69

Applied Crop Protection 2016

V Disease control in sugar beet Lise Nistrup Jørgensen, Rose Kristoffersen, Helene Saltoft Kristjansen, Sidsel Kirkegaard & Anders Almskou-Dahlgaard

Control of powdery mildew, rust and ramularia leaf spot Twofieldtrialswerecarriedoutin2016insugarbeetinordertotesttheefficacyofdifferentfungicides.The trials were sited at Aarhus University (AU) Flakkebjerg and the cultivar Fairway was used. Products forwhichhighefficacyagainstbeetrustwasexpectedwerecompared.Therateofeachproductwassplitintotwoapplications,carriedouton25Julyand26August.Rustwasthefirstdiseasetoappearinthefieldandtheinitialapplicationwascarriedoutwhenthefirstsymptomsweredetected.Alltreatmentsprovidedsignificantreductionoftheleafdiseasespresent(Table1andFigure1).Cleardifferenceswereobserved between products and also between rates. Regarding control of rust Comet at full rate was su-perior to other products but half rate of Comet, Opera and Armure also provided good and very similar control. 0.5 l/ha Acanto, 0.25 l/ha Bumper 25 EC and 0.25 l/ha Rubric were least effective in controlling rust.TherankingoftheproductsisshowninFigure1.Frommid-Septembersignificantattacksofmil-dew developed. For control of this disease Comet was superior as well followed by Opera and Armure. Ramularialeafblotchdevelopedlateandtheefficacyoftheproductsrankedequaltotheotherdiseases.At the time of the last assessment, plants treated with Comet had a more upright growth and looked healthier than other treatments.

The trial was harvested in November. During harvest the yield was measured in beets from 2 rows per plot and adjusted for content of soil. Samples from each treatment were analysed for sugar content. Yieldsincreasedsignificantlyfrommosttreatmentsvaryingbetween2.3and10t/ha.Thebetteryieldswere linked to the treatments that provided best disease control (Figure 2).

Table 1. Effects of different fungicides on leaf diseases in sugar beet as well as yield responses following 2 applications. 1 trial (16391-1).

Treatmentsl/ha

% beet rust % beet mildew %Ramularia

Yield and increase

Sugar yield

31-08 14-09 28-09 14-09 28-09 28-09 t/ha t/ha 1. Untreated 10.3 10.8 28.8 5.3 25.0 15.0 88.9 16.82. Opera 2 x 0.25 2.8 9.8 20.8 3.0 13.0 9.5 +9.8 19.23. Opera 2 x 0.5 0.7 4.5 13.5 1.1 11.0 5.8 +9.5 19.04. Rubric 2 x 0.25 3.8 8.0 23.8 3.0 18.8 12.8 +2.6 17.25. Rubric 2 x 0.5 2.8 7.3 19.3 2.0 13.5 9.5 +3.9 17.76. Comet 2 x 1.0 0.4 1.6 6.3 0.8 6.5 2.5 +8.4 18.87. Comet 2 x 0.5 0.5 3.8 11.0 1.0 10.3 4.0 +6.6 18.28. Armure EC 2 x 0.3 0.9 5.3 11.8 1.6 11.0 6.8 +10.6 19.09. Acanto 2 x 0.5 2.8 10.8 25.0 3.8 18.8 12.3 +5.0 18.110. Bumper 25 EC 2 x 0.25 6.5 9.5 22.5 4.0 17.5 13.3 +2.3 17.5LSD95 1.8 3.5 4.8 2.1 5.1 2.3 4.0 0.8

70

Untreated crop with attack of mildew, rust and Ramularia.

Crop treated with double treatments of 1.0 l/ha Comet.

Rust and mildew in sugar beet. Photo from drone (Nov.), when clear differences between treatments were still visible. (Photo: Uffe Pilegård Larsen).

71

Figure 1. Relative control of rust and mildew in sugar beet following 2 treatments with different fun-gicides.

Figure 2. Relative yield of sugar beet roots measured in total and relative sugar yield.

72

In a second trial different treatments were compared. The standard treatments from the trial are shown in Table 2. Both Propulse and Opera provided good control of all 3 diseases. A slight dose response effect wasmeasuredforPropulse.FullrateofPropulseandOperabothprovidedsignificantyieldincreases,and an increase in sugar content was measured from treated plots.

Anadditionalgreenhousetrialwasconductedtotestfungicideefficacyofbothexistingsystemicprod-uctsandnewproductsthatmighthaveaneffectagainstbeetrust.Theexperimentwasartificiallyinoc-ulatedwithfreshrustsporescollectedfromthefieldinlateAugust.ThecultivarusedwasFairwayasinthefieldtrials.Productsweretestedfortheirpreventiveandcurativeeffectandtreatmentswerecarriedout on either 22 August or 30 August.

Allproductscontainingsystemicfungicidesreducedrustsignificantly(Table3).CometProreducedrustlevelthemostasinthefieldtrial,butwasnotsignificantlydifferentfromtheothersystemicproducts.For the possible resistance inducers Serenade had some effect when used preventively and hydrogen peroxide exhibited no or very little control.

Table 2. Effects of different fungicides on powdery mildew and rust in sugar beet as well as yield re-sponses following 2 applications. 1 trial (16390-1).Treatments, l/ha %

rust %

mildew%

RamulariaYield and increase

Sugar yield

Date 15-08 31-08 14-09 31-08 14-09 14-09 t/ha t/ha1. Untreated 1.4 9.0 9.5 2.3 15.0 5.8 94.1 16.42. Propulse 1.2 0.4 2.0 1.8 0.2 0.3 0.6 +8.1 18.43. Propulse 1.0 0.4 2.3 5.0 0.2 1.6 1.8 +5.4 17.54. Opera 1.0 0.4 0.8 1.3 0.0 0.7 0.7 +9.0 18.5LSD95 0.4 1.9 2.7 0.9 3.6 1.5 5.6 1.0

Powdery mildew in beet.

Rust in beet.

73

Table 3.Efficacyofdifferentfungicidesaspreventiveorcurativetreatmentagainstbeetrustinsugarbeet. Greenhouse experiment.

Preventive treatment Curative treatmentTreatments, l/ha Rust pustules/leaf Significance letter Rust pustules/leaf Significance letter1. Untreated 122.4 b 122.4 b2. Comet Pro 1.25 0.0 a 0.1 a3. Opera 1.0 0.2 a 6.4 a4. Rubric 1.0 1.7 a 0.1 a5. Armure 0.6 7.1 a 1.4 a6. Serenade 6.0 29.1 b 131.1 b7. Hydrogen peroxide 2.0 150.9 b 72.2 b