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Double down on weeds

So what's caused weeds to resist glyphosate and other common herbicides?

Well, let's first trot out all the usual suspects:

• Repeated use of the same herbicide year after year.

• Use of below-label rates that lead to sub-lethal weed kills. This practice permits resistant weed biotypes to survive and to thrive.

• Treating weeds past their recommended growth stage. Killing enormous weeds is fun. And most of the time, glyphosate herbicide does kill them. Still, there's nothing worse than making a weed angry. Stunted weeds can snap back, produce seed, and greatly haunt you in subsequent years.

Application woes will key complexity

There's another culprit, believes Bob Wolf, co-owner of Wolf Consulting and Research in Mahomet, Illinois. “My contention is that application played a role in weed resistance to herbicides due to poor coverage and not getting enough product on the target for effective coverage,” he says.

Long-term, this will create an increasingly complex world of weed management. Here's why.

“Killing weeds is the first goal of applying a herbicide,” says Wolf, who recently retired as an Extension agricultural engineer at Kansas State University. “Minimizing drift is the second goal. Typically, small droplets improve coverage. Unfortunately, smaller droplets increase drift potential.”

Starting in the early 1990s, drift-reduction nozzles came onto the scene. They were able to make droplets bigger. Later on, this was combined with drift-control additives for stopping drift dead in its tracks. Still, this came at a price.

“With bigger droplets, you got less coverage,” notes Wolf. This was compounded by use at lower-than-recommended pressures.

“My observation is that applicators used them (drift control nozzles) just like the nozzles they used before at the normal pressures of 30 psi to 40 psi,” he says. “We found through research we did at Kansas State University that drift-control nozzles needed to be 60 psi to 80 psi to be effective.”

Subpar herbicide application also coincided with spraying at higher-than-recommended speeds. With new sprayer costs topping off close to $400,000, there's lots of pressure to get more acres to make it pay. Pressure is particularly acute for commercial applicators.

“Usually, applicators are paid to cover acres,” says Wolf. “It might not be the best incentive, but it is a challenge we have.”

Coverage vs. drift potential cuts

Weighing in on coverage vs. slicing drift potential while covering more acres will continue to be a trade-off. This is particularly true now that technology (which enables crops to resist 2,4-D, dicamba, and HPPD inhibitors) is entering the scene. Drift is particularly a concern with 2,4-D and dicamba, although manufacturers say new formulations are easing this worry.

Diversifying your weed mix also involves bringing back older chemistries you may not have used for years. Mixing multiple modes of resistance is a good way to forestall resistance.

“You cannot continue to rely on Roundup, Roundup, Roundup,” says Scott Church, a Catlin, Illinois farmer.

The bad news is this will complicate weed-management matters. Fortunately, there are technologies and strategies that can be used to thrive in this new world. On the following pages are recommendations and strategies Wolf has outlined in developing the On Target Application Academy in partnership with BASF and TeeJet Technologies.

For a change, it's the younger generation that needs to adapt, rather than their parents.

“They're Roundup babies,” says Kip Tom, a Leesburg, Indiana, farmer. “They haven't had to fight weeds with all the herbicides we had to use when we started farming.”

Dummy-Proof Sprayers

Sprayers are spendy. In exchange for spending close to $400,000 for a top-of-the-line sprayer, though, you're assured of a user-friendly implement. “Equipment manufacturers are making our systems dumb-resistant so anyone can use them,” says Bob Wolf, co-owner of Wolf Consulting and Research.

It's important,however, that you know what is going on in the process. A sprayer can be undone by something costing just a few dollars: nozzles.

4 Reasons Why Nozzles Are Important

1. They control the amount of chemical applied.

2. They determine application uniformity.

3. They affect coverage.

4. They influence drift potential.

Follow the Color

One way to match nozzles to the recommended droplet size is a color-coded chart developed by the American Society of Agricultural and Biological Engineers. It matches spray quality to a color code. (Micron size data in this chart is courtesy of TeeJet.) Thus, if a label calls for a nozzle with an orfice size and psi to deliver a medium droplet, the chart calls for you to select a yellow-coded nozzle.

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Watch Sprayer Contamination

Tolerance to dicamba in soybeans will give farmers another weed-management option. It will also give farmers headaches if they don't properly clean the spray tank and lines.

“One of the the biggest problems with dicamba is you have to fill spray and nurse tanks (with dicamba) and then go and spray something else that maybe isn't dicamba-tolerant,” says Mike Owen, Iowa State University Extension weed specialist. “Sometimes glyphosate is in those tanks.”

