Monday, March 21, 2011
Winter Annuals: Eradicate Them And Increase Your Yield And Revenue
Are you paying attention to winter annuals and their impact on yield, or are you just getting ready to plant regardless of the crop growing in your field? Warmer temperature and more sunshine will soon convert your would-be corn and bean fields into a multi-colored haven for winter annuals, which not only steal nutrients, but host SCN in time for soybean planting. There are some tricks you can pull on them, so they don’t pull down your yield.
Winter annuals started growing after harvest, paused for the winter, and will begin to green up before you are ready to head to the field. Some of them will flower by the end of April and produce viable seed by early May. Because of their schedule for rapid growth and nutrient uptake in the next several weeks, they are the most vulnerable to herbicides. But once they start showing flower color, their growth rate has diminished and herbicides are less effective, say University of Nebraska weed specialists Mark Bernards and Lowell Sandell. Their recommendation for controlling winter annuals is “controlling those weeds at least two weeks before planting to protect against yield loss. In addition, controlling winter annuals before mid-April will reduce the risk of weeds going to seed and increasing winter annual weed pressure in subsequent years.”
The Nebraska specialists say because many winter annuals are small and their growth does not overlap crop development their impact on grain yield is overlooked. However, their yield impact analysis points to a 5% impact by April 15 or 550 growing degree days, a 15% yield impact by May 15 or 1100 GDD, and a 35% yield impact by June 15, or 1700 GDD. The hypothesis for the yield decrease is the fact that the winter annuals were keeping nitrogen away from the crops, and providing a continual host to soybean cyst nematode, since SCN will reproduce on the roots of henbit. “At current prices ($6 corn and $13 soybean), the potential losses are $32-$45/ac for 150 bu. corn and 50 bu. soybeans.”
So what can you do about controlling winter annuals? Bernards and Sandell say the first step is to identify the type of winter annuals you may have. Their recommendations are based on controlling all at one time with one pass. If Marestail is one of your guests, 2,4-D or Dicamba should be part of the burndown tank mix, since some may be resistant to glyphosate. The next question is based on what you will be planting in the field, and let that determine what type of a residual herbicide you might select.
• For corn — atrazine, Balance Flexx, Corvus, Prequel, Resolve, Sharpen, Valor, and Verdict
• For soybean — Authority products, Canopy, Pursuit (and other imazethapyr containing products), FirstRate, Flexstar, Optill, Sharpen, and Valor products
The weed specialists say the application of a burndown along with a residual pre-plant herbicide will not only control the winter annuals and give you a clean seed bed, but protect the crop against early season weed competition until your post-emerge herbicide application is made before weeds are 4 in. tall. Something that will also help is knowing what weeds are predominant species in the field, and that knowledge will help select the residual herbicide.
Care must be taken when applying burndown herbicides, in connection with the planting date for both corn and soybeans. If you are applying 2,4-D to a field that will be planted with corn, the planting date cannot be less than 7 days if you are using less than 1 pint per acre, or less than 14 days for more than 1 pint per acre. If you are planting soybeans, the pre-plant interval cannot be less than 7 days for the low rate nor less than 30 days for the higher rate. If you are using Dicamba, the preplant delay must be at least 5 days for 4 fluid ounces per acre nor less than 7 days for 8 fluid ounces per acre. Do not apply Dicamba to fields where soybeans will be planted. Crop oil concentrates and methylated seed oils with a nitrogen source will enhance burndown activity. “Burndown applications without residual herbicides will likely cost $4-$8/ac, plus application costs. Adding residual herbicides will increase that to $12-$40/ac, plus application costs.”
Summary:
Your first priority in no-till fields may be eradication of winter annuals, which can hurt yields as much as 35% if soybeans are not planted until the middle of June. Winter annuals will soon begin rapid growth and seed production, but are also most vulnerable to burndown during their active growth period. Applying 2,4-D or dicamba with a residual herbicide will not only eradicate the winter annuals, but provide protection until a post-emergent application can be made.
Posted by Stu Ellis on 03/21 at 12:00 AM | Permalink