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Volume 9, Issue 2
February 2011

Creating a resilient landscape
Organic Pest and Disease Management
By Donna Prock

The first line of defense against pest and disease problems in the garden is prevention. You can prevent most problematic infestations by promoting soil and plant health from the beginning. Generally speaking, the healthier the plants, the less likely they are to succumb to pest and disease problems. So focusing on soil fertility is the first and foremost factor in prevention. To learn more about soil health and fertility see my articles from the July and August 2010 issues.

Preventive Measures

Plant clean, healthy cultivars that are suited to your site: Make sure the plants you introduce to the garden are pest and disease free, and check them for over-all health and vitality, as weak plants attract predators. Also choose disease-resistant varieties that are well-adapted to your area. Native plants are excellent choices because they are naturally equipped to resist many local pests and diseases.

Irrigation Techniques: Improper watering is a common cause of garden pest and disease problems. Under-watering stresses the plants, causing them to become more vulnerable. Over-watering promotes fungal growth. Watering plants from below, using drip irrigation, soaker hoses, or hand watering with a hose, helps to prevent and remedy fungal disease by discouraging it's growth and minimizing it's spread through water droplets sitting on the leaves. Also watering in the morning allows the water to evaporate off of the plants during the day and helps discourage fungal growth.

Space Plants Adequately: It's always tempting to place little plants close together. Read up on the mature breadth of the plant and place accordingly. Proper sunlight and air circulation helps discourage diseases such as powdery mildew. Also stake plants to keep them off the ground. Bugs will take the opportunity to munch on leaves that droop onto the soil.

Keep Your Tools Clean: Regularly clean garden tools, even if there is no sign of disease, and when working with diseased plants always disinfect your tools before moving to the next section of the garden.

Proper Fertilization: High-nitrogen fertilizers cause plants to put their energy into fast leafy growth, leaving them less resilient in the long term and more vulnerable to pests and disease. Instead…

Feed the Soil With Compost: Proper feeding of the soil with organic matter aids the growth of beneficial microorganisms that naturally kill off many pests and diseases. It also promotes strong, vigorous, resilient plants.

Minimize Insect and Disease Habitat: Keep the garden area free of debris and weeds which are breeding habitats for insects. Remove any infected plants and burn them or put them in the garbage. Do not add them to your compost pile.

Interplant and Rotate Crops: Insect pests and diseases are often plant-specific. A common practice among home gardeners is to plant a single crop in a straight row. This encourages pests because it makes it easy for them to travel along the row from one host plant to another. If different plants are intermingled and not planted in straight rows, an insect is forced to search for a new host plant, exposing it to predators. When plantings are mixed, pests are less likely to proliferate throughout a crop.

There are plants that repel predatory insects and there are others which attract beneficial insects. There are even plants that attract bad bugs away from a crop that you value. For more information on companion planting see my June 2010 article.

Planting different kinds of vegetables in a different section of your garden each year will help reduce pest infestation. Some insect pests and diseases overwinter in the garden soil and emerge in the spring and begin searching for food. If the plant they prefer to eat is located several yards away, the insect must move to the source. Many will die along the way or fall prey to birds and other insects.

Also, many vegetables will use up a large portion of a specific nutrient from the soil. By rotating your vegetable crops each year, the soil in a particular section of the garden will have the opportunity to rest and regenerate. In general, avoid planting crops in the same plant family in the same location in consecutive years. For example, potato, eggplant, and tomato are all in the Solanaceae family, so these crops should be rotated with vegetables in another plant family, such as squash (cucurbit family), beans (legume family), etc.

Regular Monitoring: Monitoring the garden daily or weekly for signs of pest or disease problems allows you to act quickly before they become a larger problem. It has been said that the best pesticide is a gardener's shadow!

When trying to identify plant problems, do not immediately assume that they are caused by pests or disease. Nutrient deficiencies, temperature extremes, soil ph, over- and under-watering, and other environmental factors should be considered first. If these are ruled out, books on plant disease can be consulted to learn about individual plants and the specific plant diseases that afflict them. The PNW Plant Disease Control Handbook can be ordered at at the Oregon State Extension website/

We will discuss common local pests and diseases next month. Planning to avoid these problems in your garden will reap its rewards in healthy crops and landscapes for everyone to enjoy.



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Published monthly by Pioneer Marketing & Design
Publisher/Editor:Virginia Bruce
PO Box 91061
Portland, Oregon 97291