How to recognize Phytophthora root and stem rot, plus steps to take to reduce risk | AgriGold

How to recognize Phytophthora root and stem rot, plus steps to take to reduce risk

How to recognize Phytophthora root and stem rot, plus steps to take to reduce risk

If you’re a soybean grower, one of the most destructive plant diseases to be on the lookout for is phytophthora root and stem rot.

While many diseases pop up during specific phases of the growing season, phytophthora can affect your plants from emergence all the way to harvest. It can survive in the soil for up to 10 years, develop resistance to certain genes, and kill both seedlings and fully grown plants.

To put it lightly, it’s important to keep an eye out for early symptoms and take precautions against its spread.

What causes it: Phytophthora root and stem rot comes from the Phytophthora sojae pathogen—an oospore specific to soybeans. These oospores develop in infected plant tissue and grow as the tissue decomposes. Wet and warm soil (59°-74°F) is the preferred breeding ground for the pathogen, especially in low, saturated, or poorly drained areas. It’s also more common in clay or compacted soils.

How to recognize it: Seeds or seedlings may rot off, either before or after emergence. Infected stems can appear soft, and sometimes leaves will turn yellow, then brown before wilting. In-season, you might notice chocolate brown stem lesions extending up from the soil. Plant wilting and leaf chlorosis and necrosis are also common at this stage. Symptoms usually show up in patches or sections, so keep an eye out for patterns within your fields. Early, constant attention to detail is also critical: plants can be infected early in the season and not show symptoms until near harvest.

Tips to reduce susceptibility: Young plants are more susceptible, so early-season seed treatments can help control your risk. Wider crop rotations are also important, as they can reduce the amount of Phytophthora in the soil.

Genetic resistance is your best bet against phytophthora root and stem rot. Plant soybean varieties with high field tolerance, and use those with genes Rps 1a, Rps 1c, Rps 1k, and Rps 3a. However, resistant pathogens do exist in some fields. So watch closely for symptoms in your seedlings and plants, even when you’ve planted a traditionally resistant variety.

Check with your local agronomist to see which AgriGold soybean varieties contain these genes and give you the best chance to protect your yield.