Spring Greenup Applications And Winter Annual Burndowns

Travis Legleiter and Bill Johnson

The harsh winter is finally winding down and we are bound to have warmer days and spring in the near future. As we look at towards the warmer weather there a few field activities that are going to start quickly, including winter wheat greenup applications and winter annual burndown applications. There are few things to keep in mind as these activities ramp up in a delayed and likely compacted spring.

Spring Greenup Applications:

There have already been reports of greenup fertilizer applications on wheat acres that survived the harsh winter and many more will likely follow as the temperatures rise. While making these applications or prior to making these applications it may be useful to look for winter annual weeds that occur on those wheat acres that may require a spring herbicide application. In typical years winter annual pressure in wheat is of less concern, but with potentially weakened wheat stands the pressure from winter annuals will be of more concern. When planning a spring herbicide application on wheat make sure you consider the wheat stage as well as soybean plant back restrictions for field with a planned double crop soybean rotation.

A desirable option for wheat producers is to combine the spring herbicide application with the topdressing pass by using liquid nitrogen as a carrier. Many of the herbicide labels do allow for liquid nitrogen to be used as a carrier, but may have differing adjuvant requirements and growth stage restrictions as compared to applying with a water carrier. The use of liquid nitrogen as a carrier also posses an increased risk of crop injury for the majority of herbicides applied to wheat in the spring. Refer to our previous article, Spring Herbicide Applications on Winter Wheat, for more information

<https://ag.purdue.edu/btny/weedscience/Documents/spring_wheat.pdf>.

Winter Annual Burndowns:

The jury is still out on how the past winter affected winter annual weeds that emerged last fall and where not controlled with a fall herbicide application. Either way it is likely that spring burndowns will need to be made to control some winter annual weeds and in particular marestail. Fields that did not receive a fall burndown will likely require an earlier application as established winter annual weeds, especially marestail, will begin growing rapidly as the weather warms up. The key for spring burndowns is the timing of the burndown with considerations of weed size and air temperatures. Applications need to be made when weeds are actively growing, but when plants are still small or prior to bolting in the case of marestail. To ensure that plants are actively growing make applications when nightly temperatures have maintained above 45°F for four to five days. It will also take time for soil temperatures to warm to a level that will encourage active weed growth.

We encourage the use of residual herbicides, especially in no-till soybean fields with marestail and pigweed species. If planning on using residuals, maximize the residual control into the cropping season by applying the products preemerge rather than tank mixing it with early spring burndown. No-till soybean fields with marestail pressure are going to require multiple spring burndowns as well as a residual product to achieve maximum control of marestail.

For more information about winter annual burndowns as well as marestail control in no-till soybeans refer to the article and publication below.

Spring Burndown Applications to Weeds and Cover Crops <https://ag.purdue.edu/btny/weedscience/Documents/SpringBurndown.pdf>
Control of Marestail in No-till Soybean <https://ag.purdue.edu/btny/weedscience/Documents/marestail%20fact%202014%20latest.pdf>

A pretty field in the spring!

Source : purdue.edu