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Corn

Seed-Applied Insecticides Inconsistently Affect Corn Forage in Continuous Corn

Crop and Soil Sci. Dep., 620 Bradfield Hall, Cornell Univ., Ithaca, NY 14853

^* Corresponding author (wjc3{at}cornell.edu)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Western corn rootworm (Diabrotica virgifera virgifera Le Conte) is the major insect pest in the corn phase of a corn (Zea mays L.) silage–perennial forage rotation. Dairy producers may prefer seed-applied instead of soil-applied insecticides for rootworm control because of ease of use and additional control of some other soil insect pests. The objective of the 2-yr NY field study was to evaluate clothianidin [(E)1-(2-chloro-1,3-thiazol-5-ymethyl)-3-methyl-2 nitroguanidine] and thiamethoxam (3-[(2-chloro-5-thiazolyl)methyl]tetrahydro-5-methyl-N-nitro-4H-1,3,5-oxadiazin-4-imine) at the 1.25 mg a.i. kernel^–1 rate for rootworm control, dry matter (DM) accumulation, DM yield, and silage quality. The control had moderately severe (1.40-node injury scale), whereas clothianidin (0.18) and thiamethoxam (0.39) had acceptable rootworm damage ratings. Clothianidin had greater DM accumulation at the 12th leaf stage (384 g m^–2) compared with thiamethoxam and the control (324 g m^–2), greater DM accumulation 3 wk after silking (1491 g m^–2), and greater DM yield (18.5 Mg ha^–1) compared with the control (1245 g m^–2 and 17.0 Mg ha^–1, respectively). Thiamethoxam had similar DM yield (17.4 Mg ha^–1) but greater milk Mg^–1 (1559 kg Mg^–1) compared with clothianidin (1475 kg Mg^–1). Clothianidin had greater calculated milk yield (27,301 Mg ha^–1) compared with the control (25,411 Mg ha^–1) but similar to thiamethoxam (27,192 Mg ha^–1). Clothianidin and thiamethoxam provided acceptable rootworm control in this study but more research is required to determine if these results are consistent across different environments in the Northeast United States.

Abbreviations: CP, crude protein • DM, dry matter • GDD, growing degree days • IVTD, in vitro true digestibility • NDF, neutral detergent fiber • NDFd, in vitro fiber digestibility • R1, silking stage • R3, milk stage • RM, relative maturity • Vn, nth leaf collar stage

Seed-Applied Insecticides Inconsistently Affect Corn Forage in Continuous Corn

Crop and Soil Sci. Dep., 620 Bradfield Hall, Cornell Univ., Ithaca, NY 14853

^* Corresponding author (wjc3{at}cornell.edu)

Received for publication March 22, 2007.
Western corn rootworm (Diabrotica virgifera virgifera Le Conte) is the major insect pest in the corn phase of a corn (Zea mays L.) silage–perennial forage rotation. Dairy producers may prefer seed-applied instead of soil-applied insecticides for rootworm control because of ease of use and additional control of some other soil insect pests. The objective of the 2-yr NY field study was to evaluate clothianidin [(E)1-(2-chloro-1,3-thiazol-5-ymethyl)-3-methyl-2 nitroguanidine] and thiamethoxam (3-[(2-chloro-5-thiazolyl)methyl]tetrahydro-5-methyl-N-nitro-4H-1,3,5-oxadiazin-4-imine) at the 1.25 mg a.i. kernel^–1 rate for rootworm control, dry matter (DM) accumulation, DM yield, and silage quality. The control had moderately severe (1.40-node injury scale), whereas clothianidin (0.18) and thiamethoxam (0.39) had acceptable rootworm damage ratings. Clothianidin had greater DM accumulation at the 12th leaf stage (384 g m^–2) compared with thiamethoxam and the control (324 g m^–2), greater DM accumulation 3 wk after silking (1491 g m^–2), and greater DM yield (18.5 Mg ha^–1) compared with the control (1245 g m^–2 and 17.0 Mg ha^–1, respectively). Thiamethoxam had similar DM yield (17.4 Mg ha^–1) but greater milk Mg^–1 (1559 kg Mg^–1) compared with clothianidin (1475 kg Mg^–1). Clothianidin had greater calculated milk yield (27,301 Mg ha^–1) compared with the control (25,411 Mg ha^–1) but similar to thiamethoxam (27,192 Mg ha^–1). Clothianidin and thiamethoxam provided acceptable rootworm control in this study but more research is required to determine if these results are consistent across different environments in the Northeast United States.

