Oakes
Carrington
P.O. Box
531,
E-mail: Blaine.Schatz@ndsu.edu
Optimizing
Fungicide Application Timing for Sclerotinia Control in Soybeans
M. Wunsch, M. Schaefer, B. Kraft and S. Kallis, L. Besemann,
H. Eslinger
METHODS
General Agronomics: The study was on a Maddock sandy loam soil type. The
previous crop was field corn and the tillage operation consisted of disking
once with a Wishek disk (April 14) followed by three passes with a multiweeder;
once (April 29) to level the seedbed and twice to incorporate the herbicide. The
maintenance herbicide applications were Trust (4 lbs/gal trifluralin; Winfield
Solutions) applied at 1 pt/acre preplant incorporated (May 19) Roundup Power
Max 30 oz/acre (June 17) and Roundup Power Max 20 oz/acre (June 30).
Experimental design: A completely randomized block design
with six replicates, with fungicide timing evaluated within each row spacing as
a separate experiment. 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. Every treatment plot
was separated by a non-harvested buffer plot.
Planting details: Dairyland ‘DSR 0711 R2’ was seeded in
the 14-inch row experiment. Dairyland ‘DSR 0305 R2’ was seeded in the 28-inch
row experiment. The study was planted on May 21, 2015. Seed treatments used
were Apron Maxx RTA (5.0 fl oz/100 lbs seed) + Imidacloprid 4ST (3 fl oz/100
lbs seed). Imidacloprid 4ST (Willowood) contains 4 lbs/gal thiamethoxam; Apron Maxx RTA (Syngenta) contains
0.096 lb/gal mefenoxam and 0.064 lb/gal fludioxonil. Cell‑Tech
granular inoculum for soybean (minimum 100 million Bradyrhizobium japonicum viable cells/gr; Novozymes, Saskatoon, SK)
was applied in-furrow 17.2 lb/acre.
Fungicide applications:
Application
details: Fungicide were applied with a 60-inch hand boom equipped with four
equally‑spaced TeeJet 8001VS flat-fan nozzles at a spray volume of 19 gal
water/acre operated at 45 psi.
Application
A: 50% of the plants were at the R1 growth stage; wind SW at 7 MPH,
temperature 74°F, relative humidity at 56% with 40% cloud cover.
Application
B: 80-100% of the plants were at the R2 growth stage and the narrow rows
were at 100% canopy closure and the wide rows at 60% canopy closure; wind NNW
at 3 mph, temperature 80°F, relative humidity 69% with 40% cloud cover.
Application
C: 100% of the plants were at the R2 growth stage; canopy closure was 100%
in the narrow rows and 90% in the wide rows, wind S at 8 mph, temperature 76°F,
relative humidity 75% with 80% cloud cover.
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 September 15 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. All plants were assessed in each plot.
Harvest, seed yield and quality assessment: The trial was harvested on October 8. 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.
Commentary: Sclerotinia disease development was low in this
trial due to high temperatures and low relative humidity experienced in July
and August.
We appreciate partial financial support for this
project form the North Dakota Soybean Council.
Oakes
Irrigation Research Site