Weed control in no-till soybeans with Axiom combinations was compared to that with commercially available products. Axiom combinations were among the most effective in controlling yellow nutsedge. Control of broadleaf weeds was highly dependent on the weed species and specific herbicide combination. Little or no soybean injury was observed. Soybean yield ranged from only 3 bu/A in the nontreated plots to 25 bu/A.

I. INTRODUCTION:

Axiom is an experimental herbicide related to Lasso, Dual, etc. that is being developed for weed control in corn and soybeans. This study was designed to evaluate weed control with Axiom combinations in no-till soybeans compared to competitive products.

II. HERBICIDES EVALUATED:

        Axiom 68 WG                                    Pursuit 2 AS
        Canopy 75 WG                                   Scepter 1.5 AS
        Dual II 7.8 EC                                 Sencor 75 WG
        Gramoxone Extra 2.5 S                          Squadron 2.33 EC
        Prowl 3.3 EC                                   Turbo 8 EC

        ABONOR: above normal                           GLXMA: soybeans
        ALLVI: wild garlic                             LAMAM: henbit
        AMATA: common waterhemp                        LVS: leaves
        AMBEL: common ragweed                          POLPY: Pa. smartweed
        BROSOI: broadcast soil                         RANAB: smallflower buttercup
        CERVU: mouseear chickweed                      SETFA: giant foxtail
        CHEAL: common lambsquarters                    W: weeds
        CYPES: yellow nutsedge                         ZEAMX: corn
        EPP: early preplant

IV. RESULTS AND DISCUSSION:

Weed control ratings and soybean injury and yield data are presented in the attached table. There was no change in weed control following the July 5 rating. Several weed species listed on the Site Description Sheet were not evaluated because of lack of uniformity throughout the plot area. The EPP14 application was made on April 27 with a anticipated planting date of May 10. However, rainfall delayed planting until May 23, thus the EPP14 herbicides were actually applied almost four weeks prior to planting.

Weed Control: This was one of the few studies since inception of this research center where no grass species were present. Yellow nutsedge had not emerged by May 23, the date of the first rating. Axiom plus Canopy or Scepter controlled nutsedge 92 and 95%, respectively, which was equal to or greater than other products. All treatments controlled redroot pigweed completely, which was rated only on May 23. In contrast, control of common waterhemp was poor with most treatments. All herbicides controlled common lambsquarters completely in this study. Initial control of common ragweed (on May 23) was complete with all herbicides. However, continued emergence throughout June resulted in a decrease in control by July 5 with most herbicides. Treatments that controlled ragweed the most completely were those that included Canopy.

Soybean Injury and Yield: Little or no soybean injury was observed in this study. Yield ranged from 3 bu/A in the nontreated plots to only 25 bu/A. The low yield was related to late planting, very low mid-season rainfall and incomplete control of one or more species in all treatments.

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Soybean No-till Early Preplant Weed Control with Authority Plus Classic, 1996.

Authority plus Classic applied early preplant (EPP) on April 27 controlled all weeds almost completely, even at rates lower than the anticipated label rate. Little or no soybean injury was observed with this combination. Soybean yield ranged from 7 bu/A in the nontreated plots to 52 bu/A.

I. INTRODUCTION:

Authority is an experimental 'broadleaf' herbicide that controls several weeds that are most difficult to control with currently available herbicides. However, several weed species are somewhat tolerant to Authority. This study was designed to evaluate weed control with Authority plus Classic applied EPP.

II. HERBICIDES EVALUATED:

        Assure II 0.88 EC
        Authority 75 WG
        Canopy 75 WG
        Classic 25 WG
        Lexone 75 WG
        Roundup Ultra 4 S
        Weedone 638 2.83 EC

III. ABBREVIATIONS USED:

        ABONOR: above normal                           CYPES: yellow nutsedge
        AFGR: after first grass rating                 EPP: early preplant
        ALLVI: wild garlic                             GLXMA: soybeans
        AMATA: common waterhemp                        LAMAM: henbit
        AMBEL: common ragweed                          POLPY: Pa. smartweed
        BROSOI: broadcast soil                         RANAB: smallflower buttercup
        CARPA: smallflowered bittercress               SETFA: giant foxtail
        CERVU: mouseear chickweed                      STEME: common chickweed
        CHEAL: common lambsquarters                    ZEAMX: corn

IV. RESULTS AND DISCUSSION:

Weed control ratings and soybean injury and yield data are presented in the attached table. There was no change in weed control following the July 22 rating. Several weed species listed on the Site Description Sheet were not rated because of lack of uniformity over the plot area. The EPP15 herbicide application was made on April 27 with an anticipated planting on May 10. However, frequent rainfall delayed planting until May 23. Thus, the EPP herbicides had been applied for about four weeks prior to planting, rather than the desired 15 days.

