What visual cue may indicate a nematode problem near the soil surface?

The presence of small knots on the root system is an important visual cue that indicates a nematode problem near the soil surface. These knots, often referred to as root galls or root knots, are typically formed when nematodes, particularly root-knot nematodes, invade plant roots. The nematodes cause the plant to react defensively, leading to the growth of abnormal swellings on the roots. This disruption in root structure can significantly hinder the plant's ability to uptake water and nutrients, impacting overall plant health.

Other indicators, such as white mold growth, bright green spots on leaves, or discoloration at the base of stems, may suggest various plant diseases or issues, but they are not specifically associated with nematode infestation. White mold is caused by a fungus, green spots may indicate nutrient deficiencies or other stress factors, and discoloration at the base of stems can be caused by different pests or environmental stressors. Thus, recognizing the small knots on roots as a specific sign of nematodes is crucial for diagnosing and managing this pest effectively.