Chlorosis

In botany, chlorosis is when leaves cannot make enough chlorophyll. Chlorophyll makes leaves green, so chlorotic leaves look pale, yellow, or yellow-white. If a plant cannot make enough chlorophyll, it may struggle to grow and could even die. Some chlorotic plants, like a special type of Arabidopsis thaliana, can survive if given extra sucrose from outside sources called exogenous.

The word chlorosis comes from the Greek word khloros, meaning "greenish-yellow" or "pale green."

In viticulture, chlorosis often appears in grapevines as yellowing leaves, especially in certain soils. This is common in places with lots of limestone, such as the Italian wine area of Barolo in Piedmont, the Spanish wine region of Rioja, and the French wine areas of Champagne and Burgundy. In these soils, grapevines sometimes cannot absorb enough iron, which is important for making chlorophyll.

Causes

Chlorosis happens when leaves can't make enough chlorophyll. This often occurs because plants lack important nutrients like iron, magnesium, or zinc. It can also happen if the soil is too acidic or basic, making minerals hard for plants to absorb. Waterlogged soil can also damage the roots.

Other causes include certain pesticides or herbicides, exposure to harmful gases, and infections from bacteria or fungi. Different plants react differently; for example, azaleas need acidic soil, while rice can handle waterlogged conditions.

In grape vines

Grape vines can get a problem called chlorosis, especially in soil with a lot of limestone. This problem became more noticed after The Great French Wine Blight. At that time, European grapevines were placed on American rootstocks to fight off Phylloxera. But these rootstocks sometimes had trouble in soil with lots of lime, which caused the vines to lack iron. This kind of chlorosis in France was called chlorose calcaire. The issue was mostly fixed by using American vines that could handle lime for hybrid rootstocks. Growers still need to balance chlorosis resistance with other needs for good wine making. One common rootstock, 41 B, is a mix of the Chasselas grapevine and Vitis berlandieri. It helps against chlorosis and Phylloxera, but not perfectly.

Main article: The Great French Wine Blight

Treatments

If a plant's leaves turn pale because it needs more nutrients, we can help it by giving it extra food. Adding iron, magnesium, or nitrogen to the soil can solve these problems. Sometimes, the soil might be too basic or too acidic. We can use lime to make it less acidic or sulfur to make it less basic, which helps the plant grow better.