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Issue No. 20, Article 1/August 24, 2012

Root Rating Results from University of Illinois Corn Rootworm Trials

Root rating results for the 2012 season are detailed in Table 1. Each year our research team evaluates root protection products (soil insecticides and Bt hybrids) targeted at corn rootworms. We establish our experiments in fields that were devoted to trap crops (late-planted corn, interplanted with pumpkins) the previous season to increase the likelihood of sufficient pressure in our control plots to adequately challenge the treatments. Our studies are conducted at the University of Illinois Research and Education Centers near DeKalb, Monmouth, Perry, and Urbana.

Table 1. Node-injury ratingsa,b for corn rootworm control products in 2012 University of Illinois research trials near DeKalb, Perry, and Urbana.

Product

Rate

Placementc

DeKalbd

Perrye

Urbanaf

Soil insecticides

Aztec 4.67GR (DKC 64-82)g

3 oz/1,000 row ft

SB furrow

0.14 e-h

0.02 c

0.77 def

Rootworm Bt Corn Hybrids

YGVT3 (DKC64-83)g

--

--

0.66 cd

0.01 c

1.38 c

SmartStax RIB (Stone 6128 RIB)g

--

--

0.17 e-h

0.0 c

0.29 ghi

Agrisure 3000GT (Garst 84U58)h

--

--

1.78 ab

0.1 bc

1.57 bc

Agrisure 3122 Garst 84U58)h

--

--

0.31 d-h

0.0 c

0.41 g

HxXTRA (Mycogen 2K592)h

--

--

0.43 c-g

0.05 bc

0.89 de

SmartStax (Mycogen 2K594)h

--

--

0.33 d-h

--

0.33 gh

Soil insecticides + rootworm Bt corn hybrids

Aztec 2.1GR + YGVT3 (DKC64-83)g

6.7 oz/1,000 row ft

SB furrow

0.1 fgh

--

0.5 fg

Aztec 2.1GR + Agrisure 3000GT (Garst 84U58)h

6.7 oz/1,000 row ft

SB furrow

0.08 fgh

--

0.56 efg

Counter 20GR + SmartStax (Mycogen 2K594)h

6.0 oz/1,000 row ft

SB furrow

0.23 e-h

--

0.03 i

Counter 20GR + YGVT3 (DKC64-83)g

6.0 oz/1,000 row ft

SB furrow

--

0 c

--

Force 2.1CS + YGVT3 (DKC64-83)g

0.46 fl oz/1,000 row ft

Band

0.17 e-h

0.02 c

0.4 g

Force 2.1CS + SmartStax (Mycogen 2K594)h

0.46 fl oz/1,000 row ft

Band

0.13 e-h

0.0 c

0.04 hi

Force 2.1CS + Agrisure 3000GT (Garst 84U58)h

0.46 fl oz/1,000 row ft

Band

0.46 c-f

0.04 bc

0.42 g

Force 2.1CS + Agrisure 3122 (Garst 84U58)h

0.46 fl oz/1,000 row ft

Band

0.03 h

0.0 c

0.04 hi

Force 2.1 CS + Agrisure GT (Garst 84U58)h

0.46 fl oz/1,000 row ft

Band

0.81 cd

0.28 bc

0.98 d

Force 2.1 CS + HxXTRA (Mycogen 2K592)h

0.46 fl oz/1,000 row ft

Band

0.35 d-h

0.01 c

0.02 i

SmartChoice GR + HxXTRA (Mycogen 2K592)h

5 oz/1,000 row ft

SB furrow

0.05 gh

0.01 c

0.04 hi

Untreated checks

DKC64-82 RR2g

--

--

0.54 cde

0.35 b

2.06 ab

Stone 6N52 RR2i

--

--

0.88 c

0.33 bc

2.1 a

Garst 84U58 GTh

--

--

1.69 b

1.4 a

1.94 ab

Mycogen 2K591 RR2h

--

--

2.32 a

--

2.08 ab

aNode-injury ratings are based on the 0-to-3 root-rating scale developed by Oleson et al. (2005): 0.00--no feeding damage; 1.0--one node (circle of roots), or the equivalent of an entire node, pruned back to within approximately 1.5 inches of the stalk (or soil line if roots originate above ground nodes); 2.0--two complete nodes pruned; 3.0--three or more complete nodes pruned (greatest rating that can be given).
bMeans followed by the same letter within a column do not differ significantly (P = 0.05, Duncan's New Multiple Range Test).
cBand: insecticide applied in a 5-inch band over the planted row; SB furrow: insecticide applied through a SmartBox insecticide delivery system and directed into the seed furrow.
dDeKalb: Planted on April 23 into an area planted to a trap crop in 2011 (late-planted corn interplanted with pumpkins). Roots were evaluated on July 16.
