early.

It's a horrible problem because there's nothing you can do about it. If the spores get to your plant, it's game over within a week or two unless you aggressively prune, and even then it's a losing battle. Luckily I was able to keep the one plant going for an extra week or so, and got some good pesto out of it. I'm hoping I can keep it away from my other plants, and even moved my containered plant out to the front of the house to see if the spacing and the physical barrier of the house might keep that very healthy and productive plant from contracting it as well.

So...does anyone else deal with downy mildew on their basil, either regularly or occasionally?

[imafan26]

I have gotten downy basil. I could not plant sweet basil for the last three years. I did plant basil this year, but I waited for drier weather and I inspected the plants every time I watered and I sprayed them with sulfur or dithane every week when the weather was muggyas a preventive . I was able to stay ahead of the mildew that way and get a crop. I have better luck with opal or purple basil, Cinnamon and lemon basil which are more resistant. Thai basil is not totally resistant but does not die off as seedlings. I have a new African blue basil which also seems to be resistant. I just got another one, a Greek basil, I have to see if that one will survive.

People who live in a northern climate or in a dry climate might have a chance since the spores may not survive winter. Here in Hawaii with a 365 growing year and average 80% humidity most of the time, downy mildew is probably here to stay. I am waiting for someone to develop a resistant cultivar. I was told to keep the seeds from the surviving Thai basil that has partial resistance as that would be the only way to develop more resistant cultivars.

[rainbowgardener]

I have not yet seen downy mildew (thankfully!). Benefit of cold winter I guess, since we have plenty of humidity in the summer .

[imafan26]

Downy mildew appeared in Florida in 2007 and spread to many states by 2009. Apparently it got here from infected seeds from Switzerland and were transported around the country.

The recommendation here was to grow basil in the drier months, avoid overhead irrigation. Scout and remove infected leaves as soon as you see them, increase plant spacing and air circulation. A few fungicides have been approved for basil.

[mattie g]

I don't think cold winters have much effect on the spores, since I've seen a lot of reports of downy mildew coming from New York. And while we've had a couple warmer winters recently, we still have plenty of nights below freezing (and many that get below 20F), so I don't quite think that's the issue. Lucky you, rainbow. It's definitely not something you want to see!

I've tried removing infected leave ASAP, and I think that has helped extend the life of a couple of my plants, but I've already pulled one and expect I may have to pull another pretty soon.

I'm not terribly interested in basils other than the sweet basil varieties, so the only thing I can think to do would be to increase plant spacing. Maybe next year I'll try growing in pots (and maybe in the ground) in the front of the house, which gets a little more wind and air circulation than my backyard does. If the one pot that I recently moved out to the front is able to hold out for most or all of the summer, then I may have the answer. If not, then I don't quite know what the next step is, other than just dealing with the disappointment each year!

[mattie g]

The containered plants that I moved out front succumbed to downy mildew last week, as did another planted in-ground. The in-ground plant was pretty close to the one that I pulled a couple weeks ago, so I'm not at all surprised that the spores got to that one, as well.

However, there are a few plants out back that are still going strong - these are in an area about 12' or so away from the ones that I had to pull. Whether that distance was enough to isolate them from the spores still remains to be seen. I'm holding on to some hope for now...

[imafan26]

Apparently the downy mildew migrates up to the northern states every year. The spores are carried by the wind and it can also come from contaminated seed.

[mattie g]

I took a trip to my local nursery yesterday just for the heck of it. When I came upon the basil section, there were numerous sweet basil and Genovese basil plants (mostly small) with yellowed leaves. Upon turning those leaves up, I saw the familiar grey splotchiness of downy mildew spores. I immediately told one of the employees who, while acknowledging the fact that he needed to remove those plants, also didn't seem to quite understand the gravity of the situation.

There's not a lot I can do fix it, but I'm kind of taking this on as a personal quest to at least help alleviate and make known the basil downy mildew problem we're now facing.

[Susan W]

Thanks for mentioning this again. It is something we all need to be watching. I had seen a reference that impatiens now have it, bad. This is a mainstay splash of color for our tree'd shady yards.

[ElizabethB]

Thankfully not an issue I have had to deal with YET! Kind of strange considering the heat and humidity in south Louisiana.

Good luck

[mattie g]

Thankfully not an issue I have had to deal with YET! Kind of strange considering the heat and humidity in south Louisiana.

Good luck

Thanks. I have a real love for basil - its flavor, its many uses, and its ease of growth all contribute to this - so this problem really gets to me.

One of the more disturbing things about my experience at the nursery is that this place is very well known and very respected, yet it didn't seem like they were fully aware of the consequences of having multiple infected basil plants sitting among many that were not affected. I don't think that most people (even experienced gardeners) are quite aware just how damaging basil downy mildew can be - how virulent it is, how quickly it spreads, and how fast a plant can go from appearing perfectly healthy to being noticeably diseased and on its way out.

