Pre-emergent Herbicides in Roundup Ready® Soybeans
In today’s world of higher input costs, farmers have to sharpen their pencils to calculate the best return on their investment. One area of the farming operation that deserves a closer look is weed control in Roundup Ready soybeans. For years, this has been the simplest, most economical system available to Midwestern soybean farmers. While the system remains relatively the same, the economics has changed a bit due to the recent higher costs of glyphosate, the active ingredient in Roundup and other generic products. With a few slight tweaks, this system can still be effective and economical. The difference would be the addition of a pre-emergence herbicide.
Adding a pre-emergence herbicide with the glyphosate burndown may provide enough weed control to eliminate a second in-crop application of glyphosate. It also helps manage weed resistance by incorporating one or more herbicide modes-of-action in the system. Monsanto’s Roundup Rewards® allows the use of one of four different residual herbicides in their Start Clean, Stay Clean Assurance Plan for soybeans. They are: Intrro, Gangster, Valor and Valor XLT. These products offer good control of morningglory, lambsquarters, pigweed, marestail and waterhemp – weeds that are becoming tougher to control with a single treatment of glyphosate in some areas of the Midwest.
So, to get the maximum effect of your Roundup Ready soybean weed control program, start with a clean field at planting by applying a burndown of Roundup plus a residual herbicide, such as one of those listed above. Then follow with an in-crop application of a Roundup agricultural herbicide at a minimum of 22 ounces/acre before weeds exceed 8” in height. Follow the Roundup Rewards guidelines and receive a second in-crop treatment of Roundup at no cost if a late flush of annual weeds develops. See the 2008 Roundup Rewards booklet for more details.
What Will Happen with Soybean Aphids in 2008?
If I told you that I correctly predicted that Kansas University would win the NCAA Men’s basketball tournament this year, you might respond by saying, “Lucky guess.” However, if I told you that I have correctly predicted the winner of the tournament every year for the last seven years, you would, at least, be mildly impressed with my foresight. Well I didn’t, but to illustrate my point about predictions, with good information provided to us we can make accurate predictions about soybean aphid infestations each year. The key is monitoring their fall flights from soybean fields to their winter host, buckthorn shrubs, with the use of suction traps.
When aphid predators (i.e. Asian lady beetles, lace wings, minute pirate bugs, etc) are absent, aphids tend to increase rapidly in a field to tremendous populations late in the season. When the crop matures, aphids develop wings and fly off to find buckthorn, and in their haste some will be caught in these suction traps. The fall’s of 2002, 2004 and 2006 had very large numbers of adult aphids caught in traps. This large population overwintered and infested thousands of acres of soybeans the following summer. Hence, the “odd-numbered” years have generally been years with heavy aphid infestations. Last year, 2007, saw less aphid pressure than other odd years mainly because of aphid mortality from cold temperatures during late April coupled with a very hot/dry summer. Predators were also in good supply during 2007 and the result was a very low (record low) number of aphids caught in traps last fall. So, our prediction for 2008 is that aphid populations will be low – at least that is how the pattern has progressed during the last 8 years.
As I mentioned above, predator populations in 2007 were fairly strong. In fact,new predators have been discovered across the Midwest and even one has been released as a form of biological control. Many of these new predatory insect findings belong to the wasp family. These very tiny, stingless wasps attack aphids and lay their eggs right inside the aphid. The larvae develop inside the aphid and later emerge from the aphid as an adult wasp. Time will tell if this new biological control introduction will significantly effect the aphid populations around here, but in China where the soybean aphid originated, this tiny wasp has helped to keep aphid populations in check. Researchers are also evaluating different strains of soybeans for natural aphid resistance. Aphid resistant varieties are a few years off, but it looks promising. So has the soybean aphid seen their better days? It appears that with the help of nature, the weather and some smart soybean breeders, this soybean pest may be on the decline in the years ahead.
Have a great rest of the week!
Dan Childs, Agronomist
