Powdery mildew is a common disease on many types of plants. In fact, it is one of the oldest plant diseases on record – Theophrastis wrote of powdery mildew on roses in 300 B.C. Although different species of fungi cause the disease on different plants (Erysiphe infects vegetable crops and flowers; Podosphaera species infects apples and stone fruits; Sphaerotheca species infects berries, roses, some vegetable crops, and stone fruits; and Uncinula necator infects grapes), the infections are all characterized by a powdery white to gray fungal growth on leaves, stems and heads.
Contary to popular belief, powdery mildew generally does not require free water to establish and grow. Infection can actually occur on dry leaves. Warm temperatures and shady conditions encourage the fungus to grow and spread. However, the spores and mycelium are sensitive to extreme heat and direct sunlight.
Powdery mildew usually shows up on leaf and stem surfaces and does not directly affect most vegetable fruits. However, it can affect the flavor of melons and squash and reduce their yield. Woody species such as grapes, fruit trees, roses, crape myrtle, and sycamore are more seriously affected; new growth is often distorted. The young fruit of apples and grapes can also develop rough skin due to powdery mildew.
All species of powdery mildew fungi require living plant tissue to grow. On perennials, they survive on buds and stem tissue. Certain weeds will also act as hosts through the winter. The optimum temperature for infection is between 68 to 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.
The mildew can spread rapidly since the disease cycle can be completed in as little as 72 hours. However, it commonly takes 7-10 days from the time of infection to the development of symptoms and secondary spore production.
In most cases, good cultural practices will adequately control powdery mildew:
- Select powdery mildew resistant varieties. This is particularly true of roses. For lawns, shade tolerant grasses such as creeping red fescue can be planted.
- Plant in full sunlight in a well-drained area.
- Do not crowd plants. Air flow and ventilation will discourage mildew growth.
- Powdery mildew thrives where high rates of nitrogen have been used. High nitrogen promotes tender leaf formation, causing dense stands that are more susceptible to infections. Adequately fertilize but avoid stimulating succulent growth. Organic fertilizers or slow-release formulations of lawn fertilizers are good choices
- Prune infected plants to get rid of infected parts and increase airflow. If the infestations are severe, remove and destroy the plants that are infected.
- Disinfect your pruning tool in a bleach solution of one part household bleach to four parts water after each cut.
- Watering plants in the morning gives the plants the rest of the day to dry off, discouraging establishment of diseases, including powdery mildew.
by Arzeena Hamir
Sulfur is highly effective against powdery mildew if used in a protectant program with a minimum of 7 to 14 days between applications. Garlic naturally contains high levels of sulphur and a few cloves crushed in water can be used to make a homemade spray. Apply a sulfur-based fungicide at first evidence of mildew and repeat applications as necessary. Proper timing of fungicide applications is critical to successful control so make sure to begin at the first sign of the disease.
However, sulfur can be damaging to some squash and melon varieties. Another option is to spray once a week with a solution of baking soda. Baking soda increases the surface pH of the leaf making it unsuitable for the growth of powdery mildew spores. Be sure to spray the undersides of leaves as well as the upper surfaces when using any of these sprays.
Here’s a recipe to make your own spray:
- 1 teaspoon baking soda
- 1 quart water
- a few drops of liquid soap
Before treating your plants, test the spray on a few leaves to make sure they are not too sensitive.
For more information on powdery mildew, you can refer to the following websites:
Arzeena Hamir is an agronomist and President of Terra Viva Organics. When she’s not planting peas or picking zucchini, she answers questions about organic gardening at: firstname.lastname@example.org
Mini Organic Gardens
by Bill Richardson
A mini organic garden can give you wonderful vegetables, which are pesticide-free and delicious. It is not really necessary to have a large garden area to grow plants or vegetables. All you will ever need in vegies will grow in a reasonably small plot.
The no-dig garden method has been proven as successful all over the world. What you need to do is identify the area where you would like to start. Choose an area where there is sunlight, with access to water, mark it out and you are ready to start planning.
What you will need to start:
- Pieces of wood or something to use to box in the area chosen.
