As the 2020 field season winds down a lot of producers in the higher rainfall areas of the PNW are assessing what went right, wrong, or sideways with their weed management this season. One thing is certain, Italian ryegrass continues to be a persistent and growing nuisance. A number of factors combined to exacerbate Italian ryegrass issues this season. Early favorable planting conditions tempted many to seed before a good flush of weeds were up in the spring.
We know earlier planting with cereals is a key to maximizing potential yields, but the practice comes with trade-offs as the bulk of your weed control burden is shifted to in-crop, selective herbicide efficacy and not pre-plant burndown or cultivation. Weed control is further complicated when the problem weed, Italian ryegrass, is likely to have resistance to at least one selective herbicide mode of action if not more. Even further frustrating good weed management is Italian rye’s facultative nature, sprouting when conditions are favorable (which they continued to be late into the spring and early summer) and requiring no cold-set (vernalization), just nine or more hours of day length to start flowering once past the vegetative growth stage.
Another complication was our ample to excessive soil moisture late into the spring. Fields with boggy or excessively wet areas at spring herbicide timing act as refuges for sprouted Italian ryegrass as the stress induced by being too wet actually makes the weed less susceptible to available selective herbicides. As a result of environmental conditions and management trade-offs, many producers were left with eyesore Italian rye patches in their fields – and a desire to address the issue.
Some have turned to burning field stubble as a method of reducing the weed seed bank. We’re probably familiar with the typical downsides to field burning; loss of organic matter, loss of nutrients, potential increases in soil erosion, increased soil acidity and smoke issues with the neighbors. However, when faced with a problem that seems to have few readily available solutions sometimes drastic steps are necessary.
How effective is field burning in controlling Italian ryegrass seed? According to Lyon et al, 2016, burning standing stubble on the Palouse did reduce Italian Rye emergence slightly compared to the unburned check but not enough to constitute an effective management practice alone or in conjunction with other methods (Italian Rye emerged at 63% in the unburned check and 48% in burned stubble). Windrowing and burning had a substantial effect, however, reducing emergence down to just 1%. Why the lack of control with unconsolidated stubble burning? The fire simply couldn’t produce enough heat for long enough to kill the weed seed unless fuels (chaff and stubble) were concentrated into a windrow.
Would I recommend stubble burning as a best management practice for control of Italian ryegrass seed? Maybe, but with a big asterisk and that being if the practice follows proven methods such as windrow burning and is used in conjunction with other BMP’s (crop rotation, herbicide MOA rotation, and sanitation practices for example) and if the downsides to burning mentioned above are understood and acceptable given the specific situation. Just burning stubble alone to control weeds is a lot like baling stubble to control weeds. The positive effects are negligible, but the costs are not.