Glyphosate Affects Roots

By: Bill Strautman, Saskatoon Newsroom

Drip rates of glyphosate can reduce root uptake of manganese to less than 20 percent, but have little effect on root uptake of iron and zinc, says an American crop scientist. 
Drip rates are 2.5 percent of the recommended herbicide rate. 

"But when you look at translocation from the root to the rest of the plant, you see for all three that the translocation mechanism is pretty much decimated, even with extremely low rates of residual glyphosate," Don Huber told Agri-Trend's recent Farm Forum. 

He said researchers have also identified specific enzymes that are inhibited by glyphosate, These enzymes are involved in root uptake of manganese and translocation of other micro-nutrients. 

If farmers are aware of the situation they can often offset some of these effects by increasing the availability of manganese. 

Huber said there's a lot of data showing glyphosate is quickly immobilized when sprayed (in the soil 

"That's true if you put it on the surface. But if you spray it on a weed or a Roundup Ready plant, it's distributed throughout the entire rhizosphere. Those roots are very leaky and you’ll get the same amount of glyphosate leaching out of a Roundup Ready crop into the rhizosphere as you get from a susceptible target weed."

Huber said when the Roundup Ready gene was inserted into crop plants, it allowed producers to put more glyphosate on more acres. 

"We see anywhere from a 10 to 50 percent reduction in manganese efficiency with the Roundup Ready gene present, compared with isogenic lines without it."

"Any manganese in the plant before the glyphosate application will be immobilized. On our low manganese soils, it takes eight to 10 days before the plant recovers. On better soils, it might take two or three days and then the plant is green again." 

Huber said farmers have a large window with plants like soybeans to recover the effect on manganese. 

"You’ve got about 20 days that we don't see any loss in yield (on soybeans) if we get the manganese levels up in that period of time. 

"Corn is a totally different picture. With corn you need to have full (manganese) sufficiency from the seedling stage or you'll have an irreversible yield loss." 

Huber said effects of glyphosate have been reported for years, including reduced manganese and iron uptake, immobilization of manganese, reduced nodulation and nitrogen fixation, increased drought stress and earlier maturity. Many of these effects can be reduced with additional manganese applications, he added.