Pre-harvest herbicide applications have been popular in western Canadian agriculture production for years, but needs change from year to year and field to field.
Your options continue to change as well which means many factors need to be considering when deciding on what action to take and which product to use.
Four questions for choosing the right product
Start by determining if you should apply any products according to these four questions:
1. Is this field going to be used for seed or malt?
Using herbicides like glyphosate hinders the germination of seeds. If you are going to be keeping a field for seed or sending away as malt, exclude glyphosate as an option.
2. What type of weeds are being targeted?
If you are targeting perennial weeds like Canada Thistle or Dandelion then glyphosate is going to be the best option for a pre-harvest application due to its systemic mobility within the weeds. If you are targeting annual weeds that you want dried down for easy combining, use a true desiccant with contact activity.
3. How quickly do you need to be in the field combining?
If you are tight on time due to weather, then a desiccant gives you a shorter wait window between application and harvesting the crop. A desiccant is typically a 4-9 days wait, and a glyphosate is at least a 10 day wait but can sometimes require over 14 days.
4. Is your crop coming in uneven?
Pre-harvest applications of both glyphosate and desiccants are great for evening out the stage of fields and allow for uneven fields to be harvested without issue.
Determining when to apply product
Now that you decided which product to apply, the next question is when to apply the products without causing yield or quality issues.
Desiccation – Proper staging is the lowest third of the pods rattle and the seed itself is hard and doesn’t split; the middle third of the plant will be hard and not juicy, but will split nicely into two halves; and, the top third will be full size but immature.
Pre-harvest glyphosate – The staging is very similar to desiccation, except only the bottom 15% or so of pods will rattle when shaken and the next 50% of the pods will split evenly in two.
Desiccation – Bottom pods are dry, translucent and the seeds are detached from pods and will rattle. The middle pods will not be juicy, but will split and the pods will have began to shift from green to yellow. Top pods will be starting to turn yellow and may have the odd immature seed. About 75-85% of the pods on the plant will either rattling, or yellow and translucent
Pre-harvest glyphosate – Staging against is very similar to desiccation, bottom and middle pods will be brown and dry, while the top pods will begin to be turning yellow.
Desiccation, swath timing and pre-harvest glyphosate are all right around the same stage and that is physiological maturity which is 30% moisture.
Glyphosate can be applied roughly 3 days prior to when a typical swath stage would be. At this point you will see the ‘peduncle’ which is the part of the stem right below the spike or the head turn from green to brown. That means no more translocation is occurring from the leaf sink source up to the head. The other way to determine this is by taking the seeds out and seeing if the seed will keep your thumb nail indent in it when pushed into the seed. If it pops back out, then you are still a little bit away from application. Applying glyphosate to early can cause some quality issues and sometimes appear as if there is minor frost damage.
Again, pre harvest, desiccation and swath timing are all around the same time in canola. This is around the 60-70% seed colour change on the main stem.
Now, the product options for desiccation include Heat (saflufenacil – please note MRL global MRL issues on some crops ie: lentils) from BASF, Reglone (diquat) from Syngenta and lesser used Aim (carfentrazone) from Nufarm. Reglone will be a bit faster acting than Heat, but Heat gives you the flexibility to tank mix glyphosate in it and get some dry down effects and perennial weed control.
When targeting a good dry down you want to be using a minimum 15-20 gallons per acre, especially on thicker crops. This is going to insure you are drying down more than just the top parts of the plants. Be sure to follow label directions for time of application, surfactant use and more.