The idea that you would have a garden outside, living and thriving, and that it would have no forms of life present other than the plants you have chosen, is not only impossible but ignores how gardens work. The soil itself is a vast menagerie of fungi, bacteria, insects and other animals in a constant drama of living, dying, recycling and aeration.
Soil that will grow healthy plants is so much more than its mineral components; remove all the living, dead and recycling elements from soil and its ability to host plant life would drop off sharply.
Most of the life that occupies soils does nothing else than enrich it and constantly make available the nutrients that are locked in dead plant tissue. Through their endless activity all the essential elements that the plant drew out of the soil are returned to it. Most of these small organisms live on the sugars they extract from cellulose, which is a major part of plant bodies. Without the constant decomposing of dead plant material, mostly by fungus and bacteria, we would be up to our necks in dead trees and other plants. There are also a host of invertebrate animals living in the soil, helping to enrich it--earth worms, flatworms, nematodes, snails, slugs, annelid worms, water bears, velvet worms and centipedes, millipedes, beetles and ants.
The kingdom of fungi includes molds, mushrooms and yeasts, all of which, when reproducing, create spores. Spores generate into slender tubes called hyphae; cross walls called septa divide hyphae into cell-like units. The growing form of most fungi is called a mycelium. Reproductive structures, also hyphae, form in response to the presence of moisture. The most common reproductive form is the mushroom. Many fungi are microscopic and all are heterotrophes, organisms that cannot manufacture organic compounds and therefore need to feed on organic material from plants and animals. They absorb food through their chitinous cell walls, after secreting powerful enzymes that break down live or dead material into absorbable solution. Sugars, proteins, and other molecules are transported thru chitinous cell walls.
Chitin is a nitrogenous long-chain polysaccharide that is a very tough material and is used in nature for many purposes, such as fingernails. It is also used extensively as exoskeletons like the hard shell of a beetle or a lobster. Fungi are tough, resisting cold, heat, and severe desiccation, as their cell walls resist water loss. The fungi are everywhere on earth, in our gardens and on our bodies.
From a tree's perspective some of the most useful fungi are the mycorrhizae. The tiny filamentous hyphae of these fungi grow around and sometimes into the tissue of tiny root hairs, greatly increasing the surface area of the roots and aiding in the uptake of minerals, especially phosphorus. Found in relation with 80% of the world's vascular plants, over 5000 species beneficial to trees have been identified.
Bacteria form the other major group of life in garden soils. Although invisible to the human eye, they are everywhere and the average spoonful of garden soil contains a whopping 10 to the tenth power of individual bacteria. Earth’s first lifeforms, they are preserved in fossil evidence 3.4 billion years old. Single-celled, without a nucleus and lacking chromosomes, they do interesting cross-species adaptations. Almost all living cells of every kind have intercellular symbiotic relationships with bacteria; a good example is our own mitochondria. Early forms of bacteria created our atmosphere. Exuding oxygen as waste, they also produced nitrogen, nitrous oxide, carbon dioxide, carbon monoxide, hydrogen, methane, and ammonia, among others. One of the approximately 10 000 identified species, Rhizobium is best known for its nitrogen fixing. Rhizobium forms symbiotic relationships with the root hairs of members of the pea family, enabling the plants to receive more nitrogen than they normally would.
Insects are another essential part of our gardens. Their role as pollinators and food for birds and small animals is critical. They also sometimes eat the leaves of "our" plants but also, unknown to them, sometimes transport diseases from plant to plant. Trade-offs are their predation of other types of insects. Through the eons many plants have become much stronger through their interaction with feeding insects and many plants manufacture chemicals, secondary metabolites, to deter excessive feeding.
How did the cheetah get to run so fast? See how fast the gazelles run; for all their speed and cunning, large cat predation in Africa yields meat only one in ten attempts. The timeless interplay between predator and prey have honed each species into a beautiful, strong and resilient creature, a fruit of this amazing planet. So it is with so many other relations in nature--bugs help keep your trees strong. Only occasionally is a tree in danger of losing its leaves and then it will generate a second set; think of forest tent caterpillars and aspens.
Insects are the largest group of living animals; a million species have been identified and named. They are everywhere on earth where there is life, often assisting in the necessary clean=up work. Insects as other animals are limited by their bodies as to where they can go and what they can do. All insect activity on plants leaves a signature, distinctive marks and changes, once interpreted proving who was where and what they did. Small holes or the loss of the edge of a leaf speak of caterpillar presence; saw dust at the base of the trunk shows the action of a boring insect. By observing where on the tree and what happened you can narrow down the choices as to which insect performed those actions.
When you see chewed leaves, look for larvae of moths or butterflies or perhaps snails or slugs. If you see discolored leaves [not yellow], streaked or mined leaves, (pockets in the leaves) look for leafhoppers, lace bugs, aphids, psyllids, spider mites or leaf miners. If you see distortion on the leaves, such as little galls or cupping of leaves, look for eriophyid mites, aphids, or psyllids. If you find die-back of twigs or dead branches or exposed roots, look for wood borers, bark beetles, scale insects, or root feeding beetle larvae.
If you find honey dew on plants, look for aphids, scales, leafhoppers, psyllids, or white flies. Fecal spots on leaves could be lace bugs, or beetles, bugs (true bugs, such as the ash plant or maple bug), sawfly or sawfly larvae. If you find tents or silken material you may have tent caterpillars, or webworms. If bags or cases are present, look for bagworms or case bearers. Spittle is formed by spittle bugs. White fluffy wax-like material, called flocculence, can mean the presence of adelgids, some types of aphids, occasionally scales, or some whiteflies. Slime on plant parts usually means snails or slugs. This is not exhaustive but you can see how insects are naturally spread about the plant parts, as their ability to consume or use the plant for their purposes dictates.
