FOLEY, Minn. — With this growing season coming to a close, it is time to be tying up those loose ends for this year and thinking about next year. While harvest has yet to happen, it is never too early to make sure those weed, disease and insect issues are recorded and available for reference for the next few years. By taking stock of what has happened in fields and recording that information now, prior to harvest, you won’t have to try and remember that information at the end of October.
It is especially important that pest issues are properly identified and recorded. While this year has fields containing the usual suspects in soybeans, such as SDS, white mold and soybean aphids, there have also been reports of top dieback issues in soybeans.
Top dieback resembles potassium deficiency and can be caused by soybean cyst nematodes (SCN), soybean aphids, clover root mealybugs, and Diapothae/Phomopsis fungi. Soil samples will need to be collected and submitted. If potassium deficiency is the primary issue, K fertilizer should be applied. If SCN is the issue, consider rotating to a non-host crop, utilize different cultivars with different sources of SCN resistance, and manage weeds, moisture and fertility to reduce stress on plants.
With the widespread reports of soybean aphids this year, it would not be surprising if that were the issue. Keep in mind soybean aphid populations which were present during R5 still should be scouted into R6 to ensure that populations don’t boom. Soybean aphids can still take yield at R6 stage soybeans in very heavily infested fields. In these instances, soybean fields may still respond to a late insecticide application.
On another note, the last date for alfalfa cutting is coming up soon. Typically, we think of that early no-cut window starting at some point during the first full week of September; with it being riskier the further into September you wait to cut.
The goal is to cut early enough so the field accumulates 500 growing degree days (GDD); or cut so late there is less than 200 GDDs left prior to a killing frost of 25 degrees. To calculate GDDs for alfalfa, use a base temp of 41 degrees. If cutting later to fit in the 200 GDD window, remember that around four inches of growth helps with overwintering. Also, consideration should be given to the winter-hardiness of the alfalfa variety, soil pH and potassium levels when looking at taking a later cutting. Waiting until the first hard frost to cut the alfalfa is not necessary. Rather, you are waiting for it to get cold enough where regrowth is going to be minimal or not occur at all. Typically, that date for late harvest is at some point in mid-October.
This article was submitted by Nathan Drewitz, University of Minnesota Extension.