Fungicide Use in Corn

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 CORN Shelby,* P.W. 1 , Newman, M.A. 2 , Thompson, M.A. 3 , Williams, R.C. 4 1 Extension Agent, University of Tennessee Extension Gibson County, 1252 Manufacturers Row, Trenton, TN; 2 Extension Specialist, University of Tennessee Extension, 605 Airways Blvd., Jackson, TN; 3 Extension Specialist, University of Tennessee Extension, 605 Airways Blvd., Jackson, TN; 4 Extension 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

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). Conclusions

Irrigated location = +14 bu/A avg. increase

100% hybrids returned on investment

Consistently predict yield increases

MREC location = +3 bu/A avg. increase

Greater than 10 bu/A yield increase

in 3 of 22 hybrids

Did not always link disease susceptibility to response

Gibson County Farm location

Greater than 10 bu/A yield increase in 1 of 20 hybrids

Figure 1. Gray Leaf Spot 7 200 207 T 6 oz/a Pioneer 33V14 Headline 12 196 208 T 6 oz/a Pioneer 33V14 Quadris 9 228 237 MS 6 oz/a Pioneer 33R76 Headline 17 225 242 MS 6 oz/a Pioneer 33R76 Quadris 25 193 218 S 6 oz/a Pioneer 32T22 Quadris 16 202 218 S 6 oz/a Pioneer 32T22 Headline Difference Bu/A Unsprayed Bu/A Sprayed Bu/A Susceptibility to GLS Rate MREC Treatments at tassel 166.7 164.3 172.4 173.2 163.9 177.1 170 166.9 172 172.4 172.9 Sprayed Bu/A 161.6 158.1 165.6 165.4 159.9 171.1 166.1 157.1 161.8 159 158 Unsprayed Bu/A 3.9 T 59 Dairyland 7212 Bt/RR2 9.8 MS-T 50 AgVenture 8036 RR2Bt 10.2 MS 30 Crows 4842S RR2/Bt 13.4 S-MS 19 Asgrow 715 RR2/Bt 14.9 S-MS 56 Dyna-Gro 57B90 RR/Bt/RW 6 MS 92 Dekalb 61-66 RR/Bt/RW 4 MS 63 Dekalb 63-46 RR/YG S S S S-MS Susceptibility to GLS 5.1 83 Vigoro V52 RP73 6.2 53 Dairyland 7611 RR2/Bt 6.8 39 Croplan 6886 RR2/Bt 7.8 30 Asgrow 715 RR2 Difference Bu/A % Tassel MREC Early RR/STX Trial 164.2 130.3 129.6 Sprayed Bu/A 160.3 124 142.5 Unsprayed Bu/A 6.3 MS 25 FFR 650 RR/Bt 12.9 S 30 Croplan 6440 RR2/Bt S-MS Susceptibility to GLS 3.9 30 Asgrow 715 RR2/Bt Difference Bu/A % Tassel Gibson Co. Farm Early RR/STX Trial