ePerry: Planted on April 19 into an area planted to a trap crop in 2011 (late-planted corn interplanted with pumpkins). Roots were evaluated on July 10.
fUrbana: Planted on April 18 into an area planted to a trap crop in 2011 (late-planted corn interplanted with pumpkins). Roots were evaluated on July 9.
gSeed treated with Poncho 500, 0.5 mg a.i. per seed.
hSeed treated with Cruiser 250, 0.25 mg a.i. per seed.
iSeed treated with Poncho 250, 0.25 mg a.i. per seed.

The results from only three locations are shown in the table because the overall level of injury in our check plots at Monmouth was very low, and the root rating results are not useful in separating product efficacy. Four different check hybrids were used at each location. Overall, root injury in the control plots was greatest in Urbana, with about two nodes of roots pruned on each check treatment. Root injury ratings in the check plots at DeKalb ranged from about one-half to over two nodes destroyed. Injury at the Perry location was least severe; however, one of the check treatments averaged well over one node of roots destroyed. This is the greatest level of root injury at Perry we have observed in our corn rootworm experiments conducted there.


Corn rootworm product efficacy trial, showing the severity of the drought and rootworm injury in one of the check plots in Urbana.

A review of the results indicates that several of the Bt treatments at Urbana had root injury greater that producers would like to see. The YGVT3 and the Agrisure 3000GT treatments had nodal injury scores of 1.38 and 1.57, respectively. Although these ratings are statistically better than the check plots, this level of protection is not satisfactory. The HxXTRA treatment at Urbana had nearly one node (0.89) of roots destroyed--again, greater injury than should be expected for this product.

The other Bt hybrids in Urbana (SmartStax, Agrisure 3122) performed significantly better than the other Bt treatments. Adding a soil insecticide with a Bt hybrid generally improved the level of root protection, but it was still common for nodal injury scores to be about 0.5 for YGVT3 and Agrisure 3000GT. Nearly one complete node (0.98) of roots was destroyed in Urbana for the Agrisure GT treatment despite the addition of Force 2.1 CS. Soil conditions at our locations were exceptionally dry this season and undoubtedly negatively affected the performance of soil insecticides. The use of a soil insecticide with some of the other Bt hybrid treatments (SmartStax, Agrisure 3122, HxXTRA) did keep root injury to nearly negligible levels (minor scarring of root tissue).

Overall, the level of root injury in DeKalb was lower than in Urbana, but injury to one of the Bt treatments (Agrisure 3000GT) was nearly equivalent to two nodes of roots destroyed (1.78) and not statistically different from two of the checks for this location. When Force 2.1CS was used with Agrisure GT at DeKalb, the nodal injury score remained near one node of roots pruned (0.81). Because of the overall low pressure at Perry, the rootworm products could not be separated statistically, but all of the products had significantly less injury than one of the control treatments (1.4).

We encourage producers to review reports of University of Illinois root evaluation experiments from previous years in our On Target report. Currently, results from our field experiments can be reviewed through the 2011 season. Results from these studies and this year's evaluations can guide product selections for the 2013 growing season.--Mike Gray, Ron Estes, and Nick Tinsley

Author:
Mike Gray

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