I don't think it's a moisture or air circulation problem, and I thought it was temperature downstairs, but now I'm seeing powdery mildew on some of the upstairs violets too. I realize prevention is the best cure, but until I figure out why this is happening, I'd like some suggestions on what I could spray on the affected plants to knock down the mildew a little. So far, the plants don't seem to be taking any damage from it, but it would probably be good to treat them before we leave for 5 days.
My initial thought was to spray with a solution of hydrogen peroxide (2 Tbsp. per gallon, like I use for watering seedlings), maybe with a little epsom salts and a few drops of dish soap added.
I don't think your mix would be effective on powdery mildew. Believe it or not, a can of regular lysol (powdery type spray) is supposed to do the trick - but I found the mildew just came back, and multiple sprayings were stressful on the plant.
Something I would be more inclined to try is that milk spray - don't have my bookmarks here, but browse through the google hits. I hear it works really well on outside plants, and the ingredients are easy on AVs. http://tinyurl.com/8zxlu
*that* is what I was trying to remember -- baking soda! (1 tsp. per quart of water, plus a few drops dish soap) I've heard of the milk spray too, but I'm less sure about using milk on indoor plants where it won't get washed off the leaves -- wouldn't it smell bad in a few days?
I will try the baking soda solution on one of my "extra" plants and see what happens. I'm assumning any ill effects would show up in 48 hours, so if the plant looks fine Thursday night I can spray the others before we leave.
I might also turn on a fan downstairs to increase air circulation... hopefully that will help and won't just spread the mildew spores around.
Hmmm... I'll see if I can find the recipe... erranding took longer than expected this afternoon, so I'm going to spray first thing tomorrow morning so the leaves have all day to dry off under the lights. (I'll towel off any big droplets, especially on the crowns.)
Powdery Mildew is caused by the Oidium fungus which thrives under conditions of high humidity and poor air circulation, especially after sudden changes in temperature. Such conditions often occur in spring when precipitation is high, and hot days alternate with cold nights. Powdery Mildew grows superficially on the leaves and flowers of African Violets, covering them with a light gray powder. If left untreated, Powdery Mildew will cause discoloration of the affected leaves and flowers. Eventually, the affected parts of your African Violet will begin to wither and die.
Leaves have a light gray powder on them.
Flowers have a light gray powder on them.
If your African Violet exhibits these symptoms, it probably has Powdery Mildew. (Note: Do not confuse the light gray powder of Powdery Mildew with the fuzzy gray mold of Botrytis. While Powdery Mildew may not affect the entire plant, those areas which are affected will be uniformly covered by the fine gray powder. The Botrytis fungus, on the other hand, has a fuzzy appearance and is typically spotty in distribution
Leaves have white spots on them.
Flowers are deformed or twisted.
Flowers are blotchy or streaked. When caused by Powdery Mildew, this symptom will normally appear as a discoloration of the flowers.
Flowers drop off.
Plant growth is slow.
First, isolate all affected plants in order to prevent the Powdery Mildew from spreading. Next, remove all dead or dying tissue from the affected plants. Space plants to increase air circulation. Reduce humidity to no more than 60 percent, and maintain a warm, constant temperature that varies no more than 10 degrees.
If you do not see improvement after two days, try spraying Lysol on the affected areas. When lightly sprayed, Lysol may cause some discoloration of the flowers, but it should not damage the leaves. Lysol is also much less expensive than other, chemical solutions. However, if you still do not see improvement after two more days, you will need to treat with a fungicide such as Benomyl or Captan (as directed on the label).
Disinfecting African Violet pots is vital, especially if you have one that has already been used. But even for new pots, disinfection is highly recommended. If you do not disinfect your pots, you run the risk of exposing your African Violets to a number of deadly micro organisms. The process is easy. Simply soak them in a 10 percent bleach solution, i.e., one part bleach to nine parts water. After soaking, rinse them with plain water.
As an alternative to traditional chemical treatments, try dusting with sulfur or spraying with a baking soda solution (about 1 teaspoon per quart of water).
Always remove spent flowers and leaves as you see them. Maintain good air circulation between your plants, especially where the air is damp and still. Be particularly watchful during the spring when precipitation is high and temperatures vary between extremes. Keep your growing area and tools clean. Before repotting, disinfect pots with a 10 percent bleach solution, i.e., 1 part bleach to 9 parts water. If Powdery Mildew is recurring problem, you may want to try placing small containers of sulfur among your plants.
Now your specks look more white in pictures than grey ?
Leaves have White Specks of "Cotton" on Leaves ?
That's what picture looks like ?? http://www.optimara.com/doctoroptimara/12400-13703/13600.html
Always isolate new plants until you are sure they are not infested. Thereafter, keep a watchful eye on your African Violets. If at no other time, do a thorough examination of the leaves and stems every time you water
hope some of this informayion can help. Allison
I think the temperature is evening out a little with the heat mats, and the plants look better. I blew on the leaves (holding the plant off to one side from the rest) and got a lot of the white stuff off... if it comes back, I'll try a spray of lysol. I think I'll sprinkle a little cinnamon around, too... if nothing else, it will make my AVs smell wonderful! :-)
Oh, and I'm quite sure it's powdery mildew and not mealy bugs or anything else, which is good because powdery mildew should be one of the easier things to treat & prevent... or so it seems at this point... we'll see if I end up battling it all winter!