Seasonal Weed Control Tips for Cotton

Weed control in cotton farming is all about timing and strategy. To protect yields and fiber quality, farmers must control weeds early and maintain over 95% weed suppression throughout the season. Here's a quick breakdown of the key methods:

• Pre-Planting: Use herbicides like glyphosate or paraquat to clear fields of winter weeds.
• Residual Herbicides: Apply products like Prowl® or Treflan® before planting to block weed growth for 4–8 weeks.
• Cover Crops: Planting cereal rye or clover after harvest reduces weeds and improves soil health.
• Mechanical Tools: Use sweeps, cultivators, or rod weeders to target young weeds early in the season.
• Post-Planting Herbicides: Apply products like glyphosate or clethodim during the first 8 weeks to protect young cotton.
• Layby Treatments: Spray targeted herbicides when cotton is 15–20 inches tall to control late-emerging weeds.
• Post-Harvest: Remove escaped weeds with herbicides, tillage, or cover crops to prevent future problems.

Cotton Field Day Online - Choosing the Right Herbicide

1. Early Plant Weed Killers

Starting the plant season with early plant weed killers is key to stop weeds. These are put on the land before planting to get rid of old weeds, making sure new small plants have the best space to grow. They work well against weeds that grow in winter like bluegrass, common weeds like henbit, and young lasting weeds like johnsongrass - when used while they grow a lot. Picking the right weed killers and how to use them can change a lot.

How Good They Work on Types of Weeds

Two good choices for cotton fields are glyphosate (Roundup) and paraquat (Gramoxone). Glyphosate kills many types of weeds, both lasting and yearly ones. Paraquat, which kills on touch, acts fast to kill weeds it hits. Mixing these with herbicides for broadleaf weeds helps a lot, mainly with hard weeds like Palmer amaranth.

Best Time to Use Them

Time it right. Early plant weed killers are best used from late winter to early spring, weeks before putting seeds in. Go for small, fast-growing weeds to kill them well. Stuff like 2,4-D or dicamba are great in March, when weeds are growing fast. The right time not only makes weed killing better but also saves money and helps the earth more.

Cost Points

While buying these killers costs some money at first, choices like glyphosate and paraquat are cheap and cut down the need for pricier, in-season weed care. By killing weeds early, farmers can keep their crops healthy and cut costs of hard or late fixes.

Earth and Soil Care

Using early plant weed killers smartly helps save the soil structure and stops earth wash away. It's key to follow use tips to dodge earth risks. For example, don't spray when it's windy, set safe zones near key spots, and, if you can, mix weed killers into the soil soon after using them. These steps help the earth and keep good soil by keeping helpful covers.

2. Residual Herbicides Before Planting

Residual herbicides form a shield in the dirt, stopping weeds before they can grow. They hold back weeds for around 4–8 weeks after seeds get in the ground, giving cotton young plants a strong start by cutting off competition from yearly grasses and small-seed broadleaf weeds. This early weed fight sets the base for a strong cotton crop.

Effectiveness for Specific Weed Kinds

For weed work in cotton fields before planting, Trifluralin (Treflan®) and Pendimethalin (Prowl®) are top picks. These herbicides work well against yearly grasses like barnyardgrass, crabgrass, and foxtail, as well as small seed broadleaf weeds. In Texas, long programs using trifluralin have done great at killing tough on-going weeds. When put in place well over two years and mixed into the dirt right, these plans cut down a lot on rhizome johnsongrass while also dealing with yearly grasses and broadleaf weeds. A big plus of these dinitroaniline herbicides is their low risk of not working in the Southern Plains, making them a safe bet as resistance to other herbicides grows.

Best Time to Put Them In

Time is key with residual herbicides. For top results:

• Prowl®: Put on 1.2 to 3.6 pints each acre.
• Treflan®: Use 0.5 to 1.0 quarts each acre for the 4EC type, or 0.8 to 1.6 pints each acre for the 5EC kind.

Mix these herbicides in the top 2–3 inches of dirt within 24 hours to avoid loss from air or light break-down. Use double disks or strong till tools for mixing, then go over it again from a new way to make sure it spreads out even.

Cost Thoughts

Residual herbicides are a smart buy. Dinitroaniline herbicides like trifluralin and pendimethalin are cheap, even with herbicide-tough cotton types. Using them cuts the need for more treatments later, saving cash on work and gas that would go toward more field work. By fighting weeds early, these herbicides help farmers dodge the high costs and hard work of handling big weeds later in the season.

