How Plants Cope Naturally with Pests and Diseases

We recently came across this article in Growing Trees from Seed, and felt compelled to share it with our readers! The book itself is a fantastic resource with in depth info and practical tips for growing native trees, vines and shrubs. The following article does a great job of discussing the role of genetic diversity, natural selection, and the overall ecosystem in a plant’s health and resilience. Consider some of these concepts when planning out your own landscape, as certain practices such as over-watering your plants may actually lead to undesirable consequences. Sometimes it doesn’t hurt to go back to the basics…If anything, growing healthy trees and shrubs has just as much to do with what not to do! Read on:

I remember my reaction – a deep sense of awe – on seeing a 2.5 billion-year-old fossil of algae in the Royal Ontario Museum in Toronto. In comparison, many woody plants are relatively new to the earth – in the 40-to-90 million-year range – but they are linked by genetic threads to all of the plants that came before.

Like all organisms, not every individual comes with a guarantee that it will live a long life. Attrition of individuals due to intolerance of drought, flooding, pests and disease is natural and important for the species – such are the rules of natural selection.

Every tree and shrub species is a member of community of mammals, birds, insects, fungi and bacteria. Most are beneficial organisms that make life possible. Look at our own bodies, coated inside and out with beneficial bacteria and occasionally invaded by harmful organisms.

Plants may control pests by depositing various toxic chemicals in their leaves and inner bark or sapwood to discourage feeding. It has been suggested that this chemical deposition can rapidly increase in response to a pest feeding event.

According to Dr. Card Otis, an entomologist at the University of Guelph, some pests feed on the leaves of a great number of species, while others have a narrow host range, sometimes a single species. Genetic diversity in the host species creates a spectrum from good to poor hosts for pest insects. The community of insect “associates” – various parasites and predators – is always in a state of flux in relation to the pests. These checks and balances have worked for millennia and are often called the “balance of nature”.

Disease control in plants is managed through selection. The weak die out and the disease-tolerant live. The oldest plants then tend to drop the seeds that are most fit for the local area and most likely to tolerate disease in the future. Healthy plants in a healthy vegetation community are generally not affected by pests, diseases, and even drought. They have cell walls that are tough enough to resist fungal invasion or entry by juvenile insects, resulting in a high juvenile-pest mortality. If you feed the plant with nitrogen (including the acidic precipitation from nitrous oxide auto emissions), water it too frequently, or breed and select for fast growth, the cell walls will be softer. Soft cell walls are more likely to be invaded by diseases or pierced by the tiny mouthparts of juvenile insects.

Some scientists want us to believe that genetic engineering is the answer. They suggest that trees can be engineered to be resistant to a particular pest or disease. In reality, the clonal release of genetically engineered organisms flies in the face of nature’s guiding and sustaining principles of life – genetic diversity. Genetically engineered plants, are unacceptable in the landscape. Evidence abounds that pests and diseases quickly build up resistance to the engineered traits. Engineered plants do not and cannot work in the long run.

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