The basics of weed management for your industrial hemp crop really isn’t different than any other crop. Know your crop. Know your enemy. Know your tools.
And the most important of all… don’t delay!
Hemp grown for seeds or fiber is planted very densely. The whole point is to grow tall, straight stalks and as much of it as possible. It is direct-seeded and requires only minimal cultivation before the plants take off and shade out weed competition.
Industrial hemp grown for cannabinoids is an entirely different matter when it comes to weed control.
To encourage a multi-branching, ‘bush’ type plant for maximum cannabinoid production, CBD hemp is planted on a much wider spacer. Most growers are planting transplants on a 4 ’x 6’ spacing (4’ in-line, and 6’ between rows).
While the ultimate goal is to get a thick stand of hemp, the wide initial in-line and row spacing of the crop means it will take longer to ‘close the canopy’ quickly, leaving opportunity for weeds to get a solid start.
Whether you are growing for fiber, food or oil, a clean, properly prepared field is key. Soil preparation should begin months ahead of planting, particularly if you are planting into a perennial crop field (like alfalfa) which will take repeated passes (and possible herbicide application) to kill off those hardy roots.
The first goal ALWAYS with weed management is reducing the need for labor. Hand-weeding is expensive. The CBD hemp farmer needs to carefully evaluate the size and scope of their operation compared to available tools and methods.
No matter what system you settle on, one rule is fundamental – keep your rows straight and your row spacing uniform. There are cultivating set-ups for your crop after it has been planted, but if you didn’t lay down straight rows and have varied spacing between rows, that means your mechanized tools will not fit.
Many hemp farmers are planting into raised plastic mulch beds. This is a technique used commonly by specialty crop growers for years.
A properly installed plastic mulch bed will eliminate the weeds under the plastic. But, you will still need to control weeds in the rows where the plastic isn’t! Also, plastic mulch growing, in most growing conditions, will require drip irrigation buried under the plastic. And don’t forget you will need to LIFT that plastic (and dispose of it) at the end of the year.
Plastic mulch may be unfeasible for large-scale industrial hemp CBD operations. In that case, make sure to have an effective solution via tractor cultivation.
Early and consistent cultivation when your hemp goes into the ground to take out weeds at thread-stage is critical. Cultivate BEFORE you see the weeds is always the rule!
There are many tools on the marketplace including finger-weeders and tine-weeders adapted for specialty crops that can undoubtedly be used on hemp. The closer you can get to your plants, lightly disturb the ground and kill thread-stage weeds, the more money you will save in expensive hand-weeding down the road.
Also, have a plan for keeping your paths clean once the hemp starts putting on growth – which happens fast! A wide wheelbase and high tractor mount to straddle rows as long as possible will be crucial.
Whatever your size, and however you develop your weed management plan, the main thing to remember applies across the board… Weeds happen! Better have a plan for that!
As of this writing (August 2019), there are no herbicides approved for hemp production in the U.S., though the EPA published a notice this month that they have received applications to add hemp to currently registered pesticides. (EPA lumps herbicides under their ‘pesticide’ definition). This means you are not allowed to use most pesticides/herbicides on hemp. However, expect the EPA to generate an approved list soon.
Until approval, the only pesticides (or herbicides) legally available for use in hemp are ones typically under the National Organic Program rules, contact your state department of agriculture for this list). If you do end up using only NOP approved pesticides, consider getting your crop organic certified. You’re already a big part of the way to getting certification and it can be an advantage in the marketplace!