The effects of climate change in Maine was already bad news for farmers and gardeners. Now it looks like the ones who rely on non-chemical weed management practices are in for another climate-induced challenge.
The trend over the last four years in Maine of periods of drought and torrential rain storms along with overall general warming conditions have created a perfect agricultural storm in which weeds can flourish. Those same conditions are going to make weed control more challenging.
At its simplest, a weed is any plant growing where it is not wanted, and is the bane of anyone who grows crops. Left unchecked, weeds can choke out vegetables, fruit trees and flowers in small backyard gardens to larger market farms.
Farmers who prefer ecological weed management are going to be particularly hard hit since controlling unwanted plants without herbicides takes a bit of skill and some luck when it comes to timing. And much of that hinges on favorable weather conditions. Thanks to climate change, those favorable conditions for weed control are getting harder to find in Maine.
Droughts and heavy rains are hard enough on crops. Too often they occur just at the right time to make direct weed control almost impossible, according to Eric Gallandt, professor of weed ecology at the University of Maine’s school of food and agriculture.
“Organic farming and ecological weed control is an interesting mix,” Gallandt said. “On the one hand you are seeing these periods of wet conditions hitting when you need to [weed] and on the other hand it’s too dry and you need to be thinking about irrigation.”
The most common type of ecological weed management is cultivation that pulls the weeds right out of the ground. Whether it’s done by hand pulling, chopping with a hoe, mechanical tiller or tractor-pulled cultivator, the goal is the same: cut the weeds off at the roots without pulling up or hurting the nearby crops.
The best time to do this is when the soil is moist, but not wet, according to Gallandt. More and more growers are stuck needing to weed, but faced with weather conditions making it all but impossible.
“We need to be thinking about weeding tools or strategies that are more robust,” Gallandt said. “If you are going to cultivate or hoe weeds, the odds of being able to nail the timing to get out there are smaller and smaller.”
That means growers need to be more efficient about getting rid of the most weeds in the least amount of time.
As recently as a decade ago growers in Maine could count on periods lasting a full week during the growing season to cultivate and pull weeds.
“Now, it’s like instead of a full week, it’s a couple of days,” Gallandt said. “Growers need to think about how to scale things for more timely weed control.”
One way they can do that, according to Gallandt, is becoming a lean, mean weed fighting machine.
“If you are using something that cultivates two rows at a time, you may want to consider getting a four-row cultivator,” he said. “If you weed by hand, you may want to switch to a [mechanical] cultivator.”
Using mechanical tractor-pulled cultivators is not an option for everyone. The implement plus the tractor can be a substantial up-front cost. Then there are the ongoing costs of fuel and maintenance.
Smaller, but still mechanical, are gas-powered tillers. These machines are pushed or guided by hand and have rapidly spinning tines that can dig up the dirt while cutting or pulling up any weeds in its path. They can be a bit cumbersome to operate, but with practice you can cover a lot of ground using one.
The speed provided by mechanical cultivators will allow farmers to take advantage of the few days when the ground is not overly muddy or too dry to work.
Old-fashioned hand weeding is going to have to speed up to take advantage of those weather windows. To be the most effective, hand weeding or hoeing should be done when weeds are small because their roots will be easier to chop or yank out. A sunny, dry period is the best time to hand weed.
Luckily, control methods like mulching or planting crop rows close together to prevent weeds from sprouting are so far not affected by extreme weather events, according to Gallandt.
In fact, mulching remains one of the most effective methods of ecological weed management. Mulch controls weeds by preventing sunlight from reaching the soil surface, which keeps the weed seeds from germinating. All you need to do is lay down a few inches of grass clippings, pine bark, straw, leaves, black plastic or landscaping fabric between your rows.
“It’s still a good idea to get out there and mulch,” he said. “Not only does it prevent weeds, it helps hold and control moisture getting to your crops.”
Not only will growers need to rethink their weeding plans, but research shows that climate change means there could be more weeds to eradicate.
Increased levels of carbon dioxide, warming trends and water stress can promote weed growth, according to a literature review conducted by Gallandt and University of Maine researchers Sonja Birthisel and Ruth Clements.
The three found that rising temperatures speed up the spread of invasive weed species that successfully adapt to variable temperature and moisture conditions.
“These broad forecasts in our region for warmer, wetter and more variable conditions already have people thinking about how they are going to grow vegetable crops,” Gallandt said. “We are going to also see changes in weed control and how [growers] will manage that in the fields.”
