Content

Efficacy testing of hymexazol in sugar beets, Sweden 2013

Conclusion

Several soil borne pathogens can cause substantial damage to sugar beet roots. One of the most important pathogens is Aphanomyces cochlioides. In warm and wet soils, A. cochlioides infect seedlings two to three weeks after emergence. Early infections are controlled by treating the seed with hymexazol (active ingredient in Tachigaren). The standard dose used on all commercial sugar beet seed in Sweden is 14 g a. i./unit. The seed treatment is effective for four to six weeks.
This project included three field trials with 3.5; 7; 14; 18; 28 and 56 g hymexazol compared with 7 g thiram and an untreated control (in total eight entries).
At 20% emergence in the field trials, the seed treatments with 56 g hymexazol showed significantly slower emergence than all other treatments, mean 3 trials 2013, prob = 0,0045, LSD 5% = 6.1. There were however no significant differences in final plant number between the seed treatments.
No phytotoxic effect following seed treatment with hymexazol in terms of chlorosis or necrosis was observed on the plants in the field. No stunting was observed on the plants treated with 28 or 56 g hymexazol.
In addition this report has analyzed the effect of seed treatment during a ten-year period.
DSI (Disease Severity Index) has been investigated in a total of 30 field trials 2004-2013. Seed treatment reduced DSI significantly in 2013 as well as in all 30 trials.
In total, 30 trials with 0, 14, 18 and 30 g hymexazol have been analyzed 2004–2013. The results show that a seed treatment with hymexazol has a significant positive impact on all yield parameters; root weight, sugar content, sugar yield, amino-N and K+Na. Sugar yield is increased by 280 kg/ha in the standard dose 14 g hymexazol.
The plant number in treatments with hymexazol is also significantly increased with more than 5000 plants/ha compared to untreated (30 trials, 2004-2013; prob. = <0.0001, LSD 5% = 2.3).

Introduction

Several soil borne pathogens can cause substantial damage to sugar beet roots. One of the most important pathogens in Sweden is Aphanomyces cochlioides. In warm and wet soils, A. cochlioides infect young seedlings two to three weeks after emergence (Harveson and Rush, 1993; Windels, 2000). The hypocotyl rots and the seedling dies. Early seedling infections of A. cochlioides may result in low plant numbers and permanent damage to the root, resulting in severe deformations. The pathogen infects sugar beet roots through the whole growing period thus causing a general growth reduction. A. cochlioides is found in most soils in Sweden and approximately 25% of the fields have a medium to high risk of Aphanomyces root rot. Identification of fields with high risk is important for disease control (Olsson et al., 2010.).

Early infections can be controlled by treating the seed with hymexazol, the active ingredient of Tachigaren. Hymexazol is the only registered product that is effective against A. cochlioides. The standard dose used on all sugar beet seed in Sweden is 14 g/unit.

Materials and methods

General field trial information

Three field trials were conducted in 2013 according to GEP (Good Experimental Practice) standards and the following EPPO guidelines: PP 1/152 (4) Design and analysis of efficacy evaluation trials; PP 1/181 (4) Conduct and reporting of efficacy evaluation trials including GEP.

Experimental design: Randomised complete block design with four replicates. The trials were located as indicated in Figure 1 and Table 1. The single net plot size was 2.88 x 9 m = 25.92 m2. The gross plot length was 13 m which made it possible to dig up plants for evaluation of root rot.

 

Table 1. Trial series in HU-1343 2013. General information

Trial ID

HUSEC

Location Coordinates WGS 84 Soil type

 

HUF102 Skibaröd WGS 84: N 55.81123 Ö 13.53795 Medium humus rich light sand
HUF103 Norrehem WGS 84: N 55.35901 Ö 13.32294 Medium humus rich loam soil
HUF104 Östrabo WGS 84: N 55.77418 Ö 13.02982 Loam soil

 

Trial ID

HUSEC

Previous crop Variety Sowing date Seed distance,

seeds/m

HUF102 Winter wheat Harpoon 21 April 5.4
HUF103 Spring barley Harpoon 9 April 5.7
HUF104 Winter wheat Harpoon 19 April 5.7

 

 

Figure 1. Location of the three trials in series HU-1343 2013.

Treatment information

Treatments 1, 2, 3, 4, 5, 6, 7, 8 were tested in three field trials (table 2).

