Villa Botcast

How Weather Impacts Herbicide Effectiveness: A Data-Driven Guide for Smarter Weed Control

• Villa Crop Protection • Season 2 • Episode 3

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In this episode of the Villa Botcast, we dive into the surprising ways weather affects herbicide performance. From temperature extremes that alter plant absorption to rainfall and humidity influencing herbicide activation and drift, we explore the science behind smarter spray decisions.

Make every spray count with METOS® weather stations. Get real-time, on-farm data like temperature, humidity, wind, and Delta T — plus detailed forecasts — to plan the perfect spray window. No guesswork — just smart, data-driven decisions. Visit metos.co.za to learn more.

When working with water-sensitive herbicides, every detail counts. That's where Class Act NG comes in. It's a powerful 4-in-1 adjuvant that neutralises salt antagonism with ammonium sulfate, enhances uptake with CornSorb technology, spreads evenly, and reduces foaming — all in one go. More absorption, more impact. Smarter spraying starts with Class Act NG. 

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Hi there and welcome to the Villa Botcast. You're on the go audio hub for smarter crop protection. Just a heads up, this episode is voiced by AI, which means it might get a little creative with pronunciations now and then. But don't worry, all the facts have been carefully checked by our Villa experts for accuracy. That means you get reliable, expert backed information anytime, anywhere.

Okay. Imagine this. You're a farmer. Maybe like Farmer Jane, right? And you're watching your, your hard earned herbicide dollars just literally evaporate. Or maybe, you know, you see these stubborn weeds, they just seem to bounce back stronger, even just because the temperature wasn't quite right. It's frustrating. Oh, absolutely. It's a daily reality for so many in agriculture.

Yeah, especially with weed management. Yeah. And weeds. They're not just annoying, are they? They're a serious serious risk to crop yield. So today we're not just talking about the weather like small talk. We're really diving into how farmers like Jane can maybe stop fighting the elements. Right. And start using them, you know, as an ally, a powerful ally in that weed battle.

That's a great way to put it. I mean, the whole point of weed management is protecting that crop production. Herbicides are. Well, they're a key tool. Sure. But for them to actually work, they need to, first stay on the plant. Yeah. Be retained. Then they need to get absorbed into the system. And finally they've got to translocate, you know, move to where they can actually do their job inside the weed.

And the weather impacts all of that every single step. It's fascinating really. The environment directly and pretty profoundly influences all those processes. So our mission then for this deep dive is to explore exactly how understanding these specific weather factors like temperature, rainfall, humidity, how that understanding can turn this, you know, tricky, often frustrating job into something highly effective, which ultimately means healthier crops.

And let's face it, probably happier farmer, definitely happier farmers. So let's start with that core problem again. Farmer Jane knows this, but, weeds compete, right? For everything. Everything. Water, nutrients, sunlight. The essentials. If you don't manage them, those yield losses can be significant. It hits the bottom line hard. And you're saying the herbicides effectiveness really hangs on the conditions before, during and after spraying?

Absolutely. It's entirely dependent on those environmental conditions. It's, Well, it's a delicate balance getting it right is just crucial for success. Okay, let's talk temperature then, because you mentioned it's it's not simple. It's like a double edged sword. Exactly. It really is. On the one hand, you know, higher temperatures can speed up how quickly the herbicide gets absorbed and moves within the weed.

But sounds good. It sounds great. Like with glyphosate, sometimes warmer conditions seem to make it work faster. But, here's the catch. That speed can also work against you. How so? Well, the plant might actually metabolize the herbicide too quickly because it's systems are running so fast in the heat. Okay. So it breaks it down before it can fully work.

Precisely. Yeah. It paradoxically reduces the effectiveness. There was, actually research on Mesotrione and herbicide used on, Palmer amaranth. Okay. They found that at really high day night temperatures like 40 Celsius day, 30 Celsius. Night. Wow. That's hot. Yeah. And even though the herbicide absorption was higher, it got metabolized so fast that less of the active ingredient actually reached the target tissues.

So less effective control. So speeding things up isn't always the answer. What about the other edge of the sword then the cold side, right. Well, conversely, cooler temperatures tend to slow down all those crucial processes the absorption, the translocation. So you might end up with insufficient herbicide uptake. Not enough gets into the plant to actually control the weed effectively.

