Herbicide Qs on tank mixing, ideal weather, spray patterns and more

June 14, 2017 - Issue 12

Here are some common agronomy-related questions that dig a little deeper into herbicide performance in canola:

What products can I tank mix? Tank mixes listed on product labels are widely tested and approved. Growers have many other tank mix options not on labels but that are still OK. Liberty and Decis is one of many examples. (Find more on this and other supported Liberty tank mixes on page 10here.) But not just anything can be tank mixed. Some mixes can clump up in the tank and some are antagonistic to each other when sprayed, negating their crop protection benefits.

What products, if left in a tank, are most likely to scrub off past residues? Liberty (due in large part to its surfactant) is one. High solvent surfactants such as Merge will as well. Read more.

What is the ultimate temperature and time to spray primary HT canola products?
Liberty: Sunny and hot
glyphosate: Sunny and warm. Avoid cool conditions.
Ares/Odyssey Ultra/Tensile: Avoid cool conditions.
Draft for Cibus SU canola: Avoid cool conditions
Read more

Why does Liberty cause cupping and bronzing in canola that supposed to be tolerant? If canola plants are growing rapidly, they can exhibit both symptoms after a Liberty application. Surfactant is the cause. The crop will grow out of it – as long as the cause is Liberty surfactant alone. If Liberty has loosened some other herbicide from the spraying plumbing, this damage could lead to some plant death and yield loss.

What stage do weeds become too difficult to control? This point is usually long after the weeds have already had an irreversible negative impact on crop yield. When it comes to specific weeds, lamb’s quarters and redroot pigweed are usually quite easy to control whereas wild oats, cleavers and kochia are more difficult to control if left too long. What weeds will have the biggest overall impact on yield in your fields? Base herbicides choice, rate and timing on these driver weeds.

Why does dust on leaves impede herbicide uptake, especially for glyphosate? Glyphosate binds strongly to clay and organic matter components of soil. The same mechanism that makes it unavailable for uptake by plants from the soil itself is the same mechanism that makes it unavailable for foliar uptake. Glufosinate (Liberty) is weakly bound to clay and organic matter so not impacted as much by dust on the surface. IMIs are weakly bound as well.

How do we know a herbicide is working? Scouting in the days and weeks after a herbicide application is an important step to see if the herbicide worked on all weeds and whether a second application is required. Some herbicides show symptoms fairly quickly. Others take a few days and some more than a week to show distinct symptoms. Here’s a quick overview:
Liberty: Quick. Symptoms will appear in 3 to 5 days.
Glyphosate: Slower – 4 to 10 days for initial symptoms, depending on species and growing conditions.
Group 2s: Slower — 7 to 10 days for initial symptoms, depending on growing conditions.
With slower systemic herbicides, plants are shut down. They are not dying yet, but not growing. Results can also depend on weed species. When Liberty is tank mixed with a Group 1, broadleaves may start dying quickly but wild oats can take longer because various actives at work.

How can we test coverage? A few sheets of water-sensitive paper placed face-up on the ground or mounted in the pathway of the operating sprayer is a relatively cheap way to see if the combination of nozzle choice and water volume is producing the coverage needed – especially for contact herbicides. Read more.

What is application window for each HT system?
Liberty Link: Liberty 150SN can be applied from crop stages cotyledon to early bolting.
Roundup Ready: Glyphosate can go from seeding to the 6-leaf stage. Eclipse III is 2- to 6-leaf stage.
Clearfield: Ares 2- to 7-leaf stage; Odyssey NXT/Odyssey Ultra 2- to 6-leaf stage; Salute: 2- to 6-leaf stage; Solo ADV/Solo Ultra 2- to 6-leaf stage; Tensile 2- to 6-leaf stage.
Cibus SU: Draft (thifensulfuron methyl) at the 2- to 5-leaf stage of the crop. More on Draft.

Further reading:

Sprayers 101: Deciding on the right way to spray

Canola Watch