Sometimes a certain strain or species of a tree’s friendly associates, the bacteria and fungi, engage the tree as predators. This is natural, but at this time it’s hard for us to think of greater ecological cycles; we want to save our tree. One of the real pluses of zone 3 living is how clean it is on a plant disease level. We trade use of snow shovels, winter tires and parkas for very few tree diseases.
Bacteria are present as two disease pathogens, fire blight and Pseudomonas. They are similar in how they are transmitted, where they enter the tree and how they act. Bacteria are microscopic and there is always a tree nearby that is harboring the disease. The problem is the great range in the defence systems of different tree species. Some trees never seem to get any symptoms, while others are killed outright. Our focus is the middle range of defence systems, of the trees that can carry the disease for years, showing lots of symptoms but never enough to kill a tree. These trees are the permanent hosts of the disease. People who know nothing of the disease never see this--so what, the tree has a few dead branches; all trees do, don’t they?
And every spring when things warm up, the birds and bees visit one of those trees, which is now showing active symptoms, and then travels to your tree, and lands on a flower or a recent cut in the bark made by a squirrel; any opening will do. Then the bacteria engage the new host, eating as much sugar as they can get, attempting to thrive, continuing the disease cycle. All apple varieties, pears, mountain ash, hawthorns, saskatoons and cotoneasters are susceptible. A first sign is wilted flowers and dried-up new shoots, which will show a shepherd's-crook-like bend at the end. The leaves quickly turn to reddish shades, instead of yellow leaves fading for weeks, which is usually shade death, leaves that are no longer getting the light they require. The next symptom is cankers in the branch bark below the first infection sites, dark blackish scallop-shaped dead areas in the bark. From there bacterial ooze may be present, leaking from the cankers, dripping onto healthy tissue below. This ooze is full of active bacteria and one drop is all you need. Further symptoms of a weak tree are major cankers in trunks, large dead sections of the leaf mass; now the tree is ready for removal.
Grim, isn't it! Back in the day, antibiotics were used to greater and less affect, but the real answer is to prune off the affected branch or branches as soon as you spot them. And you will spot them,because you know that your friend the tree is relying on you to look very closely each week and see these types of problems before real trouble sets in.
Either remove the branch at its collar or do a training cut a foot below the last visible symptom. You haven't cut into the disease, so your tool is still clean. If you want to disinfect your tools use a 10% solution of bleach in 90% water, dipping a rag in the solution and wiping the tools will do the job. Lysol and other alcohol based products do not work as well. Pruning tools that have cut through diseased branches are as effective at spreading the disease as any natural agent.
When buying fire blight susceptible species do a little reading and try to avoid highly susceptible varieties.
Pseudomonas syringae works in a very similar way. My experience is that it is not as aggressive as fire blight, but occasionally a strain will show up, especially in an Amur cherry, and go through the tree like a fire.
The pseudomonas bacteria work in a different group of plants—lilacs, of course as the name P. syringae contains the genus name for lilacs (Syringa), and predominantly the stone fruits, the genus Prunus, cherries, plums, apricots. Symptoms are similar. One thing the cherries do is exude lots of sap from canker edges; this is known as gummosis and looks like amber. Treatment is the same; prune away diseased sections to protect the rest of the tree from infection.
Lilacs, including the Japanese lilac, show blackened drooping leaves and then shoots. Prune as needed to remove all signs of the disease.
Certain fungi also get aggressive with their hosts from time to time. One of the most prevalent in North America, especially in the east where the elms are native, is Dutch elm disease (DED). A fungal wilt disease, it literally runs through elm trunks, drinking great amounts of sugar as the elm reacts by compartmentalizing infected tissue, leaving little or not enough to continue life. Carried on the bodies of flying elm bark beetles, there is nothing to stop it.
Out west things are a little different; most of our elms are in the few widely spread cities, fortresses really, where a siege situation exists. With careful observation DED will be manageable in western cities. Everyone should be able to identify an elm and notice that it is flagging. If a perfectly healthy green tree has quickly developed a yellow-leafed branch that is not broken, what could be the cause? Any time you see one of these in your city, make the call. Teach your children and friends to recognize elms and watch for flagging.
Another fungus that affects cherries, the chokecherry, mayday and Schubert cherries is black knot. (Black knot is covered in the plant profile section.)
Cytospora canker has been addressed in spruce sections and also with the aspens, as has hypoxylon canker. These are not life threatening and are good indicators of your watering habits. Most aspens and spruce that get the water they need do not get these diseases.
There was something in the air (pesticides, perhaps?) in post war North America in the ‘50s, a wind under our tails. We had won the war, and most of Europe was being rebuilt. New technologies abounded, all saving labour and time. It seemed we had life under control, nature too. The average kitchen of the day had any number of chemical sprays under the sink, ready to hand, to kill any crawling or flying beastie that dared enter the clean safe home.
The same attitude existed outside. An arsenal of chemicals was in the shop or the shed. Any insect that found its way to the property or trees was dealt with quickly, finally. Pests as all small living things were then called, had no place in the safe sterile nature they imagined. The ideology “better things for better living through chemistry" ruled. This led to what Rachel Carson called “silent spring”; silence of bird song is what she meant.
Today, fortunately, most of these chemicals are locked up by legislation. But the attitude still carries over; there is something about these deeply ingrained cultural practices that is very stubborn to change. And many people's first thought upon encountering insects is to think of spraying.
Better to do a little reading and understanding, and some watering of your trees so that they can power up their immune systems and deal with this their way, a way that is practised in the clear hearing range of many song birds, feeding caterpillars to their nestlings.