Keep Trees, Shrubs and Plants Vigorous
Give some thought to an afflicted plant’s situation. Make an effort to improve its vigor by watering it during dry periods over the summer and fertilizing it in the fall, if appropriate. Prune any injured or broken branches or stems cleanly and carefully with clean tools. Mulch it to discourage weeds, hold soil moisture, and improve the health of the soil beneath it. Make sure the plant is getting enough light as the surrounding plants may grow and block the sun a bit more.
Tip: Lawn mowers and string trimmers cause most injuries to trees that later become the front door for fungal invasion. Surround your trees and shrubs with mulch or groundcovers to keep this equipment at a distance.
Plant Resistant Varieties
Some types of shrubs, fruit trees, and flowers are relatively impervious to fungal disease problems. Certain roses, for example, resist black spot and mildews while others seem to pull it right out of the air, especially in warm, humid areas of the country. When purchasing new plants always choose those that are known for being trouble-free. Your garden center and county agricultural extension office will have lists of such plants. This information is also published in seed catalogs and, often, on plant labels as well.
As a corollary of this, get rid of plants with chronic fungal disease problems, no matter how special they are to you. If they get infected two or three years in a row, you will know it is not a fluke of the weather. They are just susceptible and will be a source of infection for other plants and lots of extra effort if you keep them in the yard.
Use Drip Irrigation
Most people water their lawns, shrubbery and planted beds from above, using an oscillating_sprinkler or watering_can. This can encourage fungal disease in your yard. Fungi like moist conditions and mildews and rusts, in particular, are encouraged by damp surfaces on foliage. Of course, leaves get wet when it rains, but if you can avoid wetting the leaves every time you water, you will definitely reduce the risk of a disease outbreak. Water lawns early in the day so leaf surfaces dry quickly.
Drip irrigation is a more efficient, effective, and time-saving method of watering. A drip irrigation system consists of a network of small-diameter plastic hoses that lie on the soil under the mulch and drip water directly to a plant’s root zone. Systems are available as soaker_hose products that “sweat” water along their entire length or as drip_irrigation kits that have lines fitted with emitters or spray heads to distribute water at certain intervals wherever you want it. Because the water never touches plant leaves, the risk of moisture-related disease is greatly reduced.
Over the long term, the best defense against pests and diseases is to build up the organic matter in the soil in your yard by mulching all the plants. The soft layer cushions rain drops so that they do not splash fungal spores up onto the lower leaves of plants. When the decomposing organic mulch becomes incorporated into the soil over plant roots by the action of weather and earthworms, it harbors lots of beneficial organisms that control disease pathogens.
Cover the bare soil under trees, shrubs and flowers with 2 to 4 inches of chopped leaves, grass clippings, compost, hay, shredded paper, evergreen needles, bark chips, or straw all season long. Keep the mulch materials away from plant stems and trunks. In cases where a plant has experienced fungal disease, remove the mulch at the end of the season and replace it with fresh to prevent spores from overwintering.
Keep Tools Clean
As with diseases in humans, keeping things clean prevents the spread of infection among plants. Keep your tools clean. Dip pruners, trowels, shovels and other frequently used tools into a pail of water and household bleach mixed 4 to 1, or spritz them with aerosol disinfectant after working in the yard and garden around vulnerable or infected plants. Pruning tools should be disinfected after each cut to avoid spreading disease. After disinfecting your tools, coat them with oil to keep them from rusting.
Fungus spores of mildews, various spots and rusts, are most likely to thrive in moist humid environments where the air is still. To assure good air circulation space trees, shrubs flowers and vegetables so that they will not be crowded when they reach their mature size. If possible, avoid planting mildew prone plants close to walls and fences or in depressions in the yard, where moist cool air tends to collect. Improve airflow at existing sites by cutting back other plants or hedges that may interfere with it.