Soybean Tolerance to Drift Rates of Roundup Ultra or Liberty, 1996.

The non-selective postemergence herbicides Roundup Ultra and Liberty have been safely applied to transgenic soybeans, however, there is a possibility of drift to non- transgenic crops in adjacent fields. This study was designed to evaluate the injury caused by a range of rates of these herbicides. The herbicides were applied at the third vegetative stage and the first reproductive stage of actively growing non- transgenic soybeans. Soybeans sprayed at the V3 stage (5 to 7 inches) were injured by both Roundup and Liberty, but recovered if the initial injury was 20% or less. Soybeans sprayed at the R1 stage (10 to 14 inches) also were injured by both herbicides, and recovery was less likely when injury was caused by Roundup Ultra than when injury was caused by Liberty. Yield in the nontreated plots was 46 bu/A. Yield in the treated plots ranged from 12 to 52 bu/A. All plots were kept weed-free all season.

I. INTRODUCTION:

Transgenic crops are the result of gene transfer, a new plant breeding technique which has allowed development of crop varieties which are tolerant to a particular non-selective postemergence herbicide at rates which will control weeds. Roundup Ready soybeans were available in 1996 and Liberty Link soybeans are expected to be available in 1998. Accidental application of Roundup Ultra or Liberty to non-tolerant soybeans could occur as a result of drift when tolerant and non-tolerant soybeans are planted in adjacent fields. Unintentional spraying of the wrong field is a possibility since an applicator cannot, by sight alone, distinguish tolerant from non-tolerant soybeans the way one can easily distinguish corn from soybeans, and thus avoid the application of corn herbicides to soybeans. This study evaluates Roundup Ultra rates of 0.075 to 1.5 pt/A and Liberty rates of 0.086 to 1.72 pt/A applied at either the V3 or R1 stage of non-tolerant soybeans.

II. HERBICIDES EVALUATED:

         Liberty 1.67 EC
         Roundup Ultra 4 SL  

III. RATES EVALUATED:

	Roundup		Liberty
% of highest rate	lb ai/A	pt/A	lb ai/A	pt/A
5	0.0375	0.075	0.018	0.086
10	0.075	0.150	0.036	0.172
20	0.15	0.30	0.072	0.345
30	0.225	0.45	0.108	0.517
40	0.30	0.60	0.14	0.67
50	0.375	0.75	0.18	0.86
100	0.75	1.50	0.36	1.72

 IV. ABBREVIATIONS USED:

        GLXMA: soybean
        GPA: gallons per acre
        LVS: leaves
        RCB: randomized complete block
        R1: soybean reproductive stage 1
        V3: soybean vegetative stage 3
                                                       

V. RESULTS AND DISCUSSION:

V3 Application:

At one week after the V3 application, both Roundup Ultra and Liberty caused discoloration and necrosis of the exposed soybean foliage resulting in almost complete burn at the highest rates. At two weeks after the V3 application, Roundup Ultra at 0.45 to 1.50 pt/A caused 21 to 79% height reduction and Liberty at 0.086 to 1.72 pt/A caused 14 to 94% height reduction. By four weeks after the V3 application, all the soybeans which had height reduction of 20% or less at 2 weeks after the V3 application had nearly fully recovered. Recovery of Roundup Ultra-injured soybeans was slower than recovery of Liberty-injured soybeans. This recovery is reflected in the height and plants per acre at the end of the season, and in the yield.

R1 Application:

At one week after the R1 application both Roundup Ultra and Liberty caused discoloration and necrosis of the exposed soybean foliage, however, only the highest rate of Roundup Ultra caused a significant reduction in soybean population. At two weeks after the R1 application, Roundup Ultra at 0.45 to 1.50 pt/A caused 13 to 87% height reduction, and Liberty at 0.67 to 1.72 pt/A caused 10 to 32% height reduction. Liberty at 0.18 lb/A or less caused less than 10% height reduction at any time, but caused as much as 17% discoloration (yellowing) at 1 week after application. The Liberty-injured soybeans nearly fully recovered by four weeks after treatment, except with the highest rate (1.72 pt/A) which was reflected in the yield. Roundup Ultra-injured soybeans were less likely to recover and often yielded lower than the nontreated.