Weed Control: Authority plus Classic applied EPP on April 27 controlled all weeds almost completely in most instances, regardless of the rate applied. Even giant foxtail control was 98 to 99% (on July 1) with this combination, prior to the application of Assure II. This is a higher level of control of giant foxtail than has been observed previously with these herbicides. Control of yellow nutsedge, common waterhemp, common ragweed, and Pa. smartweed also was essential complete with the Authority plus Classic applied EPP. Similar levels of control were obtained with most of the other treatments.

Soybean Injury and Yield: Little or no soybean injury was observed in this study with the Authority plus Classic combinations. The only treatment that caused significant injury initially was Canopy applied preemergence. Soybean yield ranged from 7 bu/A in the nontreated plots to 52 bu/A. The highest yields were associated with the most complete weed control in most instances.

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Authority combinations applied EPP 30, EPP 7, and PRE were evaluated in this no-till study. All treatments applied EPP 30 controlled winter annual weeds completely. Also, these treatments controlled all summer annual weeds almost completely in all but one instance. Little or no soybean injury was observed in this study. Soybean yield ranged from 6 bu/A in the nontreated plots to 46 bu/A. Yield level observed was related to overall level of weed control obtained and the duration of competition.

I. Introduction:

Authority is an experimental soil-applied herbicide being developed for broadleaf weed control in soybeans. It is especially effective in controlling several weeds most difficult to control with current commercially available herbicides. However, it does not adequately control grasses or several broadleaf weeds. This study was designed to evaluate weed control with several companion herbicides.

II. HERBICIDES EVALUATED:

        Assure II 0.88 EC
        Authority 75 WG
        Command 3 ME
        Dual II 7.8 EC
        F6025 25 WG (Premix of Authority plus Classic)
        Roundup Ultra 4 S
        Sencor 75 WG

III. ABBREVIATIONS USED:

        ABNOR: above normal                            GLXMA: soybeans
        ABUTH: velvetleaf                              HORPU: little barley
        ALLVI: wild garlic                             LAMAM: henbit
        AMBEL: common ragweed                          LVS: leaves
        BROFOL: broadcast foliage                      MYSMI: mousetail
        BROSOI: broadcast soil                         PANDI: fall panicum
        BROTE: downy brome                             POLPY: Pa. smartweed
        CAPBP: shepherdþs-purse                        RANAB: smallflower buttercup
        CERVU: mouseear chickweed                      SETFA: giant foxtail
        CHEAL: common lambsquarters                    STEME: common chickweed
        CYPES: yellow nutsedge                         ZEAMX: corn
        EPP: early preplant                            
        G: grass

IV. RESULTS AND DISCUSSION

Weed control ratings and soybean injury and yield data are presented in the attached table. There was no change in weed control following the July 11 rating. Several weed species listed on the Site Description Sheet were not rated because of lack of uniformity in the study area. The EPP 30 applications were  made on April 10 with an anticipated planting of May 10. However, frequent rainfall delayed planting until May 31, thus there was a 50 day interval between EPP 30 herbicide application and planting. The EPP 7 application was made on May 23 with the scheduled seven day delay between EPP 7 application and planting.

Weed Control:

All treatments that were applied EPP 30 controlled the winter annual weeds common chickweed, henbit, and little barley completely. In contrast, when the same or similar treatments were applied EPP 7, no control was observed. The primary reason for the lack of control with the EPP 7 treatments was that these treatments were not applied until May 23. By this date, the winter annual weeds were in the reproductive stage, thus were affected very little by either the Roundup Ultra or the residual herbicides. Excellent control of the summer annual weeds giant foxtail, yellow nutsedge, common lambsquarters, common ragweed, and Pa. smartweed was obtained with almost all herbicide combinations, regardless of application timing.

Soybean Injury and Yield:

Little or no soybean injury was observed with the herbicides evaluated. Where injury occurred, recovery was rapid and complete. Soybean yield ranged from 6 bu/A in the nontreated plots to 46 bu/A. Differences in yield between plots treated with herbicides were related to overall level of weed control obtained and duration of competition between the soybeans and weeds.

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Control of winter and summer annual weeds was highly related to the herbicide and rate used and the application timing. Little or no soybean injury was observed with most treatments. Soybean yield ranged from 3 to 40 bu/A and was closely related to level of control of winter and summer annual weeds.

I. INTRODUCTION:

This study was designed to evaluate several herbicides and combinations applied early preplant (EPP) and preemergence for weed control in no-till soybeans.