Impact on Nature and Dirt Health Pluses

When used right, residual herbicides go well with dirt-saving till ways, which are good for dirt health. By cutting back on field turning, these herbicides help stop ground wear and keep dirt form and organic stuff. Right mixing is key to keep the environment safe. Keep from putting herbicides on very wet dirt to stop hard packing and uneven spread, and watch the weather to stop heavy rain that may cause run-off or sinking. Following these good moves not only saves dirt and water quality but also makes sure weeds are kept under control.

3. Use Crops to Stop Weeds

Planting cover crops is a good way to hold back weeds and make soil better, adding to the use of chemicals and tools for weed control. These crops act like a wall, cutting down on weed spread and helping the soil for the next time cotton is planted. Cover crops not only take on weeds for food and water but also give off stuff that stops weed seeds from starting, working longer than many weed killers.

How Good They Work on Weed Types

Cereal rye really helps stop tiny-seed yearly weeds like Palmer amaranth and pigweed. It grows thick and stops light from hitting the weed seeds, and gives off stuff that stops them from starting. Bean-like crops, like hairy vetch and crimson clover, are good too. They deal with yearly broadleaf weeds and grasses, and add nitrogen to the soil. Although these crops may not get rid of weeds that come back each year all the way, they slow them by blocking light and taking food and water.

Best Time to Plant Them

To use cover crops well, plant them in the fall right after the cotton is picked. This lets them set up before winter. In the spring, stop the cover crops 2-3 weeks before putting in cotton - usually from late March to early April in the Southeast. This lets the cover crops grow enough to stop weeds but keeps the leftover stuff easy to deal with. You can stop the crops by rolling and squeezing them, which makes a thick cover, or by using fast weed killers like glyphosate. Mixing both rolling and squeezing often works best.

Money Matters

Even though you need to pay at first to plant cover crops, they can save money later by cutting down on the need for weed killers and plowing. On average, seeds cost from $15 to $40 for each acre, putting them in costs about $10 to $20 per acre, and stopping them adds $10 to $25 per acre. These costs are usually balanced by using fewer chemicals over time.

Helping Nature and Soil Health

Cover crops do more than just fight weeds. They make the soil better by adding stuff that used to be alive, letting water in well, and stopping dirt from washing away. The roots make the ground set up better, move water well, and help tiny life that's good for plants. This way, you don't need as much weed killer and get better stuff from the dirt. Cover crops also give homes to bugs that help plants and keep the farm's nature in good shape. By using them with chemicals and tools, growers can look after weeds in a way that lasts and works better.

For cotton growers who want to try out lasting ways, cottongins.org has tips and lists where the cotton-cleaning places are in different places and counties.

4. Tools for Growing Cotton

Using tools to grow cotton gives farmers a good way not to use weed-killing chemicals. When done right and with the best gear, it can hit young, soft weeds hard. This way works well with chemical ways and cover crop plans, giving a mixed way to keep weeds away.

How Good It Works for Some Weeds

Some tools are great for dealing with clear weed troubles. Sweeps and bed knives work well against nutsedge and grasses. Rolling cultivators, reversed disc hillers, and rod weeders do a good job on many weeds early in the season. The trick is to hit weeds when they are just small sprouts. When weeds grow up, even yearly grasses and little broadleaf ones get tough to deal with.

Best Time to Use the Tools

Timing is key with tools for growing. The first eight weeks after seeds are in the ground are key - cotton grows slow then and needs sun, which weeds can block. Working the land early in this time helps a lot. Later in the season, you can deal with new weeds, and a final "layby" run, right as cotton rows fill out, fights late weeds.

To do it well, wait 5–10 days after adding water so the dirt can settle. Keep it low when you do the “layby” part so you don’t hurt the cotton’s roots. For instance, in California's San Joaquin Valley, farmers might work the land two to three times depending on the winter rain. Putting off the first watering till late February can also deal with wet dirt problems.

Costs to Think About

Using tools to grow comes with costs like pay for work, fuel, and gear. Going over the field many times can make it pricier, mainly if rain keeps you from going into the field. Yet, using fewer weed killers might cut down on chemical costs as time goes on. In some cases, using less tilling and choosing weed-resistant crops have cut the need for many runs over the field in the season.

Helping the Earth and Soil

More than just killing weeds, using tools is good for the earth. It lets air into the soil and stops weeds without chemicals, making less chance for weeds to get used to herbicides and stopping chemical spills. But, if you work the land too much or at bad times in wet dirt, it can press down and hurt the soil. Using less harsh tilling and being careful during the "layby" phase can keep the soil right and make it healthier as part of a full weed-fighting plan.

To fight weeds well from the start, make sure your tools match the row gap. Right set up of beds, seeds, and farm gear is key. This way, the machines work well with your full plan to keep weeds away.

