If the leaves on your plants have white spots on them. This symptom may be caused by a number of problems. White spots on leaves should be distinguished from the white or light gray powder caused by powdery mildew.
What causes white spots on leaves
Fertilizer – Copper Deficiency – copper is essential to the growth and vitality of some plants. It is necessary for photosynthesis and metabolizing nutrients into usable energy sources. The most common cause of copper deficiency is either a lack of available copper in the soil or a pH imbalance in the soil which is inhibiting the absorption of copper and other nutrients. However, it may also be caused by an excess of phosphorus or zinc.
Genetic Trait – Such traits may be permanent, or they may only be temporary. The white spots, whether on the leaves or in some cases on the flowers, appear as part of the plant tissue rather than as a growth. There is no treatment or prevention for a genetic trait. However, the trait may turn out to be temporary.
Potting Soil – pH Imbalance – Correct soil pH is vital for the health of plants. Optimum soil pH ranges from 5.8 and 6.2. A good potting soil, have the correct pH. There are other factors which can affect pH, such as concentrations of fertilizer salts and soft water. If the pH of the potting soil varies too much from 5.8 to 6.2, your plant will not be able to absorb the proper amount of nutrients it needs. For instance, high pH can result in a decifiency of iron, whereas low pH can result in a deficiency in phosphorus.
Thrips – Thrips are tiny insects which measure about 1/50 inch. They can be yellow, brown or black. Thrips thrive on the flowers and leaves, especially the underside of the leaves. Because of their very small size, you may not see them unless you are using a magnifying glass. Because of this, your first clue that Thrips are present will probably be the light yellow powder which Thrips leave on the flowers. This is actually pollen which has been spilled from the anthers as they feed on the flowers. If left untreated, Thrips can cause severe damage.
The white spots, which are symptomatic of the causes above, appear as part of the leaf tissue. The white or light gray powder caused by powdery mildew is a fungus which covers the leaves superficially.
Source: www.optimara.com