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Corn Tolerance to Drift Rates of Roundup Ultra or Liberty, 1996.

The non-selective postemergence herbicide Roundup Ultra has been safely applied to transgenic soybeans and the non-selective postemergence herbicide Liberty has been safely applied to transgenic soybeans and corn. When farmers apply Roundup Ultra or Liberty to transgenic crops, there is a possibility for drift to non-transgenic crops in adjacent fields. This study was designed to evaluate the injury to corn caused by a range of rates of these herbicides. The herbicides were applied at the third and sixth vegetative stage of actively growing corn. Corn sprayed at either the V3 stage (6 to 10 inches) or the V6 stage (12 to 20 inches) was injured by both Roundup Ultra and Liberty. Corn injured by Roundup Ultra was less likely to recover than corn injured by Liberty. Corn sprayed at V3 was more likely to recover than corn sprayed at V6. Yield in the nontreated plots was 169 bu/A. Yield in the treated plots ranged from 0 to 190 bu/A. All plots were kept weed-free all season.

I. INTRODUCTION:

Transgenic crops are the result of gene transfer, a new plant breeding technique, which has allowed development of crop varieties which are tolerant to a particular non-selective postemergence herbicide at rates which will control weeds. Liberty Link corn should be available in about 1997. Accidental application of Roundup Ultra or Liberty to non-tolerant crops could occur as a result of drift when tolerant crops and non-tolerant crops are planted in adjacent fields. This study evaluated Roundup Ultra rates of 0.038 to 0.75 pt/A and Liberty rates of 0.043 to 0.86 pt/A applied at either the V3 or V6 stage of non-tolerant corn.

II. HERBICIDES EVALUATED:

        Liberty 1.67 EC
        Roundup Ultra 4 SL

III. RATES EVALUATED:

                                                 Roundup Ultra                    

      Liberty           
         % of highest rate           lb ai/A     pt/A      lb ai/A          pt/A        

           5                         0.0188           0.038       0.009          0.043
          10                         0.0375           0.075       0.018          0.086
          20                         0.075            0.150       0.036          0.172
          40                         0.150            0.30        0.072          0.345
          60                         0.225            0.45        0.108          0.517
          80                         0.30             0.60        0.140          0.67
         100                         0.375            0.75        0.180          0.86

IV. ABBREVIATIONS USED:

         GPA: gallons per acre
         LVS: leaves
         RCB: randomized complete block
         V3: 3rd corn leaf (w/collar)
         V6: 6th corn leaf (w/collar)
         ZEAMX: corn

V. RESULTS AND DISCUSSION:

V3 Application:

At one week after the V3 application, both Roundup Ultra and Liberty caused discoloration of the exposed foliage. Discoloration of corn caused by Roundup Ultra was exhibited on both the exposed foliage and the new growth. Liberty caused discoloration and necrosis of the exposed corn foliage, but the new growth was not affected. At two weeks after the V3 application, Roundup Ultra at 0.30 to 0.75 pt/A caused 80 to 99% height reduction, as opposed to Liberty at 0.345 to 0.86 pt/A which caused 1 to 11% height reduction. At four weeks after the V3 application, corn injured by Roundup Ultra had recovered very little. Corn height and population at the end of the season also were reduced as was yield. Corn injured with Liberty began to regrow by four weeks after treatment, and height and population at the end of the season were not significantly affected, nor was yield except in one instance.

V6 Application:

At 1 week after the V6 application, discoloration and necrosis of the corn foliage exposed to either Roundup Ultra or Liberty was less than 10% in most cases. Corn discolored by Roundup Ultra exhibited greater discoloration and necrosis at 2 weeks after the V6 application than at 1 week after the V6 application. Corn foliage discolored by Liberty remained discolored, but new growth was not discolored. At 2 weeks after the V6 application, Roundup Ultra at 0.30 to 0.75 pt/A caused 10 to 68% height reduction, while Liberty at 0.345 to 0.86 pt/A caused only 1 to 3% height reduction. Corn injured by Roundup Ultra as a result of the V6 application recovered slowly when greater than 10% of the 1.5 pt/A rate was applied, indicating that the corn was very sensitive to Roundup. Roundup Ultra injury was leaf rolling and height reduction followed by necrosis. Liberty injury was height reduction, discoloration (yellowing), and delayed maturity.

