Weed Invaders Are Getting Faster

Mar 16, 2021

Dr. Daniel Montesinos is a Senior Research Fellow at the Australian Tropical Herbarium, at James Cook University in Cairns. He is studying weeds to better understand (among other things) how they might respond to climate change.

He said most invasive plants are characterized by their rapid pace when it comes to taking up nutrients, growing, and reproducing—and they're even faster in the regions they invade.

"New experiments comparing populations from distant regions show a clear trend for already-fast invasive plants to rapidly adapt even faster traits in their non-native regions," Dr. Montesinos said.

This is further pronounced in the tropics and sub-tropics.

"Even though invasives' growth rates are already among the highest for plants, when they invade new territory in the tropics and sub-tropics, they develop those weedy traits more rapidly than they do when they invade in temperate climates," Dr. Montesinos said.

"This might be explained by higher chemical processing at higher temperatures, which suggests that global warming will increase invasive impacts in these regions, as long as enough water is available."

Dr. Montesinos said invasive plants usually take hold in land that has been disturbed by human intervention (for example farms and roadsides) and then spread to other habitats.

"It's important to recognize disturbed habitats as a gateway for plant invasions," Dr. Montesinos said. "If we can limit disturbance of natural environments, we can reduce biological invasions, particularly in tropical areas that are threatened by increasing human encroachment."

Dr. Montesinos said that range expansions by native species trying to 'escape' from changes in climate could be a further complication. This involves climate change enabling some native plants to grow where they previously could not.

"This can be seen as a double-edged sword—some native species will survive climate change, but they might achieve that by disrupting the habitats of others.

"The study of invasion ecology is complex, but invasive species can be models in which to study, and make predictions about, the responses of native plants to climate change, giving us clues on improved management techniques for both natives and invasives," Dr. Montesinos said.

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Video: Turning Plant Defense Into a Management Strategy

Turning Plant Defense Into a Management Strategy

Understanding how a plant responds to stress is one thing.

Using that knowledge to make better management decisions is another.

Systemic acquired resistance, or SAR, is the plant's more direct defense response. When stress or infection occurs, the plant begins signaling throughout its system and preparing defensive compounds.

But if we know that response exists, can we help prepare the plant before the stress arrives?

The answer starts with understanding what triggers the response and what the plant needs to carry it out.

The Trigger and the Fuel

Salicylic acid plays an important role in triggering the SAR pathway.

Think of it as turning the truck on.

The engine may be running, but it still needs fuel to do the work.

In this case, manganese plays an important role in supporting the enzyme systems involved in the plant's defensive response.

This makes manganese status an important part of the conversation. Whether a producer is using tissue testing, sap analysis, or simply scouting for visible deficiency symptoms, the goal is to make sure the plant has adequate manganese available.

Manganese is required in relatively small amounts, but that does not make its role small.

If the plant receives a signal to defend itself but lacks the nutrition needed to support that response, it may struggle to carry out the process efficiently.

The trigger matters.

The fuel matters too.

Prepare Before the Stress Arrives

The best time to think about stress management is before the plant is overwhelmed.

Once a crop is already struggling, management can quickly turn into a game of catch-up.

This is similar to nitrogen management. Once a plant becomes severely deficient, correcting the problem does not necessarily erase the time and yield potential already lost.

Plant defense can work the same way.

Low-rate, targeted approaches designed to support the SAR pathway may fit best ahead of an expected stress event rather than after significant damage has already occurred.

That requires producers to think about predictable stress.

We may not know exactly what the weather will do tomorrow, but we generally know summer heat is coming. We know certain field conditions increase disease pressure. We know a herbicide application can temporarily stress a crop as the plant processes the chemistry.

Even a properly timed and labeled herbicide application can create a temporary response in the plant.

That does not mean the herbicide is bad.

Weeds can create significantly more yield loss than the temporary stress caused by controlling them.

The question is not whether we should eliminate every stressor.

The question is whether we can better prepare the plant to manage necessary and predictable stress.

Not All Stress Is Bad

Stress is a normal part of plant growth.

A perfectly stress-free environment does not exist in the field.

In fact, some stress is necessary for normal plant development. A plant responds to wind, temperature, moisture, sunlight, and countless other environmental signals throughout the season.

The environment is stress.

The plant's job is to manage it.

Problems begin when the stress load becomes greater than the plant's ability to respond.

Extreme heat, drought, high salt concentrations, disease pressure, and even certain management practices can add to that load.

This is where understanding SAR becomes useful.

Instead of waiting until the plant is visibly struggling, producers can begin identifying periods when stress is likely and make management decisions around those windows.

ISR Starts With the Soil

While SAR is a more direct defense response, induced systemic resistance, or ISR, brings the conversation back to soil health.

The longevity of a farm is closely connected to the health of its soil.

Carbon plays a major role because it supports biological life within the soil. Bacteria, fungi, and other organisms interact with plant roots and influence how the plant grows, accesses nutrients, and prepares for stress.

This is why soil health cannot be reduced to one product or one application.

It is a system.

Keeping living plants in the field longer can support biological activity. Cover crops may fit some operations. Better water management can improve soil conditions.