Abbreviations: CP, crude protein • DM, dry matter • GDD, growing degree days • IVTD, in vitro true digestibility • NDF, neutral detergent fiber • NDFd, in vitro fiber digestibility • R1, silking stage • R3, milk stage • RM, relative maturity • Vn, nth leaf collar stage

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
WESTERN CORN ROOTWORM is a serious insect pest in continuous corn fields in the United States (Wright et al., 2000). Although a few populations of western corn rootworm have adapted to the traditional management strategy of a corn–soybean [Glycine max (L.) Merr.] rotation in isolated regions of the Midwest United States, crop rotation remains the major management practice for control of western corn rootworm (Wright et al., 2000). On most dairy farms, however, a perennial forage–corn silage rotation predominates, which results in continuous corn fields for 3 to 4 yr. Consequently, dairy producers in the Northeast United States have relied on soil-applied insecticides for control of western corn rootworm in corn silage fields (Davis, 1994). Dairy producers now have a keen interest in how seed-applied insecticides, which have been recently commercialized, control western corn rootworm because of their ease of use and because seed-applied insecticides control some early season insect pests that soil-applied insecticides do not control.

Clothianidin and thiamethoxam, applied at the 0.25 mg a.i. kernel^–1 rate, control most early season soil corn insects (Wilde et al., 2004), including seed corn maggot (Delia platura), wireworm (Melanotus sp.), and white grubs [Lachnosterna implicate (Phyllophaga implicata)]. Clothianidin and thiamethoxam, applied at the 1.25 mg a.i. kernel^–1 rate, control these same pests as well as western corn rootworm. Both seed-applied insecticides were first commercialized for use in the United States in the 2003 growing season (Andersch and Schwarz, 2003).

Jointz and Leist (2003) reported that clothianidin and thiamethoxam had no phytotoxic effect on corn emergence. A Farm Journal report, however, noted that four of seven seed samples from 63 samples submitted by farmers that did not pass cold and saturated cold germination tests were treated with a seed-applied insecticide (Finck, 2006). Furthermore, hybrids that ranked last in the saturated and cold saturated germination tests also had lower emergence and slower early season growth under field conditions when compared with high-ranking hybrids (Finck, 2006). Cox et al. (2007), however, reported that the low and high rates of clothianidin did not affect early season corn growth when corn followed soybean.

Corn DM yields have a strong correlation with DM accumulation at the silking stage (Muchow and Davis, 1988). Consequently, management practices that reduce DM accumulation because of negative effects on early season growth or increase DM accumulation because of soil insect control should have a major impact on DM yields. The objective of this study was to determine how clothianidin and thiamethoxam, applied at the 1.25 mg a.i. kernel^–1 rate, affect corn rootworm control, DM accumulation, DM yield, and silage quality in a continuous corn rotation.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Field experiments were conducted in 2005 and 2006 on a Honeoye silt loam soil (fine-loamy, mixed, mesic, Glossoboric Hapladalfs) at a Cornell University research farm near Aurora, NY (42°44 N lat, 76°40' W long). The 240 by 33 m field was subdivided into northern (120 by 33 m) and southern sections (120 by 33 m) in 1990. One section has been planted to corn in early May to conduct corn rootworm studies. The other section has been planted to a corn–pumpkin (Cucurbita pepo L.) mix in late June as a means to attract additional western corn rootworm beetles to increase rootworm larvae in the corn rootworm studies for the following growing season. In 2005, the northern section was used for the corn rootworm study and the southern section was planted to the corn–pumpkin mix in late June. In 2006, the southern section was used for the study. Soil tests indicated a pH of 7.8 and high concentrations (Mehlich test) of P and K in the corn rootworm sections in both years.

