With the early harvest, this fall offers a great opportunity to tackle fields with perennial weed issues in no-till fields. Control of our common perennial weeds like dandelions with our standard practice of spring burndown treatments of glyphosate and 2,4-D has been poor this year.
While results were much worse this year compared to others, we have observed many of these spring treated fields increasing in perennial weed pressure. Even though suppression is adequate in some years to establish crops with a spring burndown treatment, we have shown that these perennials can survive and believe this has resulted in larger, more difficult to control perennial weeds in our no-till fields.
So what can you do? Fortunately several affordable options exist. You may not be able to implement these in all of your fields this fall, therefore we recommend targeting fields that are badly infested with perennial weeds first. A summary of the main options for management are below.
Results from over 3 years of research have shown that the fall is the best timing to manage these perennial weeds with glyphosate, 2,4-D as well as other common herbicides that have significant residual activity (e.g. Canopy EX).
Previous data has shown that control of dandelions can be increased by up to 60% if herbicides are applied in the fall versus the spring. An added benefit of using herbicides with a residual is improved suppression of winter annuals and spring emerging weeds, so consult the label to see what herbicides may offer additional control on which weeds.
Clearly the biggest hurdle to utilizing this timing is trying to fit in the application with all the other activities in the fall. Control can be effective if applied anytime in the fall as long as plants are actively growing. With dandelions this timing can be confusing to identify as leaves often turn purple after the first frost.
Results from our research and others indicate herbicides have good uptake and control on dandelions when applied to leaves that are green to purple, as long as leaves do not show severe freeze damage.
Residual herbicides tend to have better control when applied later in the season when foliar uptake is limited. While it is unrealistic for all no-till acres to be sprayed every year, targeting fields that have historically high populations of these weeds will be the most beneficial.
With our northern proximity spring burndown treatments for perennial weeds will continue to be utilized. Realize that these applications can have reduced suppression and control in some years like 2010.
If using glyphosate and 2,4-D it may benefit to wait as long as possible before applications, as warmer conditions will result in quicker burndown. Several herbicides with residual activity can also be utilized with glyphosate and 2,4-D that can extend control. Applications often take 2-3 weeks before symptoms of herbicide damage become apparent.
Our results have shown Canopy EX, Enlite, and Synchrony can provide extended control into the summer. Make sure to follow planting restrictions for these herbicides as some of these herbicides have plant-back restrictions that exceed 30 days.
Another benefit of these herbicides is a delay in annual weed emergence, which can extend the timing needed for post applications of glyphosate similar to using a PRE herbicide at planting.
Clearly perennial weeds like dandelions are here to stay in our no-till fields and will need to be managed to maintain low populations and prevent economic loss from competition. Herbicides are our best tool, but consult the label as plant-back restrictions do exist and can be greater than 30 days for some of these combinations for some crops.