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:

Kelly.c.Cooper@ndsu.edu

Impact of Inoculation Timing on Seed Yield and Quality in Confection Sunflowers

M. Wunsch, B. Kraft, M. Schaefer and S. Kallis, L. Besemann and H. Eslinger

Methods

General Agronomics: The study was on a Maddock sandy loam soil type. The soil fertility results from the fall soil test: pH = 7.5; 1.6% organic matter; soil N 22 lbs/acre; soil P = 25 ppm, soil K = 181 ppm, soil S 24 lb/acre and soil Zn = 1.09 ppm. The previous crop was spring wheat and the tillage operation consisted of disking once followed by two passes with a multiweeder to smooth the seedbed and incorporate the herbicide Trust (4 lbs/gal trifluralin; Winfield Solutions) applied at 1 pt/acre preplant incorporated June 1.

Experimental design: A completely randomized block design with nineteen replicates. The seeded plot size was 10 feet (center to center) by 20 feet long. The harvested plot size was ten feet (center to center) by approximately seventeen feet long. There were four rows per plot and the row spacing was 30 inches. Guard plots (10 feet wide) were established along all perimeters of the trial.

Planting details: Nuseed ‘Jaguar’ sunflowers were planted on June 1 using a Monosem vacuum precision planter. The seeding rate was 3.83 seeds/linear foot of row = 60,000 seeds/acre. The final plant population was 1 plant every 12 inches of row = 17,400 plants/acre. The final population was established by manual thinning the sunflowers at the V2 growth stage June 17 and June 18.

Disease establishment: Spore solutions were prepared by adding laboratory-grown ascospores of Sclerotinia sclerotiorum to non-chlorinated water and adding one to two drops of Tween 20. Hand-held spray bottles were calibrated to determine how much liquid was released through each squirt of the bottle, and the spore solution was adjusted so that approximately 30,000 spores were delivered through 3 squirts of the spray bottle.

Inoculation methods – R5.1 to R5.3 inoculation timing: Inoculations were conducted over multiple days such that every head was inoculated at R5.1 to R5.3 (10 to 30% of the disk flowers blooming or already bloomed). In each inoculation, approximately 30,000 spores were delivered through three squirts of the spray bottle.

Inoculation methods – R5.4 to R5.6 inoculation timing: Inoculations were conducted over multiple days such that every head was inoculated at R5.4 to R5.6 (40 to 60% of the disk flowers blooming or already bloomed). In each inoculation, approximately 30,000 spores were delivered through three squirts of the spray bottle.

Inoculation methods – R5.7 to R5.9 inoculation timing: Inoculations were conducted over multiple days such that every head was inoculated at R5.7 to R5.9 (70 to 90% of the disk flowers blooming or already bloomed). In each inoculation, approximately 30,000 spores were delivered through three squirts of the spray bottle. Supplemental overhead irrigation was applied to this trial through a micro-sprinkler misting system, with the frequency and intensity of irrigation adjusted relative to weather conditions.

Disease assessments: Disease assessments were conducted on August 25 and August 26 at the R7 growth stage and on September 10 and September 11 at the R8 growth stage. Each plant was evaluated for the percent of the head exhibiting Sclerotina head rot.

Harvest and seed yield and quality assessment: Plants were manually clipped and bagged on September 16 and September 17 as the sunflowers approached maturity (sunflowers reached R9 on September 11) and subsequently run through a combine. To adjust yield data to standard moisture levels, seed moisture levels were assessed from all plots at harvest. The entire plot was harvested, and plot-level yields were adjusted to a standard 10% moisture level. The percent sclerotia (by weight) in the harvested grain was assessed by manually removing all sclerotia from a 120-gram subsample of grain from each plot.

Statistical analysis: Data were evaluated with analysis of variance except those data sets for which multiple plots included missing data (Sclerotinia heat rot severity, shattering incidence and severity; for these data sets, any plots in which no disease was observed were recorded as missing data). 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.The R9 Sclerotinia head rot incidence and severity index data and % seed over 25/64 sieve for hybrid ‘12GCF05’ exhibited a moderate deviation from normality due to outliers; a systematic transformation could not be found that addressed the problem, and the untransformed data were analyzed. For data that violated model assumptions, a systematic natural-log transformation [LN(x+1) for data sets with values less than 1, otherwise LN(x)] was applied. Assessment of whether results differed by inoculation timing and/or hybrid and whether there was an interaction between inoculation timing and hybrid: Analyses were conducted with replicate, main factor, main-factor by replicate interaction, sub-factor, and sub-factor by main-factor interaction in the model, with F-tests for replicate and the main factor (hybrid) utilizing replicate-by-hybrid interaction for the error term. Assessment of inoculation timing: The impact of inoculation timing treatments was evaluated separately for each hybrid; where no significant (P < 0.05) hybrid x inoculation treatment interaction occurred, it was also evaluated in the combined data across hybrids, with data from each hybrid considered a separate replicate (for a total of 16 replicates). 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. Analyses were implemented in PROC UNIVARIATE and PROC GLM of SAS (version 9.3; SAS Institute, Cary, NC).

Conclusions:

* Disease was most severe when sunflower heads were inoculated when 10-30% and 70-90% of disk flowers were blooming or had already completed bloom. The reduced disease development observed when inoculations were conducted when 40-60% of disk flowers were blooming or already completed bloom may have been caused by environmental conditions less favorable for disease when sunflowers were predominantly at this growth stage.

* Yields were reduced 0.44 to 0.53% for every 1% increase in the average percent of heads exhibiting head rot. The impact of disease yield was similar irrespective of whether inoculations were conducted at R5.1-5.3, R5.4‑5.6, or R5.7-5.9.

* The results suggest that, to be effective, fungicides will probably need to be applied at bloom initiation when conditions favorable to disease occur.

This material is based upon work supported by the U.S. Department of Agriculture, Agricultural Research Service, under agreement No. 58-5442-4-018. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

Table 1. Disease, Seed Yield and Seed Quality Response to Inoculation Timing.

Sclerotinia head rot

Aug. 25-26 | R7 growth stage

Sept. 10-11 | R8 growth stage

Test

Sclerotia in harvested grain

Incidence

Severity

Sev Index

Incidence

Severity

Sev Index

Yield

weight

---------------------------------%---------------------------------

lbs/ac

lbs/bu

% by weight

Non-inoculated

ab*

2715

41.3

Inoculated once at R5.1 to R5.3 (first third of bloom)

2264

41.0

Inoculated once at R5.4 to R5.6 (second third of bloom)

2534

41.9

Inoculated once at R5.7 to R5.9 (last third of bloom)

2162

40.3

14.83

4.11

14.17

13.65

13.00

16.88

10.79

3.37

12.32

P>F:

< 0.0001

0.0127

< 0.0001

0.0282

< 0.0001

CV:

27.5

20.6

34.4

6.2

6.8

10.9

10.1

4.5

34.3

SCLEROTINIA HEAD ROT YIELD LOSS RELATIONSHIP RELATIVE TO INOCULATION TIMING

Oakes:

For every 1% increase in Sclerotinia severity index, yields were reduced 0.44% when sunflowers were inoculated at R5.1-5.3, 0.46% when sunflowers were inoculated at R5.4-5.6, and 0.53% when sunflowers were inoculated at R5.7-5.9.

Carrington:

For every 1% increase in Sclerotinia severity index, yields were reduced 0.64% when sunflowers were inoculated at R5.1-5.3, 0.58% when sunflowers were inoculated at R5.4-5.6, and 0.53% when sunflowers were inoculated at R5.7-5.9.

Oakes Irrigation Research Site