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How to prevent Powdery Mildew on large Zinnias?

highlandernorth

9 years ago

Last year I grew about 6-7 large Zinnia plants in the front bed just outside a client's front door, so they were the most obvious plants you'd see anytime you looked out that door or walked up to it. They were labeled to grow about 36-40" tall, but for the 2nd time I grew these large Burpee Zinnias, they actually grew to 6 feet tall(72").

But once August and September rolled around, they became affected by Powdery mildew, which quickly covered almost every leaf on every plant, and made them look gray-ish. I tried treating them with fungicide, but it didnt really work after they were already affected, and I tried spraying off the fungus with water, but that didnt work.

So I replanted more of these same Zinnias in the same area, only I planted more of them. Its now 6-14-14, and they are between 14" to 24" tall right now, and I am wanting to find a reliable preventative measure to stop them from becoming covered with Powdery mildew again.

Previously the only issues I had with these type of Zinnia were Tree Hoppers that would literally chew all around an area on each stem, causing the stems to break off precisely where they chewed. I have sprayed with insect control already.

What can I do to prevent powdery mildew? Thanks....

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Comments (5)

Kimmsr
9 years ago
You cannot prevent Powdery Mildew from happening, but you can takes steps to minimize it by understanding when and how it will appear and which plants are most (Zinnias) susceptible.

Here is a link that might be useful: About Powdery Mildew
rhizo_1 (North AL) zone 7
9 years ago
I very much disagree with Kimmsr about not being able prevent PM. I consider it quite preventable in most cases.

The housekeeping tasks mentioned in the fact sheet linked above are essential as are cultural changes you can make. But daily rinsing is truly helpful, as is occasional mists of neem or other horticultural oil.

It's very important to understand that zinnias are very susceptible. Very. You might consider researching resistant hybrids or even using something else, entirely.
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I know the answer to this!!!! I am soooo excited!!!!! :D :D :D Ok, milk. You want to dilute the milk so it is about 10-20% of what you have, definitely less than 30% or it will make something else bad that you don't want to happen happen, and spray it on every week or two (don't do it too often or the plants will be unhappy), and this will prevent a lot of powdery mildew. It is more of a preventative measure but you can try it if you see just a little, well, you might as well try it when you see a lot, but it's better to start before you see it at all. This is probably the only answer I will ever know, thank you so much :D
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That's interesting about there being plant specific... Nature is fun. I was just going to the extreme to stress the point that I think the important word would be "delay" vs "prevent" with pm. I have one planting of an older variant of phlox and pm always gets it early right as it starts to bloom. I remove the entire plant to the ground fairly early each year.... But it always hits the exact same time the next year. I have no other phlox and I live in a garden desert in my subdivision... I don't think a single home I pass in and out of the neighborhood has anything besides the original landscaped plants.... Non being phlox. The only other perennial that gets pm for me was an old peony... Which got the axe because of it. And then of course the late season squash get it. so to the original poster... Given your circumstances ..... And this isn't a plant that you are passionate about enough to put up with tight cultural practices.... And ...You would only being delaying the inevitable maybe a bit later in the season....(as others bring up.)....Looking into a replacement species would probably work better for you.
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K, gardengal is exactly right that there's nothing you can do now. It's possible to prevent a severe infection but you can't cure a plant when it's so heavily involved. It's essential that you make a big effort this winter, however. Rake up all of the fallen leaves and dispose of them.....do not use as mulch. I strongly suggest that you plan on spraying the dormant tree a couple of times in the late winter-early spring with a horticultural oil, even neem. The oil can smother spores that are lurking on the twigs and buds waiting to infect the new leaves. When the new leaves emerge, don't forget gardengal's advice regarding a quick rinse of water. There are fungicides on the market that can prevent and cure PM, but with aggressive preventative measures I've never found it necessary to resort to chemicals.
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Ladybird larvae?? How would they possibly help to prevent powdery mildew? A baking soda solution (or even better, potassium bicarbonate) or a milk solution sprayed on the foliage in 7-10 day increments can help, So can neem oil. And good cultural practices can go a long way. Make sure there is plenty of air circulation (you can remove some of the foliage if things get crowded), as much sunlight as possible and keep fingers crossed for heat (PM spores do not tolerate above 90F). And hosing down the plants will help, as many types of PM spores are killed by direct contact with water. Do this very early in the day so foliage has plenty of time to dry.
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ken_adrian Adrian MI cold Z5
9 years ago
the number one thing to avoid ... is wetting your plants in the evening...

mildew thrives in dark and damp ... especially during the warm/hot nights of summer ...

and if you are spraying them down in the evening.. you are making matters worse ... a water wand and watering only the soil also helps ...

increasing air movement also helps keep them dry .... planting too close usually ends up being the problem ... so next year.. space them better ..

if you cant find CULTURAL information on PM .. you arent trying very hard ...

plus everything they said ...

including moving on to a new plant ... its not too late to rip them out.. and plant something else ... it took me a few years ... to learn that beating my head on a wall with problematic plants... doesnt usually work out well.. for the wall.. nor my head .. lol

ken
highlandernorth
Original Author
9 years ago
To Ken_adrian: Thanks for the advice, but I am not one to give up on a plant because I had a problem with it for a little while during 1 season. I have dealt with issues with dahlias as well from time to time, like slugs, spider mites and tree hoppers, but I stiIl grow them. I think some things are worth a little extra effort, and its really not that much more effort anyway to be honest.

I grew the same variety of zinnias about 2 years prior to last year's powdery mildew, and at that time I had more zinnias in a more shaded area that tended to hold moisture/humidity moreso than this new area does, yet I didnt have any problem with powdery mildew at that time.

I dont mind having to take 10-15 minutes 2-3 times a season mixing up some spray solution and coating the plants with a safe, relatively non-toxic spray that helps prevent fungus if it means having 5-6 foot tall flowering plants that continuously flower from June til early November.

I will also try to keep them more ventilated. Maybe they were too close last year. But we also had a generally wet first half of summer.
Kimmsr
9 years ago
As the plant pathologists from the University of California indicate in the article linked above water on plants leaves can kill off the PM spores or keep them from gaining a foothold. However, they do not recommend allowing those leaves to remain wet overnight.
Spending some time with that article may prove worthwhile.

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