II. HERBICIDES EVALUATED:

        BAS 514 34H 75 WG
        Broadstrike/Dual 7.67 EC
        FirstRate 84 WG
        Galaxy 3.67 EC
        Prowl 3.3 EC
        Roundup Ultra 4 S
        Scepter 70 WG
        Sencor 75 WG
        Squadron 2.33 EC

III. ABBREVIATIONS USED:

        ABNOR: above normal                            GLXMA: soybeans
        ABUTH: velvetleaf                              HORPU: little barley
        ALLVI: wild garlic                             LAMAM: henbit
        AMBEL: common ragweed                          LVS: leaves
        BROTE: downy brome                             MYSMI: mousetail
        CAPBP: shepherd's purse                        PANDI: fall panicum
        CERVI: mouseear chickweed                      POLPY: Pa. smartweed
        CHEAL: common lambsquarters                    RANAB: smallflower buttercup
        CYPES: yellow nutsedge                         STEME: common chickweed
        DESPI: pinnate tansy mustard                   W: weeds
        EPP: early preplant                            ZEAMX: corn

IV. RESULTS AND DISCUSSION:

Weed control ratings and soybean injury and yield data are presented in the attached table. There was no change in weed control following the May 10 rating for winter annual weeds and following the July 5 rating for summer annual weeds. Several weed species listed on the Site Description Sheet were not rated because of lack of uniformity in the study area. The EPP 30 herbicides were applied on April 10 with an anticipated planting date of May 10. However, frequent rainfall delayed planting until May 23, 42 days following the EPP 30 application. Further, the EPP 15 application was made on April 25, again with an anticipated planting date of May 10. Again, because frequent rainfall delayed planting until May 23, there was a time interval of 29 days instead of the desired 15 days between herbicide application and planting.

Weed Control:

BAS 514 34H controlled common chickweed and henbit completely at all rates evaluated. Control of the winter annual weeds smallflower buttercup and little barley was more rate dependent with BAS 514 34H when applied on April 10. When Sencor was added to BAS 514 34H, complete control of all winter annual weeds was observed. BAS 514 34H applied PRE on May 24 did not control any winter annual weeds. This may have been related to the application coinciding closely with approaching maturity of these weeds. Roundup Ultra plus Broadstrike/Dual without or with Galaxy or Scepter controlled all winter annual weeds completely. Herbicides applied EPP 15 or PRE did not control the winter annual weeds, again likely because of approaching maturity of these weeds. BAS 514 34H alone or with Sencor controlled yellow nutsedge less than 60%. Other herbicides controlled nutsedge somewhat better, but not acceptably in most instances. Control of common lambsquarters with BAS 514 34H applied EPP 30 was 90% or greater compared to no control with PRE applications, regardless of rate. Control of other summer annual weeds was highly related to the herbicide, rate, and application timing. However, very good to excellent control of common ragweed and Pa. smartweed was observed with most treatments.

Soybean Injury and Yield:

Little or no soybean injury was observed with most herbicide treatments. Soybean yield ranged from 3 to 40 bu/A. Yield in plots treated only with BAS 514 34H was no greater than in nontreated plots because of poor control of several weed species. Yield in plots treated with other herbicides ranged from 32 to 40 bu/A.

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Excellent control of common ragweed and Pa. smartweed was obtained with combinations of Gramoxone Extra plus Sencor, Canopy, or Authority, plus Twister. Basagran controlled the yellow nutsedge almost completely in most instances. Initially, the Basagran caused 25% soybean injury but recovery was rapid and complete. Soybean yield ranged from 6 bu/A in the no herbicide plots to as high as 50 bu/A.

I. INTRODUCTION:

This no-till study was designed to evaluate control of emerged weeds with Gramoxone Extra plus companion herbicides that also have foliar activity. Further, evaluations were made of the efficacy of Twister applied POST for control of weeds emerging after planting.

II. HERBICIDES EVALUATED:

        Authority 75 WG
        Basagran 4 S
        Canopy 75 WG
        Gramoxone Extra 2.5 S
        Roundup Ultra 4 S
        Sencor 75 WG
        Touchdown 6 S
        Twister 1.82 ME
        Weedone 638 2.8 EC

III. ABBREVIATIONS USED:

        ABONOR: above normal                           LVS: leaves
        AMBEL: common ragweed                          POLPY: Pa. smartweed
        CHEAL: common lambsquarters                    SETFA: giant foxtail
        CYPES: yellow nutsedge                         W: weeds
        GLXMA: soybeans                                ZEAMX: corn

IV. RESULTS AND DISCUSSION:

Weed control ratings and soybean injury and yield data are presented in the attached table. There was no change in weed control following the July 19 rating. Giant foxtail and common lambsquarters were not rated because they were not present uniformly in the study area. The below comments refer primarily to the July 19 rating.

