Evaluation of reduced risk insecticides for management of wireworms (Coleoptera: Elateridae) on spring wheat

Principal Investigator: Dr. Gadi V. P. Reddy.

Cooperators: Dr. Frank Antwi, Amber Ferda, John H. Miller and Julie Prewett Western Triangle Agricultural Research Center, Montana State University, 9546 Old Shelby Rd, P.O Box 656, Conrad, MT 59425

Introduction

Wireworms, the larvae of click beetles (Coleoptera: Elateridae) are significant and economic pest worldwide especially in temperate and subtropical parts of the world. Wireworms as soil dwelling pests have cryptic life cycles which makes sampling difficult, and this hinders plant damage prediction. Soil-dwelling insects are economically damaging pests in many agricultural ecosystems. Wireworms are severe pests persist in the soil as larvae for several years and are often present in agricultural fields at planting (Fig-1). Plant-eating wireworms are generalist and feeds on a large variety of crops. They cause damage to seeds, root, stems, tubers, other harvestable plant parts by feeding, chewing, or drilling into below-ground plant tissues and structures, thereby enhancing pathogens, stopping plant growth or killing plants. Moreover attacks later on stems stimulates heavy production of tillers which does not lead to heads production. This injury can cause wilting, stunting, thinning, plant maturity delays, death to seedlings, which leads to yield reduction and affects crop value. When wireworm populations are extremely high entire fields can be lost. In many fields these results in patches, allows weeds to get ahead, and make use of the available moisture, thereby preventing or lessening the tillering of adjacent uninjured plants. In many agroecosystems soil-dwelling insects are difficult to manage due to the fact that poor germination, herbicide carryover, or other pest damage can be inadvertently attributed to soil-dwelling insects. Key agricultural crops affected by wireworms include wheat, barley, rye, potatoes, corn, tobacco, most vegetables, and small fruits.

Figure-1: Wireworm larvae and adult click beetle

In view of the difficulties in estimating prevalence and damage, wireworms as soil-dwelling pests are managed often with preventive insecticides applied at planting. Historically, wireworms have been managed with inexpensive, and broad-spectrum insecticides (eg. organochlorines, organophosphates, and carbamates). Wireworms are resurging as key and important pest, in view of the fact that most of the effective insecticides for their management have either been cancelled or restricted due to environmental and health concerns. Seed treatments with neonicotinoid insecticides are used currently for managing soil dwelling pests. Neonicotinoids provide seed and foliar protection for several weeks after planting, and are used widely for many crop pests due to the low used rates and enduring residual activity. However, some of these chemicals have some effects in the agroecosystem and the environment on non- target organisms (pollinators and other beneficials). Reduced risk insecticides have been used to control insect pest damage on agricultural crops. Even though entomopathogenic nematodes and fungi have shown some promise, not much work has been done in evaluating their efficacy under field conditions for wireworm management. Therefore reduced risk insecticides that can complement or serve as alternative to the seed treatment can help in reducing the amount of chemical load in the environment. Field studies were therefore conducted to evaluate the effectiveness of reduced risk insecticides and their mixtures in managing wireworms in spring wheat.

Materials and Methods

Study sites

Prior to the initiation of the experiments we extensively sampled each farm site to determine the presence of wireworm through soil digging and bait traps. The experiments were initiated in 2015 on two commercial farms in Conrad and Valier in the ‘Golden Triangle’ area of Montana from April-September. Plot sizes were 3.6 m × 1.2 m, and were separated from each other by a buffer of 0.6 m to avoid cross contamination from spray drift. Each plot comprised of 4 rows, spaced 0.3 m apart. The wheat variety ‘Duclair’ was seeded at a rate of 22 seeds per 30 cm with a four-row plot drill at both locations. The herbicide glyphosate (RT3®, Monsanto Company, St. Louis, MO) was applied before seeding, at a rate of 2.5 L/ha for weed control, following regional farming practice. Fertilizer with an N, P, K ratio of 224.2, 0, and 22.4 kg/ha was broadcast while planting, and an additional application of 12.3, 25.2, and 0 kg/ha, respectively, of the three nutrients were placed through the seed plot drill. The trials were conducted under overhead irrigated conditions with a typical application of 5 cm of water as needed. The first irrigation was applied 30 days after treatment. The insecticides and rates used are as listed in Table 1.

