What to do about residual herbicides on soybeans in 2016
Share Facebook Twitter Google + LinkedIn Pinterest What makes a farmer ask this question? Many customers were happy with the weed control they saw in 2015 and are planning to use the same program in 2016. But others had soybeans that were stunted, which raised some concern.Click to enlargeThese pictures are from Page 87 of the 2014 Practical Farm Research (PFR) book. As shown in these images, various residual herbicides caused differences in emerged stand and soybean height later in the season because of additional stress from cool wet conditions at emergence.As you can see from the summary below, the control yielded less because it received no burndown and the weeds ran rampant.Click to enlargeThis year my friend and respected PFR Agronomist, Jonathan Perkins, ran the same study twice at the new southern Illinois PFR Site in Effingham. One of the plots was executed the same as in 2014 and the other was conducted with a new spin.These studies do a good job of demonstrating how compounding chemistries can affect soybeans. Residual herbicides alone have resulted in yield increases. But when compounded with cool wet conditions, they have demonstrated adverse effects on the appearance and yield in some cases.Click to enlargeSo why use residual herbicide?Residuals give you a safety net.They reduce weed competition when post herbicide treatments are delayed later into the season.They offer multiple modes of action.Relying on a single herbicide mode of action may reduce your chances of clean fields and promote the development of resistant weeds.They control smaller weeds. The smaller a weed is, the easier it is to kill. Residual herbicides are a tool to control weeds while they are germinating.“Controlling weeds before they germinate is key due to a single growing point that they are working to control at the soil level. Once weeds like waterhemp, Palmer amaranth, and marestail emerge, we begin the battle of managing multiple growing points that increase the chance of weed survival and run a higher risk of resistance developing. Although residuals may occasionally cause adverse effects on yield if soybeans are faced with less than ideal growing conditions early, the reward is typically well worth the risk involved. The key point for me is three out of the last five years, residuals have not shown injury and have provided clean fields and high yields as an end result. The main takeaway? If you can’t get a sickle bar through the field to cut the beans, they won’t have much chance to yield any higher!” – Jonathan Perkins | Southern Illinois PFR Agronomist and CCAContact your seed advisor or dealer if you have any questions regarding residual herbicides.