This is Aaron Nygren, your local agronomist with Nebraska Extension in Colfax, Cuming, and Stanton counties. If last week’s heat and wind, and this week’s rain has you behind with your soybean post spraying, listen up for a few tips on checking your soybean growth stage before you resume spraying.
In order to avoid potential injury and stay on label, it is important to know what growth stage your soybeans are at. Many herbicides restrict applications based on growth stage, while others have restrictions based on pre-harvest intervals. In addition, there are products that we need to watch the crop rotation interval, such as fomesafen, which has a 10 month interval for planting corn.
Remember that growth stages are initially based on the number of trifoliates, or the sets of three leaflets that are unrolled. On hailed fields, which we unfortunately have in the area, this is complicated by lost leafs or nodes, but remember that plants are farther along physiologically that they appear. Plants will add a set of trifoliates every 3-4 days this time of year. For an excellent resource on staging soybeans, refer to the Soybean Growth Stages publication put together by the University of Wisconsin.
With soybeans, as soon as flowers appear, growth stages are based on flower progression and then pod development. Early planted soybeans have already started to flower and with today being the summer solstice, most other fields will soon begin flowering, which is the R1 growth stage.
The next growth stage is R2, which occurs when there is an open flower at one of the two uppermost nodes with a fully developed trifoliate. So how long does it take to go from R1 to R2? The answer is only 5 to 7 days, so watch closely once you start seeing flowers, as R1 is the last growth stage for application of dicamba products to Extend soybeans. Glyphosate is typically labeled for application through R2.
The next growth stage then is R3, at which point a 3/16 inch pod is located at one of the top four nodes. Typically this is going to occur roughly 2 weeks after R2, and is when we would start looking at irrigation for soybeans as well as fungicide applications. There are some herbicides that only list a pre-harvest interval that can be applied during this growth stage, but realize that the chance of crop injury increases once we start applying to podded soybeans. For more information on other herbicides and their label restrictions, refer to EC130 Guide to Weed Management or check out the following article from the June 19, 2017 issue of CropWatch.
While it always best to scout the field to determine growth stage, one way to estimate it is to use SoyWater. SoyWater is a free online tool that uses your planting date, maturity group, and data from the closest weather station to determine growth stage and water use for irrigation.
To listen to this radio message again or to get more information, visit our local website at croptechcafe.org or give me a call at 352-3821. This is Aaron Nygren, your local agronomist for Nebraska Extension on KTIC radio.