Plot design and data collection

A randomized complete block design (RCBD) with four replications, 3.6 m*1.2 m treatment plots separated by 0.60 m buffer zones to cross contamination of treatment effects. The number of standing plants and seed yield in each plot were recorded to assess effectiveness of the treatments. A Hege 140 plot combine was used to thrash the wheat plots to collect grain kernels for yield assessment.

Plant stand count

Emerged wheat seedlings were counted by measuring off 1 m in the middle of the centermost 4 rows in each plot. The start and end of the 1 m lengths were marked with plastic labels and seedlings were counted within these marked areas for once per week for 4 weeks after treatment. Pre-treatment plant stand counts were also taken before spray applications.

Larval wireworm sampling

Stocking bait traps were used for assessing wireworm presence and estimating their abundance. Wireworm abundance in each plot was measured when soil temperatures were between 7-10oC using stocking bait traps. The stocking bait traps were placed in the center 1 m apart at (1.3, 2.3, and 3.3 m) along the length of the plot. About 90 g of wheat seeds were placed in nylon socks, tied shut with string, leaving a tail end of about 30 cm. The traps were immersed in water for 24 hours for the grain to start germinating before using in the field. These germinating grains in the stocking traps makes them attractive for wireworms. A hole of about 7-15 cm deep and 20-25 cm wide was dug with a shovel. The nylon stocking traps were pressed down to spread the grain mixture as wide as possible. The strings were left above the soil surface to help relocate the stocking trap later. The stocking traps were then covered with about 3-5 cm of soil. A black polythene sheet of about (12 cm×12 cm) of area were then placed on the covered holes and 4 metal fabric garden pegs used to secure them on the soil surface. Three stocking traps spaced 1 m apart were placed in the middle row of each plot. The stocking traps were placed a week (7 days) before the spray applications. One trap from each plot was removed just before spraying to serve as pre-treatment population trap count. The second and third traps were removed 14 and 28 days post treatment spray applications. Larvae caught inside the stocking traps were counted in the laboratory.

Statistical analyses

The data were analyzed using SAS 9.4 (SAS Institute, Cary, NC 2012). Data on number of standing plants and larvae were analyzed using ANCOVA (analysis of covariance) and treatment differences were tested using Fisher’s Least Significant (LSD) Test). Seed yield was regressed on number of standing plants using PROC REG.

Results

Stand Protection. Plant protection as determined from stand counts taken at PT, 7 DPT, 14 DPT, 21 DPT, and 28 DPT in the various treatment plots at both locations are shown in Tables 2 and 3. In general plant stand counts decreases with time as the season progresses. At the Ledger location stand counts ranged from 20.3 to 53.2 plants per meter (Table 2). At 7 DPT Xpulse treatment resulted in the highest stand count of 25.1 (Table 2). However this was not significant when compared to the seed treatment (Gaucho 600), M1 high, and Mycotrol (Table 2). BioCeres treatment resulted in in the lowest stand count of 13.8. Among the mixtures Met52 + Gaucho 600 treatment resulted in a higher stand count of 20.8 which was significantly lower when compared to 25.1 for Xpulse or 24.4 for Gaucho 600 (Table 2). At 14 DPT Gaucho 600 treatment resulted in the highest stand protection of 22.7, and this was not significant when compared to mixtures Mycotrol + Entrust (19.3), Mycotrol + Gaucho (20.3), Met52 + Aza-Direct (19.1), and Xpulse (21.7). The treatments with single active Entrust (21.1), and M1 high (19.1) were the only treatments with stand counts that were not significant when compared to Gaucho. Water as the control had a significantly lower stand count (12.4) among the treatments (Table 2). The plant stand count at 21 DPT revealed that Gaucho had a significant higher count of 19.6 (Table 2). However, this was not significant when compared to M1 low (16.2), and M1 high (16.9), or to the mixtures Met52 + Gaucho (18.1), and Xpulse (Beauveria bassiana + azadirachtin) (17.6). BioCeres treatment had a significantly lower stand count of 11.0 when compared to Gaucho the seed treatment (Table 2). At 28 DPT Gaucho had the highest stand count (23.1), and this was not significant when compared to Mycotrol (20.0), or to the mixtures Met52 + Entrust (18.6), and Met52 + Gaucho (20.6) (Table 2). Met52 + Aza-Direct had a significantly lower stand count of 10.2 when compared to Gaucho the seed treatment at 28 DPT (Table 2).

