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Producers will experience problems with crops in some Missouri fields this year. I don't know what type of problems will develop, but I do know they will occur because they always have in past years. The problems will most likely be caused by too much or too little fertilizer, too much or too little water, cold weather, crust over the planted row, insects, diseases, herbicide drift or carry over, and other things. Producers should get the cause of each problem diagnosed so action can be taken to prevent or reduce the problem from worsening or developing next year. Diagnosis of crop problems can sometimes be easy, but it is more often difficult. This article is a brief summary of the material in University of Missouri Extension Guide G4050 that describes a six-step process to help farmers and crop consultants diagnose the cause(s) of field crop problems. This guide, Troubleshooting Field Crop Problems, was written by Laura Sweets, Andy Kendig and me, and it is online at http://extension.missouri.edu/explore/agguides/crops/g04050.htm.

First, determine the variety and the age of the plant. An investigator should identify the plant variety because some are more resistant or susceptible to certain diseases, insects and herbicides, and this information may be very useful when diagnosing the cause of the problem.

Second, identify all the symptoms affecting the leaves, stems, roots and fruit. An investigator should observe all parts of abnormal plants when troubleshooting a field crop problem including the leaves, stems, fruit and roots as well as the tissue inside roots and stems. Frequently, the point of injury to the plant is not where the symptoms appear. For example, leaves on one or several branches may be discolored and withered because of a canker on a lower branch or a borer in the stem. Nutritional deficiencies and injuries from herbicides may damage both roots and leaves. Examine individual plants in detail and determine the location of symptoms on the plant. Are symptoms on old or young leaves, upper or lower stems, or perhaps on one side of the plant? Look for insects and insect feeding damage. Cut stems to check for discoloration inside the stem and for insect feeding. Hold leaves up to the light to check for mosaic, other viral symptoms, or the presence of webbing and mites. Investigators should look for leaf abnormalities in color, size, shape and texture. Also, carefully dig up roots and examine them. Check for galls, rot, abnormal root color and feeder root condition, and assess root growth. While probing the soil, check for soil compaction, soil structure, texture and organic matter, and the presence and depth of hardpans. Also take note of odors, insects, fertilizer placement and the depth of planting.

Third, estimate the percentage of plants damaged in the affected part of the field. Were all plants in an area or only 10 percent affected? Symptoms of injury due to insects and disease may appear on every plant in an area, but this is unusual. Symptoms of injury due to herbicides, improper placement of fertilizer and lightning will usually appear on every plant in an area.

Fourth, determine the distribution or pattern of the problem in the field. Look at the entire field to determine where the problem appears. Determine the distribution of the problem in the field as it relates to field characteristics such as areas with light soil, and drainage patterns. Is the problem only in wet areas? Take notice of whether the problem is associated with certain rows or areas of lower or higher elevation.

Fifth, evaluate whether the crop and weeds in the field share similar symptoms. Examine the weeds in the area where the crop is injured and in nearby fence rows. Symptoms caused by nutritional disorders are usually not plant specific. For example, most plants growing in low-pH soils, including crops as well as weeds, will be stunted. However, diseases are usually plant-specific, and weeds in the area are normally not affected by the same diseases that can attack corn or soybean.

Sixth, determine the history of the problem. Ask when the problem was first noticed, and whether crop problems were observed in the same area during previous growing seasons.

The answers to these questions may provide a clue that could be useful in diagnosing the cause of a field crop problem. Following these suggested procedures will give field crop consultants and producers a better chance of diagnosing the cause of field crop problems.

Allen Wrather
Professor Division of Plant Sciences