It won't be long before soybean farmers will need to make decisions for 2005. Before we leave 2004 all together, I wanted to review some production factors to consider for next year.
Each year, we see acres and acres of soybeans impacted by diseases and other pests like nematodes. In just about all cases, selecting a resistant variety is the only answer. Knowing if you have these problems and implementing the right management strategy is very important to avoid yield losses or total crop failure.
Identify fields showing stem and root diseases
Unfortunately, this year we have the opportunity to identify fields that have shown symptoms of diseases such as stem canker and sudden death syndrome (SDS). Since variety selection is our only defense, producers are encouraged to take notes and make records of infected areas.
History has shown us that areas within a field with only a few plants showing symptoms could wind up being wide problems in the future. Take a few minutes to identify problem fields now. The records will be important for booking varieties this winter and planting next spring. Taking a minute now may prevent a bad decision in the future.
Sample for root-knot and soybean cyst nematodes
To determine if soybean cyst or root-knot nematodes are present in a given field, samples need to be taken and evaluated by a nematode diagnostic laboratory through the local county Extension office. Collection of the samples is similar to soil samples collected for fertilizer recommendations. Each field should be sampled to 6- to 8-inch depths and each sample should give an accurate representation of the field.
Multiple samples may be needed for larger fields so that each sample should contain 1 pint of soil and represent no more than 50 acres. Samples should be collected when the soil is moist, but not flooded.
If soybean cyst nematodes are suspected and soybeans are still in the field, collect 15 to 20 soybean root systems to send along with the soil sample. It is much easier to get a sufficient quantity of cysts to conduct a race test from infected roots than from soil.
Be careful collecting the roots, so that the cysts are not knocked off. Use a shovel to dig up the plants and gently remove the soil. Soaking them in water is an effective way to remove the soil without disturbing the nematodes. Cut off the tops of the plants and discard them.
Since nematodes are living organisms and must remain alive for testing, special care must be taken in handling and shipping after collection. The following steps should be followed once the samples are taken:
Each sample should be placed in a plastic bag and sealed to prevent the soil from drying out (plastic bags should be labeled with field number or name).
Avoid exposing the samples to direct sunlight and extremely high temperatures (dashboards or back of the truck) or low temperatures. Placing the samples in a cooler (without ice) is the preferred way to protect samples for shipping.
Samples may be stored in the cooler (without ice) in an air-conditioned building for a few days. However, prolonged storage may lead to inaccurate results.
If cysts are not found on soybean roots when they are inspected, collect a soil sample only as described above. General assays will detect the presence of soybean cyst nematodes in the field, and the general assay will also detect any other types of nematodes that may be present.
The general assay will not, however, indicate the soybean cyst nematode race that is present. An additional test called a race analysis is needed to determine the race or races present. This analysis is more detailed and requires about 2 quarts of soil.
Samples for soybean cyst nematode race analysis should be collected from mid-season through September or October.
In the past, the main soybean cyst nematode races found in Arkansas were races 3, 9, and 14. However, recent surveys indicate that races 2, 4, 5, and 6 are increasing. As mentioned earlier, variety selection is our only defense for these pests and our options are limited. Proper varieties cannot be recommended until the race has been identified.
Chris Tingle is the Extension agronomist for soybeans with the University of Arkansas Cooperative Extension Service.