What should be done to control Phytophthora stem and root rot in soybeans?

Using resistant varieties is an effective approach to managing Phytophthora stem and root rot in soybeans because these varieties have been specifically bred to withstand the adverse effects of the pathogen responsible for the disease. Resistant varieties can limit the pathogen's ability to infect the plants, thus reducing the incidence and severity of the disease.

Implementing resistance is critical, especially since Phytophthora sojae, the pathogen causing the rot, can survive in the soil and can be challenging to control once the disease is established. Resistant soybean varieties often have specific genes that help them fend off the infection, allowing for improved yield and healthier crops.

In contrast, increasing irrigation could worsen the problem, as Phytophthora thrives in overly moist conditions. Lowering soil pH might not directly impact the pathogen and could create other nutrient availability issues. Using nitrogen fertilizers does not address the root of the problem concerning disease resistance. Therefore, opting for resistant varieties is the most effective and direct strategy in managing this particular disease in soybean crops.