• To evaluate the response of 22 Early RR x Stacked (STX) hybrids to foliar fungicide.

• Use replicated plots; sprayed and unsprayed block at MREC and strip plots on Gibson county farm.

• Plant April 18-19 and harvest August 22-23.

• Apply no irrigation to second year corn.

FUNGICIDE USE IN CORNFUNGICIDE USE IN CORN FUNGICIDE USE IN CORNFUNGICIDE USE IN CORN

Shelby,* P.W.1, Newman, M.A.2, Thompson, M.A.3, Williams, R.C.4

1Extension Agent, University of Tennessee Extension Gibson County, 1252 Manufacturers Row, Trenton, TN; 2Extension Specialist, University of Tennessee Extension, 605 Airways Blvd., Jackson, TN; 3Extension Specialist, University of Tennessee Extension, 605 Airways Blvd., Jackson, TN;

4Extension Area Specialist, University of Tennessee Extension Gibson County, 1252 Manufacturers Row, Trenton, TN

Gray Leaf Spot (Cercospora Zeae-maydis) is a common foliar disease that can reduce corn yields. Strobilurin fungicides can effectively control gray leaf spot (GLS) when applied at the tassel emergence growth stage VT. In 2007, UT evaluated GLS control and yields with the use of strobilurin fungicides in continuous corn in irrigated and non-irrigated fields using susceptible and tolerant hybrids. Location 1 was an irrigated, replicated test plot at the Milan Research & Education Center (MREC) in a four-year continuous corn rotation, where two strobilurin fungicides were applied in 20 gallons of water per acre. Two non-irrigated studies (Location 2 and 3) were conducted in fields with a second year corn rotation using 20 to 22 Early Roundup Ready (RR) and RR stacked hybrids and one strobilurin fungicide applied with a commercial ground sprayer at 20 gallons of water per acre. Location 2 involved replicated plots arranged as sprayed and unsprayed blocks at the MREC. Location 3 was planted on a local farm as side by side sprayed and unsprayed strip plots. The break even yield was estimated to be 3.8 bu/A at $4.00/bu corn. At Location 1 in irrigated continuous corn, yield increases of +7 to +25 bu/A resulted from a strobilurin fungicide application to corn at VT where conditions were optimal for heavy GLS infection. At Location 2, 11 of the 22 hybrids had a +3.8 bu/A yield increase while only 3 of the 20 on-farm strip plots had a +3.8 bu/A yield increase at Location 3.

Abstract

Table 1. Irrigated Corn Response to Fungicides at Location 1.

Objectives

Figure 2. Examples of Tassel Emergence

Early Tassel Full Tassel

Methods

•Utilized 3 locations

•Sprayed fungicide with ground sprayer

•Strobilurin fungicide applied at corn stage VT (tassel emerged)

•Break even yield increase @ $4.00/bu was 3.8 bushels of corn

MRECTreatments at tassel Rate

Susceptibility

to GLS

Sprayed

Bu/A

Unsprayed

Bu/A

Difference

Bu/APioneer 32T22Headline

6 oz/a

S 218 202 16

Pioneer 32T22Quadris

6 oz/a

S 218 193 25

Pioneer 33R76Quadris

6 oz/a

MS 242 225 17

Pioneer 33R76Headline

6 oz/a

MS 237 228 9

Pioneer 33V14Quadris

6 oz/a

T 208 196 12

Pioneer 33V14Headline

6 oz/a

T 207 200 7

Table 2. Non-Irrigated Corn Response to Fungicide Under Moderate Drought at Location 2 (11 of 22 hybrids made at least 3.8 bushel return).

Table 3. Non-Irrigated Corn Response to Fungicide Under Severe Drought on Local Farm at Location 3 (3 of 20 hybrids made at least 3.8 bushel return).

ConclusionsIrrigated location = +14 bu/A avg. increase• 100% hybrids returned on investment• Consistently predict yield increases

MREC location = +3 bu/A avg. increase• 50% hybrids returned on investment• Greater than 10 bu/A yield increase

in 3 of 22 hybrids • Did not always link disease

susceptibility to response

Gibson County Farm location• 15% hybrids returned on investment• Greater than 10 bu/A yield increase in 1 of 20

hybrids

MRECEarly RR/STX Trial

%Tass

el

Susceptibility

to GLS

Sprayed

Bu/A

Unsprayed

Bu/A

Difference

Bu/ADyna-Gro 57B90RR/Bt/RW

56 S-MS 172.9 158 14.9

Asgrow 715RR2/Bt

19 S-MS 172.4 159 13.4

Crows 4842SRR2/Bt

30 MS 172 161.8 10.2

AgVenture 8036RR2Bt

50 MS-T 166.9 157.1 9.8

Dairyland 7212Bt/RR2

59 T 170 166.1 3.9

Dekalb 61-66RR/Bt/RW

92 MS 177.1 171.1 6

Dekalb 63-46RR/YG

63 MS 163.9 159.9 4

Asgrow 715RR2

30 S-MS 173.2 165.4 7.8

Croplan 6886RR2/Bt

39 S 172.4 165.6 6.8

Dairyland 7611RR2/Bt

53 S 164.3 158.1 6.2

Vigoro V52RP73

83 S 166.7 161.6 5.1

Gibson Co. FarmEarly RR/STX Trial

%Tass

el

Susceptibility

to GLS

Sprayed

Bu/A

Unsprayed

Bu/A

Difference

Bu/ACroplan 6440RR2/Bt

30 S 129.6 142.5 12.9

FFR 650RR/Bt

25 MS 130.3 124 6.3

Asgrow 715RR2/Bt

30 S-MS 164.2 160.3 3.9

Figure 1. Gray Leaf Spot