Plant stand count varied from 26.8 to 54.9 for PT (pre-soil and granular application) at the Valier location (Table 3). Gaucho treatment had a high stand count (29.9), and this was however not significant when compared to the mixtures Mycotrol + Met52 (27.2), Mycotrol + Entrust (29.9), and Mycotrol + Gaucho (29.5) at 7 DPT (Table 3). Mycotrol treatment resulted in a significantly lower stand count of 16.6 when compared to the seed treatment at 7 DPT (Table 3). At 14 DPT plant stand count were significantly higher for Gaucho (29.7). Differences in plant stand counts were not significant when Gaucho (29.7) is compared with the mixtures Mycotrol + Met52 (26.8), Mycotrol + Entrust (26.8), Mycotrol + Gaucho (29.4) at 14 DPT (Table 3). Met52 + Aza- Direct (16.8), Met52 + Entrust (16.9) treatments resulted in the lowest stand counts at 14 DPT (Table 3). Gaucho treatment had the highest stand count of 19.0 at 21 DPT, and this was not significant when compared to the mixtures Mycotrol + Met52 (18.1), and Mycotrol + Gaucho (18.6), Met52 + Gaucho (18.4), and water (16.6) (Table 3). Met52 + Entrust treatment resulted in the lowest stand count of 12.1. Mycotrol + Gaucho treatment resulted in a significantly higher plant stand count of 20.1 at 28 DPT (Table 3). This was not significant when compared to stand counts of Mycotrol + Met52 (19.4) and Gaucho (19.9) (Table 3). M1 low treatment had a lower stand count of 10.5 and this was not significant when compared to Water, M1 high (13.9), Mycotrol (12.4), Met52 + Aza-Direct (11.9), Met52 + Entrust (12.4), Xpectro (13.9), and

BioCeres (12.8) (Table 3).

Wireworm sampling

Ledger location. The wireworm population ranged from 0 to 4 per trap at PT (Table 4). At 14 DPT Met52 + Entrust treatment had a higher wireworm population of 5.5 per trap (Table 4).

This however was not significant when compared to Entrust (4.0), M1 low (5.0), M1 high (2.3), and BioCeres (2.3) or to Mycotrol + Met 52 (2.3), Mycotrol + Entrust (3.0), Met52 + Aza-Direct (2.3), Met 52 + Gaucho (3.3), and Xpectro (2.8) (Table 4). Among the treatments Mycotrol had the lowest wireworm population of 0.3 per trap, and this was also not significant when compared to the seed treatment Gaucho (1.8) or to the water control (1.6) at 14 DPT. At 28 DPT Mycotrol had a higher wireworm of 4 per trap, which was not significant compared to M1 high (2.5), Met52 (1.5), and BioCeres (1.5), or to the mixtures Mycotrol + Met52 (1.5), Met52 + Aza-Direct (1.5), and Met52 + Entrust (2.5) (Table4). Mycotrol + Entrust had a lower trap count of 0.0, and this was not significant when compared to Gaucho and the water treatment with trap counts of 1.0.

Valier location. Wireworm population per trap varied from 1.8 to 5.3 at PT (Table 5). At 14 DPT Mycotrol + Met52 had a trap count of 1.8, which was only significant to Met52 when compared to products with one active component (Table 5). Among the mixtures this trap value of 1.8 was significant in comparison to Mycotrol + Entrust, Met52 + Aza-Direct, Met52 + Gaucho, and Xpulse which had trap counts of 0.3 at 14 DPT (Table 5). At 28 DPT the trap counts among the treatments were not significant (Table 5).

