Protecting production: UW research works to protect Wyoming’s dry bean production from soil-borne disease
The next time someone settles down to enjoy a steaming bowl of chili or a spicy bean burrito, they should thank a dry bean producer.
Dry edible beans, such as pinto, navy, kidney, black and white beans, are grown in 30 states, with 1.34 million acres harvested in 2021.
According to 2014 data, Wyoming was ranked eighth for dry bean production and is a leading producer of bright, packaging-quality pinto beans.
In Wyoming, dry bean production in 2007-16 ranged from 25,000 acres to 49,000 acres, and the top producing areas were the Big Horn Basin and the southeast corner of the state.
Wyoming also produces certified dry bean seed.
Soil-borne disease
One challenge of dry bean production in Wyoming and neighboring states is soil-borne disease, particularly root rot diseases. Several pathogens cause root rot diseases, and Rhizoctonia and Fusarium root rot are common in the West.
The severity of disease depends on environmental conditions, soil compaction, variety and cropping history, and growers have limited options to address these issues.
For the past eight seasons, a University of Wyoming (UW) lab has conducted 11 field studies, including a master’s project by Graduate Student Kyle Webber, which investigated ways to manage dry bean root rot.
Because more than half of Wyoming’s dry bean production is pinto beans, researchers studied several pinto bean varieties using an integrated approach to root rot disease management.
Dry bean root rot diseases limit root growth, which reduces crop yields. Stress factors such as soil compaction and dry or saturated soil can increase disease severity.
Fusarium root rot is found throughout the world in areas where dry beans are grown, and it can almost destroy a bean crop when plants are stressed by drought, soil compaction, soil saturation or oxygen stress.
Fusarium root rot is often found in association with other disease organisms, such as Rhizoctonia, in what we call a disease complex.
In a study conducted in Nebraska, respective yield reductions of 52 percent and 42 percent for Great Northern beans and pinto beans were observed because of Fusarium root rot.
In separate surveys conducted in Colorado in 1971-72, pinto bean field yield losses averaged 27 to 62 percent, with some individual field losses as high as 89 percent.
Commonly grown varieties are equally susceptible to root rots in this region, but some varieties are more tolerant to Fusarium infection than other varieties.
If producers are going to have reliable yields, they need to continue screening new and existing varieties for tolerance to fungal root rot diseases and explore potential chemical controls.
Testing an integrated approach
UW researchers’ goal was to determine if a single, in-furrow fungicide application at planting, varietal selection and deep tillage to alleviate soil compaction would protect the dry bean crop from the effects of soil-borne disease.
Specific objectives of the study were to compare the efficacy of two commercially available in-furrow fungicides for Rhizoctonia and Fusarium disease suppression, evaluate up to five locally adapted pinto bean varieties in the presence of disease and investigate the utility of deep tillage on bean root development and how it affects root disease.
These studies took place over two years, during 2018-19, at the UW Agricultural Experiment Station research sites – the Powell Research and Extension Center (PREC) and the James C. Hageman Sustainable Agriculture Research and Extension Center (SAREC).
With support from Bayer CropScience and BASF, UW also investigated other fungicides and methods of application in seven separate field fungicide efficacy studies conducted at the UW SAREC research site from 2015-21.
Results
With deep-ripping tillage treatments, researchers were able to reduce soil compaction. However, there were no positive benefits to disease suppression or yield compared to conventional field preparation.
It is widely assumed dry bean roots can tolerate root rot disease pressure more easily by having a healthy, extensive root system. Bean roots suppressed by the compaction layer found in some agricultural fields are much more prone to the effects of soil-borne diseases.
Although this is not the first time science didn’t back up conventional wisdom, it’s possible the lighter soils found at SAREC and PREC are less prone to soil compaction layers, and the roots were not stressed enough.
Because of genetic variances in breeding, the UW research team found significant differences among pinto bean varieties in terms of disease susceptibility and yields, as seen in Table One.
Sundance, a newer, slow-darkening variety whose seed does not darken with age on store shelves, had the lowest average disease severity. However, this did not translate to greater yields, most likely due to varietal differences.
The other varieties had variable yield results depending on the experimental conditions.
Othello, a common variety grown in Wyoming, is very susceptible to root rot infection. However, it was among the highest yielders in the presence of disease.
While none of these varieties are resistant to root rot disease – all varieties tested had 100 percent of the roots infected to some degree – dry beans in general can compensate for root diseases by producing extra roots once the main tap root becomes rotted. In fact, heavily infected bean plants frequently fail to show any visible above-ground symptoms.
All of the tested varieties in UW’s studies have displayed very few above-ground symptoms, but under limited water conditions this could be a different story because newer, developing roots tend to be shallower than the deeper main tap root.
In-furrow fungicide treatments – in which fungicide is applied in furrows as seed is planted – were, for the most part, ineffective when used in the integrated study.
However, in the fungicide efficacy trials, which investigated different fungicide chemistries than those used in the integrated study, researchers did reduce early- to mid-season disease by almost 50 percent in some cases.
Despite reductions in disease, in most studies this did not result in yield increases compared to the untreated treatments, and sometimes the fungicide applications hindered bean emergence.
In one out of 11 studies, scientists saw significant yield increases with fungicide treatment. Fungicide effectiveness is time-sensitive, meaning once applied in the environment, compounds are subject to degradation and lose effectiveness over time.
Unfortunately, these fungal pathogens can continue to attack the bean roots all season long.
As a rule of thumb, from years of experimentation in various cropping and disease situations, fungicide applied as seed treatment results in several weeks of protection, in-furrow applications can protect for up to a month and in-furrow application plus a foliar application to the leaves can extend protection for one and a half to two months.
Implications
Alleviating stressors such as soil compaction only makes sense to keep roots growing and healthy.
Lack of effects from the UW researchers’ attempts to reduce soil compaction were probably due to the level of compaction they were able to create in their experiment.
Degree of soil compaction can vary among soil types, and soils with a higher percentage of clay and silt have more of a problem with soil compaction compared to lighter soils found at the research sites.
Under a true compaction problem some farming operations can have, reducing compaction should have a positive effect on the health of plants.
As for varieties, it’s clear there is room for improvement in terms of increased plant resistance to these root rot organisms.
Dry bean disease resistance breeding is an ongoing process, but it is difficult because of the number of genes involved for resistance. In any event, local Wyoming varieties, at least in UW’s studies, seem to do relatively well under high disease incidence.
The viability of using fungicides is less clear.
Researchers were able to reduce severity, but some fungicides caused reduced crop emergence and short-lived plant injury.
Based on the results, it’s difficult to justify the additional expense of in-furrow and foliar fungicide applications. At the bare minimum, growers should use fungicide-treated seed, because it’s relatively inexpensive and reduces early infections.
Despite some of UW’s disappointing results, researchers still believe an integrated approach is the best bet to manage dry bean root rot. To better answer these questions, future research is required in field environments more conducive to plant stressors so these integrated approaches can be further tested.
Dr. William Stump is an associate professor in UW’s Department of Plant Sciences, Kyle Webber is UW graduate student in the Department of Plant Sciences and Wendy Cecil is a research associate in the Department of Plant Sciences. They were in charge of the research outlined above. This article was originally published in Reflections, the UW College of Agriculture, Life Sciences and Natural Resources research magazine.
