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Issue No. 21, Article 2/September 9, 2011

Preliminary Root Ratings for 2011 University of Illinois Corn Rootworm Trials

Each year investigators with the University of Illinois Insect Management and Insecticide Evaluation Program evaluate products for protecting roots from corn rootworm injury. The research trials are conducted at the University of Illinois Research and Education Centers near DeKalb (DeKalb County), Monmouth (Warren County), Perry (Pike County), and Urbana (Champaign County).

In 2010 we established a "trap crop" (late-planted corn interplanted with pumpkins) at each location; the trap crop helps concentrate egg-laying by female corn rootworms to provide a good environment for the insecticidal seed treatments, soil insecticides, and Bt hybrids we are testing. All of this year's trials were planted in early May, and conditions in late spring and early summer were favorable for the development of corn rootworm larvae. In mid-July we evaluated the various treatments by rating roots on the 0-3 node-injury scale developed at Iowa State University. A rating of 0.00 indicates that the root experienced no feeding injury by corn rootworms, and a rating of 3.00 indicates that three or more entire nodes (circles of roots) were destroyed by corn rootworm feeding.

While some producers throughout Illinois may have observed more corn rootworms in their fields this summer, the overall pressure we observed was similar to that of 2010. As in 2010, we omitted results from Monmouth and Perry because corn rootworm injury was very low. In 2011 the overall average node-injury ratings for the untreated checks were 0.26 at Monmouth and 0.37 at Perry. The comparable ratings at DeKalb and Urbana in 2011 were moderate (1.41 and 1.19, respectively) and slightly lower than in 2010 (1.86 and 1.58). However, this year's moderate level of injury may still result in yield loss, especially with the dry conditions that occurred at our trial sites. We will share the yield data after harvest is complete.

In DeKalb, the soil- and seed-applied insecticides provided adequate protection against corn rootworm injury when used alone (Table 1). In Urbana, however, roots in these treatments experienced significant feeding injury. The difference in rainfall between these locations in late spring and early summer and the solubility of the products may have contributed to the differences.

In general, the rootworm-Bt hybrids provided excellent protection against larval feeding in both DeKalb and Urbana. Herculex XTRA, SmartStax, and YieldGard VT3 provided similar levels of protection (Table 1). However, it is noteworthy that Agrisure 3111 and Agrisure 3000GT roots had more injury than other rootworm-Bt hybrids, similar to what we observed last year.

Adding a soil-applied insecticide to a rootworm-Bt hybrid did not significantly reduce node-injury ratings for the Herculex XTRA, SmartStax, or YieldGard VT3 treatments at either DeKalb and Urbana, (Table 1). However, ratings were significantly improved for Agrisure 3111 and Agrisure 3000GT with the addition of a soil-applied insecticide (Counter 20G or Force 2.1CS). Adding a soil insecticide to a Bt hybrid designed to offer corn rootworm protection is not a standard recommendation. If a producer has experienced significant infestations of white grubs and wireworms and still intends to use a Bt hybrid, a soil insecticide applied in-furrow should be considered. However, if rootworm protection is the primary goal, using a rootworm-Bt hybrid or a soil insecticide should work well independent of each other.

Table 1. Preliminary node-injury ratingsa and mean separationsb for corn rootworm control products in University of Illinois research trials near DeKalb and Urbana, 2011.

Product

Ratec

Placementd

DeKalbe

Urbanaf

Soil- and seed-applied insecticides

Aztec 2.1G (DKC61-22g)

6.70

NU furrow

0.07 e

0.31 ef

Poncho 1250 (DKC61-22h)

1.25

Seed

0.13 e

0.68 cd

Rootworm-Bt hybrids

Agrisure 3111 (Garst 84U58 3111h)

-

-

0.63 bc

0.41 de

Agrisure 3000GT (Golden Harvest H-8577 3000GTh)

-

-

0.50 cd

0.40 de

Herculex XTRA (Mycogen 2T789h)

-

-

0.17 de

0.05 f

SmartStax (Mycogen 2T784h)

-

-

0.03 e

0.05 f

YieldGard VT3 (DKC62-97g)

-

-

0.08 e

0.15 ef

SmartStax (DKC61-21g)

-

-

0.01 e

0.02 f

Soil-applied insecticides + rootworm-Bt hybrids

Counter 20G + Agrisure 3111 (Garst 84U58 3111h)

4.50

SB furrow

0.01 e

0.06 f

Counter 20G + YieldGard VT3 (DKC62-97g)

4.50

SB furrow

0.02 e

0.02 f

Force 2.1CS + Agrisure 3111 (Garst 84U58 3111h)

0.46

Band

0.04 e

0.05 f

Force 2.1CS + Herculex XTRA (Mycogen 2T789h)

0.46

Band

0.01 e

0.02 f

Force 2.1CS + SmartStax (DKC61-21g)

0.46

Band

0.00 e

0.01 f

Force 2.1CS + YieldGard VT3 (DKC62-97g)

0.46

Band

0.02 e

0.02 f

SmartChoice 5G + Agrisure 3111 (Garst 84U58 3111h)

3.50

SB furrow

0.03 e

0.06 f

SmartChoice 5G + Herculex XTRA (Mycogen 2T789h)

3.50

SB furrow

0.02 e

0.01 f

Untreated checks

DKC61-22g

-

-

0.98 b

0.87 bc

Garst 84U58 GTh

-

-

1.45 a

1.04 bc

Golden Harvest H-8577 GT/CB/LLh

-

-

1.65 a

1.15 b

Mycogen 2T777h

-

-

1.55 a

1.70 a

aNode-injury ratings are based on the 0-3 root-rating scale developed by Oleson et al. (2005).
bMeans followed by the same letter within a column do not differ significantly (P = 0.05, Duncan's New Multiple Range Test).
cFor band and furrow treatments, rate is reported as ounces of product per 1,000 row feet; for seed treatments, rate is reported as milligrams of active ingredient per seed.
dBand--insecticide applied in a 5-inch band over the planted row; NU furrow--insecticide directed into the seed furrow by modified noble metering units; SB furrow--insecticide directed into the seed furrow by a SmartBox insecticide delivery system; seed--insecticide applied to seed prior to planting.
ePlanted on May 10 into an area planted to a trap crop in 2010 (late-planted corn with pumpkins); Roots were evaluated on 18 July, 2011.
fPlanted on May 11 into an area planted to a trap crop in 2010 (late-planted corn with pumpkins); roots were evaluated on July 14.
gSeed treated with Poncho 500, 0.50 milligrams of active ingredient per seed.
hSeed treated with Cruiser 250, 0.25 milligrams of active ingredient per seed.

In the coming weeks we will begin harvest, and we look forward to sharing that information, as well as the results from many of our other insect management trials, in our upcoming annual report, On Target: Annual Review of University of Illinois Insect Management Trials.--Nick Tinsley, Ron Estes, and Mike Gray

Authors:
Nick Tinsley
Ron Estes
Mike Gray

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