How can one determine if gall-causing disease in alfalfa is due to root knot nematode?

To determine if gall-causing disease in alfalfa is associated with root knot nematodes, one effective method is to examine the nodules or stems of the plant. This is because root knot nematodes specifically induce galls or swollen areas on the roots, which can be observed by careful inspection. Rubbing off the stems or nodules allows for direct observation of any abnormal growths or galls that may indicate the presence of these nematodes.

Other choices, such as sampling more of the crop or simply sampling the roots without further examination, do not provide the same level of diagnostic insight. While sampling roots might be part of a broader assessment, it is the close examination of the visible growths (the galls) that is critical to diagnosing the issue effectively. Hence, inspecting the nodules or stems where gall formation can be readily seen is a key step in identifying whether the root knot nematode is the cause of the gall-causing disease in alfalfa.