- A bale of alfalfa hay
- A bale of straw
- Some old newspapers
- A load of compost
- Manure or a complete organic fertilizer
- A bit of energy, motivation and enthusiasm
Be thorough with the preparation. Don’t make it big to start, say 10 feet (300 cm) by 5 feet (150 cm) and choose which vegetables you would like to grow. Good choices are lettuce, beans, tomatoes, Swiss chard, and radish.
The site to choose?
Choose an open area, preferably facing north/south. Plenty of sunshine and not much wind are important factors to consider. If you are working on concrete your windbreak could be shrubs in pots. This is an ideal way to do it as you can move pots around and place them where they will be more effective.
Mark out your site and box it in. If it is on concrete, join the boards to make it strong. If it is on ground, do a bit of leveling first. Don’t worry about grass as we are going to cover this over. Even if the ground is rock-hard, this method works. You can build a no-dig garden on any base.
Now that you have the base down, cover the bottom of the box with newspapers. Use complete papers, opened up and overlapped. Tuck the paper under the framework if you are building on an old garden bed. After the paper, cover the bed now with the Lucerne hay and use each layer piece as bedding. This needs to be about 2 inches (50 cm) in thickness. Water this area very thoroughly at this stage.
Sprinkle some of your fertilizer, blood and bone, or even a liquid organic fertilizer over the whole area. Next, we need to add the compost and this needs to be only about 1 inch (25 cm) in thickness over the area. At this stage, rake it over so that the compost is even and flat across this area.
Now, put a layer of straw fairly loosely over the area. Add some more fertilizer. Put another layer of compost on top of this and add some more fertilizer on top again. It’s time now to put the final layer of Lucerne hay, making sure that it is all fairly level.
Buy your seeds or seedlings as its time to plant. This is the most rewarding part of this job, other than the harvesting later on. Make small holes in the hay and plant into the compost, firming the hay around the plants. This hay will act as an insulator and stop any drying out. Alternatively, you could place another layer of compost on top and plant into this.
It’s just a matter of maintenance, watering and waiting for those vegies to come up. You will love the crops of herbicide-free foods.
You’ll wonder why you didn’t start earlier!
Bill Richardson lives in Gippsland in Victoria, Australia and specializes in growing South African bulbs and other species. He is involved in horticultural training and development of programs included organic gardening, worm farming, and bee keeping. He is a member of the International Bulb Society and have photos and some articles on the International Bulb Society page. His specialty area is growing the South African species Ixia.
Fertility in the Organic Garden
by Deborah Turton
Soil tests done in a lab are one way to check the health of your soil. However, the ultimate test is how well your plants are doing. By carefully observing your plants, you can tell which nutrient your plants are lacking. With this information, you can choose which amendments should be added to the soil to maximize the soil health.
When adding amendments to your soil, always start with very small amounts. Too much of a nutrient is can be worse than too little. If there is a serious nutrient imbalance, your plants may be unable to absorb the nutrients they need. Therefore, your plant may exhibit signs of a nutrient deficiency, but the problem is an excess of other nutrient. Therefore, observe your plants closely and if they don’t improve, go ahead and have a lab check your soil. Excess nutrients can also pollute our water and soil and waste energy during manufacturing and distribution. So use soil amendments carefully.
The chart below contains symptoms of major nutrient deficiencies, how these nutrients function in the plant, and what organic amendments contain the nutrient.
