Published in Agron. J. 96:1357-1363 (2004).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Paper
Influence of Certain Postemergence Broadleaf Herbicides on Soybean Stressed from Iron Deficiency Chlorosis
D. W. Franzena,*,
J. H. O'Barrb and
R. K. Zollingerc
a North Dakota State Univ., Dep. of Soil Sci., Box 5758, Fargo, ND 58105-5758
b Dep. of Soil and Crop Sci., Texas A&M Univ., 2474 TAMU, College Station, TX 77843-2474
c North Dakota State Univ., Dep. of Plant Sci., 470H Loftsgard Hall, Fargo, ND 58105
* Corresponding author (dfranzen{at}ndsuext.nodak.edu)
Received for publication August 15, 2003.
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ABSTRACT
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Postemergence herbicides are widely used in soybean [Glycine max (L.) Merr.]. Although yield is seldom reduced following herbicide applications to soybean under normal growing conditions, little is known regarding their application when the crop is under stress. Iron deficiency chlorosis (IDC) is a common problem in the Red River Valley of North Dakota and Minnesota. Postemergence herbicide applications are usually made early in the season when IDC is most expressed. The objective of this experiment was to compare the effects of selected postemergence soybean herbicides applied to soybean under stress from IDC. Treatments were applied at 12 locations during a 3-yr study. Stunting and necrosis were evaluated at 14 and 28 d after treatment (DAT), and plots were harvested to determine grain yield. There were treatment differences in stunting at 11 locations 14 DAT and at nine locations 28 DAT. Differences in leaf necrosis were found among treatments at 11 locations 14 DAT and at four locations 28 DAT. Lactofen significantly lowered yield at six locations, and imazamox and imazethapyr lowered yield at three locations. These results suggest that herbicides with harsh contact activity (lactofen) and some acetolactate synthase (ALS) inhibitors (e.g., imazamox, thifensulfuron, and imazethapyr) may have potential for greater injury under these soil and environmental conditions. It may be important to consider herbicide injury effects, in addition to weed spectrum, when selecting herbicides for use on IDC-stressed soybean.
Abbreviations: DAT, days after treatment • EC, electrical conductivity • IDC, iron deficiency chlorosis
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INTRODUCTION
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IRON DEFICIENCY CHLOROSIS (IDC) in soybean is common in many areas where soybean is grown in the North-Central United States and is especially common and severe in the calcareous soils of the Red River Valley of eastern North Dakota and northwestern Minnesota. Calcareous soils interfere with iron uptake by soybean (Inskeep and Bloom, 1987; Uvalle-Bueno and Romero, 1988; Goos and Johnson, 2000). Iron is essential for chlorophyll production, and IDC is characterized by stunted plants with interveinal pale green or yellow to nearly white leaves with green veins (Anderson, 1982; Clark, 1982).
Iron deficiency chlorosis is not usually observed until the first trifoliolate emerges since before this stage, iron from the seed is translocated to new growth (Clark, 1982). After the first trifoliolate emerges, iron becomes immobile, and the soybean plant must rely on soil availability to supply iron (Vose, 1982). Due to a combination of soil factors, including pH, temperature, CaCO3 content, water content, and the concentration of HCO–3 in the soil solution (Inskeep and Bloom, 1984, 1986; Goos and Johnson, 2000), iron uptake may be reduced (Inskeep and Bloom, 1987; Chaney et al., 1992). Chlorosis develops when insufficient iron is supplied to leaves (Lin et al., 1998). Iron deficiency chlorosis may be so severe that necrosis and death of the leaf or entire plant may occur. Cool, wet soil conditions or poorly drained soils intensify IDC in calcareous regions where iron deficiencies are common (Moraghan and Mascagni, 1991).
Several studies have been conducted to ascertain why soybean becomes iron deficient under calcareous soil conditions. Soil pH in the Red River Valley typically ranges between 7.5 and 8.5 (Franzen, 1999). High soil pH, calcium carbonates, organic matter, and soluble salts (Dahiya and Singh, 1979) in combination with high moisture contribute to IDC in this region (Bloom and Inskeep, 1986; Inskeep and Bloom, 1987; Springer et al., 1999; Franzen and Richardson, 2000).