Weed Control: All treatments except one controlled yellow nutsedge 95% or greater on July 17. This level of control reflects the application of Basagran on June 28 with the Twister, specifically to control the yellow nutsedge. All herbicide combinations controlled common ragweed completely. Control of Pa. smartweed was most complete with combinations that included Sencor, Canopy, or Authority at 5.33 oz/A or greater.

Soybean Injury and Yield: The preemergence herbicide caused no soybean injury. The 25% injury noted on July 5 was caused by the Basagran applied June 28, but complete recovery of soybeans occurred by July 19. Soybean yield ranged from 6 bu/A in the nontreated plots to 50 bu/A. There was no difference in yield between most treatments that had herbicides applied to them.

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RATES MENTIONED IN THIS REPORT ARE ACTIVE INGREDIENT RATES.

Weed control in no-till soybean using only Roundup Ultra was evaluated. Winter annual weed infestation was light. Therefore, winter annual weed control with early preplant applications of Roundup Ultra were not evaluated. Roundup Ultra at 0.75 lb ai/A applied preemergence and four weeks after planting (WAP) controlled 99% of the wild garlic, giant foxtail, yellow nutsedge, common waterhemp, common lambsquarters, common ragweed, and Pennsylvania smartweed. No application of Roundup Ultra was needed after the four WAP application. Soybean yield ranged from 10 to 52 bu/A.

I. INTRODUCTION:

The development of Roundup Ready soybean facilitates the use of Roundup Ultra for weed control in soybean. In addition, Roundup Ultra is the only current postemergence herbicide in soybean that has the potential to control both perennial and annual grass and broadleaf weeds. Therefore, this study was initiated to evaluate weed control in no-till soybean using only Roundup Ultra.

II. HERBICIDES EVALUATED:

        Roundup Ultra 4 S

III. ABBREVIATIONS USED:

        ALLVI: wild garlic                             GLXMA: soybean
        AMATA: common waterhemp                        PANDI: fall panicum
        AMBEL: common ragweed                          PRE: preemergence
        CHEAL: common lambsquarters                    POLPY: Pennsylvania smartweed
        CYPES: yellow nutsedge                         SETFA: giant foxtail
        EPP: early preplant                            WAP: weeks after planting

IV. RESULTS AND DISCUSSION:

Weed control data are presented in the attached tables. There was no change in weed control following the last rating noted in the attached tables. Weeds that are listed in the 'Site Description Sheet' that were not distributed uniformly throughout the study area were not rated. All comments referring to weed control are in reference to the last rating unless noted otherwise. Winter annual weed control will not be discussed because of the extremely light infestation of winter annual weeds.

Giant Foxtail, Fall Panicum, Yellow Nutsedge, Common Waterhemp, Common Lambsquarters, Common Ragweed, and Pennsylvania Smartweed:

Roundup Ultra at 0.75 lb ai/A applied only preemergence provided poor season long control of these weeds. Roundup Ultra at 0.75 lb/A applied preemergence and 4 WAP controlled 98 to 100% of all weeds evaluated. A third application of Roundup Ultra was not required to obtain season long control of these weeds. The lack of later emerging weeds may be due to soybean planted in 15 inch rows.

Soybean Yield:

Soybean yield ranged from 10 to 52 bu/A. Yield tended to be greater with Roundup Ultra applied preemergence and four WAP regardless of an early preplant application.

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Authority alone applied preemergence caused severe injury (necrosis) to smallflower buttercup, common lambsquarters, and Pennsylvania smartweed and controlled 100% of these weeds. Authority alone also caused injury to common ragweed. However, Authority alone controlled only 17 to 33% of the common ragweed. FirstRate tank-mixed with Authority increased control of common ragweed with control ranging from 93 to 98%. Canopy also caused severe injury to smallflower buttercup, common lambsquarters, common ragweed, and Pennsylvania smartweed with control of these weeds ranging from 97 to 100%. Roundup Ultra plus Squadron controlled 97 to 100% of the same weeds. Authority caused no visible soybean injury. Soybean yield ranged from 1 to 33 bu/A.

I. INTRODUCTION:

Authority is an experimental broadleaf herbicide for soybean. It has residual soil activity and postemergence activity. Therefore, it may be used as a þburndownþ herbicide plus provide residual weed control in no-till soybean production. This study was designed to evaluate and compare no-till weed control with Authority combinations.

