Glyphosate Exposure Contributes to Internal Browning of Apples during Long-Term Storage
Glyphosate (Round-Up and generics) is an important tool for managing ground cover beneath apple trees. According to the last available data from the USDA’s National Agricultural Statistics Service, 54% of New York apple acreage was treated with glyphosate at least once in 2007, and 10 percent of that acreage received two applications ( Anonymous , 2008). However, there are increasing concerns that glyphosate may sometimes damage fruit trees in subtle ways that may be largely unrecognized.
Glyphosate kills plants by blocking a critical enzyme pathway known as the shikimic acid pathway. The blocked enzyme is essential for respiration in plants, so plants that receive a full dose of glyphosate cannot survive unless they are bioengineered to be glyphosate-resistant or have evolved to be resistant as is the case with some weed species in the Midwest. At lower concentrations, however, glyphosate can adversely affect plants without producing any immediately visible effects.
In other crops, glyphosate exposure has been shown to reduce root growth and seed production and affect seed quality and plant nutrient balances. In soils, the affinity of glyphosate for cations can reduce availability of calcium, magnesium, manganese, copper, iron, nickel, and zinc either by direct chemical interactions or by negative effects on soil microbes involved in making these minerals available to plants. Glyphosate taken up by roots can also interfere with movement and availability of some of these minerals inside plant tissue (Cakmak et al., 2009). Glyphosate tends to accumulate in meristematic tissue and storage organs. No one knows how much of the glyphosate taken up by apple trees is transported to apple fruit, but it seems possible that glyphosate may influence apple fruit physiology either by partially blocking the shikimic acid pathway or by affecting nutrient balances within fruit.