Depletion of soil manganese

Glyphosate limits plant absorption of micronutrients like manganese after application and may lead to a reduction of manganese in the food supply. Crops that are normally high in manganese, such as soybeans, leafy vegetables, coffee, tea and whole grains, are commonly sprayed with glyphosate for weed control. Soybean growers are familiar with yellowing of glyphosate-tolerant beans after application, also known as “yellow flash.” Glyphosate chelates with manganese, causing a deficiency within the plant and the resulting yellow leaves. The plants were not deficient in manganese without the application of glyphosate. Field experiments from 1999 to 2001 found that adding manganese into the herbicide solution reduced the effect of the herbicide on weed control. To overcome the reduced control, they made larger applications of glyphosate.