Does Lorsban 4E applied at planting (T-Band) for corn rootworm larval control provide yield protection not different from Lorsban 15G applied at planting?

John T. Shaw and James W. Finger

Summary

Plot Information and Methods

Location

University of Illinois Foundation Shaw Farm, Urbana, Illinois.

Plot Size

Each treatment was applied to 2 rows 70-feet long.

Experimental Design

A randomized complete block with 8 replications was utilized as the experimental design. Included within each replication were 2 untreated control plots. Data collected from the untreated control plots were averaged for the ANOVA.

Planting Date and Agronomic Factors

See Table 7.1.

Pre-treatment Population

Trial area was planted to a trap crop (late planted corn and pumpkins) in 1995 in an effort to enhance oviposition and increase larval densities in 1996.

Method of Application for Granules at Planting Time

Granular insecticides applied at planting were metered through Noble units mounted on each of the four planter units (John Deere, 7000 series, four-row Max-Emerge planter). The planting-time granules were applied in a 7-inch band ahead of the firming wheels on the planter. Spring tines mounted behind each planter unit were used to incorporate the insecticide.

Method of Application for Liquids at Planting Time

Liquid applications of Lorsban 4E were applied in a 7-inch band at planting through 2 (650067) flat fan nozzles (1 per row) calibrated to deliver 4.2 gpa at 34 psi and a speed of 3 mph.

Stand Counts

Stand count data were determined for each location by recording the number of plants per 0.001 acre (17.4 linear feet of row).

Phytotoxicity

There were no indications of phytotoxicity in this trial.

Post-Treatment Evaluation of Rootworm Injury

Five plants per treatment per replication were evaluated for rootworm injury. The root-rating system used was the Iowa State University root-rating scale described by Hills and Peters (1971):

1. No visible damage or only a few minor feeding scars.
2. Some roots with feeding scars but none eaten off to within 1.5 inches of the plant.
3. Several roots eaten off to within 1.5 inches of the plant but never the equivalent of an entire node of roots destroyed.
4. One node of roots destroyed or the equivalent.
5. Two nodes of roots destroyed or the equivalent.
6. Three or more nodes of roots destroyed.

The consistency ratings were based on the percent of the total number of roots examined for each treatment that had root ratings below 4.0. The 4.0 rating was used because it more closely approximates the larval injury that current corn hybrids can tolerate without economic loss (research currently in progress by Michael E. Gray and Kevin L. Steffey).

Yield

Yields were determined from grain weights obtained by mechanically harvesting the remaining plants in both treated rows for all 8 replications. A Gleaner K combine with electronic scales mounted in the hopper was used. All weights were converted to 15.5% moisture and reported as bushels per acre (Table 7.3).

Weather Information

See Appendix A, Table A.3 and Table A.4

Soil Information

See Appendix B.

Statistical Analysis

Data were analyzed with the Pesticide Research Manager version 5.0, from Gylling Data Management, Inc.(GDM).

Results and Discussion

All three treatments in this trial, Lorsban 4E, Lorsban 15G, and Counter 20CR, were significantly better than the untreated control plots for root ratings (Table 7.2) and yields (Table 7.3).

References Cited

Hills, T.M. and D.C. Peters. 1971. A method of evaluating post-plant insecticide treatments for control of western corn rootworm larvae. J. Econ Entomol. 64: 764-765.

Table 7.1: Agronomic factors for the DowElanco corn rootworm soil insecticide trial at Urbana, Illinois, 1996

Variables

Urbana

Planting date

May 21

Hybrid

Pioneer 3394

Plant population

26,100

Row spacing

30-inch

Soil condition
(top 2-3 inches)

moist

Wind

5-10 mph

Previous crop

trap crop (corn + pumpkins)

Soil insecticides

none (95)

Herbicides

Dual II 2.5 pt/A, 2 qt/A Atrazine,
1 qt Crop Oil
post emergence

Fertilizer

N 150 lb/A anhydrous
May 17

Fall tillage

chisel plow

Spring tillage

disk (twice)
tilthmaster (once)

Cultivation date

June 20

Evaluation date

July 15

Harvest date

November 11

Table 7.2 Mean root rating and consistency ratings for the DowElanco corn rootworm soil insecticide trial, Urbana, Illinois, 1996

Treatment

Rate¹

Placement²

Root rating³

Consistency rating³

Counter CR

1.3

band

2.55 b

100

Lorsban 15G

1.3

band

2.81 b

95

Lorsban 4EC

1.0

band

2.98 b

83

Control

4.14 a

16

Table 7.3 Mean stand count and mean yeild for the DowElanco corn rootworm soil insecticide trial, Urbana, Illinois, 1996

Treatment

Rate¹

Placement²

Stand count³

Mean yield bu/A^4,5

Control

25.63

111.8 b

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