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5. Using Herbicide After Planting

After the first and lasting herbicide plans, ones that come later help add a new layer of weed fight. These herbicides are made to hit weeds that pop up after the seeds go in the ground. How well they work has a lot to do with the right timing. Putting them on at the right time means not only do you guard the cotton, but you cut down on weed battle too.

How Well It Works for Types of Weeds

These later herbicides are great for hitting many kinds of weeds. Glyphosate, for one, does well against grasses that come back every year and those that don’t, plus wide-leaf weeds. It's also good on hard grasses like johnsongrass and bermudagrass when used at the right plant stage. If grass is the big worry, sethoxydim and clethodim are top picks for tough ones like yearly bluegrass and johnsongrass.

Yet, Palmer amaranth that won't give in to glyphosate has become a big wall for many U.S. cotton growers. To face this, growers in the Southern Plains now start to use dicamba or 2,4-D with other herbicides soon after planting. This way helps ease the blow of hard weeds while keeping up crop amounts. The wide cover these herbicides give makes sure young cotton plants are safe when they need it most.

Best Time to Put It On

When you put on these herbicides is key. The first eight weeks after seeds go into the ground are key since small cotton plants can’t handle weed fights well then. For cotton that can take glyphosate, the best time to apply is from when you first see leaves to the 14th node. To get top results, put herbicides on when weeds are under 6 inches tall. Keeping fields almost all weed-free in this time is a must for the best yields. Checking fields often then can help pick the best times to apply.

Think About the Cost

Putting herbicides on at the right times not only works well but also helps with costs. For example, glyphosate is about $10 to $20 for each time on each acre. This makes it cheaper than pulling weeds by hand or many rounds of working the ground, mostly on big farms. Big-spectrum herbicides have also made it so you don’t have to work the ground as much during the season, making the whole process smoother.

Still, leaning too much on one herbicide can make weed groups that are tough to it, which could make costs go up later. To steer clear of this, it’s good to switch between types of herbicides and use tank mixes. These steps help keep weed control going strong while keeping costs fair.

Impact on the Earth and Soil Health

These later herbicides also help look after soil health. By cutting down on heavy field work, they save soil layout and cut down on soil wash away. But, it’s key to apply it right to keep from unwanted harm to our surroundings. For example, don't spray when it's windy or during weird air mixes, and you need to use the right sprayers, pressures, and follow what the label says - this is very big in places like California’s San Joaquin Valley.

When used with other ways like machine work and crop covers, postemergence herbicides help form a full plan to manage weeds. This united way not only helps keep the soil healthy over years but also cuts down the chance of weeds that won't die from treatment, making sure cotton farming can keep going strong.

6. Layby Herbicide Treatments

Layby herbicide treatments are applied late in the growing season, typically when cotton plants are 15–20 inches tall. This timing targets weeds that escaped earlier control efforts, especially after the final cultivation. Directed sprays are used to avoid contact with cotton foliage, making this step a critical part of an integrated weed management plan.

Effectiveness for Specific Weed Types

These treatments are especially effective against late-emerging weeds like annual grasses - such as johnsongrass and bermudagrass - and tough broadleaf varieties. Herbicides like cyanazine, diuron, oxyfluorfen, and prometryn are commonly used to tackle specific weed challenges. For grasses, options such as sethoxydim, fluazifop-p-butyl, and clethodim are most effective when grasses are actively growing and less than 6 inches tall.

Each herbicide works differently. For instance, oxyfluorfen disrupts cell walls, while diuron and prometryn inhibit photosynthesis, essentially starving the weeds of energy. In California’s San Joaquin Valley, growers using Roundup Ready cotton systems have achieved excellent results with glyphosate and clethodim, applied immediately after the final cultivation using directed sprays. This approach has proven highly effective in controlling late-season weeds without harming the cotton crop.

Optimal Timing for Application

The ideal time to apply layby herbicides is when cotton plants are 15–20 inches tall, as this allows for directed sprays that avoid damaging the foliage. This stage is usually reached after the final cultivation, as the rows begin to close. For the best results, apply herbicides 5 to 10 days after irrigation. This timing ensures weeds are actively growing and most vulnerable. Waiting too long allows weeds to mature, while applying too early risks damaging the crop due to spray drift.

Cost Considerations

Layby herbicide treatments can save money by reducing the need for additional cultivation. For example, Prowl (pendimethalin) is typically applied at rates of 1.2 to 3.6 pints per acre, with costs varying based on the product and application method. In fields with weaker cotton stands, where late-season weeds can significantly reduce yields, a well-timed layby application often offsets its cost by preventing the need for further cultivation.