Yield traits

The yield (F33,143 = 2.52, P = 0.0002) and location effects (F1,16 = 56.48, P < 0.0001) effects were significant. However, treatment (F1,16 = 0.76, P = 0.7230) and location*treatment (F1,16 = 0.83, P= 0.6482) effects were not significant.

Ledger location. Xpulse treatment resulted in the highest yield (4743.7 kg/ha) (Table 6). However, this yield value of 4743.7 kg/ha was not significant when compared to Gaucho (4133.1 kg/ha), Entrust (4060.7 kg/ha), and Mycotrol (4033.1 kg/ha) (Table 6). Among the mixture treatments the yield due to Xpulse was not significant in comparison to Mycotrol + Met52 (3990.7 kg/ha), and Met52 + Gaucho (4420.4 kg/ha) (Table 5). The yields due to Xpectro (3436.2 kg/ha), Met52 (3445.9 kg/ha), and water (3498.5 kg/ha) were low and were however not significant when compared to Gaucho the seed treatment (Table 6). Protein content (%) of seeds were not significant among the treatments (Table 6).

Valier location. Yield due to Entrust (3541.3 kg/ha) was significant when compared to the seed treatment Gaucho (2336.3 kg/ka) (Table 7). The Entrust yield was also significant when compared to the mixtures Mycotrol + Met52 (2512 kg/ha), Met52 + Aza-Direct (2349.1 kg/ha), Met52 + Entrust (2448.1 kg/ha) (Table 7). Percent protein content of seeds were high in M1 low (15.06), and M1 high (15.15), and these were only significant when compared to the Mycotrol treatment with 13.96 % protein content (Table 7).

Yield and plant stand relationships

The relationship between seed yield and plant stand at Ledger, and Valier locations are presented in Tables 8, and 9, respectively.

Ledger location

Water. The regression models explained 0.24 to 57.36 % of the total response variation. A unit change in plant stand resulted in yield variation of -46.38 to 126.11 kg/ha at 0 to 28 DPT (Table 8).

Gaucho 600. At 0 to 28 DPT the models explained from 8.63 to 69.79 % of the variation in total response. The yield responses ranged from -175.33 to 58.85 kg/ha at 0 to 28 DPT (Table 8).

Entrust WP. The regression models explained 5.49 to 74.12 % of the total yield variation. A unit change in plant stand resulted in yield variation of -349.42 to 71.44 kg/ha at 0 to 28 DPT (Table 8). M1 low. At 0 to 28 DPT the models explained from 6.01 to 37.02 % of the variation in total yield. The yield responses ranged from -273.05 to -77.01 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 8).

M1 high. At 0 to 28 DPT the models explained from 6.08 to 99.13 % of the variation in total yield response. The yield responses ranged from -66.42 to 21.92 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 8).

Met52. The regression models explained 1.40 to 86.16 % of the total yield variation. A unit change in plant stand resulted in yield varying from -210.74 to 86.07 kg/ha at 0 to 28 DPT (Table 8).

Mycotrol. At 0 to 28 DPT the models explained from 5.24 to 67.80 % of the variation in total yield. The yield responses ranged from -106.84 to -47.80 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 8).

Mycotrol + Met52. The regression models explained 0.59 to 71.52 % of the total yield response variation. A unit change in plant stand resulted in yield variation of 6.67 to 128.44 kg/ha at 0 to 28 DPT (Table 8).

Mycotrol + Aza-Direct. The regression models explained 10.13 to 37.30 % of the total yield variation. A unit change in plant stand resulted in yield varying from -60.15 to 804.75 kg/ha at 0 to 28 DPT (Table 8).

Mycotrol + Entrust. The regression models explained 0.06 to 59.51 % of the total yield variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -63.93 to 197.81 kg/ha at 0 to 28 DPT (Table 8).

