PEST and disease control continues to be one of the most challenging problems for gardeners to solve.
I understand that everyone is having trouble changing their control methods from last century's outdated practice of spraying everything with poisonous pesticides to more modern methods of analyzing the plant's growing conditions and taking a "holistic" approach to pest and disease control.
Holistic P&D control is not difficult. You don't have to be a scientist or horticulturist. You do need to look at the plant, its growing conditions and any underlying or contributing factors that are causing the P&D problem.
Contrary to the environmentally damaging chemical approach that dictates "see it, spray it and walk away," holistic P&D control looks at factors such as plant selection, soil fertility, excessive fertilizer application, incorrect pruning practices and other issues that relate to plant growth within the garden's entire ecosystem.
Some plants cannot be saved and every good gardener must learn to replace chronically P&D prone plants, with the understanding that it's cheaper and more effective to remove and replant versus continually battling P&D problems over many years.
I realize that many people cannot part with certain plants for nostalgic or other reasons. However, continuing to battle chronic P&D problems on any given plant while not being able to enjoy the very plant you love seems ironically futile, expensive and stressful. And so, problem plants must die for other plants to live. Or, continue to spend time, energy and money for little benefit.
Soil fertility issues can also have a large impact on plant health and therefore the prevalence of P&D problems.
It is important to understand that ornamental plants do not require fertilizer to live a healthy and productive life. I have never chemically fertilized my garden and it is lush and healthy. And while I was at Park & Tilford Gardens, we never fertilized garden beds and the garden was a thriving oasis for more than a decade.
If you are fertilizing the garden or lawn on a regular basis you are negatively impacting plant growth by forcing unnaturally soft, lush growth on your plants, which allows the P&D banquet table to be set for every hungry insect or opportunistic disease.
To grow healthy plants you need to build healthy soil. If your soil is poor, then amend the planting beds once with manure or compost and that will be enough. Then apply the single most important P&D control product to the garden - mulch.
Mulched soil is protected, virtually weed free and mulch provides a life-matrix that allows naturally occurring beneficial microbes and insects to moderate and control P&D problems while improving soil fertility and therefore plant health.
Those are just a few of the underlying growing issues that affect plant health and therefore affect the possibility of P&D problems. To help focus our understanding on specific P&D issues let's look at powdery mildew on roses, grapes, onions, phlox, rhodos or some tree species.
Powdery mildew is a fungal disease that attacks the host's leaves and usually appears as a white downy or powdery substance on the leaves. It is known that powdery mildew thrives in locations with high humidity, poor air drainage and where a dry soil or dry root condition is prevalent. It is also known that many plant selections are prone to powdery mildew infestation.
Dinosaurs will tell you to spray the leaves with fungicide and you'll have no problem, for about seven to 10 days. But then you must continue spraying for the entire growing season and for the rest of the plant's life and your life.
My first question for powdery mildew infestation would be: Is this specific species or variety prone to this disease? If the answer is yes, then the control method is to remove the plant and replant a species that is resistant or not prone to powdery mildew.
If the plant is not known to be prone to powdery mildew, then the problem is a localized growing issue of poor air circulation, poor soil, over-fertilization, dry soil or all of those issues. In the localized attack scenario improve airflow by pruning surrounding plants if possible. Or relocate the plant to a location with better airflow. Stop fertilizing if that is occurring. Mulch the soil if not already done. And wash the powdery mildew off the leaves while watering the plant's root zone to solve the dry root condition. Multiple controls applied simultaneously work better than just one control method. And none of those controls are expensive or environmentally damaging.
Remember that pest and disease attack is merely a symptom, not the problem. To cure the problem you have to diagnose all of the plant's growing conditions and fix the out-of-balance growing issue in order to remedy the symptom.
Todd Major is a journeyman horticulturist, garden designer, consultant and organic advocate. For advice contact him at stmajor@ shaw.ca.