The environment surrounding a plant above and below the ground is crucial to its health. Disruptions or changes in environmental conditions can cause certain disorders in otherwise healthy plants. Above the surface of the soil, the vagaries of wind, rain, light, air temperature and humidity cause such problems as dieback, leaf scorch, and sunscald. Environmental conditions below the surface of the soil, such as the tilth of the soil, nutrient deficiencies or excesses, moisture content, soil temperature and an inappropriate pH reading, cause other disorders. Unlike vegetables and flowers, trees and shrubs are prone to diseases caused by various kinds of damage to the bark, trunk, and roots that might take years to become a problem. Environmental disorders can weaken a plant and lead to real pathogenic diseases. For example, anthracnose and powdery mildew are fungal diseases encouraged by hot, dry summer weather.
Of the five groups of plant diseases, environmental disorders are the easiest to correct once they have been properly diagnosed. Getting a proper diagnosis, however, takes some skill and experience.
Symptoms and Causes of Environmental Diseases
The following list of symptoms and causes will help you identify the environmental problems in your landscape.
Chlorosis -Chlorosis is the yellowing of leaves. Its appearance on your plant differs, depending on the type of problem your plant has.
On All Leaves. This may be caused by a lack of nutrients, extremely bright light, or high temperatures.
On Youngest Leaves. A lack of iron or manganese, or insufficient light, may cause yellowing of the youngest leaves.
On Older Leaves. Chlorosis on older leaves only may mean the soil lacks nitrogen or potassium, or it may need aeration.
On Leaf Edges. This is often a sign of a deficiency in both magnesium and potassium.
Between Leaf Veins. This may indicate a deficiency in iron or manganese, or there may be sulfur dioxide in the air.
As Irregular Spots. Cold water can cause irregular yellow spots on leaves.
As Mosaic Pattern. Cold water can cause a mosaic pattern of yellow spots on leaves.
Dead Areas on Leaves - Environmental disorders are often signaled by the rotting of areas on leaves.
On Leaf Edges or Tips. This could indicate a potassium deficiency, boron excess, fluoride excess, excessive heat or cold, or insufficient water.
As Spots or Sections. Cold water can cause dead areas on leaves.
On Edges and Inner Sections. This may be caused by too much light, too cool temperatures, or too cold water.
With Water-soaked or Greasy Appearance. Excessive heat or cold, or cold water on foliage may produce this effect.
The causes of environmental ailments most frequently fall into one of four categories:
1. Soil deficiency, which includes pH problems and basic mineral imbalances;
2. Improper watering;
3. Improper of fertilization, which involves the quantity of and balance of nutrients you add to the existing environment, or
4. Some kind of physical damage to the bark or the roots.
Control of Environmental Diseases
Environmental disorders can usually be quickly remedied by applying the appropriate foliar spray to a weakening plant. However, you can also take long-term measures to control environmental problems without ever pinpointingg the specific cause. Simply follow these steps:
1. Make sure the soil is healthy, and has the proper pH level, nutrient balance, drainage, and sufficient water-holding capability.
2. Making sure the plant gets the appropriate amount of water.
3. Make sure the plant gets the appropriate amount of fertilizer.
For example, if you spread an inch of organic mulch on the soil under your shrubs and throughout the garden every year, you will over time be correcting many of the soil deficiencies most commonly found in the new landscape. If you spray your plants once or twice a season with a kelp extract, your plants will get the necessary micronutrients, even if there are some deficiencies in the soil. If you make sure that the plants get a consistent level of water (about 1 inch a week), you eliminate over- or underwatering. And finally, if you add an appropriate amount of slow-acting fertilizer (roughly 1 cup per 25 square feet of yard or garden) once a season, you will eliminate most nutritional problems. So even though it may be difficult to identify the specific environmental cause of a problem, these easy steps will help to remedy and prevent the current problem and any potential environmental diseases.