Glyphosate now is so widely used on so many crops that the focus of research has become how to help growers get even more benefit and performance from it.
A recent advance in nutrient formulation technology is producing more plant weight and yield in glyphosate-tolerant crops by averting the herbicide’s chelating activity.
University research has shown that glyphosate molecularly combines with metals such as zinc and manganese, locking them up so they lose mobility and efficacy when applied to the crop.
Zinc is the cornerstone for leaf, root and vascular system development, while manganese is a key player in photosynthesis, nitrogen assimilation and other essential biochemical reactions within the plant.
To effectively provide these nutrients to glyphosate-tolerant crops, growers have had to wait eight or more days for the residual glyphosate in crop tissue to move out through root exudates, and then make another pass across the field with the nutrients.
In the new Sysstem-Ready formulation, zinc and manganese are linked to phosphite ions that resist glyphosate chelation, enabling rapid nutrient absorption and mobility within the crop plant.
This makes the nutrients available during peak demand, increases the flush of new roots and accelerates maturation to produce better yield.
Also, the phosphite formulations are not antagonistic to glyphosate, which typically loses some weed control activity when chelation has occurred in a tank mix with nutrients.
Don Huber, professor emeritus in the Botany and Plant Pathology Department of Purdue University, is one of several experts in plant physiology and metabolism who have studied how nutrients enter, translocate and act upon the plant, interact with one another and impact the surrounding soil rhizosphere. He has spent several years working on the problem of glyphosate immobilization of nutrients.
“Many growers have been hesitant to meet their crop’s manganese needs with a second trip across the field, so we began to look at tank mixes,” Huber said.
“But the trouble with micronutrients is that glyphosate is a chemical chelator, and you couldn’t get good weed control or nutrient movement with the combinations.
“Although we found that certain sources of manganese were less reactive so we could retain 90 percent weed control, the benefit from the manganese was greatly minimized because glyphosate still immobilized the manganese in the tank mix. The only option previously was to wait and make another pass with the nutrients.
“Work with glyphosate-tolerant corn and soybeans in Indiana showed that waiting eight or nine days for an application of manganese was adequate for development needs of the soybeans, but not for corn.
“With soybeans there is a larger window of forgiveness for manganese deficiency without impacting the final yield. But, for corn, wheat and cereals there is no window at all.
“Any lag in the period when the crop needs manganese, and you have reduced yield potential. It’s why you see the yellowing after an application of glyphosate.
“It has chelated and immobilized micronutrients in the crop tissues. For a while, the crop will be just sitting there in suspended animation from a development standpoint, which impacts yield.”
Wet, cool spring conditions limit nutrient availability for root growth. Zinc and phosphorus can be especially difficult for young plants to extract fast enough to provide optimum early season growth.
Other soil factors can limit zinc availability, making foliar early-season applications of zinc critically important.
The Sysstem-Ready phosphite ions give the zinc and manganese systemic movement through the plant and down into the roots to keep the plant physiology at optimal level.
“If the nutrients don’t reach into the roots because they’ve been immobilized, the crop is going to have difficulty fending off disease and will come up short in yield even though the vegetative tissues appear normal and functional,” Huber said.
“Adding micronutrients to the soil doesn’t always help because soil micro-organisms rapidly immobilize nutrients. That’s why it’s so important that these phosphite ions can provide high levels of mobility within the plant after a foliar application.”
“Sysstem-Ready formulation technology finally allows growers, consultants and ag retailers to beneficially add zinc and manganese to glyphosate without diminished activity by any of the compounds,” said Chapman Mayo, the president of Minneapolis- based Agro-K Corp., which developed the new phosphite-linked nutrient system.
“A one-pass nutrient plus glyphosate application also helps growers avoid unnecessary costs for energy, wear and tear on equipment, delays due to adverse weather and soil compaction.”
The benefit of adding the nutrients to glyphosate was demonstrated in 2008 trials in the Western Corn Belt conducted by Philip Westra, professor in the Department of Bioagricultural Sciences and Pest Management at Colorado State University, and by field agronomists of the J.R. Simplot Co., one of the Sysstem- Ready distributors.
Additional distribution is expected to be in place by the typical time for a first glyphosate application, said Agro-K National Sales Manager Ken Dart.
The CSU trials showed that with Sysstem-Ready added to the tank mix with glyphosate there was no statistically significant reduction in control of weeds such as green foxtail, pigweed, kochia and barnyard grass.
There was nearly twice as much total plant weight in sampled corn plants treated with the tank mix versus glyphosate alone. Westra attributed this added biomass to better plant development and vigor.
The average corn yield increase in four replicates in the Simplot trials was more than 11 bushels per acre with the tank mix treatment versus glyphosate alone.
The CSU corn replicates averaged 10 bushels per acre more with the tank mix. If the glyphosate was applied alone, followed by Sysstem-Ready 10 days later, the yield differential was more than 15 bushels per acre versus glyphosate without the nutrients in the tank.
The CSU soybean trials showed a 7.4-bushels-per-acre improvement with the tank mix. When Sysstem-Ready was applied to soybeans 10 days after glyphosate alone, the yield increase was 5 bushels per acre.
Simplot’s trials with the new glyphosate tolerant sugar beets resulted in a yield increase of 4.5 tons per acre.
“I was generally pleased with the nutrient system,” Westra said. “I thought the crop plants that received Sysstem- Ready with the glyphosate had more color and shine, better root systems and better overall vigor.
“They appeared healthier, and this may be due to the disease resistance that important nutrients like manganese provide. Crops in high alkaline and calcareous soils may be particularly responsive.”
Dart said Sysstem-Ready is a real problem-solver for growers who want to maximize production of glyphosate- tolerant crops, but that Sysstem-Ready can be an effective tool to maximize yields in conventional varieties and hybrids, as well.
“With Sysstem-Ready, zinc and manganese are rapidly transported to the developing roots and foliage when and where they are most needed during peak demand,” he said.
“We recommend applications at V-4 to V-6 in corn or R- 1 to R-3 in soybeans. With or without glyphosate, Sysstem- Ready effectively enhances plant development and yield potential.”
The Sysstem-Ready technology also is available in calcium, magnesium and potassium formulations. Each is compatible with the other.