GARDENER'S READING ROOM
Fertilizers, Pest Control and Soil Management
Organic Gardening

Disease Control... the Organic Way

The Pacific Northwest is a great place to live and garden. The ocean and mountains give rise to a variety of microclimates that allow us an unmatched breadth of plant material. This same wet, mild climate makes our area a great incubator for plant diseases.

Let's look first at how disease occurs. You need three things all at once: a host, a favorable environment, and a disease organism. This is why you can see identical plants with only one of them diseased. This is also why plants can only be bred to be disease "resistant" and not disease "proof". If all the conditions are right, any plant can become diseased.

Organic disease control starts at the very beginning - with good garden design and practices. Putting the right plant in the right place with good soil preparation leads to more robust plants that are less likely to become infected. Some diseases require a specific host, so your plant choices dictate if you even see some diseases (e.g., rust on hollyhocks). So the first line of defense is good plant selection and soil preparation, followed by proper fertilizing and watering.

So you do all that, and still have a problem? First, identify the problem. Is it really a disease? Bring a sample in to Sky Nursery to have it identified. Some things look like disease but are not (e.g. shothole on laurels can be bacteria or stress). If it's truly a disease, is it fungal or bacterial? That will point us to the proper control.

Once the problem is identified, you can choose a course of action. The first step is usually cultural. Remove dead foliage on and around the plant. You may need to prune out affected wood. Watering in the morning and avoiding overhead water can control many fungal diseases. Sometimes removing a susceptible plant is the best control. Sometimes you need to ask yourself how much damage is really being caused. Many deciduous azaleas, for instance, will have powdery mildew by the end of the season, which does not affect them much. Control, then, is more a question of appearance than of health.

Finally, you may need to spray. Organic spraying choices range from baking soda derivatives to lime-sulfur - but remember that "organic" does not necessarily mean "benign". Always read and follow the label instructions and wear the proper protective gear. Here's a general list of organic disease controls. Be sure to ask at Sky Nursery about specific problems. We are always here to help you make a less toxic choice for disease control.

	Product	Typical Use
	Oils: (Work by smothering)	Disease & insect control
	E.g., Lilly Miller Superior Type Spray Oil™   (petroleum based) Year Round or Summerweight -lighter, paraffin or vegetable based E.g., Lilly Miller Superior Type Spray Oil™	Dormant spray (winter only) Dormant or in-season control
	Botanical:	Disease & insect control
	-derived from specific plants (neem, jojoba) or essential oils E.g., Greenlight Rose Defense™	Typically used in-season
	Lime Sulfur	Disease control
	(calcium polysulfide) E.g., Lilly Miller Polusul Summer & Dormant Spray™	Dormant or in-season; sometimes used in combination with an oil spray
	Elemental Sulfur	In season, broad-spectrum fungal control
	E.g., Bonide™Sulfer Plant Fungicide
	Baking soda & derivatives	In season, powdery mildew control
	Copper-based	Broad spectrum fungal and bacterial control
	E.g., Lilly Miller Kop-R-Spray™

By Charlie Shull
Skylights Spring 2007 Vol 22, No. 1

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