While still early in the growing season, root rot may begin to appear in multiple crops. However, it can be difficult to determine if plants are impacted by root rots or other ailments, and even more difficult to identify which root rots are causing the problem.
Sam Markell, a plant pathologist at North Dakota State University Extension, explains some of the differences between root rot and other crop ailments, as well as how to manage for them:
Weather. Roots rots are commonly caused by two groups of organisms:
- oomycetes (such as aphanomyces, pythium, phytophthora, downy mildews)
- fungi (such as rhizoctonia and fusarium)
The oomycetes are favored by very wet soils, while fusarium and rhizoctonia can cause issues even without much water. Each root rot pathogen has a preferred temperature range as well — from very cool to hot. Understanding which pathogens are favored by the environment in your field will often give you a short list of potential suspects.
Pattern. When root rots impact crops, they are generally not evenly distributed across a field. Root rots tend to be more commonly found in patterns where the environment is similar. This can take many forms, such as a large low spot in a field or several plants dying in a row. Pattern in the field is an important factor to consider. Also, remember what had happened in these fields in the past. Many root rot pathogens will survive in the soil for several years.
Management tools. Crop rotation, seed treatments and variety selection (resistant, tolerant or susceptible varieties) may impact the severity of your disease and the pathogens that are causing it. Notably, no management tool is bulletproof, but they can make a difference. Taking into consideration your management tools will help you identify what problem you are seeing and, potentially, what options you should consider in the future.
Symptoms and signs. Get close! A shovel, a light, a knife and a magnifying glass are all helpful when identifying root rot. Root rot symptoms can be subtle and overlooked. When you dig the plants are the seeds rotting and the seedlings damping off (an indication of pythium)? Do you see a black lesion creeping up the soybean stem, which starts at the soil line (and indication of phytophthora)? Do you see a reddish canker on tap root (an indication of rhizoctonia)? Is the inside of the stem a color it shouldn’t be?
The closer you get, the more likely you are to identify the problem. Notably, there may be multiple pathogens causing rot in the same field or plant.
A good resource can be invaluable in the field. NDSU has created disease diagnostic card sets for:
These diagnostic series focus on the diseases in our state (and region). They are designed specifically to help you identify the diseases, and include high-quality images and brief information on favorable conditions, symptoms and signs, and other important factors to consider.
NDSU’s plant diagnostic laboratory can help you determine the cause of a root rot problem if you submit a sample. Follow the instructions at NDSU’s website to be able to submit a sample.