Changes in the environment (as well as changes in your gardening techniques) can easily affect and interfere with normal plant functions, so they are technically considered diseases. Unlike infectious diseases, however, non-infectious diseases (also referred to as "disorders") cannot be transmitted between plants. These disorders, once they occur, can become very serious, but they are often easy to prevent and remedy if you implement good gardening practices such as regular soil improvement. The symptoms for these disorders vary widely, depending on the cause and the plant.

Disease Look-a-likes
Although plants have an ability to adapt to an array of different environments, all plants have certain conditions they require in order to grow their best. Factors such as air pollution or widely fluctuating temperatures can upset a plant's normal functions, causing disease-like symptoms.

To help you become familiar with the most common types of disorders, below is a listing of the symptoms they produce with detailed descriptions of each.

• Excessive Water - Too much water means that most or all of the tiny soil pores, which normally hold some oxygen, are filled with water. When roots are deprived of the oxygen they need, they cannot function properly and become more prone to infectious diseases (such as root rot). Affected plants lack vigor and may wilt; leaves become yellow. Raised beds can help improve drainage.

• Drought - A shortage of soil water can stunt plant growth and slow flower and fruit production. Leaves either turn pale and wilt or develop scorched, brown areas. Shallow-rooted annual plants are often most affected by drought. Regular deep irrigation can help mildly affected plants recover and prevent future problems. Soaker hoses are also an efficient way to give your plants the water they require.

• Cold Stress - Sudden cold bouts can kill tender buds, growing tips, and other woody plant parts. Leaves turn yellow or drop, buds may drop, stems can crack, and bark can split. Unseasonably low temperatures during the growing season can damage warm weather vegetables like corn, beans, and tomatoes. Protect your actively growing plants with floating row covers or another type of frost shield. Avoid fertilizing after midsummer as later fertilization promotes soft growth and is more resistant to frost.
  When the ground is frozen, dry winter winds can pull moisture out of buds and evergreen leaves, causing browning and tip dieback. You can protect against this with windbreaks or an anti-transpirant spray to help block moisture loss.

• Heat Stress - Young plants exposed to high temperatures often wilt and may even die. Cold weather vegetables (such as lettuce and spinach) stop producing new leaves and will bolt. Shade and water may help your plant recover, as well as prevent damage. Water well in the early morning and again in the evening if necessary. Try to avoid planting cool weather crops that will mature in midsummer. Pull out and compost plants that bolt.

• Insufficient Light - Plants become spindly and are more susceptible to lodging (falling over) when there is not enough light. Green leaves will turn pale, and variegated or colored leaves may turn evenly green if they don't have the light they need. If your plant shows these symptoms, move it to a sunnier spot.

• Excessive Light - When exposed to direct sunlight, some fruits and leaves develop sunscald, discoloration, or blisters. Too much light has the potential to burn the foliage of shade-loving plants, causing brown patches or dead leaves. Plants with purple or yellow leaves oft fade or burn in direct sunlight. If you're unsure of how much light a plant needs, first see how it grows in partial shade. If it turns pale or spindly, gradually move it into more sunlight. Always place seedlings or young plants in the shade, slowly introducing them to more light as they grow.

• Strong Wind - Leaves develop a silvery discoloration and tattered leaf edges when exposed to prolonged high winds. Windblown plants may lose large amounts of water through its foliage, causing the leaves to appear wilted. Walls and windbreaks are good remedies for this problem.

• Deficient Nutrients - When nutrients are lacking, plants are less vigorous and yield poorly. Common deficiency symptoms are abnormal leaf color, curled or stunted leaves, and dead growing tips. Regular soil tests can alert you to developing deficiency problems.

• Excessive Nutrients - High concentrations of nutrients may cause the same symptoms as nutrient deficiencies. In some cases, the effects of excessive nutrients are indirect. Too much nitrogen, for example, often produces lush plants with few flowers or fruit. Soil tests can show you if an imbalance is developing or already occurring. Follow package directions for fertilizer application rates.

• Ozone Pollution - Ozone pollution, from car exhaust or other internal combustion engines, causes stippling or yellowing of leaves. Damage is especially severe on the upper surfaces of the leaf and on matured leaves.

• Herbicide Drift - Under windy conditions, herbicides applied along roadways, in farm fields, or even in your neighbor's yard may drift over to your property and injure your plants. Depending on the product used, leaves may appear bronzed, burned, distorted, or discolored, or the plant may die. Protect your plantings with walls, windbreaks, or another type of barrier.

 

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Non-Infectious Diseases