Any examples of that? Yeah. There were findings with, Clethodim in resistant rye grass, low temperatures, especially frost. If the plants experienced frost, a few nights before the herbicide application. Even before? Even before. Yeah, it's significantly reduced. How much Clethodim was absorbed and translocated.

So the takeaway here isn't just temperature matters. It's that both high and low extremes can kind of mess things up.

Exactly. You're looking for that Goldilocks zone. Not too hot, not too cold. And it's not just the general air temperature, is it? You need to know what's happening right there on the leaf surface. That's critical. The conditions right at the leaf surface dictate a lot. It really highlights why precise timing is just so important for getting good results.

Let's shift gears. What about, rainfall. That seems pretty fundamental, especially for herbicides that go on to the soil. Absolutely fundamental. For those soil applied herbicides, you need adequate soil moisture. That's essential for them to, activate. Yeah. Basically dissolve and become available and then move through the soil to where the weed seeds are germinating.

Okay. But it's that balancing act again, too much rain, especially a heavy downpour soon after application washes it away. Exactly. It can cause leaching. The herbicide gets washed down past the target zone or even off the field entirely. Yeah, totally in effect. And too little rain. Then the herbicide might just sit there on the soil surface. It doesn't activate, doesn't move into the soil water.

So those weed seeds are completely unaffected, just waiting to sprout. So timing your application around rainfall, that's absolutely critical. Paramount. Yeah. Especially now, you know, with climate change making rainfall patterns so much more erratic and unpredictable, it adds another layer of complexity for sure. You need to make sure the product not only gets applied, but then it actually gets a chance to work once it's there.

Right? Okay. Temperature, rainfall. But what about humidity? You hear less about that one. Maybe it's often overlooked. You're right. Yeah. But it's a really significant player, particularly for herbicides that are applied directly onto the leaves, the foliage. How does humidity affect things? Well, high humidity levels can actually, dramatically enhance herbicide absorption really simply by keeping the spray droplets moist on the leaf surface for a longer period.

It gives the active ingredient more time to penetrate into the leaf. Okay, that makes sense. Longer wetness, more absorption. Exactly. And there's another factor plants tend to keep their stomata, those little pores they use for gas exchange, open longer when humidity is high. So more entry points are open exactly, which can lead to greater absorption and better translocation throughout the plant.

Okay, so high humidity is generally good for foliar herbicides. What about low humidity? That's where you run into problems. Low humidity means rapid evaporation. The droplets dry up too quickly on the leaf reducing uptake. Less time to get in. Right. And there's another risk volatility. Some herbicides can turn into a gas more easily in dry conditions meaning they just drift away.

Yeah. They can vaporize and drift off target.

Potentially damaging sensitive crops nearby which is obviously something you want to avoid. Yeah definitely. Is there data on that volatility risk. Oh yes. For instance some research looked at 2040 dimethylamine and oxen type herbicide. They found this volatility was significantly higher at a low relative humidity like 20% compared to when it was say?

50%. Wow. So even what seems like a modest change in the air's moisture can have a pretty big impact. It really can affect efficacy effects, drift risk. It's important
 
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METOS® weather stations give you real-time, on-farm data – from temperature and humidity, to wind speed, Delta T, and soil moisture. That means you can plan your spray applications precisely when conditions are right… not just when they seem right.

No more guesswork. Just smarter decisions, backed by hyper-local data you can trust.

And here’s the kicker – METOS® doesn’t stop at real-time monitoring. It stores historical weather data and offers accurate short- and long-term forecasts, helping you plan better, farm smarter, and stay ahead of the curve in a changing climate.

So, if you’re serious about protecting your crop and making every herbicide droplet count — it’s time to take your weather data seriously.

Visit metos.co.za and discover how METOS® can transform the way you spray.

 

okay. So we've got temperature rainfall humidity all these factors interacting. What does this mean for you know the farmer on the ground for making practical decisions. Yeah. How do you actually use this.

Well this brings us to a really

critical metric that kind of ties temperature and humidity together. It's called delta t. Delta T okay. What's that Delta T. It's measured in degrees Celsius. And it essentially tells you about the evaporation rate how quickly the spray droplet will dry. Exactly. Will it stay wet long enough on the leaf to be absorbed, or will it evaporate too fast?

We calculate it using the air temperature, the dry bulb temp, and what's called the wet bulb temperature, which accounts for humidity's cooling effect. Okay, so it combines both. Is there an ideal range? There is generally the guideline for spraying is to aim for a Delta T between 2 and 8°C. That's kind of the sweet spot. And what happens outside that range if it's too low, say below to a low Delta T below two usually means conditions are very humid, maybe close to dew point.

