Oakes Irrigation Research Site
Carrington Research Extension Center * North Dakota State University
P.O. Box 531, Oakes, ND 58474-0531, Phone: (701) 742-2744, FAX: (701) 742-2700,

                                                            E-mail:  Blaine.Schatz@ndsu.edu

 Leonard.Besemann@ndsu.edu

 

Optimizing Fungicide Application Timing for Sclerotinia Control in Soybeans

Leonard Besemann, Michael Schaefer, and Michael Wunsch

 

METHODS

General agronomics:  The study was on an Embden sandy loam soil type. The soil fertility from the fall soil test:  pH = 6.9; 2.0% organic matter; soil N 44 lbs/acre; soil P = 32 ppm, soil K = 208 ppm, soil S 18 lb/acre and Zn = 4.48 ppm.  The previous crop was pinto bean and the tillage operation consisted of disking twice followed by two passes with a multiweeder to smooth the seedbed and incorporate the herbicide.  Rhizo-Flo granular inoculant for soybeans (Bradyrhizobium japonicum; Becker Underwood / BASF Corp.) was mixed with the seed immediately before planting and applied in-furrow with the seed at 170 grams per 1000 feet of row.  The maintenance herbicide applications were Trust (1 pt/acre) preplant incorporated on May 22 and two applications of Roundup Power Max (20 oz/acre) on June 20 and July 9.

 

Experimental design:  A completely randomized block design with six replicates.  The seeded plot size was 5 feet (center to center) by 20 feet long.  The harvested plot size was 5 feet (center to center) and approximately 17 feet long.  Untreated buffer plots were established between treatment plots, and guard plots were established on the edges of the trial. 

 

Planting details:  Mycogen ‘5B005R2’ was seeded at the rate of 165,000 pure live seeds/acre.  Row spacing was 14 inches (with 4 rows per plot) and 28 inches (with two rows per plot).  The study was planted on May 26, 2014.  Seed treatments used were Apron Maxx RTA (5.0 fl oz/100 lbs seed) + Cruiser (1.28 fl oz/100 lbs seed).

 

Fungicide applications:  At the R1 growth stage, fungicides were applied July 16 at 3:37-3:45 PM when 80-90% of plants had an open blossom; wind = ESE @ 3 MPH; RH 45%; 78° F; Canopy closure:  Fourteen inch = 100%; 28 inch = 60%.  At the R2 growth stage fungicides were applied July 21 at 10:37‑10:48 AM; approximately 90% of plants had an open blossom at one of the two nodes (90% at R2); wind = E @ 6 MPH; RH 79%; 86° F; Canopy closure:  14 inch = 100%; 28 inch = 90%.  In 30-inch rows, 90% canopy closure:  fungicides were applied concurrently with the R2 application timing on July 21 from 10:50-10:53 AM approximately 90% of the plants were at R2 growth stage (open blossom at one of the top two node); wind = E @ 7 MPH; RH 79%; 86° F.  In 30-inch row, 95% canopy closure:  Fungicides were applied July 22 from 1:22-1:24 PM; R2 growth stage; wind = N @ 7 MPH; RH 79%; 77° F. 

In 30-inch row, 100% canopy closure:  fungicides were applied July 25 from 11:22-11:25 AM at the late R2 to early R3 growth stage; wind = N @ 9 MPH; RH 93%; 67° F.

 

Notes and disease establishment:  The trial was established on a site with a previous history of Sclerotinia epidemics.  To promote apothecia development and disease establishment, supplementary overhead irrigation was applied to this trial via a linear irrigator.  Sclerotinia incidence and severity were assessed on Sept. 11 at the R7 growth stage using the 0 to 3 scale developed by Craig Grau (Grau and Radke 1984; Plant Disease 68: 56-58):  0 = no symptoms, 1 = lesions on lateral branches only, 2 = lesions on main stem, no wilt, and normal pod development, 3 = lesions on main stem resulting in wilting, poor pod fill, and plant death.  In each plot, 90 plants were evaluated (30 plants in each of three locations per plot).

 

Harvest, seed yield and quality assessment:  The trial was harvested on October 9.  To facilitate accurate yield assessment, plot lengths were measured shortly before harvest.  Yields were calculated on the basis of a 5-ft plot width and the measured plot length.  Seed moisture was assessed after the grain was cleaned.  Seed yield and quality results were adjusted from the grain actual moisture to a standard 13% moisture level.


