Newsletter for January 2009

Powdery Mildew & Organic Controls

Powdery mildew looks a lot like confectioners sugar poured on the plants leaves. At first it might appear on just a small portion of the leaf as an irregular circle. It quickly spreads and soon appears on the surrounding vegetation and in other areas of the garden. Soon the entire leaf is covered and at the same time, colonies develop. The plant becomes infected when an airborne spore, or conidia, lands on a leaf and germinates. It soon grows a guide tube that attaches tightly to the leaf. Then it pierces the plant cell wall and membrane and inserts a hollow tube that sucks up plant nutrients, weakening the leaf and slowing growth. Within a week, the fungus produces tiny mushroom stalks that release millions of spores, ready to infect more leaf surfaces. The fungus also produces a secondary spore, which over-winters outdoors and may also hide in a greenhouse or other garden area, even weeks old. Two different fungus species are responsible for powdery mildew. L. taurica is more likely to attack warm gardens. It prefers a temperature of about 77 degrees F. S. Macularis prefers a cooler temperature, however, the virulent strain of S. Macularis found in gardens today has adapted to tolerate more heat. Both strains thrive in moderate humidity, and are not insured by water. Their conidia can live in water for short periods and are mobile in it. However, strong water sprays do destroy some conidia.

Organic and IPM Control

Here are some sprays that you can use to control the powdery mildew in your crop. All of these are safe to use on herbs or edible crops. Sprays are washed away by water, including rain.

Cinnamon Oil and Tea

Cinnamon is a great destroyer of powdery mildew, with an effectiveness of 50-70%. It also potentiates other suppressive sprays, so it's good to use in combination. To make your own, boil water, turn off the heat and add one ounce of cinnamon to one and a half pints of water. Let the tea cool to room temperature. Add half a pint of 100-proof grain alcohol or rubbing alcohol and let sit. Strain out the cinnamon. The spray is ready to use. A faster method is to use 2 teaspoons of the cinnamon oil with one pint of water and a dash of castile soap. Other herbs are also fungicidal: clove, rosemary, and wintergreen oils are used in some botanical fungicides. The solution should consist of no more that 2% oil.

Garlic

Garlic is antifungal and anti-bacterial and has several pathways for destroying fungi, including it's high sulfur content. It can also be added to other antifungal sprays. Several garlic sprays are available commercially. A homemade formula: soak 3 ounces of crushed garlic in 1 ounce of neem or sesame oil and 100 proof or higher drinking alcohol, or 70% or higher rubbing alcohol for a day or two. Strain. Then soak the garlic in a cup of water for a day. Strain. Mix the oil/alcohol, soaked water and 1 tablespoon liquid castile soap in a gallon container. Fill with water and shake. The frmula is ready to use. A simpler brew consists of a teaspoon of garlic oil in a pint of water. To keep the oil and water mixed, add 1/8 teaspoon of soap (emulsifier). Use garlic as a vaccination. Spray on new growth before there is any sign of infection. Garlic is a generl-purpose insecticide as well as plant pests.

Hydrogen Peroxide

Hydrogen peroxide (hp) is a contact fungicide that leaves no residue. It's an oxidized product of water and has an extra oxygen atom that's slightly negatively charged. When it comes in contact with the fungi, the oxygen atoms attach to molecules on the cell walls, oxidizing or "burning" them. Household hp sold in drugstores has a concentration of 3%. Garden shops sell 10% hp Zerotol containing 27% hp and an unstated amout of peroxyacetic acid. Together they have a more potent chemistry than hp, with an activity of about 40% hp. It's considered hazardous because it can cause skin burns similar to that caused by concentrated acids. To treat plants with drugsture grade 3% hp, use 4.5 tablespoons and fill to make a pint of solution, ora qurt of hp to 3 puarts of water. With horticultural grade 10% hp, use about 4 teaspoons per pint of water, or 5 ounces per gallon. With Zerool, use about 1 teaspoon per pint of water or 2.5 tablespoons per gallon.

Limonene

Limonene is refined from the oil of citrus rinds. It has a pleasant citrus odor and is the active ingredient in many of the new "orange" cleaning products. It also has fungicidal qualities. I've used pure diluted limonene and it controlled powdery mildew, but did not eradicate it. Perhaps a higher concentration would have. Start using 0.5% - 1% limonene in water (0.5% to 1% = .5 - 1 tsp per pint).

Milk

Milk kills powdery mildew so well that both home and commercial rose growers all over the world have adopted it for their fungicidal sprays. Use 1 part milk to 9 parts water. I've only used 1% milk, but other recipes call for either whole or skim milk and use up to 1part in 5 milk. Some recipes add garlic of cinnamon to the mix. When using more than 30% milk, a benign mold is reported to grow on top of the leaves. Use a milk spray at the first sign of infection. Then protect the new growth weekly.