II. HERBICIDES EVALUATED:

        Assure II 0.88 EC                              FirstRate 84 WG
        Authority 75 DF                                Roundup Ultra 4 S
        Canopy 75 DF                                   Sencor 75 WG
        Classic 25 WG                                  Squadron 2.33 EC

III. ABBREVIATIONS USED:

        AMBEL: common ragweed                          PRE: preemergence
        ALLVI: wild garlic                             POLPY: Pennsylvania smartweed
        CHEAL: common lambsquarters                    RANAB: smallflower buttercup
        COC: crop oil concentrate                      SETFA: giant foxtail
        GLXMA: soybean                                 V4IN: three trifoliates if need

Weed control and soybean injury data are presented in the attached tables. There was no change in weed control following the last rating noted in the attached tables. Weeds that are listed in the 'Site Description Sheet' that were not distributed uniformly throughout the study area were not rated. All comments referring to weed control are in reference to the last rating unless noted otherwise.

Smallflower Buttercup:

All herbicides and combinations controlled 100% of the smallflower buttercup.

 Wild Garlic:

All herbicides and combinations controlled 25% of the wild garlic.

Giant Foxtail Control:

Prior to the application of a postemergence grass herbicide, Authority alone controlled 87 to 90% of the giant foxtail. Canopy controlled 87% of the giant foxtail. Squadron controlled 97% of the giant foxtail.

Common Lambsquarters:

All herbicides and combinations caused severe necrosis to common lambsquarters and controlled 100% of the common lambsquarters.

Common Ragweed:

Authority alone, Authority plus Sencor, and Roundup Ultra caused minimal injury to common ragweed. Canopy, Authority plus FirstRate or Classic caused 50 to 78% injury to common ragweed. Authority alone did not control common ragweed. FirstRate tank-mixed with Authority increased control of common ragweed with control ranging from 93 to 98%. Canopy and Squadron controlled 97% of common ragweed.

Pennsylvania Smartweed:

All herbicides and combinations caused severe necrosis to Pennsylvania smartweed and controlled 100% of the Pennsylvania smartweed.

Soybean Injury:

No visible soybean injury was observed due to Authority. Soybean yield ranged from 1 to 33 bu/A. Yield was reduced with Authority alone due to poor common ragweed control.

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Weed control in no-till soybeans was evaluated with Roundup Ultra applied at several rates and several application timings in 7 and 30 inch row spacings. Weed control with a single application of Roundup Ultra applied the day of planting resulted in poor weed control because of later emerging weeds. In contrast, Roundup applied as a single application at 3 to 4 inch weeds and especially sequential applications at 3 to 4 inch weeds plus at 3 to 4 inch weed regrowth provided almost complete control of all weeds, especially in the 7 inch row spacing. The high level of control of the broadleaf weeds may have been influenced by the relatively small size at application. Roundup plus Squadron preemergence followed by Roundup postemergence controlled weeds similarly. Soybean yield ranged from 25 to 62 bu/A in this study. Yield consistently was higher, up to 26 bu/A, in the 7 inch spacing compared to the 30 inch spacing.

I. INTRODUCTION:

The commercial availability of Roundup Ready soybeans in 1996 makes available an excellent postemergence herbicide for weed control strategies. Although Roundup has been available commercially for about 15 years, it has been used as a nonselective herbicide for burndown weed control for no-till crop production. When used for this purpose, the weed spectrum usually is substantially different from that observed in tilled crop production. Therefore, there is limited information on control of many summer annual weeds with Roundup. This study was designed to evaluate control of winter and summer annual weeds with Roundup Ultra in no-till soybeans.

II. HERBICIDES EVALUATED:

        Roundup Ultra 4 S
        Squadron 2.33 EC

III. ROUNDUP ULTRA RATES EVALUATED:

        1.0, 1.5, and 2.0 pt/A

IV. APPLICATION TIMINGS:

        Preemergence only (at planting)
        Preemergence plus at 3 to 4 inch weed height
        At 3 to 4 inch weed height only
        At 3 to 4 inch weed height plus at 3 to 4 inch weed regrowth
        At 6 to 9 inch weed height only
        Preemergence plus at 3 to 4 inch weed height plus at 3 to 4 inch weed regrowth

V. ROW SPACINGS:

        7 and 30 inch

 VI. ABBREVIATIONS USED:

        ABONOR: above normal                           PHBPU: tall morningglory
        AMATA: common waterhemp                        RG: regrowth
        AMBEL: common ragweed                          SETFA: giant foxtail
        BROSOI: broadcast soil                         W: weeds
        GLXMA: soybeans                                XANST: common cocklebur
        IPOHE: ivyleaf morningglory                    ZEAMX: corn
        LVS: leaves

VII. Irrigation: one inch on August 5 and one inch on August 20

VIII. RESULTS AND DISCUSSION:

Weed control ratings and soybean yield data are presented in the attached tables. There was no soybean injury related to herbicide application, thus injury data is not presented in the attached tables. The first table presents weed control data only for the final rating of the season, on Aug. 23, 56 days after herbicide application. In this table, weed control for each weed is presented side-by-side for the 7 and 30 inch row spacings, for ease in comparing results. The second table (multiple pages) presents control for each of the rating dates - June 29, July 12, July 26, and Aug. 23. Soybean yield data also is presented in each table.

