CropLinks September 3, 2020
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Winter wheat pre-emergent herbicide options:
The critical weed-free period for winter wheat is between 500 and 1000 growing degree days (base temperature set at zero degrees). This translates roughly from tiller emergence in the fall to stem elongation next spring. Historically, it has been a rush in spring to apply herbicides before the spring window closes, and the flag leaf has emerged. Applications at this late timing do little to increase yield as the yield loss from weed competition has already occurred. These late applications can “clean up the straw”, make combining easier and may be necessary to clean up late-emerging annuals before they go to seed. This may be critical for some vegetable producers in order to help decrease the weed load in some fields. Fields with low weed pressure and vigorous wheat may not need a spring herbicide application if a fall herbicide is applied.
Weeds that are present before the wheat crop is planted, and those winter annuals and perennials that emerge just after planting have the greatest impact on yield. Compared to spring germinating weeds, winter annuals and perennials have the greatest effect on overall winter wheat yield because they become established in the fall and can compete with the wheat throughout the spring. By the time the traditional window for herbicide application rolls around, these fall weeds can be quite large and have already started to flower, maybe even set seed and are therefore very hard to kill. Pre-plant/pre-emergent herbicide applications generally give better/longer-lasting control of perennials like dandelion because they take advantage of the “dormancy cycle” of the weed to translocate the chemical right to the root as the weed is moving energy to the root for over wintering.
Over the past couple of years, there has been a number of herbicide products marketed to be applied pre-plant or pre-emergent to the wheat, giving residual control that will last at least through the fall period. In no-till situations, these products can be tank-mixed with glyphosate during burn down applications.
Eragon (Saflufenacil) has been used quite often in the last five years in Nova Scotia. In fields with heavy fall weed pressure, it does a nice job of holding back fall weeds. When using it as a fall burn down, it is necessary to mix in glyphosate and a surfactant. This burn down will advance much more quickly than glyphosate alone. If you are using it in a full tillage situation, pre-emergent, the Eragon can be used alone (if no green weeds are emerging, there is nothing to burn down). In this situation, you are using the product for its residual weed control, and you want to use it at its highest labelled rate. Eragon can also be used as a desiccant, pre-harvest in the soybean crop to even the crop, dry it up and hasten harvest. This allows the grower to plant their winter wheat a little earlier. You would think that this application would give very little residual control, but you can expect control to be quite similar to that given when Eragon is applied pre-emergent.
Eragon is very good on most broadleaf weeds but shines on cleavers, shepherds purse, purple deadnettle, Canada thistle and chickweed. Eragon will NOT control most grasses.
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Control of Purple Deadnettle with a pre-emergent application on Eragon and Surfactant
Source: Mike Cowbrough, OMAFRA
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For those growers who frost seed red clover into their wheat, Eragon is a safe and versatile product for them. The residual weed control has decreased by spring and will not cause damage to the clover. Eragon controls the fall weeds making product selection for spring weed control much easier, as herbicides are limited when clover is added to the system. By using Eragon, a producer can control the fall weeds, introduce the red clover and clean up spring germinating annuals with Burctril M or MCPA sodium without injuring the clover. (If a spring herbicide is needed at all.)
For more product information on the herbicide Eragon, click here.
Focus (Pyroxasulfone + Carfentrazone-ethyl) has been used in western Canada for many years and received a label expansion for eastern Canada last year. It has been marketed as a grass product but controls a surprising number of broadleaf weeds. Of interest for winter wheat, it has activity on wild oats, bluegrass and cheatgrass (Downey brome), but also controls cleavers, wormseed mustard and chickweed. I’m told the residual of this product will last into the spring to control early emerging cleavers, but the weather conditions govern the length of control.
This product will cause some injury on the spring frost seeded clover but will probably not take it out completely.
This product also has some warnings on the label about crop injury on low organic matter soils, light soils and seed which is placed too shallow (and I know that no Nova Scotia winter wheat producers would ever plant their seed less than an inch deep). So make sure you read and understand the label.
For more product information on the herbicide Focus, click here.
The other product that has a label for pre-emergent application on winter wheat is Fierce. Fierce (flumioxazin + pyroxasulfone) contains one of the active ingredients in Focus and is priced a little high compared to Eragon and Focus, so doesn’t receive much of the winter wheat action. Fierce is an excellent residual product for the soybean market. The reason I bring it up is there may be a part jug in your chemical storage, and this may be a good opportunity to use it up.
So, where to position these products? Consider fields that have high weed pressure, early planted wheat (late-planted wheat will often have less annual weeds) and those fields containing problematic weeds such as cleavers, purple henbit or bluegrass. If it is dry enough to plant, most often, it will be dry enough to spray pre-emergent herbicides, allowing growers to control some of these troublesome fall germinating weeds.
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Where is the corn at?
I’ve calculated the CHU from May 1st up until August 31st:
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So we are about a week ahead of the ten-year average. The nighttime temperatures in the two-week forecast look quite warm, so the corn will continue to develop quite quickly. To stage corn silage harvest, check out a past issue of CropLinks.
As soon as I hit send on this newsletter, I will likely get a call from a young lady in the Truro area saying her corn is more advanced than one week. Why is that? Well, I would suggest that most farmers have backed off on their CHU after last year’s poor maturity. As well, it’s been quite a while since we’ve had a “normal year,” early May was also quite cold, which sets my calculated CHU back slightly compared to other years. But since the corn was planted end of May, the corn has never looked back.
There is some drought-stressed corn out there for sure, with leaves burnt up above the ear leaf.
It will be nice to get the corn off without wallowing in the mud giving some farmers a chance to no-till wheat in after silage is harvested.
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Gordon (Sonny) Murray
Field Crops Specialist
Perennia Food and Agriculture Inc.
902-670-4892
smurray@perennia.ca
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CropLinks and other notices are now digital. If you would prefer to have them come to a different e-mail address please contact Sonny.
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