Potato Progress

Volume 24 Number 3

9 April 2024

Effect of Anastomosis Group and In-Furrow Fungicide on Rhizoctonia Canker and Black Scurf of Potato

Jeff Miller, Trent Taysom, Terry Miller, Cheryn Suarez, and Scott Anderson

Miller Research

James Woodhall, Mackade Murdock, Hayden Woods

University of Idaho, Parma

Introduction

The fungal pathogen Rhizoctonia solani is associated with both yield and quality losses in potatoes. Yield losses result from the development of lesions on stems, stolons and roots (Figure 1). Quality losses are associated with the development of sclerotia (black scurf, Figure 1) and elephant hide on progeny tubers. Other symptoms include growth cracks and corky spots on tubers. Marketable yield losses approaching 30% have been reported (Banville, 1989) along with reductions in specific gravity and chip color quality (Otrysko & Banville, 1992).

Isolates of R. solani can be categorized into anastomosis groups (AG). Presently 13 AGs are known to exist, several of which are divided into subgroups. Individual AGs are often associated with a particular host, for example AG 1 with rice and AG 8 with cereals. Isolates of AG 3, or more specifically the subgroup AG 3-PT, are often associated with disease on potatoes. However, recent survey work funded by the Northwest Potato Research Consortium has shown that four different AGs of R. solani are present in Idaho potato crops. These are AG 3-PT, AG 2-1, AG 4 HG-II and AG 5. AG3-PT is the predominant strain, with AG 2-1 and AG 4 HG-II the next most frequently isolated. There was only one single occurrence of AG 5 being isolated from Idaho potatoes (Woodhall et al., 2022).

‍Knowledge of the AG present in a field is important. AGs can differ in host range, and thus may require different crop rotation strategies. Individual AGs appear to be more tuber-borne than soil-borne and this may indicate different management practices are needed. Different AGs can also differ in fungicide sensitivity (Kataria & Gisi, 1999, Muzhinji et al., 2018). They can also differ in growth and pathogenicity at different temperatures (Ritchie et al., 2009). For example, AG 4 and AG 5 will rarely cause significant potato disease below 59°F whereas AG 2 and AG 3 can (Carling & Leiner, 1990). AGs can also vary in the types of symptoms they cause in potato. For example AG 8 only infects roots while AG 3-PT infects roots and tubers of the potato plant (Woodhall et al., 2008) and has been shown to be the most prolific producer of black scurf on tubers (Woodhall et al., 2022). 

The source of Rhizoctonia can be seed or soil. Fungicides, as either seed treatments or in-furrow sprays, are commonly used to manage these sources of inoculum. When soil is the primary source of inoculum, in-furrow fungicides are the most effective (Atkinson et al., 2011). Azoxystrobin (e.g. Quadris) is one of the most common fungicides used as an in-furrow spray in southern Idaho and typically is one of the most effective fungicide in trials conducted at Miller Research. At a recent pest management meeting sponsored by Miller Research, 70% of attendees used an azoxystrobin-based fungicide at planting (Miller, unpublished data). Other common in-furrow fungicides that target Rhizoctonia include fluxapyroxad + pyraclostrobin (Priaxor), flutolanil (Moncut), penthiopyrad (Vertisan), and the relatively new benzovindiflupyr + azoxystrobin (Elatus). Fluopyram (Velum Prime) is a relatively new fungicide product which has found a use in-furrow for nematode control, but it has not shown activity against Rhizoctonia. In 2018 the Consortium funded a research project evaluating biological products for Rhizoctonia control. None of the biological products tested in this study had a significant effect on reducing disease severity.

A two-year research project sponsored by the Northwest Potato Research Consortium was conducted in 2021 and 2022 to evaluate disease development and impacts on yield and grade by three different AGs of R. solani under field conditions in the Northwest. A second aim of the project was to evaluate three common in-furrow fungicides versus an untreated check and to determine if fungicide effectiveness varies among AGs. There is currently no information for the Northwest comparing Rhizoctonia control in the field among different AGs.

‍Materials and Methods

Field trials were established at the Miller Research Experimental Farm near Rupert, ID in 2021 and 2022. Three different isolates of R. solani (AG 2-1, AG 3-PT, and AG 4 HG-II) were grown on sterilized rye and incorporated into the hill at planting. During the planting operation, different in-furrow fungicides were applied as a banded spray over the open furrow. Potato stems were evaluated for incidence and severity of Rhizoctonia canker in June and July (approximately 55 and 80 days after planting, respectively). At the July evaluation, below-ground stem samples were collected to evaluate the amount of DNA of the different AGs.