 

Table 2. Treatment information of trial series  HU-1343 in 2013

Trtm
No.
Treatment

Fungicide

g a. i. /unit  

Insecticide g a. i. /unit

1 Untreated 0 Imidacloprid 60
2 Thiram 7 Imidacloprid 60
3 Hymexazol 3,5 Imidacloprid 60
4 Hymexazol 7 Imidacloprid 60
5 Hymexazol 14 Imidacloprid 60
6 Hymexazol 18 Imidacloprid 60
7 Hymexazol 28 Imidacloprid 60
8 Hymexazol 56 Imidacloprid 60

In late autumn 2012, soil samples were taken from a number of different locations in the south of Sweden and tested for root rot potential in a bioassay. Sugar beet seeds were sown in pots with test soil and then put in greenhouse under conditions favorable for infection of soil borne pathogens.

 

 

 

 

Table 3. The risk of infection in soils analyzed for disease severity index (Ewaldz, 1992)

Index Risk Evaluation
0 – 20

20 – 50

50 – 70

70 – 100

No risk

Low

Medium

High

Normally no problems

Growing sugar beets could be hazardous

Under favourable conditions, damping-off is highly likely

The soils are classified into one of four risk groups (Ewaldz, 1992); no risk; low; medium and high (table 3). Three field trial locations were chosen on the basis of the results from the soil tests. The results of the analyses of soil type on each locality are shown in the appendix.

Plant number

The number of plants in the harvest rows, rows three and four, was counted three times during emergence (20%, 50% and final emergence).

Plant vigour

Plant vigour was assessed once in each trial using a scale from 0 to 100 where values below 50 indicate plants in severely reduced growth (50% yield reduction), 50–79 indicate some-what reduced growth that probably will affect yield. Values between 80 and 90 indicates that the plants only show minor damage that seldom has any effect on yield and values above 90 are nearly healthy plants.

Disease severity index

Assessments of disease severity index on field collected seedlings were performed twice in early spring. The first assessment was done when the plants had developed cotyledons and the second assessment two weeks later. In the sample area 20 randomly chosen plants were dug up and each plant was assessed for symptoms of damping-off and classified into one of six groups: 0 (healthy), 10, 25, 50, 75 and 100% (roots totally rotten, plant dead). A disease index (DSI) was calculated using the following equation developed by Larsson and Gerhardson (1990):

DSI = ((n0 * 0 + n20 * 20 + n50 * 50 + n75 * 75 + n100 * 100)/plant number)
where n = number of beets in each class.

The results are shown in the appendix. Pieces of roots were placed on agar plates and fungi were determined to genera and species based on morphology.

Harvest

After harvest, the beets in each plot were assessed for symptoms of chronic root rot using a scale 1–7. The evaluation of chronic root rot was carried out at the tare house in Örtofta (Agri Provtvätt, Örtofta Sockerbruk, Nordic Sugar).

Table 4. Assessment of chronic symptoms of Aphanomyces root rot

Score Evaluation
1 Big healthy roots without deformations
2 Big healthy roots, some with deformations
3 Roots of normal size, several with slight deformations
4 Roots with reduced size, most with slight deformations
5 Roots with reduced size, most with medium deformations
6 Roots with reduced size, most with severe deformations
7 Very small roots, all with severe deformations

 

 

 

 

 

 

 

 

 

 

 

 

Statistical analysis

All variables were analysed using Proc GLM in SAS, SAS Institute Inc. All shown treatment means are adjusted means (LSmeans) unless otherwise stated. In case of no missing values in the data set, LSmeans are equal to the aritmethic means.

Results

Weather conditions 2013

Temperature and accumulated rainfall 2012 and 2013 at Borgeby and Anderslöv is shown in Appendix 1. The growing conditions after drilling 2013 were cold which led to low disease development.

Field trials

The pre-testing of soils for the field trials showed that the DSI before drilling was 66 at Norrehem, 66 at Skibaröds gård and 74 at Östrabo. Aphanomyces cochlioides was isolated from plants in the bioassay as well as from plants collected in the field trials.

Plant number

When the plant number was counted at 20% emergence in the field trials, the seed treatments with 56 g hymexazol showed a significantly slower emergence than all other treatments, mean 3 trials 2013, prob = 0,0045, LSD 5% = 6.1 (figure 1). There were however no significant differences in final plant number between the seed treatments.

