Guy Padgett | 3/21/2012 11:19:51 PM
Click on the link above to return to the Soybean Disease Atlas home page.
Disease diagnosis is difficult because symptoms of some diseases are very similar, and symptoms vary depending on environmental conditions and plant growth stage. As a result a second opinion from someone experienced with soybean diseases may be beneficial. Unless this individual can visit the site, you may have to collect and submit high quality specimens. Following are some suggestions for collecting plant samples.
Disease samples should include both diseased and healthy plant tissue for comparison purposes. Suspect plants which are already dead are generally of little value. Whole plants are best because leaf symptoms may be caused by damage to the stem or roots. After the sample is collected it should be protected from deterioration and taken to the professional as soon as possible. Place the sample in a plastic bag and store in an ice chest or refrigerator to prevent drying. Do not place the specimen in direct sunlight or near extreme heat.
Finally submit pertinent information regarding cultural practices, pesticide applications, and cultivar. This information will be useful to the pathologist in disease diagnosis.
Soil samples are helpful in diagnosing a nematode problem or assessing potential problems. Before sampling, contact the local county agent or extension specialist to determine the procedure recommended for your area. The following is a general procedure which may be used.
When collecting soil samples for the purpose of determining the kinds and levels of nematodes present, it is best to divide the field into units of five acres. A total of ten soil cores from a depth of six to eight inches, containing soil and embedded root fragments, should be collected in a systematic manner from each of ten uniformly situated sampling blocks. The soil cores then are mixed thoroughly and a 1-2 pound subsample is bagged, labeled and submitted for analysis. When the objective of the sampling is to determine whether or not nematodes are responsible for damage in localized areas, separate samples are collected from adjacent symptomatic and non-symptomatic areas.
The time of year to sample soil is important. With field crops the best time to take samples is in the fall immediately after harvest. Nematode levels are generally highest at this time of year, and it is easiest to determine if a potential nematode problem exists for the following year. However, in some areas nematodes survive the winter, and may be sampled in the spring prior to planting. Consult with the local county agent or extension specialist for the best time to sample.
Nematodes are sensitive to heat and cold extremes, and to excessive drying. Keep the sample out of direct sunlight and store in a cool place until it can be processed for analysis. Samples should be processed as soon as possible.