Dr. Audrey Kalil, Plant Pathologist, NDSU Williston REC
Seed treatment options for the management of seed rot and seedling blight in chickpea
Chickpea is very susceptible to seed rotting and seedling blight pathogens and infection can result in reduced plant populations and yield when disease is severe. The organisms responsible for these diseases include species of the water mold (oomycete) Pythium and fungal pathogens Rhizoctonia solani and Fusarium species. Since Pythium and Rhizoctonia prefer cool, wet soils, symptoms will be more severe in earlier planted chickpeas. Later-planted chickpeas may have more challenges with Fusarium, which prefers warm soils (above 50°F). Fortunately, seed-applied fungicides can be highly effective in the control of seed rot and seedling blight caused by these pathogens.
There are many seed treatment options for chickpea growers. Seed treatments that include the active ingredients metalaxyl, mefenoxam (Fungicide Resistance Action Committee Number – FRAC 4), or ethaboxam (FRAC 22) are effective for the management of Pythium. Seed treatments frequently contain other active ingredients for the control of Rhizoctonia, typically in the SDHI fungicide class (FRAC 7). This includes the active ingredients sedaxane, fluxapyroxad, penflufen, and carboxin. Active ingredients in the DMI class (FRAC 3), such as prothioconazole and ipconazole, have been very effective against Fusarium. Fludioxonil (FRAC 12) has shown good control of Fusarium species and strobilurin fungicides (FRAC 11) have activity against Fusarium and Rhizoctonia.
In addition to seed rot and seedling blight management, fungicide seed treatments are also effective in suppressing pathogens that are transmitted on the seed and can cause disease to the above-ground plant parts at later plant growth stages. One important example is Ascochyta rabiei, the causal agent of Ascochyta blight. This disease affects the foliage, stems, and pods and can be quite devastating in chickpeas if not controlled with foliar fungicides. Thiabendazole (FRAC 1), sold commercially as Mertect 340-F and in the pre-mixes Vibrance Maxx Pulses and Cruiser Maxx Vibrance Pulses, is used to control seed-borne Ascochyta rabiei. The use of a seed treatment may reduce the spread of the pathogen from the seed to the seedling and can help reduce early-season disease pressure.
While it may seem redundant to include so many fungicide active ingredients in one seed treatment, there is good reason to do so. There are many different fungal pathogens present in the soil that can attack the seed and seedlings, but it is often unknown which pathogens specifically are already present in the soil and what diseases will thrive with the environmental conditions during the field season of that year. Choosing a broad-spectrum fungicide seed treatment with multiple active ingredients against a range of pathogens is therefore a good strategy to protect the crop. Moreover, fungi and oomycetes can develop resistance to fungicides over time. For example, Ascochyta rabiei is resistant to the FRAC 11 fungicide class in North Dakota. Pythium with resistance to metalaxyl/mefenoxam has been documented in the U.S. When fungicide resistance develops, a fungicide active ingredient or even entire group of fungicides (a FRAC) loses its effectiveness in managing a given pathogen. Stacking effective fungicide active ingredients can be a tool to slow the occurrence of pesticide resistance. Growers will have to balance cost, efficacy, and resistance management to make fungicide seed treatment decisions. The North Dakota Field Crop Plant Disease Management Guide is an excellent reference for growers wishing to know more about these products.
Research to evaluate seed treatments at the Williston Research Extension Center
With many different seed treatment products and different combinations of active ingredients on the market, it can be difficult to select a product that will provide effective disease management at minimum cost. We conducted two studies at the Williston Research Extension Center in North Dakota to determine the effect of various seed treatment products on chickpea seed rot disease as measured by plant population, and yield. Seed of the chickpea variety CDC Frontier was treated with commercially available fungicide products at recommended application rates (Table 1) and the seed was planted on April 22nd, 2021, and May 5th, 2022. Soil temperatures at planting were 48°F and 57°F in 2021 and 2022, respectively.
