Tests show dicamba’s vo­latil­ity

UA re­searchers say new­est her­bi­cides ca­pa­ble of drift­ing

Northwest Arkansas Democrat-Gazette - - BUSINESS & FARM - STEPHEN STEED

The new­est dicamba her­bi­cides on the mar­ket — ap­proved by fed­eral reg­u­la­tors less than a year ago — are volatile, but less volatile than the older for­mu­la­tions that have al­ways been il­le­gal for in-crop use, ac­cord­ing to re­cent tests by sci­en­tists with the Univer­sity of Arkansas Agri­cul­ture Di­vi­sion.

A farmer can abide by all the reg­u­la­tions and spray the her­bi­cide cor­rectly and still have the her­bi­cide move off tar­get dur­ing cer­tain weather con­di­tions at least 36 hours af­ter ap­pli­ca­tion, the UA sci­en­tists told about 150 farm­ers, in­dus­try rep­re­sen­ta­tives and oth­ers Tues­day at the an­nual “field day” at the UA’s North­east Re­search and Ex­ten­sion Cen­ter in Keiser, about 50 miles east of Jonesboro.

“Lower vo­latil­ity doesn’t mean no vo­latil­ity,” Tom Bar­ber, a UA weed sci­en­tist, said, re­fer­ring to cer­tain cli­mate con­di­tions when the her­bi­cide, many hours af­ter ap­pli­ca­tion, can lift off tar­geted plants as ei­ther a va­por or liq­uid and move miles away to sus­cep­ti­ble crops and other veg­e­ta­tion.

The state Plant Board, a di­vi­sion of the Arkansas De­part­ment of Agri­cul­ture, has re­ceived nearly 900 com­plaints of dam­age to hun­dreds of thou­sands of acres of soy­beans, peanuts, pro­duce and or­na­men­tal shrubs and bushes.

The flood of com­plaints be­gan in early June, prompt­ing the state on July 11 to im­ple­ment a 120-day emer­gency ban on the sale and use of all dicamba prod­ucts.

In field tests this sum­mer, UA weed sci­en­tists stud­ied the three new­est dicamba her­bi­cides on the mar­ket — Mon­santo’s Xtendi­max with Va­porGrip, BASF’s En­ge­nia, and DuPont’s FeXa­pan, all touted by their man­u­fac­tur­ers to be less volatile and less sub­ject to drift. The sci­en­tists also stud­ied older for­mu­la­tions such as Clar­ity and Ban­vel.

Arkansas reg­u­la­tors re­ceived about three dozen com­plaints of dicamba dam­age a year ago, when there was no dicamba her­bi­cide on the mar­ket that was le­gal for in-crop use. Mon­santo in­tro­duced the new seeds be­fore the fed-

● eral En­vi­ron­men­tal Pro­tec­tion Agency ap­proved any of the three her­bi­cides now touted by Mon­santo, BASF and DuPont, and farm­ers used the older, il­le­gal for­mu­la­tions.

Bar­ber told vis­i­tors at the UA’s field day that the prob­lem is big­ger this year sim­ply be­cause “we have more crops that are dicamba tol­er­ant, and so we have a lot more use” of the dicamba her­bi­cides.

The Keiser ex­per­i­ment farm was among the early ca­su­al­ties. Farm man­agers there in early July had to plow up about 100 acres of soy­beans that had been the site of an ear­lier test plot for the Xtendi­max prod­uct.


The UA sci­en­tists have been joined by col­leagues from uni­ver­si­ties across the South and Mid­west to say that prob­lems are in the prod­ucts them­selves, not just in how they are sprayed, tak­ing is­sue with com­ments by rep­re­sen­ta­tives of the her­bi­cide-mak­ers putting most of the blame on er­rors by ap­pli­ca­tors or by farm­ers us­ing il­le­gal dicamba prod­ucts.

At least 17 states have re­ported dam­age af­fect­ing sev­eral mil­lion acres. Yield loss in soy­beans won’t be known un­til har­vest.

Mon­santo has said its dicamba-tol­er­ant soy­beans are on 1.5 mil­lion of Arkansas’ 3 mil­lion acres of soy­beans this year. About 300,000 of Arkansas’ 500,000 cot­ton acres are planted in Mon­santo’s dicamba-tol­er­ant cot­ton seed. The re­main­ing acres, es­pe­cially soy­beans, are highly sus­cep­ti­ble to dicamba.

His­tor­i­cally, Bar­ber said, dicamba has been used on corn and dur­ing “burn down” of a field, just prior to plant­ing.

“When you’re spray­ing dicamba for corn or burn down, it’s ear­lier in the sea­son and it’s cooler,” Bar­ber said. In the sum­mer, as heat and hu­mid­ity rise, the vo­latil­ity of dicamba also rises, he said.