Environmental Impact and Soil Health Benefits

These treatments also offer environmental benefits by reducing the reliance on mechanical cultivation, which can compact soil and increase erosion. This is especially important in conservation tillage systems, where maintaining crop residue helps protect soil health. Additionally, strategic layby applications can slow the development of herbicide resistance by minimizing the frequency of chemical use. To maximize these benefits, always follow label instructions, avoid spraying in windy conditions, and use tools like drop nozzles or hooded sprayers to ensure precise application.

7. Post-Harvest Weed Control

Wrapping up the seasonal weed management process, post-harvest control plays a crucial role in stopping escaped weeds from adding to the seed bank. After harvest, weeds that slip through earlier treatments can continue to grow and produce seeds, which increases the problem for future seasons. Acting quickly after harvest is essential to prevent these weeds from taking root and reproducing. Just like earlier in the season, timing is everything when it comes to long-term field management.

Common post-harvest weeds include perennial grasses like johnsongrass and bermudagrass, as well as broadleaf weeds such as nightshades and field bindweed. These weeds thrive after cotton harvest, making the most of available moisture and nutrients in the soil.

Effectiveness for Specific Weed Types

Post-harvest weed control methods are particularly effective against annual weeds and younger perennial weeds. However, well-established perennials often require multiple treatments over several seasons to see lasting results. Strategies include mechanical tillage to remove young weeds, applying herbicides like paraquat or glyphosate before weeds mature, and planting cover crops - such as wheat or barley in the fall - to naturally suppress weed germination.

Optimal Timing for Application

The best time for post-harvest control is immediately after harvest, before weeds have a chance to mature. For chemical treatments, fall or winter applications are most effective, especially when applied before weeds emerge or while they are actively growing.

Mechanical tillage should be timed carefully, avoiding wet soil conditions that could lead to compaction. Depending on winter rainfall and weed pressure, two or three passes may be necessary to achieve the desired results.

Cost Considerations

Investing in post-harvest weed control can lead to savings in the following season. Mechanical cultivation, while requiring labor and fuel expenses, can reduce the need for more expensive herbicides later. Costs will depend on factors like field size, equipment, and the number of passes needed.

Herbicide treatments come with both chemical and application costs but often provide broader control compared to mechanical methods alone. Products like paraquat and glyphosate are especially effective when used at the right time.

Cover crops, though they involve upfront expenses for seeds and planting, offer long-term benefits. These include weed suppression and better soil health, which may reduce the need for herbicides in future seasons.

Environmental Impact and Soil Health Benefits

Post-harvest weed control, when done properly, can benefit the environment and improve soil health. Cover crops contribute organic matter, reduce soil erosion, and enhance water infiltration, making them a valuable addition to your management practices.

Using reduced tillage systems, supported by timely herbicide applications, helps preserve soil structure and minimizes erosion compared to intensive tillage. It’s critical to follow herbicide label instructions carefully to avoid issues like overapplication or contamination near water sources. Conservation practices, such as maintaining crop residue and limiting excessive tillage, help protect soil from wind and water erosion. Additionally, always observe plant-back intervals for subsequent crops and check local extension guidelines for any region-specific restrictions.

Mechanical vs Chemical Weed Control Comparison

When it comes to managing weeds in cotton production, choosing the right method depends on your field's specific needs and your long-term goals. Both mechanical and chemical weed control methods come with their own set of benefits and challenges, and understanding these can help you optimize your strategy. Let’s break down the key differences, focusing on efficiency, cost, and environmental impact.

Mechanical weed control involves physically removing or disrupting weeds using tools like cultivators, sweeps, bed knives, and rod weeders. This method works best on young weeds when soil conditions are favorable. One of its main perks is reducing herbicide use, which can help delay herbicide resistance.

Chemical weed control, on the other hand, relies on herbicides applied at different growth stages - such as preplant burndown, preemergence, postemergence, and layby - to suppress or eliminate weeds. It offers speed and flexibility, even when weather conditions aren’t ideal.

Here’s a quick comparison of the two methods:

To achieve strong yields, cotton needs at least eight weeks of weed-free growth after planting, with over 95% weed control being crucial . Both mechanical and chemical methods aim to meet this standard, albeit in different ways.

Cost Considerations
Mechanical methods can be expensive due to labor, fuel, and equipment upkeep, particularly if multiple passes are required. Chemical control, while reducing labor demands, can have high input costs depending on the herbicides used and how often they’re applied.

Weather Impacts
Weather plays a big role in determining which method to use. Wet conditions can delay mechanical weed control and increase the risk of soil compaction. Chemical applications, however, can often continue under a wider range of conditions, though wind can cause herbicide drift and create challenges with certain products.