Mycotrol + Gaucho. At 0 to 28 DPT the models explained from 0.15 to 78.69 % of the variation in total yield response. The yield responses ranged from -155.77 to 128.18 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 8).

Met52 + Aza-Direct. At 0 to 28 DPT the models explained from 2.13 to 69.26 % of the total yield response variation. The yield responses varied from -138.08 to 299.05 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 8).

Met52 + Entrust. The regression models explained 0.07 to 42.86 % of the total yield variation at 0 to 28 DPT. A unit change in plant stand resulted in yield response variation of -51.75 to 94.87 kg/ha at 0 to 28 DPT (Table 8).

Met52 + Gaucho. At 0 to 28 DPT the models explained from 12.54 to 39.41 % of the variation in total yield response. The yield responses ranged from -21.45 to 14.70 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 8).

Xpectro. At 0 to 28 DPT the models explained from 1.17 to 41.08 % of the variation in total yield response. The yield responses ranged from -36.31 to 119.23 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 8).

BioCeres. The regression models explained 0.01 to 65.70 % of the total yield variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -62.37 to 69.98 kg/ha at 0 to 28 DPT (Table 8).

Xpulse. The regression models explained 1.29 to 66.41 % of the total yield variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -101.70 to 150.04 kg/ha at 0 to 28 DPT (Table 8).

Valier location

Water. The regression models explained 0.02 to 92.72 % of the total yield response variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -77.69 to 88.97 kg/ha at 0 to 28 DPT (Table 9).

Gaucho. The regression models explained 0.09 to 92.39 % of the total yield response variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -253.62 to 165.15 kg/ha at 0 to 28 DPT (Table 9).

Entrust. At 0 to 28 DPT the models explained from 0.88 to 70.60 % of the variation in total yield. The yield responses ranged from -143.80 to 153.70 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 9).

M1 low. At 0 to 28 DPT the models explained from 2.87 to 94.00 % of the variation in total yield responses. The yield responses ranged from -351.49 to 281.05 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 9).

M1 high. The regression models explained 6.11 to 87.43 % of the total yield response variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -18.59 to 140.08 kg/ha at 0 to 28 DPT (Table 9).

Met52. The regression models explained 1.32 to 92.20 % of the total yield response variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -109.56 to 110.88 kg/ha at 0 to 28 DPT (Table 9).

Mycotrol. At 0 to 28 DPT the models explained from 10.91 to 98.26 % of the variation in total yield. The yield responses ranged from -169.55 to 222.47 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 9).

Mycotrol + Met52. At 0 to 28 DPT the models explained from 0.31 to 60.23 % of the variation in total yield responses. The yield responses ranged from -112.80 to 31.03 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 9).

Mycotrol + Aza-Direct. At 0 to 28 DPT the regression models explained from 0.31 to 60.23 % of the variation in total yield responses. The yield responses varied from -112.80 to 31.03 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 9).

Mycotrol + Entrust. The regression models explained 0.23 to 64.84 % of the total yield response variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -84.93 to 35.83 kg/ha at 0 to 28 DPT (Table 9).

Mycotrol + Gaucho. The regression models explained 0.05 to 77.92 % of the total yield response variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -144.16 to 142.56 kg/ha at 0 to 28 DPT (Table 9).

Met52 + Aza-Direct. At 0 to 28 DPT the models explained from 0.01 to 41.98.23 % of the variation in total yield responses. The yield responses ranged from -164.23 to 105.13 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 9).

Met52 + Entrust. At 0 to 28 DPT the regression models explained from 0.78 to 86.69 % of the total yield response variation. The yield responses varied from -587.29 to 95.74 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 9).

Met52 + Gaucho. The regression models explained 5.35 to 82.91 % of the total yield response variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -79.57 to 240.79 kg/ha at 0 to 28 DPT (Table 9).

Xpectro. At 0 to 28 DPT the models explained from 0.47 to 86.29 % of the variation in total yield response. The yield responses ranged from -197.44 to 124.74 kg/ha at 0 to 28 DPT for a unit change in plant stand (Table 9).