Postemergence herbicides are used by nearly all soybean growers in North Dakota (Zollinger et al., 1998) and are an important component of an integrated weed control strategy. Following herbicide label directions and using proper application techniques may not prevent crop burning, stunting, and chlorosis (Wichert and Talbert, 1993). Though postemergence herbicides are effective at controlling weeds (Kapusta et al., 1986), crop injury and reduced yield have been observed. Soybean can be stressed by iron deficiency and soluble salts but may also be stressed from postemergence herbicides. Common foliar effects of postemergence herbicides may include stunting, chlorosis (not associated with iron deficiency), bronzing, and crinkling or burning of the leaves. Although soybean may express symptoms from herbicide activity, soybean growth and yield usually are unaffected if all other stresses are minimized (Browde et al., 1994). Kapusta et al. (1986) observed that bentazon [3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide] and acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} caused early crop injury. However, the soybean recovered by 21 d after application without any significant effect on yield.
Some herbicide labels caution users that temporary injury may result from use, without affecting yield under some conditions. Current research suggests that under certain stress, some yield loss is possible. Harvey and Ateh (1996) conducted an experiment in Wisconsin to measure the effects of postemergence herbicides on soybean yield. Labeled rates of 12 common postemergence herbicides were applied to soybean. Compared with the nonsprayed soybean, the herbicide treatments averaged an 11, 1, and 4% reduction in yield in 1993, 1994, and 1995, respectively. These researchers concluded that the use of postemergence herbicides resulted in only a slight soybean yield loss compared with a hand-weeded check. It was noted that environmental conditions after herbicide application could influence soybean recovery.
Since there was evidence of soybean stress due to herbicides under normal growing conditions, research was needed to determine the extent of yield loss from soybean plants exhibiting IDC at the time of herbicide application. It is hypothesized that combining these two stresses will result in severe visible injury as well as a significant yield loss. It is also hypothesized that each herbicide will affect the yield differently. Currently, there is no published research regarding herbicide treatment and IDC on soybean yield.
A 3-yr (1998–2000) field study was conducted in the Red River Valley of North Dakota and Minnesota to quantify the effects of POST herbicides applied to soybean exhibiting IDC symptoms. The objectives of this research were to determine whether certain soybean postemergence broadleaf herbicides reduced soybean yield when soybean was stressed from IDC and whether some herbicides reduced yield more consistently and at greater magnitude than others.
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MATERIALS AND METHODS
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Field Experiments
Ideally, fertility experiments are conducted on uniform sites with similar cultivars seeded on each site. However, IDC is an ephemeral quality that varies in area of appearance and severity due to a number of uncontrollable soil and environmental factors, such as soluble salt level, soil moisture, and temperature. It would be impractical to set up a number of field studies related to IDC without first finding locations that actually exhibit chlorosis in a given year. Therefore, it was important to establish the studies in farmer fields with soybean already exhibiting IDC although by doing so, the ability to combine all sites statistically was lost since most fields were seeded to different soybean cultivars. However, the frequency of treatment differences across a number of sites would support the study objectives and were similar to methods used by Haq and Mallarino (2000).
From 1998 to 2000, 12 sites were established on production fields exhibiting IDC (Table 1). Sites were also selected with a history of low weed pressure. Soils from each location and selected chemical properties are listed in Table 2. Since soybean plants do not exhibit IDC until the first trifoliate leaves have emerged, field locations were selected when the soybean was in the one to two trifoliate stage. Uniformly chlorotic areas within each field were selected to reduce variability within each experiment. Chlorosis was evaluated as follows: 0% = no chlorosis; 20% = slight general chlorosis of the upper leaves; 40% = moderate interveinal chlorosis of upper leaves; 60% = chlorosis of the entire plant with necrosis and stunting observed; 80% = severe chlorosis, stunting, and necrosis with dead growing point; and 100% = entire plant dead.
Plots were 3 m wide by 6 m long with a 1.5-m border strip between blocks and a 1.5-m border around the entire experiment. Buffer strips were used as a precaution to minimize cooperator-applied herbicide, from adjacent acres, from drifting into the experimental areas. The experimental design was a randomized complete block experiment with 10 to 11 herbicide treatments depending on the location and year. Plant populations were recorded for each plot immediately before herbicide application and before harvest. Two rows, approximately 6 m long, were measured from each plot. Soybean plants were counted, and mean stand count for the plot was recorded. Following herbicide application, plots were hand-weeded weekly to ensure that yield differences between treatments were the result of the herbicides and not uncontrolled weeds. Weeds present before herbicide application likely had little or no effect on soybean grain yield since they were small and present at low populations.