The experimental design was a randomized complete block design with six treatments and four replications. Each plot measured 30 by 3 m with a 15-m length designated for grain and a 15-m length designated for silage harvest. We will discuss only the silage data in this manuscript.

Treatments included a control; the soil insecticide, tefluthrin (2,3,5,6-tetrafluoro-4-methylphenyl)methyl (1R,3R)-rel-3-[(1Z)-2-chloro-3,3,3-trifluoro-1-propenyl]-2,2-dimethylcyclopropanecarboxylate), at a 0.12 kg a.i. ha^–1 rate that was applied at planting as an 18-cm band in front of the planter-press wheel over the open seed furrow and incorporated with the press wheel (T-band); 1.25 mg a.i. kernel^–1 of thiamethoxam; 1.25 mg a.i. kernel^–1 of clothianidin;, and combination seed–soil insecticide treatments of 0.25 mg a.i. kernel^–1 of clothianidin–tefluthrin (as described previously) and 1.25 mg a.i. kernel^–1 of clothianidin–tefluthrin (as described previously). All treatments, including the control, were treated with the seed-applied fungicides Apron XL {methyl-N [methoxyacetyl-N (2, 6-xylyl-D-alaninate)]} and Maxim XL {[fludioxinil (R)-2-(2, 6-dimethylphenyl)-methoxyacetylamino]-propionic acid methyl ester}. Gustafson (Plano, TX) treated the Pioneer brand, ‘34B23’, a 108-d relative maturity hybrid used in this study, with the seed-applied insecticides.

The experimental site was moldboard plowed and harrow-cultipacked a couple of days before planting in both years. Pioneer brand 34B23 was planted on 5 May 2005 and 2 May 2006 with a four-row planter (0.76 m row spacing) at 81,500 kernels ha^–1. A banded started fertilizer, 10–20–20 (N–P–K), was applied at planting at a rate of 277 kg ha^–1. The insecticide hopper was turned on in the plots that received the soil-applied insecticide, tefluthrin, and turned off for the other plots. Pre-emergence herbicides provided excellent weed control in 2006 but in 2005 the plots were hand-weeded twice to achieve satisfactory weed control. All plots were injected (0.1 m deep between the center of each row) with 150 kg N ha^–1 as a 32% weight volume^–1 solution of urea [(NH₂)Co] and ammonium nitrate (NH₄NO₃) at the fifth leaf stage (V5, Ritchie et al., 1993).

Final plant densities of each plot were determined at the V4 stage by counting all the plants along the 30-m length of the two center rows. Five corn plants were harvested at the soil line from the two center rows (three consecutive plants from one center row and two consecutive plants from the other center row) on the south end of each plot (excluding two end border plants) at the V12 stage, from the north end of each plot (excluding two end border plants) at the silking stage (R1), and from the interface of the grain and silage sections at the early grain fill stage (R3). The V12 stage occurred on 7 July in both years, the R1 stage was on 22 July 2005 and 28 July 2006, and the R3 stage was on 6 Aug. 2005 and 11 Aug. 2006. All harvested plants were placed in a forced-air drier and dried at 60°C to constant moisture. Total DM accumulation was calculated on a per-area basis determined from the five-plant sample weight and final plant densities in each subplot. Ten plants were also dug at the interface of the grain and silage sections at the R1 stage and the roots were washed and rated for rootworm injury using the 1 to 3 node-injury scale (Oleson et al., 2005).

