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Powdery mildew and pots

jacqueinthegorge

10 years ago

1) Some of my dahlias already have powdery mildew - we are having a long, cool, moist spring. I made up a baking soda solution and sprayed. Well, I overdid the application, and quite a few leaves have shriveled in protest. But on the bright side, the new growth coming in looks to be free of powdery mildew. In order to keep them that way, how often do I need to repeat the application? (more sparingly of course).

2) Gophers ate two of my dahlias planted in the ground. So I dug the rest up, and put them back into large pots. Interestingly, the root balls were smaller after 3 weeks in the ground than they were when I took them out of the pots - I suspect due to the aforementioned long, cool, moist spring, the ground was a bit too cold to be welcoming. But soon, the soil in the pots will get too hot, and I know they don't like that. I wonder, has anyone here experimented with partially burying the pots in the ground? How did that work for you? Any other solutions to the gopher issue?

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Comments (3)

CCvacation
10 years ago
Jacque, I am anticipating mildew mold this season because I planted way too close this year, and because some plants I got at auction had some already on their leaves.

I immediately took those leaves off, and will be stripping all leaves from about a foot down once the plants achieve three feet height. This allows ventilation through the plants, drying the leaves from rain and morning dew to discourage mildew.

I've not heard of the baking soda solution, but many people swear by using milk. Here's a recipe I recently copied from a dahlia discussion:

Mildew- Mix 1/3 cup milk with 2/3 cup water and spray on the leaves. Whole milk, not skim.

As for planting pots in the ground, there are some growers that do that all the time. It allows the ground moisture to keep the pot soil from drying as quickly, and protects from underground attacks. Perhaps someone else can go more in depth about growing in sunk pots, as I haven't tried it.

As for gophers... Elmer Fudd is the best solution I've found, fighting with a rabbit population that decimated the new growth of a dozen plants each day. Three types of deterrents have not worked, and I'm not fencing at this late date. Some tender-hearted souls advocate catch and release. One gopher for a taste of dahlia can do a lot more damage then my bunnies in a day... Imagine a family of them moving into your garden.
jacqueinthegorge
Original Author
10 years ago
Thanks CCvacation, I will try the milk spray. Seems like it would not be as damaging to the leaves.

Oh the gophers are terrible on dahlias here. We gas the tunnels, and it keeps the population down, but all it takes is one...

Another thing I may try is planting a trap crop for the gophers. Jerusalem artichokes are a lot cheaper to replace than a named dahlia, and I imagine the tubers are very similar in food value to a rodent.

I'll let you know how plunging the pots works. Because it's so windy here, the tallest dahlias I grow are 3 feet. I have some 10 and 15 gallon pots I can put them in, so maybe that will work. Between the heat and the damage from the baking soda, some of my dahlias look really sad! and many of the others are showing the beginnings of mildew. Crossing my fingers...
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There have been numerous postings of success treating powdery mildew with milk. Mix up a spray of 3 tablespoons milk (any kind) to one cup of water and spray the plant throughly. I haven't tried this so would be interested in hearing if you have good results. Also, rather than repotting your fern do the following. Using a large serrated knife cut a deep circular core out of the center of the fern. Fill the remaining hole with fresh potting soil. This method works well on potted ferns including Rabbit's foot and Boston ferns. It may be necessary to do this twice a year.
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Japanese maples are very sensitive to foliar applications of any pesticides. They can often do more damage than the problem you are trying to control. I would limit any treatment to something like Cornell formula (1 Tbsp baking soda to gallon of water with a few drops of salad oil) or just a 50-50 milk and water mixture. Both of these approaches work by altering the pH of the leaf surface, making it inhospitable for the development of fungal spores. And are unlikely to create a phytotoxic reaction. To be on the safe side, apply very early in the day or just before dusk to minimize sun exposure. The primary reasons any plant contracts PM is due to climate and/or cultural conditions. Provide adequate air circulation and keep any water off foliage as much as possible. Often PM develops when humidity is high but soils are dry -- you may need to water potted JM's a bit more frequently to balance this out. Soil should always be just moist to touch - not too dry nor too wet.
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It's been years since I've dealt with this, I had one climber that got this every year. There wasn't anything back then, in the 80's that would stop it. I would have to say if it's shriveled that you'd need to prune it, you have to cut off the affected area, powdery mildew spreads on dry foliage. Why don't you take this and post it on the main rose forum and see if someone will offer up a solution since you're not getting any answers here. I'd also go and look at the Lowe's or someplace at the spray's and see if there is anything topical that you can use. Sorry I'm not much help. There may be something you can use to keep it from spreading, one method suggested is to wash off the spores each day late in the afternoon or spraying it with Neem Oil. I'm sorry, I lost alot of plants in the freeze too. Good Luck to you. Leslie
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better than a sharp stick in the eye ... eh frankly ... im surprised it would be that big a deal in 5 days ... but you know your micro climate better than i do ... ken
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jacqueinthegorge
Original Author
10 years ago
The soil in the sunk pots is definitely cooler. But I think that even my shorter-statured dahlias would be happier in 10-gallon containers. I know at least some of the fabric pots are meant to be in the ground, but I'm wondering how they hold up when attacked by gopher teeth. Anyone have any experience? I've also thought about drilling lots of holes in my containers to give the feeder roots more running room, while keeping the tubers safe. I'd think the heavier duty injection-molded containers would be somewhat resistant to gopher teeth, I'd appreciate some opinions.

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