Soil samples were taken from all plots before herbicide treatments and consisted of four to five random cores (2.5-cm diam.) taken from the 0- to 15-cm depth to form the composite sample from each plot. Soil pH and soluble salts [electrical conductivity (EC)] were measured in 1:1 soil/water (Watson and Brown, 1998). Calcium carbonate equivalent (CCE) was determined by adding 2 M hydrochloric acid (HCl) and measuring pressure resulting from the reaction (Nelson, 1982) (Table 2).
Herbicide treatments were applied to the entire area within each plot using a bicycle-wheeled-type plot sprayer equipped with drift cones (devices designed to minimize drift to neighboring plots) delivering 80 L ha–1 at 280 kPa (delivered by CO2) through 8001 flat fan nozzles. Weeds at the time of spraying were small, ranging from one to two leaves in size and were at the proper stage for treatment according to herbicide labels. At the time of application, the date, time, air and soil temperature, relative humidity, wind speed and direction, percentage cloud cover, and crop chlorosis ratings were recorded (Table 3). Herbicide treatments used are listed in Table 4. Visual evaluations for stunting and necrosis, on a scale of 0 (no effect) to 100% compared with an untreated area, were collected 14 and 28 d after herbicide application.
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Table 3. Spray date, time, temperature, humidity, wind speed and direction, percentage clouds, and percentage initial soybean chlorosis by location.
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At maturity, a 1.4-m-wide strip 6 m long was harvested from the center of each plot using a plot combine. Soybean from each plot was dried to uniform moisture, cleaned, and weighed for yield determination.
Since the locations were not seeded to the same variety, location effects with respect to soil properties could not be statistically evaluated between locations. Due to considerable variability in soluble salts, as measured by EC between plots in some experiments, EC was used as a covariate in analysis of covariance within each location, reducing any possible interference of EC differences on treatment effects. A correlation analysis was also conducted for each treatment between soil EC and yield to determine whether some herbicide–soybean interactions were more sensitive to EC than others.
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RESULTS AND DISCUSSION
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Generally, chlorosis due to IDC was more severe in 1999 than in 1998 or 2000 (Table 3).
There were statistical differences between treatments in stunting 14 DAT (Tables 5, 6, and 7) among treatments at 11 locations. Soybean stunting was most commonly observed with the lactofen {2-ethoxy-1-methyl-2-oxoethyl5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate} treatment (seven locations). Acifluorfen, bentazon/acifluorfen 2:1, imazethapyr {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid}, imazamox {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-(methoxymethyl)-3-pyridinecarboxylic acid}, and fomesafen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-N-(methylsulfonyl)-2-nitrobenzamide} also resulted in significant stunting in at least one location. Stunting was still evident at 9 of the 12 locations at the 28 DAT evaluation. At this rating, stunting due to lactofen was evident at nine locations. Other treatments with stunting injury were imazethapyr (three locations), bentazon/acifluorfen 2:1 and imazamox (two locations), and bentazon/acifluorfen 4:1, acifluorfen, fomesafen, thifensulfuron {3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino] sulfonyl]-2-thiophenecarboxylic acid}, and cloransulam {3-chloro-2-[[(5-ethoxy-7-fluoro[1,2,4]triazolo[1,5-c]pyrimidin-2-yl)sulfonyl]amino]benzoic acid} (one location).
There were significant differences in necrosis 14 DAT at 11 of 12 locations (Tables 8, 9, and 10). Necrosis was most often observed with lactofen (11 locations). Fomesafen and bentazon/acifluorfen 2:1 resulted in higher necrosis at three sites. Other treatments with necrosis injury were bentazon, acifluorfen, imazethapyr, and imazamox (one site). Necrosis was observed at 4 of 12 locations by 28 DAT (Tables 5, 6, and 7). At this rating, necrosis due to lactofen was evident at three locations. Other treatments with necrosis were imazethapyr and imazamox (two locations) and bentazon/acifluorfen 2:1, fomesafen, thifensulfuron, and cloransulam (one location).
In 1998, significant yield differences among herbicide treatments were observed at three of six locations (Table 11). At Fairmount, acifluorfen, thifensulfuron, imazethapyr, and imazamox treatments were lower in yield than the bentazon/acifluorfen (4:1), fomesafen, and cloransulam treatments. At Arthur, soybean treated with lactofen produced the lowest yields. At Rothsay, bentazon/acifluorfen 2:1 and thifensulfuron were the lowest-yielding treatments. The magnitude of differences among treatments is particularly remarkable. At Fairmount, for example, the highest-yielding treatments were nearly double the yield of the lowest-yielding treatments.