Table 1. Fungicides used in seed treatment study. Active ingredient and application rates are from the 2021 North Dakota Field Crop Plant Disease Management Guide (PP622-21)
|Fungicide name||Application Rate/cwt||Active ingredient(s)|
|Mertect 340F||2.04 fl. oz.||Thiabendazole (42.3%)|
|Intego Solo||0.6 fl. oz.||Ethaboxam (34.2%)|
|Obvius||4.6 fl. oz.||Metalaxyl (1.26%), Pyraclostrobin (1.58%), Fluxapyroxad (1.58%)|
|Rancona CTS||1.53 fl. oz.||Metalaxyl (1.94%), Ipconazole (2.42%)|
|Apron Maxx RTA||5 fl. oz.||Mefenoxam (1.1%), Fludioxonil (0.73%)|
|Cruiser Maxx Vibrance Pulses||5.0 fl. oz||Mefenoxam (1.06%), Sedaxane (1.41%), Fludioxonil (0.71%), Thiabendazole (4.24%), Thiamethoxam (8.48%)|
|Allegiance||0.75 fl. oz||Metalaxyl (28.35%)|
|Vibrance Maxx||1.54 fl. oz.||Mefenoxam (3.52%), Sedaxane (4.69%), Fludioxonil (2.35%)|
|Vibrance Maxx Pulses||5 fl. oz.||Mefenoxam (1.07%), Sedaxane (1.43%), Fludioxonil (0.71%), Thiabendazole (4.3%)|
Seed treatment had a strong impact on plant population, which was assessed at the V1-V5 growth stage (Figure 1). In both study years, plant population was lowest in the no fungicide and Mertect 340F treatments (Table 2). Mertect does not include an active ingredient for control of Pythium or Rhizoctonia. While we did not determine which pathogens were present in the soil, our findings suggest that these pathogens were causing disease. Plant population was also lower in the Intego Solo treatment, compared to the other products tested (Table 2). It is possible some phytotoxicity occurred at the high rate, so perhaps a lower rate (0.3 fl oz) of Intego Solo should have been used.
Figure 1. Plot images representing three different seed treatments, taken July 14th, 2021.
The desiccated chickpea plots were harvested on August 17th in 2021 and August 19th in 2022. In 2021, yield was greatly reduced where no seed treatment was used (Table 2). This was surprising as 2021 was a very dry year, and thus we did not expect high levels of seed rot, nor that this would affect crop yield. This demonstrates the importance of using a seed treatment in chickpea even in years when environmental conditions are not considered favorable for disease. However, yield did not differ between the various seed treatment products in 2021. In 2022, yield data showed a similar numerical trend to 2021, but no statistical differences were observed. Plant population was significantly correlated with yield in both study years (p < 0.002) and was higher in 2022. Pythium and Rhizoctonia are generally less problematic in warmer soils, thus the warmer soil temperatures at seeding in 2022 may explain the lack of statistical separation for yield among the treatments that year.
Table 2. Results of 2021 and 2022 chickpea seed treatment trial. Statistical significance determined by ANOVA (α < 0.05). Means followed by a common letter within columns are not significantly different as determined by Tukey’s HSD (α < 0.05).
|Treatment||Plant Population (Plants/ft2)||Yield (lb/ac)|
|Cruiser Maxx Vibrance Pulses||3.3||ab||4.5||abc||1079||a||2111|
|Vibrance Maxx Pulses||3.7||a||4.8||ab||1113||a||2225|
|Apron Maxx RTA||2.6||abc||5.0||a||1152||a||2063|
|ANOVA (α < 0.05)||< 0.0001||< 0.0001||< 0.0001||0.0597|
The findings from this study suggest that selection of a seed treatment product that provides protection against Pythium, Rhizoctonia and Fusarium will likely provide a benefit to plant population, and the impact of seed treatment on yield is determined by the severity of disease. Testing seed for seed-borne pathogens, such as Ascochyta, will help drive seed-treatment decisions. While late planting may reduce the risk of seed rot and seedling blight, it does not eliminate it entirely and a seed treatment may still improve plant population.
Acknowledgements: This research was made possible through funding provided by the USDA Pulse Crop Health Initiative. Thank you to the research technicians, specialists and summer interns who helped collect these data.
Dr. Audrey Kalil is the Plant Pathologist at the NDSU Williston Research Extension Center. Since she began her position at NDSU in 2015, Audrey has led an applied research program focused on management of plant disease in durum, peas, lentils, chickpeas, and sugar beet, as well as nodulation and nitrogen fixation in pulse crops. Number: 701-774-4315 Email: firstname.lastname@example.org Twitter: @Audrey_Kalil
Published May 26, 2023