Cotton Response to Topical Fungicide Application Darrin M. Dodds 1 C. L. Main 2, L. T. Barber 3, J. E. Woodward 4, R. Boman 4, J. Whitaker 5, K. Edmisten 6, N. W. Buehring 1, and T. Allen 1. Mississippi State University 1, The University of Tennessee 2, University of Arkansas 3, Texas AgriLife Extension Service 4, University of Georgia 5, North Carolina State University 6

Introduction Extension Cotton Specialists Working Group Research initiated in response to: –Pyraclostrobin (Headline) – 2007 –Azoxystrobin (Quadris) – 2008 –Incidence of foliar disease over past several growing seasons

Common Diseases Alternaria – lesions with brown or purple margins –Older lesions have concentric rings with center falling out in some Cercospera – small red lesions that enlarge and have white to brown center –Avoid all stress – esp. potassium, destruction of residue Ascochyta – light brown lesions that coalesce on leaves –Lesion have dark brown borders Stemphylium - small circular brown lesions with concentric rings –Older lesions have a white center which can drop out. Helminthosporium leaf spot Sciumbato 2009

Loss Due to Disease – 2008 DiseaseState ALARGALAMS Foliar Diseases% Yield Reduction Trace4 Bales Lost , ,500 Boll Rots% Yield Reduction42164 Bales Lost25,03130,33719,07520,24132,500 Total Loss% Yield Reduction Bales Lost25,65630,33785,83820,24165,000 Dollars Lost$0.65 per pound$8.0 million $9.5 million $26.8 million $6.3 million $20.3 million Blasingame et al. 2009

Leaf Spot Disease and Yields Defoliation from leaf spot diseases reduced by up to 85% following fungicide application –Not always the case Preventative fungicide applications can be effective in reducing foliar disease –Minimal effect on yield Application of fungicide in the absence of disease did not impact yield Kemerait et al Padgett et al Woodward et al. 2009

Fungicide Effects on Hardlock Hardlock –Thought to occur due to interaction of Fusarium spp. and flower thrips Results of fungicide application to control hardlock have been mixed Decreased incidence of hardlock and increased yield following Quadris application Lawrence et al Woodward et al. 2009

Fungicide Effects on Hardlock Yield increases following fungicide application have been observed Fungicide application when hardlock occurrence is <30% is ineffective Limited utility of fungicides for control of hardlock –No yield response due to foliar application Jones et al Padgett et al Mailhot et al Woodward et al. 2009

Justification Previous research has yielded mixed results –Warrants further study to determine proper utility Previous research is limited Increased sales pressure Tremendous pressure to make every dollar count

Materials and Methods Small plot research –RCBD – 4 replications Participating states: –Arkansas –Georgia –Mississippi –North Carolina –Tennessee –Texas

Treatments Common Name Trade Name Application Timing Application Code Application Rate Kg ai ha -1 oz prod ac -1 AzoxystrobinQuadris1 st BloomA st BloomA DAAB st BloomA DAAB PyraclostrobinHeadline1 st BloomA st BloomA DAAB st BloomA DAAB0.2212

Materials and Methods Locally adapted varieties utilized All agronomic and pest management practices performed according to local standards Data analyzed using Proc Mixed –Data pooled over environments Plant height Total nodes % Hardlock Gin turnout Yield Fiber quality

Figure 1. Untreated cotton foliage

Figure 2. Quadris 6 oz early bloom + 6 oz 21 d.

Figure 3. Headline 6 oz early bloom + 6 oz 21 d.

End of Season Plant Height LSD (0.05) = NSD Fungicide % of Untreated Check 5 Locations in 2008 and 2009 p = 0.47

Growth and Development FungicideRateTotal NodesHardlockTurnout # % Quadris12 oz oz oz Headline 12 oz oz oz Untreated p LSD (0.05)NS 0.01

Yield LSD (0.05) = NSD Fungicide % of Untreated Check 6 Locations in 2008 and 2009 p = 0.55

Fiber Quality FungicideRateMicStapleStrengthUniformity inches g tex % Quadris12 oz oz oz Headline 12 oz oz oz Untreated p LSD (0.05)NS NS

Return on Investment Fungicide $ Returned 6 Locations in 2008 and 2009

Conclusions Fungicides can control foliar disease –Application timing is critical No differences in plant growth and development No yield benefits No fiber quality benefits More research needed

Discussion Important to determine cause of foliar disease and/or boll rot Disease pressure usually exacerbated by other factors Fertility –Foliar disease often associated with potassium –Boll rot can be enhanced by excess nitrogen Are low nutrient levels in the soil the culprit? –What about adequate nutrients in the soil and shortages in leaf tissue?

Discussion Peak potassium uptake during 3 rd – 4 th week of bloom Early maturing, fast fruiting varieties Fungicide application is not cheap

Equivalent Costs FungicideRate Fungicide Cost Equivalent Potash Equivalent Lime w/application Quadris12 oz$ lbs1 ton oz$ lbs1.2 tons oz$ lbs1.6 tons Headline 12 oz$ lbs1.1 tons oz$ lbs1.3 tons oz$ lbs1.7 tons

Take Home Message Proper utility of foliar fungicides yet to be determined –Avoid use where not necessary due to resistance concerns Reduce plant stress Maximize profit every dollar spent

Questions