The two center rows of the inner 11 m of the silage section of the study were harvested with a three-row retrofitted New Holland corn silage chopper (Model 1890, New Holland, PA) at about 330 g kg^–1 DM content (26 Aug. 2005 and 1 Sept. 2006). A border row was removed by hand and discarded so the 3-row chopper would harvest only the two center rows. Percentage root lodging (plants leaning more than 30 degrees), as described by Sutter et al. (1990), was determined in the two center rows on the day of harvest. Five plants were also hand-harvested from the center rows on the harvest date to calculate DM content and to analyze for corn forage quality characteristics. The five-plant sample was ground through a chipper–shredder in the field and an approximate 1-kg sample was taken from the shredded material and dried at 60°C in a forced-air drier to constant moisture. The subsample was further ground through a Wiley mill (Thomas Scientific, Sweetboro, NJ) fitted with a 1-mm screen.

Subsamples (0.5 g each) were analyzed by wet chemistry for neutral detergent fiber (NDF), using the ANKOM system (ANKOM Technology, Fairport, NY) according to procedures by van Soest et al. (1991), and for total N using a Leco FP528 N analyzer (LECO Corp., St. Joseph, MI) with Dumas combustion (Tate, 1994; Wiles et al., 1998). The crude protein (CP) concentration was calculated by multiplying total N by 6.25. Subsamples (0.25 g each) were also analyzed for in vitro true digestibility (IVTD) according to Stage 1 of the procedure described by Marten and Barnes (1980), using a 48-h incubation period at 39°C in 5 mL of buffered rumen fluid containing 20 mL of the Kansas State buffer supplemented with 0.5 g L^–1 urea. In vitro fiber digestibility (NDFd) was determined as described by Cherney et al. (2004) using the rumen buffer described by Marten and Barnes (1980) and using the Daisy II ^200/220 in vitro incubator (ANKOM Technology, Fairport, NY) and the ANKOM ^200–220 fiber analyzer. The buffer contained urea. Ruminal fluid inoculum was obtained from a nonlactating, rumen-fistulated Holstein cow, offered a medium quality orchardgrass (Dactylis glomerata L.) hay diet for ad libitum intake. Digestibility samples (0.25 g) were incubated in duplicate for 48 h at 39°C, and undigested residues were treated with neutral detergent solution.

Subsamples (1.0 g) were also analyzed for ash content by combustion at 510°C for 4 h. Subsamples (0.1 g) were analyzed for starch by Dairy One (DHI Forage Testing Lab, Ithaca, NY). The subsamples were pre-extracted for sugars, and then a glucoamylase enzyme was used to hydrolyze starch to dextrose. The subsamples were then injected into a YSI 2700 SELECT Biochemistry Analyzer, where dextrose is oxidized to hydrogen peroxide and lactose. Hydrogen peroxide is detected by an electrode, and current at the electrode is directly proportional to hydrogen peroxide concentration, which is directly related to dextrose and starch concentrations.

Potential milk yield indices were then estimated from the spreadsheet, Milk 2006 (Shaver et al., 2006). Milk Mg^–1 (kg milk Mg^–1 corn forage), a forage quality index, was calculated from NDF, NDFd, CP, ash, and starch concentrations. Milk yield (kg milk ha^–1 corn forage) was calculated as the product of milk Mg^–1 and DM yields.

Treatments were considered fixed and years and replicates were considered random effects in the analysis of variance using PROC MIXED (SAS Institute, 1998). The Shapiro-Wilk test indicated normality for all data. Least square means of the treatment were computed and the PDIFF option of the LSMEANS statement was used to determine differences among least square means at = 0.10. Also, the REG procedure was used to identify linear or quadratic relationships between root damage ratings and DM accumulation at the V12, R1, and R3 growth stages and DM yield and between DM accumulation at the V12, R1, and R3 growth stages and DM yield.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Weather conditions differed markedly between growing seasons (Table 1 ). The 2005 growing season was exceptionally warm and dry. Monthly GDD exceeded the 30-yr average by 82°C in June, 47°C in July, and 60°C in August. Precipitation totaled 55 mm less than average in May, 32 mm less in July, and 21 mm less in August. Warm and dry conditions greatly reduce the minimum root node injury by corn rootworm that causes economic damage (Oleson et al., 2005).

