1. The strain (or pathotype) commonly creating problems here in the Upper Midwest is called Phytophthora sojae, and it can infect the seed or seedling at any point after it has absorbed moisture.
2. P. sojae belongs in the water molds family of organisms called oomycetes. Other examples of diseases in this family are pythium and downy mildew.
3. PRR can develop quickly in warm, wet, or saturated soils.
4. PRR favors poorly drained, low areas of the field, along with compacted soil with high clay content.
5. This disease is very adapted to saturated soils. As the disease cycle ends, oospores are created, which can survive in the soil for many years. When wet conditions return, the oospores germinate, producing sporangia, which in turn produce zoospores. Zoospores thrive in saturated soils and are attracted to chemicals emitted by plant roots, which draw them in to infect the plant.
6. If conditions become wet in the mid-season or late season, PRR can activate and emerge later in the year. Phytophthora loves soil temps greater than 60 degrees.

1. Typically, symptoms first appear in low areas of the field. Check plants that have a brownish lesion on the stem starting right at the soil line.
2. Stems may develop a pinched look. This is called ‘damping off.’ However, if you see damping off in your fields, it is not necessarily phytophthora. Damping off is a symptom of many seedling diseases, including pythium and stem canker. Be careful not to misidentify the root cause of this condition by looking for additional symptomology that points specifically to PRR. Specifically, the location of the brown lesions on the stems right at soil level would be indicative of PRR, as mentioned in my previous point.
3. Once PRR takes hold within the lower stem structure, the top part of the stem may remain green, but it will also eventually die. The leaves will stay attached to the plant.

1. FIX THE DRAINAGE ISSUE. Remember, we are trying to fight a water mold that thrives in saturated soils. Drain tile can alleviate a significant percentage of PRR incidence.
2. ROTATE TO OTHER CROPS. In severe cases of infection, this may have to be a multi-year rotation.
3. USE THE LATEST GENETICS. Soybean breeding companies have developed genetic resistance to certain races or pathotypes of phytophthora, with the 1a, 1c, 1k, and 3a genes being most common. These genes give the plant resistance to PRR by preventing colonization of the roots at the early stages of infection. In some cases, breeders have developed stacked varieties of two of the above-mentioned genes, as well, providing additional protection. Breeding of tolerant and resistant varieties continues to improve each year, as genetic resistance within the plant helps combat the disease throughout its entire life cycle.
4. LOOK AT PRR FIELD TOLERANCE RATINGS. Regardless of genetic makeup, seed companies will rate soybean varieties based on observed overall immunity to PRR. Researchers will typically begin observations at around V2 and continue throughout the year. In some cases, even though the variety doesn’t have a resistance gene, a high field tolerance will allow it to fend off the disease.
5. USE A COMPLETE SEED TREATMENT. Teresa Hughes, Ph. D., a soybean pathologist with Bayer Crop Science, emphasizes the importance of using a seed treatment to defend against PRR. To paraphrase, she compared not treating our soybeans to being dropped into the middle of New York City with no home, no job, and no money and being asked to survive. Seed treatments are there to combat the fungus; and while they are not a silver bullet for PRR control, they are an invaluable tool in the fight against this fungus. Active ingredients such as metalaxyl, ethaboxam, thiamethoxam, and propiconazole are just a few to consider including in your seed treatment in order to help prevent infection.

We may never fully eliminate phytophthora from our soils, but with diligent scouting, improved management of the field environment, and diligence to resistance and tolerance in variety selection, we can still achieve great yields while managing this disease.