“As we move into the 2020 crop year, we need to put some thought into the management of prevent plant acres,” said John Swanson, Federated agronomist at the Ogilvie location. “The biggest concern we will have is fallow syndrome.”
What is fallow syndrome? It is the reduction of yields following years with lack of crop growth. It is evidenced by stunted, weak, and/or uneven plants caused by reduced uptake of nutrients such as phosphorus (P) and zinc (Z).
More specifically, Swanson noted, “fallow syndrome is the direct result of reduced populations of fungi called vesicular arbuscular mycorrhizae (VAM); this reduction is due to no crops/plants in the field. The VAM fungi has a symbiotic relationship with plants, especially corn and small grains. The mycorrhizae develop around the roots and assist the roots in taking up nutrients such as P and Z. Conversely, the mycorrhizae benefit by getting sugars from the host plant.
Swanson described how to minimize the effects of fallow syndrome: Let weeds grow in the field – though this is not the recommended option – or plant a non-Brassica cover crop (e.g., small grains, annual grasses, and annual clovers).
For fields not planted with a cover crop in 2019, Swanson offered these recommendations to overcome fallow syndrome:
- Give the new crop its best possible chance of getting enough P and Z with at least 40 units of banded P, while also using a phosphate stabilizer such as P-Max, USA 500™, or Trivar™. Broadcasting P has shown very little effect on helping fight fallow syndrome. (Foliar P and Z applications will help a little, but root uptake is needed to get significant levels taken up by the plant.)
- Apply banded Z as well.
- Ensure adequate Nitrogen (N) to reduce plant stress.
Because they are less susceptible to fallow syndrome than corn or small grains, soybeans following a fallow year are a good planting option.
A “major concern following prevent plant acres is making sure we have a good weed control plan,” said Swanson, since “most likely these fields got real weedy before they were tilled or sprayed … likely some of these weeds even went to seed.”
Swanson recommended setting up a “very extensive weed management plan ahead of time.” He said, “This may even require having a planned two-pass program [because] the weed seed bank was just built up and we need to work aggressively to get it back under control.”