Producers will experience problems with crops in many Missouri fields this year. I don’t know what types of problems will develop in each field, but I do know they will occur; not in every field but it many. The problems will most likely be due to too much or too little fertilizer, too much or too little water, insects, diseases, herbicide drift or carry over, and the damage to the crop may be mild or severe. Producers should get the cause of each problem diagnosed so action can be taken to prevent spread of the problem this year, if it is spreading, or prevent it from 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. For the novice, troubleshooting can be intimidating in the absence of a systematic process. For those with experience, a systematic process to troubleshooting can help prevent the bias of looking only for the familiar and thwarting the investigative process.

First, determine the variety and the age of the plant. An investigator should identify the plant variety so that a basis exists for defining its normal appearance. In addition, the variety should be noted because some are more resistant or susceptible to certain diseases, insects, or 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 and the severity of damage. Do you observer damage on all plants in an area or only 10 percent? 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 or inadequate fertilizer 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 all plants (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, low-pH soils will cause stunting of most plants in the field, including crops as well as weeds. Leaf spots caused by drifting droplets of a contact herbicide (e.g., paraquat) are not plant specific, and several plant types in the area may show similar leaf spotting due to paraquat drift. 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 may provide a clue that could be useful in diagnosing the cause of the problem.

Extension Guide sheet G4050 gives more details about troubleshooting field crop problems. Following these suggested procedures will give field crop consultants and producers a better chance of diagnosing the cause of field crop problems. Some information that may help with troubleshooting will be presented during the 2006 Delta Center Field Day on August 31.

Allen Wrather
Professor Division of Plant Sciences