[Kludgel]

I'm sure this has been covered elsewhere, but I had to mention it just in case.

Most of us are fairly aware of how easily downy mildew can spread, but what I didn't know (until my mother, the Master Gardener, told me) is that downy mildew infects the soil as well as the plant, which is of particular importance when growing basil in containers.
Say you have a potted basil plant die due to downy mildew. You're bummed, but luckily you have some cuttings that have already rooted, so you pull out the dead plant—even a big chunk of the roots to be safe. You mix in some fresh soil and plant your cuttings. Your cutting will now die of downy mildew.

Even if, out of respect for your dearly departed basil, you wait a full year to plant new basil, there's a very good chance it will happen again. EVEN IF YOU TOSS THE SOIL, if you don't sterilize the pot, the dastardly downy may very well rise again.


I have had good luck with neem oil as a treatment, though—it saved all my basil last year. The key is to make sure to use a fine spray (basically mist) to completely coat the plant, top and bottom. I also sprayed the whole terra cotta pot the basil was in, so that may have helped keep it from coming back once. After about 3 weeks, my basil was mildew free, if a bit shaken by the whole experience. I hit it again every 3-4 weeks to be safe, but I never saw any signs of it coming back. Good luck!

[Admajora]

Thanks for the advice on the neem oil. It is interesting to hear from other people experiencing this mildew problem.

The mildew has ruined all of my basil for the past two years. I've had lemon basil, ruffle basil, thai and genovese, and by far the genovese is the most susceptible. The only bit I've been able to harvest have been from thai basil volunteers that happened to come up between my marigolds--perhaps because the bugs that transfer the spores are less attracted to the marigolds? Who knows.

Either way, the mildew problem is so aggressive and catastrophic I don't see much of an alternative to giving up on growing it outside entirely.

[Susan W]

My basil crop got trash bagged. I can't confirm downy mildew, but probable. The plants in different areas, in containers. I have a few starts in 4" pots that show signs. I am keeping them aside, trashing bad leaves, and trying copper spray just to see if it keeps it in check. Ugh.

[Lindsaylew82]

I'm not having ANY trouble with basil this year. It's behaving normally. I DO USE neem oil, though....on pretty much everything, with really good results.

[rainbowgardener]

May be the Neem, or it may just be that the downy mildew spores are not in your area (yet?). I have never seen it and my basil are doing great (with no sprays). But I'm knocking on wood that the disease doesn't make it to my location very soon.

[Lindsaylew82]

Oh no, it's here. I DO have it on cukes and had it on squash.

[mattie g]

Oh no, it's here. I DO have it on cukes and had it on squash.

Actually, basil downy mildew is a different disease than downy mildew on curcurbits. As I noted in the "GAGA Over Basil" thread
(https://www.helpfulgardener.com/forum/vi ... it#p330358):

"Basil downy mildew is caused by Peronospora belbahrii , while curcurbit suffers downy mildew attacks from Pseudoperonospora cubensis, so it makes sense that your basils might be left unaffected while your curcurbits are hit."

Seems to me that basil downy mildew is more virulent than it is on other crops, but maybe that's just because I've been hit so hard by it the last few years. It shows up on a plant, and within a week or two that plant is toast.

[Lindsaylew82]

Interesting! I need to go look at that thread some more! Thank you!

[mattie g]

I noticed some yellowing and droopy leaves on one of my plants yesterday, so I reluctantly checked the underside for fear of seeing the telltale fuzz of downy mildew. Lo and behold, there it was.

So that's the first of my four plants to go this season. I'm guessing that the relatively mild and dry conditions have helped me get that extra month out of my plants this year. I got pretty good production from this plant, so I'm not totally devastated, but of course I was hoping to go a season without seeing the downy mildew. Now I'm just waiting for the other shoe to drop by finding the fuzz on my other plants. I'd imagine it's just a matter of time. I just hope it doesn't show up when I'm on vacation and the plants give up the ghost before I get home...

[Angela5237]

I had beautiful basil growing from the end of May until the middle of July-ish. At first I thought all of the mildew underneath the leaves was just dirt- until it wouldn't wash off. All of my basil was thrown out along with the dirt it was planted in and the plastic containers. I then tried again, thinking if I used different containers and soil that maybe I could avoid it. About two weeks after planting new basil I noticed the same symptoms and now I have no basil again so sad.

[Lindsaylew82]

Does it kill off the whole plant? I'm wondering if you could get it to go to seed and save them, then re grow, they might relate resistance. Is that how that works?

[imafan26]

I tried neem oil and sulfur, I am glad it worked for you. I read up on the approved fungicides for downy basil mildew. One of them was oxidate. The active ingredient is hydrogen peroxide.

I have a couple of basil now and I have been spraying them weekly with hydrogen peroxide as a preventive. This is the longest that sweet basil has lasted post infection.

