Wednesday, April 29, 2009

What is the white powdery stuff on my rose plants ?

I live in southern Cali and I water my rose plants regularly but lately I am seeing white powdery stuff on my rose plants, mostly on stem, and leaves. is this some kind of disease and if so, what is the cure for it ?

TIA :)

What is the white powdery stuff on my rose plants ?
This is a fungal disease. Sphaerotheca species infect roses. It generates a powdery white to gray fungal growth on leaves, stems and buds.

Infection can occur on dry leaves if the air is still and humid. Warm temperatures, poor air circulation, and shady conditions encourage the fungus to grow and spread. The optimum temperature for infection is between 68 - 77 degrees F and relative humidity between 40 to 100% is sufficient for the spores to germinate. Low, diffuse light also seems to favor powdery mildew development. There is a general belief that wetting the rose leaves will cause this or black spot but watering is not a direct cause though splashing soil borne spores onto the branches is not a good idea. Clean up all fallen leaves and dust the area with corn meal at 2 pounds of cornmeal into the soil for every 100 square feet. Water well to activate the fungus killing properties. There is a cheap, nonfood grade available at garden centers.

Powdery mildew thrives where high rates of nitrogen have been used promoting tender leaf formation. Organic fertilizers or slow-release lawn fertilizers are good choices.

Sulfur is effective against powdery mildew when used every 7 to 14 days. Garlic naturally contains high levels of sulfur and a few cloves crushed in water can be used to make a homemade spray.

To make garlic tea, liquefy 3-4 bulbs of garlic in a blender 1/2 to 2/3 full of water. Strain the solids and add enough water to the garlic juice to make 1 gallon of concentrate. Use 1/4 cup of concentrate per gallon of spray. Add 2 T of blackstrap molasses as a sticker.

Bonide makes 141 sulfur dust, Lilly Miller Sulfur Dust,

Cooke's wettable, Safer Garden Fungicide, %26amp; Microthiol Special Sulfur.

Do not use sulfur within two weeks of an oil spray.

Soap sprays can dessicate the fungus on the rose.

Cornell oil spray

Mix into one gallon of water, in the order listed:

1 T dishwashing soap (Palmolive, Dr Bonner or Ivory) optional with Sunspray

2 T of ultrafine horticultural oil ( Sunspray brand contains a sticker so no soap is necessary)

4 tsp of baking soda

1 T of fish oil/seaweed emulsion

3-5 drops of Superthrive (plant vitamins)

Spray leaf surfaces LIGHTLY, not to dripping. Reapply every two weeks.

Cornmeal Juice

Make by soaking horticultural cornmeal in water at one cup per gallon of water. Put the cornmeal a nylon stocking bag to hold in the larger particles. Soak over night. Spray without further diluting just pour through a coffee filter to use.
Reply:Powdery mildew affects many other plants too. It is very easily controlled with commercial fungicides, like Daconyl or home remedies like sulfur powder (cheap) either sprinkled or dusted on dry, or wetted and sprayed on. Make sure you don't spread it by walking on clippings or touching other bushes with your unwashed hands. It loves grass and other bushes even better than roses.
Reply:It is called powdery mildew. I use the solution of 2 teaspoons of baking soda and 1 qt. of water. Spray it on the affected part. If it's not everywhere, it should contain it and fix the problem. Keep eye on it and keep spraying it until it goes away. Do not try to spray on entire tree or bush!
Reply:This happens in the fall here with my zinnia flowers. The moisture encourages mold growth on the leaves.
Reply:Its called a powdery mold - you can get a spray for it at

your local garden center - I spray my rose every Sunday

for this and black spot.

No comments:

Post a Comment