As our landscape comes alive, we are like a bunch of mother hens ready to pick and pluck any leaf that doesn’t look like we think it should look.

Maybe that is how it should look at that point of breaking bud; perhaps it experienced an unseasonal dip in temperature or it’s starting to show the beginning of a plant disease.

You can be totally mystified when a plant shows signs of a disease. How did it happen? Will it spread? Will all my plants die?

An important phenomenon to understand in gardening is what is called the disease triangle.

Disease can only happen when three things coincide: You have a plant that gets sick (called a host), a pathogen (fungus, bacterium or virus) that can attack the plant and environmental conditions (like humidity or drought) that promote the disease. If any of these things is not present, the disease will not happen. Prevention is the key to knocking out at least one side of the triangle.

Rather than waiting for a problem to arise, you might consider the best defense against disease is a good offense.

Pathogens

Pathogens won’t be able to gain a foothold if you examine plants carefully before purchasing. Don’t take home a plant with dead spots, rotted stems or insects. In addition to checking the top of the plant, check the root system. Place your hand on the soil surface with the plant stem between your fingers. Gently invert the pot and shake the plant loose. The roots should appear firm, usually white or light colored and spaced all over the root ball. Even if the top appears healthy, if the roots are dark or appear mushy it is not a good sign and just a matter of time before real problems appear. Time is well spent determining what the normal healthy appearance of a plant should be. If you know the plants normal appearance you are better able to determine if what you are looking at is normal or abnormal.

Diseases can overwinter on dead leaves left in the garden in the fall. If a perennial has shown some signs of distress last fall, it is best to clean the area of debris and leaves as soon as possible to keep emerging growth from being affected. Never add any plant showing signs of disease to your compost pile. Unfortunately, our cooler climate doesn’t encourage the hot temperatures needed to kill any suspected pathogens.

We’re often tempted to play nursemaid to plants offered at extremely low pricing. Unless you are willing to put them in quarantine until they improve, you are risking the health of other plants.

The host

The second side of the triangle would be the plant, referred to as the host.

Healthy plants can fight off disease. Too much of any fertilizer can burn roots, reducing their ability to absorb water. This makes the plants more susceptible to stress from drought, cold or heat. An overabundance of a particular nutrient could also put the plant under stress. Everything in moderation, much like how humans should live.

Seed packets often will list the disease-resistance of the plant, but rarely is that information found on plant tags. This practice is usually evident on vegetable seed packets.

Environment

The third side of the triangle is environment and learning how to avoid conditions that promote disease. Choosing the right plant for the right site is critical. A shade plant planted in full sun has the kiss of death headed its way. Be aware of your planting zone, and plant accordingly. You may not be able to enjoy plants that were favorites in a different geographic area. Keep that memory close to your heart, but start building a new garden.

I often think we are our own worst enemy when it comes to water issues. Most of the time we overwater. Diseases need water to move, grow and reproduce. If it is possible, choose watering methods that limit moisture on a plant’s foliage. Soaker hoses and drip irrigation accomplish this.

The most common leaf problems increase when leaves are wet. If overhead watering is the only option, water at a time when the leaves will dry quickly but the roots will have time to absorb the moisture before it evaporates. Water-logged soil or pots can either promote root-rotting fungi or suffocate roots making them a target for the rotting fungi.

Don’t crowd plants. Keep an eye on established plants as they spread. Crowded plants create a humid environment, which allows diseases like powdery mildew, rust and downy mildew to thrive. Improved airflow around plants reduces the humidity and allows foliage to dry more quickly.

To lessen the possibility of disease, trim out crowded, damaged or old stalks on plants that might be prone to powdery mildew like phlox.

Sometimes it seems that putting the puzzle pieces of gardening together is overwhelming, but you will be a more successful gardener if you understand some of the why’s and wherefores.

A site that should be on your resource list is pnwhandbooks.org/plantdisease. Contact your county OSU Extension Office for information on Plant Clinic, which can help solve gardening problems.

— Reporter: douville@bendbroadband.com