When considering your options for a pre-harvest application there are several tools available. These include swathing, systemic herbicides and contact herbicides. These can be a great harvest management tools to clean up dirty/ weedy fields, accelerating harvest and ensure seed for the following spring.
Systemic Herbicides (Glyphosate)
A pre-harvest Glyphosate application is typically used for controlling the late flush of weeds before they set seed and contribute to the fields seed bed. Where allowed, Glyphosate can be used alone, or tank mixed with Heat to desiccate crops. This application should only be applied once the grain moisture is less than 30% in the least ripe part of the field. Applying Glyphosate too early can contribute to MRL’s (maximum residue limits), which creates marketing risks. Compared to Diquats quick dry down period, Glyphosate can take 10-14 days for the crop to mature.
Contact Herbicides (Diquat)
The use of Reglone and other diquat products can provide quick dry down and effective harvest management. The active, Diquat shuts the plant down quickly and stops the plant from maturing. For most crops, spraying Diquat can typically have you harvesting within in 4-7 days. However, unfavourable weather conditions such as cool temperatures and rainfall may delay that timeframe. To improve the effectiveness of Reglone and other diquat products apply at high water volumes and on cloudy days/ at darkness. Crop staging is very important, as applying prematurely can result in increased risk of locking in immature seeds.
You want to ensure the field has turned to a yellow brown colour and there are minimal green patches. On the bottom third of the plant the pods should be dry and translucent, seeds are detached and rattle. The middle third of the pea plant the seeds are yellow, full sized, firm, and seeds split when. The top third the peas are still fleshy but starting to turn from green to yellow.
The lentil field should have an overall colour change of tan, brown. The bottom third of the plant the seeds should be dry and rattle. Middle third the seeds should be mature, yellow and can be split. The top third can be green but with some colour change starting.
With applying pre-harvest desiccating you want to see at least 70-80% seed colour change. The bottom third of the plant needs to be completely black/ brown. The middle third must be brown, with some speckling. The top third can be green but must be firm when rolled. When scouting the field it is important to step in and open the pods, as pods may appear green but seeds will be dark.
The easiest way to determine if a wheat crop is ready for a pre-harvest application is the thumbnail test. Put a reasonable amount of pressure from your thumbnail into the kernel and if it leaves a dent without splitting it is ready. This is better known as the hard dough stage and must be present throughout different areas of the field. After application, harvest is typically 7-14 days away.
It is important to check with grain buyers and KeepItClean.ca to ensure your desiccated seed will be accepted at time of marketing. Accurate crop staging is essential when it comes to desiccation timing, to ensure herbicide isn’t being applied too early and locking in immature seeds. Please contact your local SynergyAG for any crop staging questions.