Don’t abandon your pre-seed application in a cold spring. Follow these protocols when spraying FMC pre-seed herbicides when there’s frost.
A cold spring shouldn’t force you to change your overall weed-control strategy. Watch daily temperatures closely, choose the right timing, and spray your pre-seed herbicide when the right opportunity shows itself.
FMC pre-seed herbicides are a critical part of successful weed management. They set you up to plant into a clean slate. This allows your crop to grow during the critical weed-free period without having to compete with weeds for moisture and soil nutrients. That’s especially important when crops are stressed – be it from drought or because they struggled through a stretch with low soil temperatures.
There are three main categories of FMC pre-seed herbicides: Burnoff, extended weed control, and complete solution herbicides.
We’ll tackle extended weed control herbicides first because it’s straightforward.
Using an extended weed control product in a cold spring
The extended weed control products from FMC create a soil-barrier once the herbicide goes into a solution with an activation rain or moisture event. This soil-barrier provides control of later weed flushes, reducing weed competition.
The extended weed control herbicides from FMC include Authority® 480 herbicide, Authority® Supreme herbicide, Command® 360 herbicide, and PrecisionPac® SZ blends. They can be applied with or without glyphosate.
If you tank-mix any of these products with glyphosate, follow the recommendations below for managing burnoff herbicides.
Managing burnoff herbicides in a cold spring
FMC burnoff herbicides include Aim® EC herbicide, Intruvix™ herbicide, PrecisionPac burnoff blends, and the Express® brand herbicides.
In a cold spring, follow the same best practices using an FMC pre-seed burnoff herbicide that you would when spraying glyphosate. The products are designed to perform in a range of temperatures. The main thing you’re evaluating is the health of the target plant.
Spray burnoff herbicide when weeds are actively growing
Like most herbicides, no matter when you’re spraying, you want to spray a pre-seed herbicide when weeds are actively growing. Obviously, that can be trickier when temperatures dip below freezing at night.
Temperatures below freezing at night can cause the emerged weeds to shut down. When metabolic activity stops, there is nothing occurring in the plant for the weed control to affect.
Time your spray with at least one good growing day before a frost
It’s best to have at least one good growing day before a significant frost when spraying annuals and winter annuals. If you’re targeting mainly perennials, try to get three or more growing days before a significant frost. Those good growing days allow the herbicide to translocate into the root system.
Spraying after a frost
Check for visible plant injury after a frost. Injury is indicated by the loss of a healthy green color, such as yellowing or lighter colored tissue. Severe injury will look like dark green “water-soaked” tissue, which dries up quickly.
- Frost of -1 to -4°C does not usually cause major damage to winter annuals, perennials or volunteers that are growing early in the season.
- Frost of -5°C or colder often results in plant injury. Check plants for tissue damage. If there is no visible damage, then spraying could resume within 2 to 3 days or when weeds are actively growing again.
If no injury is visible, spraying can resume later that day once temperatures reach 8-10°C for a couple hours. However, it’s best to wait until the next day to allow plants to resume normal metabolism.
Spray when temperatures are above 8-10°C. If daytime temperatures remain below 10°C and frost occurs on subsequent nights, plants will be slow to recover and spraying should be delayed until weeds are actively growing again.
Complete solution herbicides
The FMC complete solution herbicides are Command® Charge herbicide and Focus® herbicide. They both offer extended control but they also provide burnoff control so need to be treated like a burnoff herbicide.