Messenger

Messenger is a commercially available product. Messenger's active ingredient is a naturally occurring protein called harpin that stimulates the plant's own natural defense system. It's been proven to promote mor vigorous, hardy plants that are more resistant to disease and have increased yields. It is used to preven infection and decrease it's virulence.

Neem Oil

Neem oil is pressed from the seed of the neem tree (Azadirachta Indica) native to southeast Asia, but now cultivated worldwide. Neem oil has low mammalian toxicity. It degrades rapidly once it is applied, so it's safe for the environment, including non-target species and beneficial insects. Neem oil protects plants with it's fungicidal properties: it disrupts the organism's metabolism on contact, it forms a barrier between the plant and the invading fungus, and inhibits spore germination. It has translinear action; that is, it's absorbed by the leaf and moves around using the leaf's circulatory system It can also be used as a systemic. Whin it is applied to the irrigation water, it's absorbed by the roots and delivered throughout the plant. Adding a 0.5% solution, about 1 teaspoon per quart, to the irrigation water will protect the plant from infection. Neem oil is best used before the plant or garden exhibit's a major infection. By using it before powdery mildew appears, it prevents the spores from germinatng. It should not be used on herbs or directly on the fruit or vegetable.

Oil Spray

Gardeners have used different oil sprays to prevent and cure fungal infections. Until recently, most horticultural oil sprays were mad from petroleum distillates. However, most organic gardeners have switched to using botanical oils. Aside from the safety factor, botanicals such as cottonseed, jojoba, neem, and sesame oils have fungicidal properties. They can be used in combination with other spray ingredients listed here. The oils are mixed at about 1 teaspoon per pint or 3 tablespoons per gallon. Add Castile soap to help the ingredients mix. Oil sprays should only be used on leaves. Us weekly on new growth.

pH Up

pH Up is a generic term for alkaline pH adjusters, used to increase water pH in gardens. They come as either a liquid or powder. It's active ingredient is usually lye (KOH) or potash (K2CO3). Fungi require an acidic environment to grow and die in alkaline environments. Changing the leaf surface environment from acidic to alkaline cleans up the infection. An alkaline solution with a pH of 8 will make the environment inhospitable for the fungus and will stop it's growth. This is one of the simplest means of controlling the fungus. It can be used on critically infected plants.

Potassium/Sodium Bicarbonate

Potassium Bicarbonate (KHCO3) and Sodium Bicarbonate (NaHCO3) are powders that change the ph of the leaf surface toward alkaline. Another reaction takes place; the fungus cell wall actually burst in the presence of bicarbonate. Potassium is one of the macronutrients used by plants and therefore is preferred over Sodium, as Sodium can build up in the soil. Sodium Bicarbonate can be found in your kitchen (baking soda), so some prefer it in ease of obtanning. Both are more effective when used with an oil and a spreader such as castile soap. The can be used to cure bad infections and to prevent new ones. Use 1 teaspoon of bicarbonate powder, 1 teaspoon of oil, and a few drops of castile soap in a pint of water, or 3 tablespoons each potassium bicarbonate and oil, and one half teaspoon soap in a gallon of water. Spray on new growth.

Serenade and Sonata

Commercially available Serenade and Sonata are composed of different bacteria. They use different pathways to stop mycelia growth. They're considered totally safe to humans and animals since the bacteria attack only fungi. Watch out if you are a mushroom; otherwise you are safe! The two bacteria work will together. They are easy to use, quite safe and effective.

Sulfur

Sulfur has been used to control powdery mildew for centuries. Sulfur sprays can be used indoors, but they'r not popular because of residues that remain on the plant. In greenhouses, gardeners us sulfur vaporizers that heat elemental sulfur to the point of vaporization. The sulfur condenses on all surfaces, including the leaves. A fine depost of very-low-ph sulfur granules covers the leaf surfaces. The low-ph environment inhibits the fungal growth. The heaters use a 60-watt light bulb to heat the sulfur, which is held in a container above the light. The bulb supplies enough heat to evaporate the sulfur, but not enough for it to ignite. The problem with vaporizers is that they leave a fine film of sulfur on everything.

Vinegar

Apple cider vinegar is toxic to powdery mildew because of it's high acidity (low ph). Us at the rate of 1 tablespoon per quart of water, severl times a week. Some gardeners recommend alternating vinegar with potassium bicarbonate (KHCO3) and milk.

HAPPY GARDENING!!!

Remember; cleanliness is key to prevention of all things!