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Soil, Compost & Mulch

powdery mildew in soil?

12 years ago

I planted a small bed of tall zinnias earlier in the summer (don't remember the variety) which then became badly infested with powdery mildew. I really would like to plant zinnias in that same spot again in the spring, and of course this time stay aggressively on top of the mildew by using the milk/water spray. My question to you soil experts: is the soil in this bed now contaminated with mildew spores? I am wondering if I should even attempt to grow zinnias there again. I am hoping that the powdery mildew dies as soon as the plant does. Thanks for any insight!

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Comments (5)

Nevermore44 - 6a
12 years ago
i could be wrong, but i believe it's pretty much everywhere. So it will blow in on the wind from surrounding plants. I periodically have issues with PM on zinnias. I do grow them in the same local each year. I typically just get what ever type strikes my fancy each year, so depending on your weather, growing conditions and variety you are growing... will all have a say.
Kimmsr
12 years ago
The spores that will become Powdery Mildew might live on plant tissue in the soil, but apparently not in the soil itself.

Here is a link that might be useful: Powdery Mildew
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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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Powdery mildew needs plant tissue to overwinter spores. The spores do not remain viable in the soil over winter. As long as you practice good garden sanitation and clean out and remove any infected plant parts that remain at the end of the season, there is no concern about the soil. It's helpful to understand how powdery mildew works. First, there are many, many different types of PM with very similar appearance but these are by and large host-specific. IOW, the PM that infects squashes and other cucurbits is not the same species that can affect greens, or beans, etc. PM is mostly due to cultural and climatic conditions, meaning that specific gardening practices can either encourage or deter the development of PM, most specifically air circulation and shade (and of course good garden clean-up). But there is little you can do about climate. Infection is favored by high humidity (50 to 90%) during twilight hours, and temperatures between 60° and 80° F and dry soil conditions. These conditions create an almost ideal incubation situation and is why this disease typically shows up in mid to late summer when these conditions are most prevalent. PM does not require moist conditions to germinate and grow and spores can be killed or inhibited by water on the plant. Sometime just hosing/spraying down the plant well on a routine basis is sufficient to quell the development. Shady conditions (which are most conducive to retaining humidity) and vigorous plant growth favor disease development while high temperatures (above 90°F) have an inhibitive effect.
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User
Original Author
12 years ago
Thanks for the helpful info, Nevermore44 and Kimmsr. I think I'll just go ahead and grow zinnias in that spot next spring and be more diligent with my prevention measures!
Belgianpup
12 years ago
Also, consider looking into the Pinwheel, Profusion and Blue Point varieties of zinnias, that are supposed to be more mildew-resistant.

And when you plant, try to give them a little more space for air circulation, and see if that helps at all. But in Georgia... *sigh*

Sue
tapla (mid-Michigan, USDA z5b-6a)
12 years ago
What sue said ......

PM afflictions are more the product of cultural conditions and some of our habits than of where the spores reside, though good housekeeping can help reduce the likelihood of infection somewhat. Clean up the old leaves & stalks in the fall & rake the area. Plant in the open and in full sun where air circulation is good. Try to avoid wetting foliage as much as possible, especially late in the day when foliage won't have an opportunity to dry quickly. Fungal spores need an incubation period that includes moist conditions and a favorable temperature range for intervals that vary by species (of fungus). Denied the incubation period the fungus can't get a start.

While there are some fixatives that will clear up mild cases of PM and work well as prophylactics (ask if interested), the best approach is prevention.

Al

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