Although the USDA has forecasted corn acres to be up in 2019, there will no doubt continue to be some acres of soybeans-following-soybeans. For many growers, soybeans require less input cost and the ability to forecast a more consistent yield, making soybeans a desirable crop when the farm economy is down. Growing soybeans multiple years in a row may not be as easy as it sounds, however. Researchers at the University of Wisconsin suggest as much as a 5% decrease in yield for 2nd year soybeans and 12% in 3rd year soybeans. Here are some tips to help make soybean-following-soybean rotation more successful.
Don’t forget to fertilize. Fertilizing ahead of corn is a surprisingly common practice. If corn has not been in the rotation for more than 1 year, remember to fertilize for your soybean crop. Sixty bu/ac soybeans use almost 100 lbs. of DAP/TSP and 115 lbs. of Potash. Failing to apply the required levels of fertilizer will cause your soils to become depleted of nutrients.
Evaluate options for SCN. While every county in the state has confirmed presence of soybean cyst nematode (SCN), populations are likely to be higher in soybean-following-soybean. Choose varieties that have the best resistance to the pest. Seed treatments can also be effective in protecting against the damage of SCN. But more importantly, pull representative soil samples for egg count to know the risk level.
Manage for seedling diseases. Many seedling diseases like Pythium and Phytophthora will overwinter in residue in our soils. Therefore, without crop rotation their presence is more likely and disease risk is higher. Utilizing fungicide seed treatments will help manage seedling diseases. Choosing varieties with higher resistance ratings to these diseases is also key, and avoid planting into cool, wet soils. Even though Sudden Death Syndrome (SDS) isn’t typically observed until later in the season, it infects soybeans early in their life cycle. Applying ILeVO® seed treatment is recommended in fields with a history of SDS. And if a field has a high risk of SDS, consider planting that field last and when soil conditions are warmer and drier.
Consider your weed control options. Planting the same crop for multiple years in a row can easily lead to utilizing the same herbicide sites-of-action (SOA) every year. With limited effective options available for control of waterhemp, particularly in soybeans, you may end up relying on the same 1 or 2 SOA repeatedly. Be sure to utilize residual herbicides in a pre- and post-emergence herbicide application. Rotating SOA is highly recommended to help prevent further resistance. Consider planting soybeans with a different herbicide trait package on these acres as well as introducing a new SOA.
Scout for foliar diseases. As with seedling diseases, foliar diseases are more likely to be problematic in the absence of crop rotation. If you are in the northern part of the state where white mold exists be sure to choose varieties with good white mold tolerance, consider planting in wide (30”) rows and apply fungicides closer to R1 than R3. Frogeye leaf spot may also be more prevalent in soybeans-following-soybeans. Choose resistant varieties and apply fungicides that are effective in controlling this pathogen, as there has been documented resistance to strobilurin fungicides.
As with every year, we will need a little help from Mother Nature to guarantee a successful season. It’s important to control the things we can control and accept the things we cannot. Following these simple guidelines will provide you with the best opportunity for success on your acres of soybean-following-soybean.