It may have helped that I tossed all of the thai basil before I actually saw the spores on the undersides.

Unfortunately walmart is again selling basil. They look yellow but it was not the typical basil downy mildew yellow, so I am hoping for the best.

I have some holy basil, that I know is resistant to downy. I am hoping to get my sweet basil old enough to cross with it. I might try opal basil too, it may be a little more resistant and I can also try to cross that with holy basil. My holy basil is older and it is flowering now, but it is a longer lived basil so I hope the sweet basil can catch up to it.

[mattie g]

imafan...I'm glad to hear that you're at least having a little luck holding it off. It just takes so much effort to even attempt to keep it at bay, and even then I think it's a losing battle in the long run. Hopefully a cross will eventually come out that proves resistance to the fungus.

Does it kill off the whole plant? I'm wondering if you could get it to go to seed and save them, then re grow, they might relate resistance. Is that how that works?

It does kill the whole thing. Once a leaf has spores on it, it usually shrivels up within a week or two, and the spores are very good at spreading, so once it's on a plant, it's just a matter of a short time before the whole thing becomes infected (my plants are generally done within two weeks from when I first notice infection). The concern with using seeds from a plant that's infected is that the spores may remain on the seeds, which then introduce more spores wherever the seeds are planted. If there were a way to ensure that the seeds were disinfected, then maybe that would help. I do think there are people working on a treatment and/or breeding resistance into the sweet basils, but I'm not aware of any real successes so far.

[mattie g]

I had beautiful basil growing from the end of May until the middle of July-ish. At first I thought all of the mildew underneath the leaves was just dirt- until it wouldn't wash off. All of my basil was thrown out along with the dirt it was planted in and the plastic containers. I then tried again, thinking if I used different containers and soil that maybe I could avoid it. About two weeks after planting new basil I noticed the same symptoms and now I have no basil again so sad.

That's rough...sorry to hear that. I have a feeling that the second set of plants you bought were infected when you bought them. I mentioned in a previous post that I went to my local nursery (which is very well regarded) back in June (I think) and saw nearly their whole sweet basil display covered in fuzz and looking rather sickly. Anything that wasn't already showing symptoms would surely show them soon enough. The disease can be spread so easily by people unknowingly buying infected plants, and since the spores are known to lie dormant in the soil, once spores are transmitted in that way, it's fairly certain that anyone who has encountered the disease once will keep seeing it again and again if they plant in the same/near the same spots.

[Susan W]

Just to review, I trash bagged most of the basic crop. There are several purples holding their own. I also have some starts that I was about to split between keeping and putting out to sell. Oopsies! They had it. Between trashing and trying copper on the remaining 3 is iffy.

I presume I have downy mildew. The top green leaves get streaked, lower leaves go yellow. I see pock marks on underside of leaves, and just a few had the fuzz. The plant also doesn't just droop -drop in a couple of weeks as some of you have mentioned.

Varieties -as mentioned, purple holding its own the best. I had a few Holy basil starts and sold, along with other varieties. With sigh of relief 2 different people stopped to tell me how well their holy basils are doing! I did mention my woes and glad theirs are fine. I was trying to get into the Gen basil this year, and that may not work out, well until chemicals or resistant varieties are developed.

I do have a couple sets of regular green basil started, trying to keep apart from problem areas, and watching close.

Now, do tell on the hydrogen peroxide. Do you use straight from bottle, spray leaves once/week?

[rainbowgardener]

Now, do tell on the hydrogen peroxide. Do you use straight from bottle, spray leaves once/week?

The bottle you get at the drugstore is a 3% solution of hydrogen peroxide, so yes you can spray it straight from the bottle.

[imafan26]

This is the first time I am using it. I am using it undiluted from the bottle. It is a good sporicide although not great on bacteria. I concentrate spraying the underside of the leaves. I am using it mainly for prevention. It says it can be used twice a week in humid weather and once a week at other times. It does not last, so it was recommended to be used as an adjunct to some other longer lasting fungicide like neem. So far it looks promising. I lost one of my basils already to a snail that chewed the top off.

Seed should not be saved from plants that have downy mildew. Contaminated seeds from Europe were suspected as the source of the contamination in Florida.

[mattie g]

I noticed some yellowing and droopy leaves on one of my plants yesterday, so I reluctantly checked the underside for fear of seeing the telltale fuzz of downy mildew. Lo and behold, there it was.

So that's the first of my four plants to go this season. I'm guessing that the relatively mild and dry conditions have helped me get that extra month out of my plants this year. I got pretty good production from this plant, so I'm not totally devastated, but of course I was hoping to go a season without seeing the downy mildew. Now I'm just waiting for the other shoe to drop by finding the fuzz on my other plants. I'd imagine it's just a matter of time. I just hope it doesn't show up when I'm on vacation and the plants give up the ghost before I get home...

Plant #2 pulled yesterday...