The risk there is that droplets might not evaporate much at all, potentially leading to runoff if the leaf is already wet. So it just slides off. And if it's too high up above eight or maybe even higher. Yeah, if Delta T gets too high, say above ten degrees Celsius that indicates conditions are getting pretty dry and potentially warm.

Evaporation will be rapid, meaning poor absorption, poor absorption, and crucially, a much higher risk of spray drift because the droplets shrink quickly as they evaporate, becoming lighter and more easily carried by wind. So that's when your herbicide might end up visiting the neighbors Organic tomatoes? Precisely. Not the outcome anyone wants. So monitoring Delta T is really key for making good spray decisions.

this makes a lot of sense. And connecting all these factors, these metrics like Delta T back to the farm. This really highlights the value of modern tools right. Precision agriculture stuff. Absolutely. Especially things like, on farm weather stations, they must be almost indispensable now with climate being so unpredictable, they really are becoming that way. These stations like, you know, media stations, for example, they provide real time hyper localized data right there on your farm.

What kind of data? Temperature, humidity, crucially, wind speed and direction, rainfall, even soil moisture levels, all in real time. And they help with planning too. Yeah, that's a huge benefit. Many offer planning tools like calculating optimal spray windows based on forecast. Looking ahead three, seven, even 14 days sometimes. Wow and importantly coming back to Delta T, these stations continuously monitor it so the farmer can see okay, now's a good time to spray.

We're within that 2 to 8 range or nope, pulled off Delta T is too high right now, so it takes the guesswork out. It really does. It directly improves the chances of that herbicide staying on the leaf, getting absorbed, and ultimately leading to much better weed control. It turns guessing into, grounded database decisions that real time data is obviously powerful.

That's a fantastic point. Yeah, because it's not just about the right now. You know, that famous quote often attributed to Jim Barksdale? Which one? If we have data, let's look at data. All we have are opinions. Let's go with mine. Right.

Data trumps opinion. Exactly. And these weather stations, they don't just provide live data. They store historical data too. So you can see trends, you can analyze patterns, you can look back at past seasons, past spray events, what worked, what didn't, under what specific conditions did we get great control or maybe poor control. So you learn from experience, but backed by actual numbers?

Precisely. It allows farmers to truly refine their long term weed management strategies. It's about moving towards a genuinely data driven approach, getting beyond just gut feeling or, you know, what grandpa used to do. So let's try and wrap this up. The main insights here really understanding how temperature, rainfall, humidity, all these things interact. It's just crucial for making herbicides work well, absolutely crucial.

using modern tools like these on farm weather stations lets farmers make incredibly precise, effective decisions. It feels like turning the weather from this like unpredictable enemy. Yeah, into more of a strategic partner, maybe to get healthier crops. That's a perfect way to summarize it. It's all about empowering farmers with the right information at the right time. This whole data driven approach, it leads to more sustainable weed management.

How so sustainable? Well, better targeting means potentially less herbicide needed overall or at least less waste from ineffective applications. Less risk of off target drift. It translates to healthier crops, for sure, but also reduced environmental impact and just much more efficient farming. Better for the farm, better for the environment. Okay. Win win. This does raise a really interesting question though for you listening.

Think about this given how precisely we see environmental conditions impacting something like herbicide effectiveness, what other areas, maybe in our own lives, completely outside of farming, could benefit from a similar data driven approach? Where could we optimize outcomes by paying closer attention to environmental factors? Something to mull over?

When you're working with water sensitive herbicides, every detail counts. That's where Class Act NG comes in a 4 in 1 adjuvant that gets the job done. It neutralizes salt antagonism with ammonium sulfate, enhances uptake with CornSorb technology, spreads evenly and reduces foaming all in one pass. More absorption, more impact Class Act NG the smart choice for tough tank mixes.

Thanks for listening to the Villa Botcast. Powered by AI, driven by Insight.

Class Act NG registered number L10477. Act number 36 of 1947 W1301268 Active ingredient ammonium sulfate plus non ionic surfactant 480g/l. Warning. Hazard statements. Causes eye irritation. Precautionary statements. Wash skin and eyes thoroughly after handling. Do not touch your eyes. If in eyes rinse cautiously with water for several minutes. Remove contact lenses if present and easy to do so.
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