Herbicide layering:
The practice of using herbicides from multiple groups in sequential applications to target the same weeds and will include soil-applied herbicides combined with pre-seed burnoff, followed by an in-crop herbicide application.
Layering three to four herbicide groups is shown to be the most effective. First, a burnoff with a soil-applied herbicide will control early emerged and spring germinating weeds. Then the in-crop application of a different herbicide group will control weed escapes and weeds germinating later in the season. . It also means that any weeds germinating later will be smaller and therefore more easily controlled by the in-crop herbicide.
In research trials in Saskatchewan on kochia control in lentils, herbicide layering with Edge® herbicide, Focus® herbicide, Fierce® herbicide and Valtera® herbicide in the fall was followed up with glyphosate or glyphosate plus Heat® herbicide pre-seed and then an application of Solo® herbicide in-crop on a Clearfield® lentil variety.
Compared to the glyphosate-only treatments, the fall layering herbicides all reduced kochia populations. The highest yielding treatments included Focus® herbicide and Fierce® herbicide with spring-applied glyphosate. (Enns et al. 2020)
What follows is an example of what herbicide layering with lentils as part of the crop rotation over four growing seasons could look like.
Herbicide layering scenario in a field that has Group 2 and 9 resistant kochia.
YEAR 1
The rotation starts with lentils but in-crop herbicides are limited for lentils. The following approach begins with a multi-mode of action pre-seed application:
Pre-seed
Group 14 (carfentrazone) and Group 9 (glyphosate), along with herbicide layering Group 15 (pyroxasulfone) to achieve extended activity on herbicide resistant kochia, wild mustard and stinkweed.
In-crop
A Group 5 (metribuzin) can be used in-crop to target any additional broadleaf weeds. The Group 15 (pyroxasulfone) has extended activity on the grassy weeds and is keeping them at bay.
Pre-harvest
Group 22 (diquat)
Post-harvest
To set up the next season’s crop for success, a fall-applied application of a Group 3 (triallate) and Group 15 (trifluralin) can be used.
YEAR 2
Barley is planted and the following herbicide plan is implemented:
Pre-seed
Group 2 (tribenuron) + Group 4 (dicamba) + Group 9 (glyphosate) to clean up any winter annuals or annuals.
In-crop
The extended control of the soil-applied herbicide the previous fall means grassy and broadleaf weedshave been suppressed. To maintain yield, a timely application of a Group 1 (pinoxaden) and Group 4 (fluroxpyr) to ensure the wild oats and kochia do not set seed.
Pre-harvest
Nothing, because it’s malt barley.
Post-harvest
Nothing. Thanks to a rigorous herbicide strategy early in the season combined with a competitive crop there was little weed growth in the fall.
YEAR 3
InVigor® canola is planted, which opens up the opportunity to use:
Pre-seed
Group 14 (carfentrazone), Group 6 (bromoxynil) and Group 9 (glyphosate).
In-crop
Group 10 (glufosinate) and Group 1 (clethodim).
Pre-harvest
Research at the University of Saskatchewan has shown that pre-harvest herbicide applications at canola swath timing are too late to result in any appreciable weed control benefits as most weed seeds have already matured. https://www.canolacouncil.org.
Post-harvest
Fall applications of a soil-applied herbicide — like Authority® 480 herbicide (Group 14 - sulfentrazone) — to control early germinating weeds like kochia the following year. Combining it with Group 9 (glyphosate) and Group 4 (2,4-D) will control any winter annuals that have emerged after canola harvest.
Year 4
The crop is durum. Since durum is seeded early and fall-applied products set up the field for minimal to no weed pressure in the spring, no pre-seed herbicide is applied.
Pre-seed
Nothing; durum is seeding early and fall applied products have set up the field.
In-crop
Rotating wild oat graminicides is important to delay herbicide resistance. Take advantage of the durum year to use a Group 2 graminicide (pyroxsulam), combined with multi-mode of action broadleaf products (Group 2 - tribenuron, thifensulfuron, Group 4 - fluroxypyr, MCPA Ester).
Pre-harvest
Nothing.
Post-harvest
Nothing.