In 1999, there were yield differences at two of three locations (Table 12). Chlorosis was much more intense in 1999 (Table 3) than in 1998 or 2000. At Walcott, the bentazon, acifluorfen, bentazon/acifluorfen (4:1), and bentazon/acifluorfen (2:1) treatments were higher in yield than other treatments. This site was particularly high in EC compared with other sites. This may have contributed to the lower yields within the experiment and the high level of stunting and necrosis symptoms evident at 14 and 28 DAT (Table 6) compared with Moorhead 99. Yields of the highest-yielding treatments were more than three times the yield of the lowest-yielding treatment. At Rothsay, the lactofen and imazamox treatments were lower in yield than other treatments. The Rothsay site included glyphosate [N-(phosphonomethyl)glycine]. It is notable that the glyphosate treatment was not higher in yield than most treatments. The variety used at Moorhead was so unadapted to the soil conditions that the soybean plants in the plots never greened up all season. The cooperator tilled under several areas of soybean surrounding these plots before harvest. There were no significant yield differences due to treatment at this location.
In 2000, there were yield differences due to herbicide treatments at all three locations (Table 13). Two of the locations, Walcott and Rothsay, were glyphosate-tolerant soybean varieties, and the treatments included glyphosate. At Walcott, soybean treated with lactofen was lower in yield than all other treatments. All other treatments were similar in yield. At Arthur, soybean treated with cloransulam, imazamox, thifensulfuron, acifluorfen, bentazon/acifluorfen 4:1, and fomesafen was higher in yield than other treatments. Soybean treated with bentazon/acifluorfen (2:1), imazethapyr, and lactofen had the lowest yield. At Rothsay, bentazon/acifluorfen 2:1 and lactofen were lower yielding than other treatments. Significant differences in yield were observed. Imazethapyr had the highest yield. Although some treatments tended to be consistently high or low yielding, some treatments, such as acifluorfen, were both higher or lower yielding depending on the site and year.
One of the factors that might have influenced activity of the herbicide was environmental conditions at the time of spraying. There were wide ranges of temperature, clouds, humidity, and application time of day between sites. Several herbicides, including acifluorfen, are known to be sensitive to these conditions (Zollinger, 2001).
Yield and EC were significantly correlated at 4 of 12 sites within the imazethapyr treatment; 3 of 12 sites within the cloransulam, acifluorfen, and bentazon/acifluorfen 2:1 treatments; and 2 of 12 sites within the fomesafen and thifensulfuron treatments (Table 14). In each correlation, yield was negatively correlated with soil EC. Analysis of covariance was conducted at each site; however, in only one site, Colfax 1998, was the level of significant yield differences improved. However, the results shown in Table 14 are an indication that EC may have more influence on the effect of some herbicides than others. Within the bentazon treatments, no sites exhibited significant correlation between yield and EC. This suggests that soybean treated with bentazon may be less affected by variation in soil EC than those herbicide treatments with a higher frequency of correlation among sites, such as imazethapyr.
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SUMMARY
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Soybean treated with lactofen had significantly less yield than other treatments at six of eight locations where significant treatment differences were observed. Soybean treated with imazamox and imazethapyr yielded significantly less than most other treatments at three of eight locations. Soybean with glyphosate and the bentazon/aciflourfen 4:1 treatments were not lowest yielding at any location. These results suggest that herbicides with harsh contact activity (lactofen) and some herbicides in the general class of acetolactate synthase (ALS) inhibitors, e.g., imazamox, thifensulfuron, and imazethapyr, may have potential for greater injury than other types of postemergence herbicides.
There were significant differences in soybean yields stressed from IDC between treatments at 8 of 12 locations. Stunting and necrosis 14 DAT were observed at 11 locations. Visual symptoms of stunting and necrosis were observed at nine and four locations, respectively, 28 DAT. Use of EC as a covariate was useful at one location in removing variable soil EC effects from treatment effects.
It may be important to evaluate soybean stress before herbicide selection or to factor in possible injury into the economic analysis of the use of a certain postemergence broadleaf herbicide before application. Some of the labels of the herbicides tested in this experiment currently have warnings against use while soybean is under stress. Those that do not may consider reevaluating their products so that they contain such wording.
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REFERENCES
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ABSTRACT
INTRODUCTION
