By Dusty Sonnenberg, CCA, Field Leader, a project of the Ohio Soybean Council and Soybean Check-off
Not all Soybean Cyst Nematode (SCN) are created equal. There are specific SCN populations that are more challenging than others. “The active way to manage SCN is with a soil sample,” said Horacio Lopez-Nicora, OSU Extension Plant Pathologist. “Hopefully farmers do not have SCN in their field, but if they do, then they need to know the numbers so they can plan a strategy to manage the SCN and reduce numbers to below the damage threshold.”
In addition to knowing if SCN are present and the numbers, it is also helpful to know the specific population of SCN. “Some SCN populations can easily be managed with any source of SCN resistance. Those populations are the 80 type zero, formerly known as Race 3,” said Lopez-Nicora. “Other populations that have adapted and reproduce on the most commonly used source of resistance that we have available in commercially produced soybeans, which is PI 88788. These SCN populations are known as 80 type two. It is a different population that can reproduce on a source of resistance that we have on our beans.”
Knowing the numbers of SCN eggs in the field, and knowing the population of SCN in the field is necessary to create an effective management plan. “If a farmer knows the SCN numbers and the specific SCN population, they can make a better decision on the variety of beans they plant with which source of resistance,” said Lopez-Nicora. “That is very important to reduce SCN damage in the fields.”
A research project being conducted by Lopez-Nicora in Northern Ohio looked at the different sources of SCN resistance that can be used. The trial looked at both PI 88788 and Peking, the two most common SCN resistance sources available. The population of SCN in the field where the trial was conducted was the 80 type two, which by definition can reproduce on varieties with the PI 88788 source of resistance, but not on Peking. The SCN numbers in the field were on average 13,000 eggs per 100 cc, which is extremely high. The typical high range in Ohio which SCN damage is detected in a soybean crop is 5,000 eggs per 100 cc of soil. This was an extremely high SCN pressure environment. There are ranges in the field with higher and lower SCN densities in different parts.
“We planted the different varieties with different sources of resistance, and then collected samples of soil at planting to obtain the initial population of the nematode, and then at harvest to collect samples to obtain the final population of nematodes,” said Lopez-Nicora. “By collecting two samples at two different points, we can determine the reproduction factor by dividing the final population by the initial population. A reproduction factor of 1, means that the SCN population did not increase or decrease. If the reproduction factor is greater than 1 then we had an increase in the SCN population at the end of the season, and whatever we did was not effective. A reproduction factor of 5 means that we ended up with 5 times more nematode eggs than when we started the season. If the reproduction factor is below 1, then it means whatever we did was able to help reduce the SCN population. Tactics that could reduce the SCN reproduction factor include the use of an effective resistance gene, or it could be a seed treatment/protectant.”
The trial was taken to harvest, with yield data collected as well. In the field, half of trials were treated with a seed protectant, and half were not. “We know that SCN management is the integration of multiple management tools. Resistance remains the best way to manage SCN if we cannot rotate to a non-host crop. Adding a seed protectant will enhance the soybean health during the season and reduce the damage of the SCN” said Lopez-Nicora.
Lopez-Nicora said he evaluates different seed treatments and different environments when there can be a combination of different pathogens. “A field has a complex of pathogens that can interact synergistically and cause more damage to the plant. It is more than just SCN that threatens the soybeans.”