The widespread adoption of broad-spectrum herbicides like glyphosate has reduced the need for in-season cultivation, making weed control faster and more reliable. This shift has also encouraged more growers to adopt conservation tillage systems. However, it has led to increased reliance on chemical methods.

Combining Both Methods
Many growers find success by integrating mechanical and chemical approaches. For instance, mechanical cultivation can tackle weeds between rows, while herbicides handle in-row and residual weeds. This combined approach reduces dependence on a single method and helps delay herbicide resistance.

Regional Insights
Different regions have developed strategies tailored to their conditions. In California, growers often use rolling cultivators on fallow cotton beds to manage young weeds, though wet weather can limit this method. In the Southern Plains, season-long herbicide programs are typically the best defense against resistant weeds like Palmer amaranth.

For those looking to connect with local resources, cottongins.org offers a directory of U.S. cotton gins across various counties and states, providing links to nearby services and industry expertise.

Conclusion

Keeping cotton fields weed-free requires a season-long, integrated strategy that combines various methods applied at the right times. Studies show that cotton needs at least eight weeks of weed-free growth after planting to reach its full yield potential, with over 95% weed control being critical for success. No single method - whether chemical, mechanical, or otherwise - can maintain this level of control throughout the growing season. A well-rounded plan ensures every stage of the season is covered effectively.

The key to this strategy lies in timing and diversification. Start with preplant burndown herbicides, follow up with residual and postemergence treatments, and wrap up with layby applications to create a comprehensive defense. Adding mechanical cultivation and cover crops to the mix strengthens the overall approach while reducing dependence on any single method.

Rotating herbicide modes of action and combining techniques slows down resistance development, ensuring consistent, season-long weed control.

Tailoring these strategies to your regional conditions is essential, as weed types, climate, and farming systems vary across U.S. cotton-growing areas. Weekly scouting during the critical early weeks is crucial for identifying and addressing emerging weed problems. This proactive approach not only protects current yields but also supports long-term field health and productivity.

For localized advice, visit cottongins.org to connect with experts in your area. This resource links you to local contacts who understand the specific weed challenges and management practices suited to your region. Whether you're managing herbicide-resistant weeds in the Southern Plains or fine-tuning cultivation schedules in California, tapping into regional expertise can make all the difference.

FAQs

How can cover crops help control weeds and improve soil health in cotton farming?

Cover crops bring plenty of advantages to cotton farming, especially when it comes to managing weeds and improving soil quality. Planting them during the off-season helps block weed growth by shading the soil and limiting the space weeds need to sprout. This natural method of weed control can cut down on the need for herbicides, saving both time and money.

Beyond weed management, cover crops play a big role in boosting soil health. They help prevent erosion, add organic matter to the soil, and improve water retention. Plus, they can break up compacted soil and encourage the growth of beneficial microorganisms, creating a healthier and more productive environment for cotton plants. Adding cover crops to your farming practices is a smart way to improve yields while keeping your fields in good shape for the long haul.

What are the best ways to combine mechanical and chemical weed control for cotton throughout the growing season?

To keep weeds under control in cotton fields, a mix of mechanical and chemical strategies should be used, adjusted to fit the crop's growth stages. Before planting, consider pre-plant tillage or cultivation to disrupt weed development. After planting, applying pre-emergence herbicides can help stop weeds from germinating. Throughout the growing season, target specific problem areas with post-emergence herbicides and use mechanical cultivation to manage weeds between rows.

The timing of these actions is crucial - keep a close eye on weed growth and address issues early to reduce competition with your cotton plants. Combining these approaches can lead to cleaner fields and healthier cotton yields.

How can I effectively manage herbicide-resistant weeds like Palmer amaranth in cotton fields?

Managing herbicide-resistant weeds in cotton fields, like Palmer amaranth, calls for a mix of strategies to keep them in check. One effective approach is rotating herbicides with different modes of action to slow down the development of resistance. Pair this with natural suppressors like crop rotation and cover crops, which can help reduce weed growth over time.

You can also tackle resistant weeds with timely mechanical methods, such as cultivation or even hand-pulling, to prevent them from spreading further. Regular field monitoring is a must - catching weed problems early ensures you can maintain control throughout the growing season.

Related Blog Posts

• Effective Weed Control Strategies for Cotton Farmers: Complete Guide
• Integrated Weed Management in Cotton Farming: Strategies for Effective Control
• Integrating Cover Crops in Cotton Farming
• Strategies for Managing Herbicide-Resistant Weeds in Cotton Farming