Plant diseases are a common concern to home gardeners and farmers.
Obviously, the growth and yield of plants depends on their protection.
Knowing methods of preventing disease, controlling the damage and what to do when symptoms are noticed, are vital to their health.
Viruses, bacteria, nematodes and fungus are biotic agents that require the 3 fundamentals of the disease triangle to exist: host, pathogen and environment.
Because of the extreme weather conditions this year, powdery mildew and blossom-end rot are running amok in local gardens.
Powdery mildew (PM) (Blumeria graminis) is a very common, conspicuous and easily recognized fungal disease. It only grows on a plant’s leaves and stems.
It has the appearance of spots or patches of white to grayish, powdery, mildew growth on the upper side of leaves.
Gardeners may notice leaf twisting and curling before the fungus appears. PM is not fatal but can speed up defoliation and fall dormancy.
It affects cereals and grasses, vegetables, weeds, shrubs, fruit, trees and ornamentals.
The disease is carried through spores. Once released, they will germinate and cause infection to susceptible plants. High humidity or a film of water on the plant surface is not needed. It will continue to spread regardless of the moisture conditions once infection starts.
Lower leaves are the most affected, but the mildew can appear anywhere on the foliage. Once, the disease progresses, the spots will increase in size and intensity.
As large numbers of spores are formed, the mildew may spread up and down the length of the plant.
Gardeners must remove and destroy (burning) infected plant material. Do not compost as it overwinters and will be spread by rain, wind or insects.
It can be controlled by lime sulphur or other fungicides applied frequently to the susceptible plants.
One tablespoon baking soda plus 2.5 tablespoons oil in 4 L of water is effective on roses. Lots of air circulation around plants is essential.
Water in the morning or use soaker hoses or drip irrigation to avoid wetting leaves.
Do not over fertilize. Increased use of nitrogen will produce succulent growth which powdery mildew prefers.
Blossom-end rot is a physiological disease that affects tomatoes and other vegetables and fruit.
It depends on a number of environmental conditions, in the supply of water and calcium to the developing fruit.
This disease does not spread from plant to plant or from fruit to fruit.
Symptoms occur at any stage of development, but is most commonly found when the tomato is one-third to one-half of its full grown size
Symptoms appear only at the blossom-end (bottom) of the fruit. A small, water soaked spot may get larger and darkens as fruit develops, although some may remain small and superficial. But more often than not, a large dried out, black leathery lesion forms. Hence, the name “blossom-end rot” is very appropriate.
Plants become susceptible in periods of sudden drought or when cultivating too close to the plant that causes the feeder root to become damaged.
Tomatoes planted in cold, heavy soils often have poorly developed root systems.
Gardeners can easily control the disease by planting in warm, well drained, aerated soils to promote good root growth.
A soil test will ensure correct fertilization.
Choosing a fertilizer that is low in nitrogen, high in superphosphate (4-12-4 or 5-20-5) is appropriate.
Too much fertilizer at one time makes plant susceptible.
Spraying 59 ml (4 level tablespoons) of calcium nitrate or calcium chloride per 3.79 L (1 gal) of water 2 to 3 times a week, beginning at the time the second fruit clusters bloom is an excellent remediation.
Often, disease fruit is not discovered until near the completion of the growing cycle. Selecting plant varieties that are resistant to the disease will prevent disappointment at harvest time.
The welfare of plants is a concern of home gardeners and farmers.
The growth and yield of plants depends on protection from diseases, insects, weeds and unfavourable weather (e.g. drought).
Commercial growers select plants that have a genetic resistance to the disease, and use careful cultivating methods.
Similarly, home gardeners will find this troublesome disease in their tomato patch. Severe losses may occur if early preventative measures are not taken.
Heavily mulching around plants helps maintain moisture.
Kathy Granger is a master gardener and a member of the Fergus Horticultural Society.