Seed or soil-applied insecticides did not affect plant densities at the V4 stage (Table 2 ). Seed-applied insecticides control soil insects such as seed corn maggot and wireworm that can reduce plant densities of corn (Cox et al., 2007). Evidently, these soil insects were not present in adequate numbers to affect plant densities in this study.

Root node damage ratings at the R1 stage averaged 1.40 in the control (Table 2), which indicate that one full root node was pruned with significant damage to the second node (Oleson et al., 2005). Limited root lodging, however, was observed at harvest and all plants that had root lodging were harvestable. Nevertheless, a 1.40 root node damage rating should result in economic injury to corn under conditions of moderate environmental stress, even at low corn prices (Oleson et al., 2005). All seed-applied and seed/soil-applied insecticide treatments had root node injury levels of less than 0.40, which indicate commercially acceptable control of corn rootworm in an environment with moderate environmental stress (Oleson et al., 2005). The soil-applied insecticide treatment, tefluthrin, however, had a root damage rating of 0.57, which was similar to all treatments, including the control. Wright et al. (2000) reported that tefluthrin did not have as good a control as other soil-applied insecticides but did provide commercially acceptable control. Under moderate environmental stress, a 0.57 root node injury score could result in economic injury to a high-valued corn crop (Oleson et al., 2005).

The 1.25 mg a.i. clothianidin treatment had greater total DM accumulation at the V12 stage when compared with the control and treatments with the soil-applied insecticide, tefluthrin, and seed-applied insecticide, thiamethoxam (Table 3 ). Godfrey et al. (1993) reported a reduction in corn DM accumulation at the V12 stage when corn rootworm damaged more than one root node. Likewise, Riedell and Reese (1999) reported a reduction in corn DM accumulation at the V12 stage with severe larval feeding damage in a greenhouse study. Spike and Tollefson (1991) and Hu et al. (1997), however, reported no reduction in total DM accumulation at the V12 stage when corn rootworm damaged less than one root node. Corn rootworm damage may help explain why the control had less DM accumulation but it is not clear why the tefluthrin and thiamethoxam treatments has less DM accumulation at the V12 stage when compared with the 1.25 mg a.i. clothianidin treatment. The correlation between root node damage ratings and DM accumulation was significant but weak (r = –0.28, n = 48), which indicates that other factors also contributed to differences in total DM accumulation among treatments at the V12 stage.

The 1.25 mg a.i. clothianidin and the 1.25 mg a.i. clothianidin–tefluthrin treatments had greater total DM accumulation at the R3 stage, 3 wk after silking, when compared with the control and tefluthrin treatments (Table 3). Root node damage ratings and total DM accumulation at the R3 stage once again had a significant but weak negative correlation (r = –0.32, n = 48). Spike and Tollefson (1991) reported a reduction in total DM accumulation, a few weeks after silking, in a stressful year with significant root damage ratings but no reduction in a year with minimal stress and moderate root damage ratings. Evidently, corn rootworm damage affects total DM accumulation of corn during vegetative and early reproductive stages but the response is not predictable or consistent and is very dependent on the degree of damage and environmental conditions.

The 1.25 mg a.i. clothianidin and 1.25 mg a.i. clothianidin–tefluthrin treatments had greater DM yields when compared with the control (Table 4 ). The 9 to 12% lower yield in the control, which had moderately severe root damage ratings, is consistent with results of another corn silage study in New York under conditions of moderate environmental stress (Davis, 1994). The control also had 9 and 7% lower grain yields, respectively (data not shown). The 1.25 mg a.i. clothianidin–tefluthrin treatment had greater DM yield compared with all other treatments except the 1.25 mg a.i. clothianidin treatment. Root node damage ratings and DM yields had a significant negative correlation, but root damage ratings explain only 20% of the DM yield variation (y = 18.5 – 1.56x, r² = 0.20, n = 48). Evidently, other factors, in addition to corn rootworm damage, contributed to DM yield variation in this study, as indicated by the similar DM yields between the control and the thiamethoxam treatment, despite different root node injury ratings.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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