DIAGNOSIS OF DISEASE PROBLEMS

The first step in successful management of a disease problem is the correct identification, or DIAGNOSIS, of the cause of the problem. Often I equate the diagnostic process to the investigation of a murder. For some reason your plants have died, and now you have to collect information in order to piece together what has happened. The sort of information that you may need to collect to correctly identify a disease includes information on the crop type and variety, soil characteristics (nutrients, pH, etc.), weather patterns, insect pests, crop rotation, disease problems in previous growing seasons and planting practices. Knowing the kinds of questions to ask and important symptoms to look for requires training and a great deal of experience.

The disease problem shown in this photo is an example of a situation where a bit of detective work was required to determine why half of the alfalfa crop in this field (on the left) did so poorly. The critical clue in this situation was to notice the sharp line between diseased and healthy sections of the field. Such distinct lines typically indicate that some human factor is involved in disease development. After talking with the grower, the person who eventually made a diagnosis found that the alfalfa in this field was planted with an oat companion crop. The oats in the section of the field on the right was harvested early as a green manure and the oats in the section of the field on the left was allowed to mature and was harvested as a grain crop. The shading effect of the maturing oats, as well as humid conditions under the oat canopy increased stress on the alfalfa, and provided a perfect environment for a variety of alfalfa diseases to develop.