Mis­souri banned the sale and use of dicamba the same day as Arkansas, but only for a week, be­fore set­ting new reg­u­la­tions on how to use the chem­i­cal, such as lim­it­ing spray­ing from 9 a.m. to 3 p.m. De­spite the new rules, com­plaints in Mis­souri con­tinue to be filed, amount­ing now to at least 240.

The EPA a year ago gave the new dicamba her­bi­cides a fed­eral la­bel for two years, com­pared with the usual five, and said re­cently it is study­ing the her­bi­cide again be­cause of com­plaints. While the EPA is­sues fed­eral reg­is­tra­tion, states can set other re­stric­tions, in­clud­ing a ban.

Of the three new dicamba her­bi­cides, the Plant Board al­lowed only BASF’s En­ge­nia in the Arkansas mar­ket. UA sci­en­tists had deemed it, based on re­sults from test plots, to be less volatile and a po­ten­tial tool for farm­ers in their fight against pig­weed and other weeds now re­sis­tant to other her­bi­cides.

Arkansas reg­u­la­tors re­fused to al­low the use of Mon­santo’s Xtendi­max for­mula in the state be­cause the com­pany per­mit­ted UA sci­en­tists to study the chem­i­cal only for its ef­fec­tive­ness against weeds, not for its vo­latil­ity. The EPA’s ap­proval of DuPont’s FeXa­pan came at the start of this year’s grow­ing sea­son in Arkansas — too late for the Plant Board to act on that la­bel.


For its ex­am­i­na­tions of the her­bi­cides, the UA sci­en­tists set up weather sta­tions across test fields to mea­sure soil and air tem­per­a­tures, wind di­rec­tion and wind speed, and ex­per­i­mented with var­i­ous noz­zles to limit the size of droplets and the height of boom sprayers. Smaller droplets and low boom heights are ways to limit off-tar­get move­ment.

“At the end of the day, it goes back to the dicamba her­bi­cide it­self and to soy­beans’ ex­treme sen­si­tiv­ity to dicamba, the wide­spread use of dicamba, and the di­ver­sity of other crops that are sen­si­tive to dicamba,” Bar­ber told vis­i­tors who trudged through Mis­sis­sippi County gumbo clay to his sta­tion in the mid­dle of a soy­bean field.

A farmer can abide by all the reg­u­la­tions, Bar­ber said, “but I can tell you, none of that mat­ters if [the her­bi­cide] is volatile. What if I do the best spray­ing job pos­si­ble and it still walks off the field?”

A field test by Ja­son Nor­swor­thy, an­other UA weed sci­en­tist, said amount of dam­age to crop is re­flected in the vol­ume of dicamba sprayed. In one test plot, Nor­swor­thy took soy­bean plants di­rectly from a green­house to a field where dicamba had been sprayed 30 min­utes ear­lier, 24 hours ear­lier, and 36 hours ear­lier.

Plants showed dam­age in all three time frames, Nor­swor­thy said.

An­other ex­per­i­ment in­volved cov­er­ing plants with 5-gal­lon buck­ets and then spray­ing the field.

“Should I get drift or any dam­age on a plant sit­ting un­der a bucket?” Nor­swor­thy asked a group at his sta­tion. “I shouldn’t.”

Plants un­cov­ered 30 min­utes later had symp­toms of ex­po­sure to dicamba, as did plants that were un­cov­ered as long as 36 hours af­ter spray­ing, show­ing that the her­bi­cide was volatiliz­ing from the soil, Nor­swor­thy said.

Other tests showed dam­age to fields more than 220 feet away — twice the EPA buf­fer — even when ap­pli­ca­tions of Xtendi­max and En­ge­nia were done cor­rectly, Nor­swor­thy said. “Whether it was En­ge­nia or Xtendi­max, there is con­sid­er­able dam­age an hour af­ter ap­pli­ca­tion, even more than 20 hours af­ter ap­pli­ca­tion,” he said.

“The more you spray, the more you load the at­mos­phere, and the more it moves,” Nor­swor­thy said of the dif­fer­ences be­tween run­ning small test plots for a prod­uct and spray­ing a prod­uct over mil­lions of acres.

The UA sci­en­tists said dicamba dam­age will re­sult in more than just yield loss at har­vest. Dam­age also will show up in seed pro­duc­tion, lim­it­ing avail­abil­ity next plant­ing sea­son of soy­beans that are not dicamba tol­er­ant.

Arkansas Demo­crat-Gazette/STEPHEN STEED

Farm­ers and agri­cul­ture in­dus­try work­ers walk through a Mis­sis­sippi County soy­bean field Tues­day at the Univer­sity of Arkansas’ North­east Re­search and Ex­ten­sion Cen­ter in Keiser dur­ing UA’s an­nual “field day.”

Arkansas Demo­crat-Gazette/STEPHEN STEED

Ja­son Nor­swor­thy, a Univer­sity of Arkansas weed sci­en­tist, talked to field day vis­i­tors in Keiser about the ten­dency of the her­bi­cide dicamba to drift from fields.

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