Yield and grade were measured after harvest, and tubers were evaluated for incidence and severity of black scurf. Tuber peel samples were collected to evaluate different AG DNA concentrations on tubers and the presence of elephant hide and scab were also assessed.

‍Results and Discussion

In the first year of the study, AG 3-PT and AG 2-1 were similar in their ability to cause stem and stolon canker (Figure 2). In 2022, AG 2-1 was not as aggressive in causing disease as AG 3-PT (Figure 3). In both years, AG 4 HGII caused relatively few canker symptoms. 

In both years, the interaction between AG and fungicide was not significant. This means that fungicides performed similarly in reducing disease across all of the AGs tested. In 2021, all three fungicides were similarly effective in reducing canker (Figure 2). In the second year, Elatus separated from the untreated check, but Quadris and Moncut did not (Figure 3). 

Rhizoctonia canker severity increases as the season progresses. Symptoms in late July (about 80 days after planting) were more severe than in June. The statistics were similar to what was observed in June, however (data not shown).  

AG inoculation did not have a significant effect on total or marketable yield (Table 1). Yield was numerically lower with AG 3-PT in 2022. In-furrow fungicide application with Elatus and Quadris increased total yield in 2021, but fungicides did not have the same effect in 2022. AG 3-PT inoculation significantly increased the percentage of culls in both years of the trial (Table 2). Most other measures of grade were not affected by inoculation or fungicide treatment (data not shown).

‍Black scurf severity was highest with AG 3-PT in both years of the study and similar between AG 2-1 and AG 4 HG-II (Figure 4 and Figure 5). In year 1, in-furrow fungicides did not significantly reduce black scurf severity (Figure 4). All fungicides reduced black scurf severity in 2022, however (Figure 5). 

‍In both years, AG 2-1 and AG 3-PT DNA was detected at higher concentrations from stems in those treatments that were inoculated with the respective AGs. This was not observed for AG 4 HG-II. All AGs were detected at similar levels in AG 4 inoculated treatments (data not shown). A similar trend was observed with tuber peel DNA.

‍Summary

AG 3-PT was significantly more aggressive at causing both stem canker and tubers scurf than AG 2-1 and AG 4 HG-II. The three in-furrow fungicides used in this trial (Elatus, Quadris, and Moncut) were generally effective in reducing canker and black scurf. AGs did not show differential sensitivity to the fungicides used in this trial. For example, Elatus usually had the lowest disease score for both phases of the disease (stem and tuber) and this was true for all three AGs. This means that potato growers currently using these fungicides do not need to change their fungicide of choice to manage Rhizoctonia for any of the three most common strains of Rhizoctonia encountered in Idaho. 

‍References

Atkinson D, Thornton MK, Miller JS, 2011. Development of Rhizoctonia solani on stems, stolons and tubers of potato II. Efficacy of Chemical Applications. American Journal of Potato Research 88, 96-103.

Banville, GJ. 1989. Yield losses and damage to potato plants caused by Rhizoctonia solani Kuhn. American Journal of Potato Research 66, 821-834.

Carling DE, Leiner RH, 1990. Effect of temperature on virulence of Rhizoctonia solani and other Rhizoctonia on potato. Phytopathology 80, 930-4.

Kataria H, Gisi U, 1999. Selectivity of fungicides within the genus Rhizoctonia. In: H L, Pe R, H-W D, Hd S, eds. Modern Fungicides and Antifungal Compounds. Andover, UK: Intercept, 421-9. 

Muzhinji N, Woodhall JW, Truter M, Van Der Waals JE, 2018. Variation in fungicide sensitivity among Rhizoctonia isolates recovered from potatoes in South Africa. Plant Disease 102, 1520-6.

Otrysko BE, Banville GJ, 1992. Effect of infection by Rhizoctonia solani on the quality of tubers for processing. American Potato Journal 69, 645-52.

Ritchie F, Bain RA, Mcquilken MP, 2009. Effects of nutrient status, temperature and pH on mycelial growth, sclerotial production and germination of Rhizoctonia solani from potato. Journal of plant pathology 91, 589-96.

Woodhall JW, Brown L, Harrington M, et al., 2022. Anastomosis groups of Rhizoctonia solani and binucleate Rhizoctonia associated with potatoes in Idaho. Plant Disease 106, 3127-32.

Woodhall JW, Lees AK, Edwards SG, Jenkinson P, 2008. Infection of potato by Rhizoctonia solani: Effect of anastomosis group. Plant Pathology 57, 897-905.

www.nwpotatoresearch.com | Contact | Unsubscribe