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Corn Tolerance to Simulated Drift Rates of Gramoxone Extra, 1996.

The nonselective postemergence herbicide Gramoxome Extra has been safely applied prior to crop emergence and has been a cost effective alternative for burndown in no- till crop production. With the increased interest in no-till practices, the possibility for Gramoxone Extra drift to emerged crops also increases. This study was conducted to evaluate the injury caused by a range of rates of Gramoxone Extra. Gramoxone Extra was applied at the third and sixth vegetative stage of actively growing corn. Corn sprayed at the V3 stage (6-10 inches) was badly 'burned' at 1 week after treatment but recovered well with less than 10% height reduction by the end of the season. Corn sprayed at V6 (14 to 22 inches) was not as badly 'burned' initially, but height reduction was evident even four weeks after treatment and yield often was reduced. Yield in the nontreated plots was 129 bu/A. Yield in the treated plots ranged from 57 to 131 bu/A, depending primarily on corn stage at application, but also on the Gramoxone Extra rate applied.

I. INTRODUCTION:

Gramoxone Extra controls emerged weeds by desiccation of the foliage. The desiccation is rapid (within 2-3 days) and often results in death of the plant, especially newly emerged annual weeds. Gramoxone Extra is applied prior to crop emergence to avoid crop injury; however, accidental spray drift to adjacent emerged crops remains a possibility. This study was conducted to evaluate Gramoxone Extra rates of 0.20 to 2.0 pt/A applied to either the V3 or V6 stage of corn in order to simulate Gramoxone Extra drift.

II. HERBICIDE EVALUATED:

         Gramoxone Extra 2.5 S

                                                    Gramoxone Extra        
         % of highest rate            lb ai/A          pt/A
         10                           0.063                  0.20
         20                           0.125                  0.40
         30                           0.188                  0.60
         40                           0.25                   0.80
         50                           0.313                  1.0
         100                          0.625                  2.0

IV. ABBREVIATIONS USED:

         GPA: gallons per acre
         LVS: leaves
         RCB: randomized complete block
         V3: 3rd corn leaf stage (w/ collar)
         V6: 6th corn leaf stage (w/ collar)
         ZEAMX: corn

V3 Application:

At one week after the V3 application, the exposed corn foliage was completely necrotic (burned) regardless of Gramoxone Extra rate. Yet because the growing point of the corn was not injured, new growth was already evident and the corn was on its way to complete recovery with no significant yield reduction. New growth on corn plants sprayed with 1.0 or 2.0 pt/A was lighter green and plants were slightly shorter than the nontreated, yet yield was not significantly lower than the nontreated.

V6 Application:

At one week after the V6 application, 'burn' of the exposed corn foliage ranged from 23 to 79%. By two weeks after the V6 application, corn plants began to recover except at the highest (2.0 pt) rate. Height reduction was evident even at eight weeks after treatment and yield was significantly reduced except at the lowest rates. The average yield for corn sprayed at V6 was 95 bu/A compared to 123 bu/A when the corn was sprayed at V3 and 129 bu/A in the nontreated.



The Site Description Sheet lists pertinent information such as planting and application dates, weed species present, and soil characteristics.

Treatment Lists and Data Tables will require the Adobe Acrobat and WebLink (TM) plug-ins.

The best way to look at our Treatment Lists and Data Tables is to print them using your laser printer.

If you are unable to access our Data Tables using Adobe Acrobat and your laser printer .

Go to the Weed Control Progress Reports Homepage .

Go to the Plant and Soil Science Department Homepage .

Go to the Southern Illinois University at Carbondale Homepage .