At the time of soybean planting, a dense stand of giant foxtail had emerged which reduced the population of broadleaf weeds. In addition, giant foxtail emergence continued following the application of the preemergence (PRE) application. Emergence of broadleaf weeds did not occur until after application of the PRE herbicides, which reflects on the control obtained with some treatments in this study. Most comments in this report will relate to the Aug. 23 rating.

Giant foxtail (SETFA) Control:

Control of giant foxtail with a PRE only application ranged from 25 to 55% in 30" rows and 62 to 80% in the 7" rows. The incomplete control reflects continued emergence of foxtail following the PRE application on May 25. All foxtail emerged at application of the PRE herbicide was controlled. In contrast, complete control of foxtail was obtained with all treatments that included at least one application at the 3 to 4 inch height. Additionally, Roundup Ultra even at 1.0 pt/A applied at 6 to 9 inch foxtail (actual height was 16 to 24 inches) controlled it completely, indicating the susceptibility of foxtail to Roundup.

Common waterhemp (AMATA) Control:

Waterhemp control was only 0 to 17 and 25 to 66% in the 30" and 7" row spacings, respectively, when Roundup Ultra was applied PRE only. As had been observed with giant foxtail, all waterhemp emerged at PRE application was controlled. However, waterhemp continued to emerge for several weeks following the PRE application. Where Roundup Ultra was applied following soybean emergence, complete control was obtained in both row spacings, at all rates of Roundup Ultra, even where the waterhemp was 8 to 10 inches at application (6 to 9" schedule).

 Common ragweed (AMBEL) Control:

Control of common ragweed was zero in both row spacings with Roundup Ultra at 1.0 pt/A applied PRE. Roundup Ultra at 1.5 pt/A PRE did not control any common ragweed in 30" rows but 50% control was obtained in 7" rows, indicating the value of narrow rows in improving weed control. When Roundup Ultra was applied PRE at 2.0 pt/A, complete control was obtained in both row spacings. Emergence of common ragweed occurred for a shorter time period than that of other weeds. Roundup Ultra at all rates applied to 3 to 4" or 6 to 9" ragweed controlled it completely.

Ivyleaf (IPOHE) and Tall (PHBPU) Morningglory Control:

Control of these two species was almost identical, thus their control will be discussed together. As had been observed with the previous weed species, Roundup Ultra applied PRE resulted in poor control of morningglory because of continued emergence following application, regardless of row spacing. A single application of Roundup Ultra at 3-4" morningglory height controlled this weed 42 to 67% in 30" rows, depending on rate. In contrast, control was 85% with all Roundup Ultra rates in the 7" row spacing, again indicating the value of early canopy development in improving weed control. Sequential applications of Roundup Ultra at 3 to 4" morningglory (June 28) plus at 3 to 4" regrowth (July 15), improved control of morningglory to 80 to 93% in the 30" rows, but a second application was of much less benefit in the 7" rows. A single application of Roundup Ultra at the 6 to 9" scheduled height (actual height ranged from 4 to 12") controlled morningglory only 42 to 75%, at the several Roundup Ultra rates.

Common Cocklebur Control:

Roundup Ultra applied PRE controlled no cocklebur, because it had not yet emerged at application on May 25. In contrast, Roundup Ultra at all rates applied at 3 to 4" or 6 to 9" height controlled this weed with a single application, indicating the high susceptibility of this weed to Roundup Ultra.

Weed Control with Roundup plus Squadron:

Roundup Ultra plus Squadron applied PRE followed by Roundup Ultra POST at 3 to 4" weeds controlled giant foxtail, waterhemp, common ragweed, and cocklebur completely and controlled ivyleaf and tall waterhemp 85%. This level of control is very similar to that with several of the Roundup Ultra only treatments.

Soybean Yield:

Soybean yield in 30 inch rows ranged from 25 to 55 bu/A and in the 7 inch row spacing the yield ranged from 27 to 62 bu/A. Yield in the 7 inch row spacing consistently was higher than in the 30 inch spacing, reflecting the more complete weed control in the narrow row spacing. 

