The effects of climate change in Maine were already bad news for farmers and gardeners. Now it appears that those who rely on non-chemical weed management practices will face another weather-induced challenge.
The trend over the last four years in Maine of periods of drought and torrential rainstorms coupled with general warming conditions have created a perfect agricultural storm in which weeds can flourish. Those same conditions will make weed control more challenging.
In its simplest form, a weed is any plant that grows where it is not wanted, and is the bane of anyone it cultivates. Left unchecked, weeds can choke out vegetables, fruit trees, and flowers in small backyards and larger commercial farms.
Farmers who prefer organic weed management will be particularly affected, as controlling unwanted plants without herbicides requires a bit of skill and some luck when it comes to timing. And much of that depends on favorable weather conditions. Thanks to climate change, those favorable conditions for weed control are becoming harder to find in Maine.
Droughts and heavy rains are already hard enough on crops. Too often, they occur at just the right time to make direct weed control nearly impossible, according to Eric Gallandt, a professor of weed ecology in the University of Maine’s School of Food and Agriculture.
“Organic farming and ecological weed control is an interesting combination,” Gallandt said. “For one thing, you’re seeing these periods of wet conditions when you need [weed] and on the other hand, it is too dry and you have to think about watering”.
The most common type of ecological weed management is cultivation that pulls weeds directly from the soil. Whether hand pulling, hoeing, power cultivator or tractor-drawn cultivator, the goal is the same: nip weeds in the bud without uprooting or damaging 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 forced to weed, but the weather conditions make it almost impossible.
“We need to think about more robust weeding tools or strategies,” Gallandt said. “If you’re going to be cultivating or hoeing weeds, the odds of being able to hit the timing to come out are getting smaller and smaller.”
That means growers need to be more efficient at getting rid of the most weeds in the shortest amount of time.
As recently as a decade ago, Maine growers could count on full week periods during the growing season to cultivate and pull weeds.
“Now instead of a full week, it’s a couple of days,” Gallandt said. “Growers need to think about how to scale things up for more timely weed control.”
One way they can do that, according to Gallandt, is to become a lean, mean weed-fighting machine.
“If you’re using something that grows two rows at a time, you might want to consider getting a four-row cultivator,” he said. “If you hand weed, you may want to switch to a [mechanical] cultivator.”
The use of mechanical tractor-drawn cultivators is not an option for everyone. The implement plus the tractor can be a substantial initial cost. Then there are the ongoing fuel and maintenance costs.
Smaller, but still mechanical, are gasoline-powered cultivators. These machines are pushed or hand-guided and have rapidly rotating tines that can dig into the ground while cutting or pulling weeds in their 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 tillers will allow farmers to take advantage of the few days when the soil is not too muddy or too dry to work.
Traditional hand weeding will need to be sped up to take advantage of those weather windows. To be most effective, hand weeding or hoeing should be done when the weeds are small because their roots will be easier to cut or uproot. A sunny, dry period is the best time to hand weed.
Fortunately, control methods such as mulching or planting rows of crops together to prevent weeds from sprouting are so far unaffected 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 prevents weed seeds from germinating. All you need to do is place a few inches of grass clippings, pine bark, straw, leaves, black plastic, or garden cloth between the rows.
“It’s still a good idea to go outside and mulch,” he said. “Not only does it prevent weeds, but it also helps retain and control the moisture that reaches 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.
Rising carbon dioxide levels, warming trends and water stress can promote weed growth, according to a literature review by Gallandt and University of Maine researchers Sonja Birthisel and Ruth Clements.
The three found that rising temperatures accelerate the spread of invasive weed species that successfully adapt to variable temperature and humidity conditions.
“These broad forecasts in our region of warmer, wetter and more variable conditions already have people thinking about how they are going to grow vegetables,” Gallandt said. “We are also going to see changes in weed control and how [growers] He’ll handle that in the fields.”