|Plant Symptoms||Deficiency||Plant Uses||Sources|
|Slow growth Leaves are uniformly yellow-green Cucumbers are pointed at the tips||Nitrogen||Chlorophyll, proteins, genetic material, hormones, and other chemicals||Fish, alfalfa, or blood meal; green manures|
|Purplish leaves Yellow or streaked leaf margins Leaf tips die off Fruits late, poor or absent||Phosphorus||Genetic material, root growth, storage and use of energy||Manure, bonemeal, rock phosphates|
|Brown leaf margins on lower leaves Shriveled fruit Plants not as healthy Weak stems||Potassium||Aids in nutrient movement, protein synthesis, and carbohydrate metabolism||Greensand, granite dust, Kelp, compost, manure|
|Leaves curled upward|
Leaves are scalloped Buds dried out or absent Buds drop off early while the stem is still stiff and erect Tomato blossom end rot Weak stems
|Calcium||Cell wall manufacture and regulation, activates several enzymes||Limestone, ground clam and oyster lime shell, gypsum, wood ashes|
|Leaves at branch tips turn down Stems are hard and brittle||Sulfur||Found in amino acids, vitamins and co-enzymes||Manure, Sul-Po-Mag, gypsum, elemental sulfur|
|Leaves are thin and brittle; purplish red or brown to bronze; striped or yellow to brown between veins; curl upward; or don’t grow long Plants mature late and don’t thrive||Magnesium||Chlorophyll; |
aids in carbohydrate metabolism, energy use, and genetic material manufacture
|Kelp or fish extract, mulch dolomitic limestone, compost|
|Pale yellow color between leaf veins||Iron||Part of enzymes, aids in chlorophyll manufacture||Iron sulfate, chelated iron|
In the trace element chart below, I’ve only included what the symptoms of the deficiencies. I haven’t included what nutrients you can use to fix the problem. Because trace elements are needed at such low levels, it is very easy to add too much and seriously harm your plants. If you suspect a trace element problem, use compost, rock powders, and kelp to improve the health of your soil. Your compost should contain ingredients from outside your immediate vicinity. Clearly, if your entire property is lacking in zinc, compost made from your grass and leaves will also be lacking in zinc. Import manure or compost from a safe source to supplement your regular compost.
|Leaves are smaller and have mottled, stripped, or dead areas Buds have dead tips and margins Buds drop off the plant early while the stems are stiff and erect||Zinc|
|Symptoms appear first on new growth Leaves are misshapen or curled downward Buds are pale green Flowers drop off at higher than normal rate Decreased stem growth Beets and turnips have “corklike” areas Broccoli and cauliflower have a hollow stem||Boron|
|Pale yellow color between leaf veins Brown or gray spots on leaves Leaves drop off||Manganese|
|Leaves are blanched|
Fruit is sour
|Imitates nitrogen deficiency Cauliflower has reduced or irregular leaves Citrus fruit has ‘yellow spot’||Molybdenum|
Bradley, F.M. (Ed). 1991. Rodale’s Chemical-Free Yard and Garden. Emmaus, PA: Rodale Press, Inc.
Mikkelson, R. and J. Camberto. 1995. Potassium, Sulfur, Lime and Micronutrient Fertilizers. in Soil Amendments and Environmental Quality. J. E. Richcigel (ed) Boca Raton, FL: CRC Press, Inc.
Miller, C. and M.L. Facciola. 1995. Let’s get Growing: a Dirt-under-the-nails Primer on Raising Vegetables, Fruits, and Flowers Organically. Emmaus, PA: Rodale Press, Inc.
Schultz, W. 1989. The Chemical-Free Lawn. Rodale Press, Inc., Emmaus, PA.
Deborah Turton is an organic gardener and writer who’s worked with a variety of environmental groups.
Fusilli with Wilted Greens, Goat Cheese and Raisins
Since the garden is starting to produce lovely spring greens, we though this recipe from CooksRecipes.com would be ideal:
- 1/3 cup golden raisins
- 1/3 cup fresh lemon juice
- 4 tablespoons olive oil
- 1 medium red onion, finely chopped
- 4 garlic cloves, minced
- 1 bunch red or green Swiss chard, stems trimmed, coarsely chopped
- 1 bunch beet greens, stems trimmed, coarsely chopped
- 2 tablespoons minced peeled fresh ginger
- 1 1/2 tablespoons grated lemon peel
- Salt and freshly ground black pepper to taste
- 1 pound fusilli pasta, cooked according to package directions
- 5 ounces soft fresh goat cheese (such as Montrachet)Combine raisins and lemon juice in small bowl. Set aside.
Heat 2 tablespoons oil in large pot over medium-low heat. Add onion and sauté until softened. Add garlic and sauté about 30 seconds. Add Swiss chard, beet greens and raisin mixture. Cover and cook, stirring occasionally, until greens wilt, about 5 minutes.
One of the nutrients that we can get from these plants is protein. To know more about it, get the right information on this page.
Stir in ginger and lemon peel. Season greens to taste with salt and pepper.
Toss hot, fresh cooked pasta with remaining 2 tablespoons olive oil. Add greens mixture and goat cheese. Toss to combine. Season to taste with salt and pepper and serve.
Serves 4 to 6.