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Weed control in no-till soybeans with Roundup Ultra only was evaluated in this study. The effect of Roundup Ultra rates, application timings, and row spacings was evaluated. Planting was delayed until May 31 because of frequent rainfall, resulting in excessive height of several species by the time of planting. Some weeds exceeded three feet in height. A single application of Roundup Ultra at planting failed to control many weeds, in part due to the tall weeds and in part due to emergence of new weeds following the PRE application. The most consistent control of the wide spectrum of weeds in this study was with two applications. A third application did not improve control to any great extent. Soybean yield ranged from 14 to 60 bu/A. Yield consistently was greater - by as much as 23 bu/A - in the 10 inch row spacing compared to the 30 inch spacing.

I. INTRODUCTION:

Roundup has been available commercially for almost two decades with abundant information available on control of many weeds, especially those weeds that emerge prior to crop planting, such as in no-till. However, relatively little information is available regarding control of summer annual weeds (those that emerge following crop planting). This study was designed to evaluate control of weeds emerged prior to planting and those normally emerging after planting (summer annual weeds) with Roundup Ultra.

II. HERBICIDES EVALUATED:

        Roundup Ultra 4 S
        Squadron 2.33 EC

III. ROUNDUP RATES EVALUATED:

        1.0, 1.5, 2.0, 3.0, and 4.0 pts/A

IV. APPLICATION TIMINGS:

        Preemergence only (at planting)
        Preemergence plus at 3 to 4 inch weed height
        At 3 to 4 inch weed height only
        At 3 to 4 inch weed height plus at 3 to 4 inch weed regrowth
        Preemergence plus at 3-4 inch weed height plus at 3 to 4 inch weed regrowth

V. ROW SPACINGS:

        10 and 30 inch

 VI. ABBREVIATIONS USED:

        ABONOR: above normal                           PANCA: witchgrass
        ALLVI: wild garlic                             PHBPU: tall morningglory
        AMPAL: honeyvine milkweed                      PHTAM: common pokeweed
        APCCA: hemp dogbane                            PHYSU: smooth groundcherry
        BROSOI: broadcast soil                         PLAMA: broadleaf plantain
        CHEAL: common lambsquarters                    POLPY: Pa. smartweed
        CMIRA: trumpetcreepter                         RG: regrowth
        CYPES: yellow nutsedge                         RUMOB: broadleaf dock
        ERICA: horseweed (marestail)                   SETFA: giant foxtail
        ERIFL: tall fleabane                           SOLCA: horsenettle
        GERCA: Carolina geranium                       SOLPT: eastern black nightshade
        GLXMA: soybeans                                W: weeds
        IPOHE: ivyleaf morningglory                    XANST: common cocklebur
        LVS: leaves                                    ZEAMX: corn
        OEOLA: cutleaf evening primrose
        OXAST: yellow woodsorrel

VII. RESULTS AND DISCUSSION:

Weed control ratings and soybean yield data are presented in the attached tables. There was no observable soybean injury related to herbicide application, thus injury data is not presented in the attached tables. The first table presents weed control data only for the final rating of the season (dates differ depending on weed species, but mostly for the Aug. 14 rating). In this table, weed control for each weed is presented side-by-side for the 10 and 30 inch row spacings, for ease in comparing results. The second table (multiple page) presents control for each rating date. Soybean yield data also is presented in each table.

Because of delayed planting (May 31) due to frequent rainfall in April and the first half of May, many weeds exceeded 10 inches in height with some over 24 inches in height (see site description sheet) at the time of planting and application of preemergence (PRE) herbicides applied at planting. The weeds were even taller at application of the þ3 to 4"þ weed application timing. The weed height at herbicide application obviously had some influence on control of several of the weed species.

Several of the weed species listed on the Site Description Sheet were not rated because their distribution was not sufficiently uniform to evaluate. Further, several weed species were not rated on each rating date because they were difficult to detect under the developing soybean canopy.

Horseweed (marestail) (ERICA) Control:

Horseweed control was rated only on June 19 and July 3 because the weeds had been completely controlled or had matured by July 3. All treatments except three controlled horseweed completely regardless of the Roundup Ultra rate or application timing, or row spacing.