Figure 1. Plant number at 20%, 50% and 100% emergence, average over three trials 2013.
Plh20%: prob = ns; Plh50%: prob = 0.0298 LSD 5% = 4.3; Plh100%: prob = ns. T7 = tiram 7g.a.i; H3,5-H56 = hymexazol 3,5-56 g.a.i

Vigour

There were significant differences in vigour between the treatments at Skibaröd 7 June, prob = 0.0031, LSD 5% = 6.1 (figure 2).

Figure 2. Evaluation of vigour at Skibaröd 2013, 7 June. T7 = tiram 7g.a.i; H3,5-H56 = hymexazol 3,5-56g.a.i.

Disease severity 2013

The cold weather after emergence resulted in low infections of A. cochlioides. There were no significant differences in DSI 1 and 2 between the seed treatments in 2013.

Disease severity 2004-2013

DSI has been investigated in a total of 30 field trials 2004-2013. Seed treatment reduces DSI significantly in both evaluations.

Figure 3. Evaluation of DSI, 30 trials 2004-2013. DSI 1 Prob. = 0,0024, LSD 5% =1.4; DSI 2 Prob. = 0,0003, LSD 5% =1.7. Numbers under the bars indicate amounts of ingredient hymexazol (g.a.i/seed unit).

Sugar yield 2013

There were no significant differences in yield 2013.

Sugar yield 2004–2013

In total, 30 trials with 0, 14, 18 and 30 g hymexazol have been studied since 2004. The results show that a seed treatment with hymexazol has a significant positive impact on all yield parameters; sugar content, sugar yield, amino-N and K+Na.

Sugar yield is increased by 280 kg/ha in the standard dose 14 g hymexazol.

Figure 4. Sugar yield in 3 trials 2004–2013. Prob. = 0.0057, LSD 5% = 0.2.Numbers under the bars indicate amounts of ingredients hymexazol (g.a.i/seed unit)

Phytotoxicity

When the plant number in the field trials was counted 2013 at 20% emergence, the seed treatments with 56 g hymexazol showed a significantly slower emergence than the other tested doses and the control at Östrabo. There were no significant differences in the other trials.

There was no phytotoxicity in terms of necrosis or chlorosis observed on the plants in the field trials.

Conclusions

When the plant number in the field trials was counted at 20% emergence, the seed treatments with 56 g hymexazol showed a significantly slower emergence than all other entries in one of the three trials. Final plant number was however not affected.

No phytotoxic effect due to seed treatment with hymexazol in terms of chlorosis or necrosis was observed on the plants in the field. No stunting was observed on the plants treated with 28 or 56 g hymexazol.

In total, 30 trials with 0, 14, 18 and 30 g hymexazol have been analyzed 2004–2013. The results show that a seed treatment with hymexazol has a significant positive impact on all yield parameters; root weight, sugar content, sugar yield, amino-N and K+Na. Sugar yield is increased by 280 kg/ha in the standard dose 14 g hymexazol.

The plant number in treatments with hymexazol is also significantly increased with more than 5000 plants/ha compared to untreated (30 trials, 2004-2013; prob. = <0.0001, LSD 5% = 2.3).

References

Ewaldz, T. 1992. Determining the risk of damping-off in sugar beets. In: New approaches in biological control of soil borne pathogens. Eds.: Jensen, D.F., Hockenhull, J., Fokkema, N.J. OIBC/WPRS Bulletin

Harveson, R.M., Rush, C.M. 1993. An environmentally controlled experiment to monitor the effect of Aphanomyces root rot and Rhizomania on sugar beet. Phytopathology 83,
1220–1223.

Larsson, M. and Gerhardson, B. 1990. Isolates of Phytophthora cryptogea pathogenic to wheat and some other crop plants. Journal of Phytopathology 129: 303–315.

Olsson, Å., Persson, L., Olsson, S. 2010. Variations in soil characteristics affecting the occurrence of Aphanomyces root rot of sugar beet – risk evaluation and disease control. Soil biology & biochemistry 43:316–323.

Persson, L. and Olsson, Å. 2006. Åtgärder mot jordburna svampar i sockerbetor under odling och lagring 2003–2005. Project report SBU. http\:rapporter.sockerbetor.nu.

Windels, C.E. 2000. Aphanomyces root rot on sugar beet. Online. Plant Health Progress:10.1094/PHP-2000-0720-01-DG.

 

Borgeby in January 2014