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5 Factors to Consider When Discussing Early-Season Spraying

Apr 29, 2021

5 Factors to Consider When Discussing Early-Season Spraying from Winfield United Agronomist, Tyler Steinkamp

When spring rolls in, farmers have one thing on their mind: planting. But it’s important to balance planting with a strategic early-season herbicide plan to ensure effective weed control and minimize the development of weed resistance. Based on common patterns and habits we often see in the field, many farmers have room to improve their spray strategies in these five areas.

1. Establishing a Spray Schedule

Many farmers will apply their burndown chemistry in the same pass as their nutrients and residual control herbicide. The problem with this approach is that it reduces control of the targeted cover crop or weeds, while also reducing the active window of the residual chemistry because its being applied so early. It is recommended to split those applications and apply the burndown chemistry by itself, such as a 2,4-D or glyphosate, then come back in with residual control and nutrients.

In terms of application timing for residual control, it’s best to get it done as close to planting as possible. For logistical reasons, sometimes there is a need to apply ahead of planting. If this is the case, getting that application as close to the planting pass as possible is critical for maximizing the residual control.

For the first post-emergence application, spraying is recommended 21-28 days after the residual control application as that’s generally when the weeds start coming in. It’s important to take action while weeds are small or at least before they reach 4 inches tall. Once they’re past that benchmark, they’re much more difficult to control. Some farmers may be hesitant to apply before they can see substantial weed populations in their fields but encourage them to stick to their application plan. This proactive approach will pay off when fields stay clean, and they’re not scrambling to eliminate weed competition down the line.

To keep applications on track, it is recommended to plan a spray schedule based on calendar dates versus visual observation. For example, if the pre-emergence application was made May 1, post-emergence applications should be scheduled for May 21 and wrapped up by May 28. When marking the calendar, remember that the goal is to get the activity of these two applications to last from planting until the canopy shades the row.

2. Choosing the Right Nozzle

Selecting and calibrating sprayer nozzles is an important step to ensure even, consistent coverage across the entire spray boom and, ultimately, the entire field. However, many rarely take the time to change and select the right nozzles for each application. Plus, there is limited information available to advise in these decisions. Here are a few guidelines:

Nozzle size is determined by three factors: gallons per acre, pressure and speed of the application. Charts can be found in the back of any nozzle manufacturer’s book that will help you pick the size of droplet and nozzle type you need.

Droplet size is determined by the type of pesticide. For contact-type chemistries, coverage is extremely important, which means higher carrier volumes and smaller droplet sizes are needed. For systemic chemistries, coverage is less critical so nozzles with lower carrier volumes and larger droplets can be used.

Nozzles should be calibrated each spring before heading out to the field. Many will visually check their nozzles to make sure they’re outputting a satisfactory spray pattern. While this method will catch many faulty nozzles, it’s hard to see when nozzles are wearing down and dispensing less than others. Calibrating doesn’t take long but helps catch discrepancies like this to ensure each nozzle is distributing product consistently throughout the field.

3. Accounting for Factors That Impact Efficacy

For post-emergence applications, time of day is critical. Weeds will only uptake chemical if they’re actively growing, which means the most optimal growing conditions make for the most optimal spraying conditions. It’s important to note that certain herbicides are more sensitive to environmental factors than others. For example, 2,4-Ds and dicamba are less sensitive, while glyphosate is more sensitive and glufosinate it is extremely sensitive to time of day.

Humidity and temperature are two other major factors in efficacy. If humidity is high, the droplet stays wet on the leaf for longer, increasing opportunity for penetration. When temperatures are higher, the plants will grow more actively, allowing more herbicide to be taken up by both the weed and crop. Generally it is best to back down on surfactant and oil rates if you add the relative humidity and the temperature together and it equals greater than 150 because that benchmark tends to indicate an increase in crop response. Adjusting for humidity and temperature will vary in different regions.

4. Incorporating Adjuvants

Adjuvants like water conditioners and surfactants are often overlooked but can be extremely important for herbicide efficacy. Generally, chemicals that need water conditioners are referred to as a weak-acid herbicides, which means they have a negative charge that grabs onto calcium, magnesium or iron in the water and deactivates the chemical. When a water conditioner is included, it occupies that negative charge to prevent this from happening. While glyphosate is the most well-known weak-acid herbicide, many often don’t realize that 2,4-D, dicamba, glufosinate and many other chemistries also fall into this category and are more effective when applied with water conditioners.

Surfactants are also an important tank-mix addition because they help keep the herbicide droplet wet longer and spread the droplet out on the leaf surface. Both of these actions increase penetration and absorption by the plant.

5. Establishing a Backup Plan

The reality is that planting happens extremely fast these days. This makes it challenging to properly time herbicide applications, so it is recommended to have a backup plan for situations where optimal timing isn’t possible. Maybe a field got planted and, due to rain or other factors, residual control applications can’t be made at the ideal time. In some situations, it may be okay to apply a week to a week and a half later, but if growing conditions are good and the crop is up within a few days, you’re going to be in a tough spot.

For help scheduling spray applications please contact your local Centra Sota Crop Advisor.

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