Giant Foxtail (SETFA) Control:

Roundup Ultra applied PRE only (at time of planting) controlled giant foxtail 58 to 83% in 30 inch rows and 83 to 90% in 10 inch rows on Aug. 14. On June 19, control ws 99% in most instances, but decreased with time because of new emergence. This highly suggests that a single application of Roundup Ultra at planting likely will not suffice for season-long control of giant foxtail. In contrast, control of foxtail was complete in most instances where the Roundup Ultra was applied initially on June 19 at the 3 to 4 inch weed height. Complete control was observed in all 10 inch row spacing plots. In contrast, Roundup Ultra plus Squadron controlled giant foxtail 66 and 99% in the 30 and 10 inch row spacings.

Pa. Smartweed (POLPY) Control:

Control of smartweed was 99% in almost all instances in 10 and 30 inch row spacing when Roundup Ultra was applied as a single application at þ3 to 4"þ weed height or as sequential applications, even though the smartweed was 6 to 10 inches in height at application. In contrast, control was less complete and less consistent when the Roundup Ultra was applied only PRE (at planting), probably because of continued emergence following the PRE application. There was no consistent advantage for 10 compared to 30 inch rows regarding control of smartweed.

Ivyleaf Morningglory (IPOHE) Control:

PRE only applications of Roundup Ultra controlled morningglory only 0 to 25%, regardless of rate or row spacing. The morningglory may have been too tall at time of application for optimum control in addition to continued emergence. A single application of Roundup Ultra at the 3 to 4 inch morningglory height resulted in improved control, but still was less than acceptable (8 to 66%). The most effective treatments for control of morningglory were sequential applications at 3 to 4 inch plus repeat applications at 3 to 4 inch regrowth, resulting in 91 to 99% control with Roundup Ultra at 1.5 pt/A. Three sequential applications consisting of a PRE, a 3-4 inch application, plus a 3 to 4 inch regrowth application did not improve control to any extent. Roundup Ultra plus Squadron PRE controlled morningglory 0 and 58% in the 30 and 10 inch row spacings, respectively.

Common Cocklebur (XANST) Control:

Control of cocklebur was complete with all Roundup Ultra treatments in 10 inch rows regardless of rate or application timings. In contrast, control in 30 inch rows was less consistent, ranging from 33 to 99%. The less complete control in 30 inch rows was related to continued emergence in June and July. The more consistent and complete control in 10 inch rows was related to less emergence because of the canopy effect resulting in a greater shading effect.

Eastern Black Nightshade (SOLPT) Control:

Nightshade emergence occurred mid-season (mostly following mid-June) which greatly influenced control with the several treatments. No control was observed with PRE applications only, because the nightshade emerged well after the PRE application, regardless of row spacing. Similarly, applications made at PRE plus 3 to 4" or only at 3 to 4 inch weed height resulted in poor control in most instances, because of the later emergence of the nightshade. In contrast, applications of Roundup Ultra made at 3 to 4 inch weed height plus a sequential treatment at 3 to 4 inch regrowth resulted in essentially complete control of nightshade. The sequential application was made following emergence of essentially all nightshade, resulting in almost complete control. Roundup Ultra plus Squadron applied PRE at planting controlled nightshade 0 and 75% in 30 and 10 inch rows, respectively.

Honeyvine Milkweed (AMPAL) Control:

Control of ivyleaf morningglory was poor in most instances in both row spacings. The only treatment that appeared to control the milkweed almost completely was three applications of Roundup Ultra at 1.5 qt each time, in 10" rows.

Tall Fleabane (ERIFL) Control:

All treatments controlled tall fleabane completely in both row spacings. This weed was emerged at the time of the PRE application on May 31 and no new emergence occurred later in the season.

Common Pokeweed (PHTAM) Control:

Pokeweed was 25 to 30 inches tall at the time of the PRE application on May 31 and about 36 inches tall on June 19 when the þ3-4" weedþ application was made. Excellent control was obtained with most treatments in both 10 and 30" row spacing. The most complete control occurred where two or more applications of Roundup Ultra were made.

Trumpetcreeper (CMIRA) Control:

Control of trumpetcreeper was poor in all but a few instances, regardless of Roundup Ultra rate, number of applications, or row spacing. However, some to considerable injury (stunting) was observed, thus þstuntþ of trumpetcreeper also was rated. In addition to some control, Roundup Ultra caused 25 to 99% stunt of the trumpetcreeper. Combined with the soybean canopy, this stunt was influential in reducing the competitiveness of the weed.

Horsenettle (SOLCA) Control:

Treatments that included two or three applications of Roundup Ultra controlled horsenettle completely in the 10" rows but less completely in 30" rows. A single application at planting gave poor control of horsenettle.

Soybean Yield:

Soybean yield ranged from 14 bu/A to 60 bu/A. Yield consistently was higher in the 10 inch compared to the 30 inch row spacing. Yield differences within row spacings were related to differences in weed control in most instances.

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

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