Garden Pests and Diseases
When well-sited, any plant will be healthier and more resistant to problems, and the plants in this book have been chosen because they are naturally healthy and pest and disease resistant. But in any garden pest problems will pop up sooner or later. Whether those problems are due to insects or diseases, prompt intervention greatly improves your chances of saving plants from unnecessary suffering. Check your garden plants often for signs of trouble, and be prepared to administer first aid right when the need arises.
It may be comforting to know that a pest or disease problem on one plant seldom poses a serious risk to neighboring plants of a different species. With few exceptions, notably slugs, snails, grasshoppers, and Japanese beetles, each species of insect and disease-causing microorganism specialize in a narrow range of plants. In other words, aphids that cluster on your roses are unlikely to colonize lilacs, because their physiology is such that they cannot digest the juices from lilac plants. The same is true of many diseases, including those that cause dark spots or light patches to form on leaves. So, when a zinnia suffers from powdery mildew, it is not likely that your marigolds will be similarly affected. Translated into a practical plan of attack, this means that you can focus on pest and disease problems as rather isolated incidents when your landscape is comprised of a diverse collection of plants.
Gentle Interventions
When you first notice a pest problem, simply removing and disposing of the affected plant part is sound practice, especially when the problem is a disease, most of which are caused by microscopic fungi. Yet this is impractical when the problem is more widespread, as when spider mites have colonized the leaf undersides of a large shrub. Instead, spraying plants thoroughly and often with a strong spray of water from a hose will dislodge and disable these and other fragile sucking insects like aphids. If more serious treatment is indicated, apply insecticidal soap or horticultural oil, both of which are available as concentrates at most garden centers. Insecticidal soap kills small insects by corroding their bodies with fatty acids, and horticultural oil smothers them, leading to their rapid decline. Use these and other pest-products according to label directions only on plants listed on the label and for insects listed on the label.
If more aggressive measures are needed to control an insect pest, look for a general-purpose commercial garden pesticide labeled for use on the plant and the pest that you want to control. In addition, a botanical pesticide derived from the bark of the neem tree, azadirachtin, controls a number of common insects and suppresses some diseases, as does pyre thrum, which is derived from natural plant toxins, and its synthetic equivalent, pyrethrin. Neem has the added benefit of repelling insects for a limited amount of time after application, which reduces the need for repeat applications.
When a Fungicide is Needed
Fungal leaf and root-rot diseases are usually most active in humid weather and in wet soil. They can often be avoided by siting plants in an area with good air circulation, pruning plants to allow sun and air to circulate to inner branches, and planting in soil that is naturally well drained, amending soil with compost to improve drainage, or building shallow berms or raised beds so that plants can be set above the surrounding soil.
But, often in late summer when days are humid and nights are cool, spores of disfiguring leaf diseases like powdery and sooty mildew can erupt. Unfortunately, there is no one-size-fits-all fungicide that will control all fungal plant diseases. Instead, you must check product labels to see if the affected plant is listed. You can do more harm than good to a plant by treating it with a fungicide that it cannot tolerate, or by mixing the concentrate at a stronger rate than is recommended on the label. Also, be very careful when using fungicides near water, because many of them are toxic to fish and other aquatic animals. Warnings of any environmental dangers will be listed on all product labels.
For fungicides to work well, you must get excellent coverage with the spray. Many fungi colonize leaf undersides, so spraying from the bottom up as well as from the top down is always wise. Avoid spraying just before rain is expected, as the product may be washed off before it has a chance to work.
Safe Storage
Before you purchase a pesticide or herbicide, read the label carefully. Check to see that it is labeled (registered) for use on the pest, disease, or weed that you want to treat, and that it is also labeled for safe use on the plant that you want to apply it to. Do not use a pesticide on a plant or pest for which it is not labeled. Study the product label for guidelines about protective clothing and application; what is the best season, time of day, and weather for application. For instance, you should never apply such products on a windy day to avoid damaging nearby plants, and also to avoid having the pesticide drift from your yard into a neighboring one. You also should avoid applying pesticides before rain is expected, and you should apply them when the temperatures are between 65 °F (18C) and 85 °F (29C).
Consult a physician before spraying to be sure that you have no medical conditions that should prevent you from spraying. If you are in doubt, hire a professional licensed applicator.
Keep children and pets away from the area during and after application, for as long as the label instructs, and inform neighbors that you will spray.
Measure and mix chemicals in a well-ventilated area and precisely as directed on the product label. Applying a stronger-than-recommended solution is illegal, and may harm plants. Wear old clothing with long sleeves and long legs and dispose of it, or wash it separately and store it with the product. Do not touch your face or eat or drink until you finish the task and then bathe thoroughly.
Many garden pesticides remain viable for years when stored in a cool, dry place. In the interest of safety, store lawn and garden chemicals in their original containers, in a locked cabinet out of reach of children and pets, and label the cabinet door with its contents.
If you experience a chemical spill or suspect pesticide poisoning, consult the product label for first-aid action, or a hot-line phone number. Also, telephone 911, your physician, or a poison-control center (the number should appear at the front of your telephone directory). Keep the product nearby so that you can read the active ingredients, which are listed on the label, to the help-line person who answers the telephone.
The Fall Cleanup
When the first blasts of winter cold cause leaves to flutter down and perennials to die back and become dormant, you have an excellent opportunity to interrupt the life cycles of many pests and diseases by cleaning up your garden. Many fungal plant diseases overwinter in old fallen leaves and stems, and some insects find safe harbor in plant debris as well.
Before winter makes working outdoors uncomfortable, gather dead plant material that lies on the ground and pull up withered annuals, roots and all. Gloved hands and a stiff rake will be your primary tools, though you may also need pruning shears to snip off the stems of perennials flush with the soil. Before traces of their presence disappears, mark the locations of plants you intend to divide or move in spring. After the first hard freeze, apply a thick, fluffy mulch of straw or evergreen boughs to insulate marginally hardy plants against damage from freezing and thawing. Then, when the new season begins, you will be ready to sail into it quickly.