How does Brown Stem Rot in soybeans manifest in relation to harvest time?

Brown Stem Rot in soybeans typically becomes visible as the plants approach maturity, often around one month before harvest. This disease is caused by the fungus Phialophora gregata and primarily affects the vascular system of the soybean plant. As the infection progresses, symptoms such as yellowing leaves and wilting become apparent, but these manifestations often develop late in the growing season.

Around one month prior to harvest, as the plant matures, the effects of the disease can be observed more clearly because the plant is under stress and the fungus disrupts its nutrient transport. The presence of brown discoloration in the stem and a characteristic browning of the vascular tissue can be noted during this time, marking the transition to visible symptoms.

In contrast, symptoms do not appear immediately after planting because the disease has an incubation period during which the pathogen develops without causing visible signs. Likewise, if the disease remains undetectable until after harvest, it would not align with the usual manifestation timeline that show clear symptoms before the harvesting period. Lastly, while some symptoms might be present throughout the season at a microscopic level, they typically do not become distinctly noticeable until closer to harvest. Therefore, the correct answer aligns with the established knowledge regarding the timing of the symptoms in the