BioCeres. The regression models explained 0.27 to 42.28 % of the total yield variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -232.78 to 175.76 kg/ha at 0 to 28 DPT (Table 9).

Xpulse. The regression models explained 0.06 to 43.63 % of the total yield variation at 0 to 28 DPT. A unit change in plant stand resulted in yield variation of -6.80 to 125.86 kg/ha at 0 to 28 DPT (Table 9).

Summary and conclusion

Plant stand counts raged from 10.2 to 53.2 plants/m at PT to 28 DPT across the treatments at Ledger. At Valier stand counts varied from 10.5 to 54.9 plant/m at PT to 28 DPT across the treatments. Trap counts of wireworm population of at Ledger were 0 to 4 at PT, 0.3 to 5.5 at 14 DPT, and 0 to 4.0 at 28 DPT across the treatments. At Valier trap counts were 1.8 to 5.3 at PT, 0.3 to 1.8 at 14 DPT, and 0 to 1.5 at 28 DPT across the treatments. Xpulse, Met52 + Gaucho, Gaucho, Entrust, and Mycotrol resulted in high yields at Ledger. At Valier, Entrust treatment resulted in high yield. At Ledger the regression models explained 0.01 to 99.13 % of the total yield response variation across the treatments. For a unit change in plant stand, yield responses varied from -349.42 to 804.75 kg/ha across the treatments. At Valier the regression models explained 0.01 to 98.26 % of the total yield response variation across the treatments. For a unit change in plant stand, yield responses varied from -587.29.42 to 311.85 kg/ha across the treatments.

In general plant stand counts decreases with time as the season progresses. Xpulse treatment resulted in the highest yield at Ledger. Gaucho (seed treatment) resulted in lowest yield at Valier. The results showed that active biopesticide (Beauveria bassiana, Metarhizium brunneum or spinosad can be used to complement the seed treatment for stand protection.

Acknowledgements

This work was supported by Montana Wheat and Barley Committee. We would like to thank Dawson Berg and Kristal Juisch for assistance with field work.

Table 1: Materials and rates of application in each treatment.

Table 1. contd.

a, Gaucho 600, seed treatment application rate unit (ml/45.35 kg seed).

b, Entrust WP, application rate unit (g/L).

c, Gaucho 600, seed treatment application rate unit (35.49 ml/45.35 kg seed).

d, BioCeres GR, application rate unit (20 g/m2).

Table 2. Plant stand count of wheat seedlings treated with reduced risk insecticides: Ledger

a, PT, pre foliar and granular application.

b, 7 DPT, days after foliar and granular application. c, 14 DPT, days after foliar and granular application. d, 21 DPT, days after foliar and granular application. e, 28 DPT, days after foliar and granular application.

Table 3. Plant stand count of wheat seedlings treated with reduced risk insecticides: Valier

a, PT, pre foliar and granular application.

b, 7 DPT, days after foliar and granular application. c, 14 DPT, days after foliar and granular application. d, 21 DPT, days after foliar and granular application. e, 28 DPT, days after foliar and granular application.

Table 4. Wireworm population per trap on wheat seedling plots treated with reduced risk insecticides:

Ledger

a, PT, pre foliar and granular application.

b, 14 DPT, days after foliar and granular application.

c, 28 DPT, days after foliar and granular application.

Table 5. Wireworm population per trap on wheat seedling plots treated with reduced risk insecticides:

Valier

a, PT, pre foliar and granular application.

b, 14 DPT, days after foliar and granular application.

c, 28 DPT, days after foliar and granular application.

Table 6. Yield of wheat seedlings treated with reduced risk insecticides: Ledger

Table 7. Yield of wheat seedlings treated with reduced risk insecticides: Valier

Table 8. Relationship between yield and plant stand of wheat seedlings treated with reduced risk insecticides: Ledger

Table 9. Relationship between yield and plant stand of wheat seedlings treated with reduced risk insecticides: Valier