 

Statistical analysis:  Data were evaluated with analysis of variance.  Assumptions of ANOVA: (1) The assumption of constant variance was assessed with Levene's test for homogeneity of variances and visually confirmed by plotting residuals against predicted values.  (2) The assumption of normality was assessed with the Shapiro-Wilk test and visually confirmed with a normal probability plot.   (3) The assumption of additivity of main-factor effects across replicates (no replicate-by-treatment interaction) was evaluated with Tukey's test for nonadditivity. All data met model assumptions.   Assessment of fungicide treatment effects:  Analyses were conducted with replicate and treatment as main factor effects.  Single-degree-of-freedom contrasts were performed for all pairwise comparisons of isolates; to control the Type I error rate at the level of the experiment, the Tukey multiple comparison procedure was employed.  Analyses were implemented in PROC UNIVARIATE and PROC GLM of SAS (version 9.3; SAS Institute, Cary, NC).

 

 

z Fungicide application timing:

R1 growth stage:  fungicides were applied July 16 at 3:37-3:45 PM when 80-90% of plants had an open blossom

and 100% of the ground was covered by the canopy (closed canopy); wind = ESE @ 3 MPH; RH 45%; air temperature = 78° F

Early R2 growth stage:  fungicides were applied July 21 at 10:37-10:48 AM; approximately 90% of plants had an open blossom at one of the top two nodes (90% at R2) and the canopy was closed (100% canopy closure);

wind = E @ 6 MPH; RH 79%; air temperature = 86° F

y Sclerotinia stem rot incidence:  assessed by evaluating 90 plants in each plot (30 plants in each of three locations per plot). 

   Evaluated on September 11 at the R7 growth stage (at least one pod on the main stem had reached its mature pod color).

x Sclerotinia severity:  Average disease severity among plants expressing Sclerotinia stem rot.  A 1 to 3 scale was employed: 

   1 = lesions on lateral branches only, 2 = lesions on main stem, no wilt, and normal pod development, 3 = lesions on main

   stem resulting in wilting, poor pod fill, and plant death.  Evaluated on September 11 at the R7 growth stage (at least one

   pod on the main stem had reached its mature pod color).

w Sclerotinia disease severity index:  Average disease severity across all plants, including those without any disease. 

   A 0 to 3 scale was employed:  0 = no symptoms, 1 = lesions on lateral branches only, 2 = lesions on main stem, no wilt,

   and normal pod development, 3 = lesions on main stem resulting in wilting, poor pod fill, and plant death.  In each plot, 90

   plants were evaluated (30 plants in each of three locations per plot). Evaluated on September 11 at the R7 growth stage (at

   least one pod on the main stem had reached its mature pod color).

* Within-column means followed by different letters are significantly different (P < 0.05; Tukey multiple comparison

   procedure).

 

 

 

 


 

z Fungicide application timing:

R1 growth stage:  fungicides were applied July 16 at 3:37-3:45 PM when 80-90% of plants had an open blossom

and 100% of the ground was covered by the canopy (closed canopy); wind = ESE @ 3 MPH; RH 45%; air temperature = 78° F.

R2 growth stage:  fungicides were applied July 21 at 10:37-10:48 AM; approximately. 90% of plants had an open blossom at one of the top two nodes (90% at R2) and 90% of the ground was covered by canopy (90% canopy closure); wind = E @ 6 MPH; RH 79%; air temperature = 86° F.

R2, 95% canopy closure:  fungicides were applied July 22 from 1:22-1:24 PM; R2 growth stage; wind = N @ 7 MPH; RH 65%; air temperature = 77° F.

R2 to R3, 100% canopy closure:  fungicides were applied July 25 from 11:22-11:25 AM at the late R2 to early R3 growth stage; wind = N @ 9 MPH; RH 93%; air temperature = 67° F.

y Sclerotinia stem rot incidence:  assessed by evaluating 90 plants in each plot (30 plants in each of three locations per plot). 

   Evaluated on September 11 at the R7 growth stage (at least one pod on the main stem had reached its mature pod color).

x Sclerotinia severity:  Average disease severity among plants expressing Sclerotinia stem rot.  A 1 to 3 scale was employed: 

   1 = lesions on lateral branches only, 2 = lesions on main stem, no wilt, and normal pod development, 3 = lesions on

   main stem resulting in wilting, poor pod fill, and plant death.  Evaluated on September 11 at the R7 growth stage (at least

   one pod on the main stem had reached its mature pod color).

w Sclerotinia disease severity index:  Average disease severity across all plants, including those without any disease. 

   A 0 to 3 scale was employed:  0 = no symptoms, 1 = lesions on lateral branches only, 2 = lesions on main stem, no wilt,

   and normal pod development, 3 = lesions on main stem resulting in wilting, poor pod fill, and plant death.  In each plot, 90

   plants were evaluated (30 plants in each of three locations per plot). Evaluated on September 11 at the R7 growth stage (at

   least one pod on the main stem had reached its mature pod color).

* Within-column means followed by different letters are significantly different (P < 0.05; Tukey multiple comparison

   procedure).

 

Partial funding for this project was provided by the North Dakota Soybean Council.

 

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