Initially, glyphosate was an industrial cleaner. It can play that role in a spray tank or spray lines. If just a touch of dicamba remains, glyphosate will release it. These residues will be sprayed on the next crop, possibly on soybeans with no dicamba tolerance.

“So, contaminated spray tanks and lines may be more of a problem than physical drift or volatilization,” says Owen.

Watch the Label

Nozzles are also important because herbicide labels now specify which droplet size must be applied. For example, Liberty's label specifies it must be applied in medium-size droplets.

“You will have to figure out how to meet the standard,” says Wolf.

If you don't, regulators will ask why if a drift complaint is filed against you. These days, drift impacts more than neighboring row-crop and small-grain farmers. Acreages and vineyards represent some high-dollar targets if your chemical goes that way. Regulators will get down to the fine print, looking at how the pesticide was applied.

“If they find you applied the incorrect droplet size, you will be found off-label,” says Wolf.

A double whammy may be poor weed control resulting from using the wrong size droplet, says Wolf. (Too large in this case). Thus, may simultaneously battle regulators and peeved landlords. 

A Win-Win?

The proper nozzle can help you slice drift while achieving good weed control, says Wolf. He says drift-reduction nozzles like low- and high-pressure venturi nozzles create less driftable fines. “The result is bigger droplets for drift control compared to earlier nozzles that had lots of fines that would drift,” he says. “If droplets get too big, the challenge of coverage becomes important. If we don't get proper coverage with certain chemistries, the challenge is getting good weed control.”

This has been improved through a plethora of drift-control nozzles that have hit the market, says Wolf. These range from chambered flat-fan nozzles to low-pressure venturi to double-outlet nozzles.

“The best of them can be set up to deliver the right droplet size with the chemical and any tank-mix partners you are using,” Wolf says.

Still, regularly check nozzle performance. Cases like a grain of sand wedged in a nozzle can impact application performance, he says. 

Clean the Whole Sprayer

It's important the whole sprayer be cleaned out. “In the future, we need system cleanout, not just tank cleanout,” says Wolf.

“One spot that is often overlooked are the filters,” he says. Typicallly, there can be up to five major filters on late-model sprayers, in addition to individual screens.

Wolf says areas prone to accumulating chemical residues on some sprayers are boom ends. Wolf notes Hypro has a remedy for this with its Express Nozzle Body End Cap. This device places the last nozzle location at the boom end. It also has venting holes to ensure removal of all spray solution from the boom at each end location. 

Rate Controllers Are Great, but …

Rate controllers assure the rate that sprayers apply will be constant. Bear in mind, though, that droplet size can still vary.

“If you apply 10 gallons per acre and speed up, more pressure is needed to increase flow out of the boom,” says Wolf. “If you increase pressure, droplets get smaller because you are going through a fixed orifice.”

That's why it's a good idea to calibrate your sprayer before the season starts. This is easier to say than do. A 120-foot boom being used for 20-inch spacing would involve testing 72 nozzles – a process likely to last an hour and a half.

One tool that can ease the time crunch is the SpotOn calibrator. This tool proved to have excellent accuracy in tests that took just 10 to 20 seconds per spray nozzle. These tests were conducted by six universities during the summer of 2010 and were sponsored by Successful Farming magazine.

Flowback Control

Airplanes applying chemicals can immediately shut off application at the field end.

That typically hasn't been the case for ground sprayers. Booms continue to spray until the check valve pressure, which may range from 8 to 10 or 40 to 50 psi, is reached, says Wolf.

That's changing. With flowback control, suction pulls away the product from the boom. This prevents chemical from spilling from the boom. One such system on the market is the TeeJet's Flow Back Valve. 

The 20/20 Rule

Several automated spray boom height-control systems are on the market that maintain boom height above the ground or crop canopy. Still, you'll need to remember the 20/20 rule, says Wolf. That is a 20-inch boom height flanked by 20-inch nozzle spacings.

Twenty inches is lower than you likely run now for good reason: Booms at low heights can be torn up as you traverse fields. Still, that needs to change, he says.

“One focus of the new chemistry will be the lowering of the boom height,” says Wolf. “This also means slowing down. If you are too high, you are more prone to drift, and you will also have some coverage issues.” 

Pulsing Technology

Pulsing technology is one way to keep droplet size constant despite speed changes. Wolf likes the Aim Command, Sharpshooter and the PinPoint pulse-width modulation technology from Capstan Ag Systems. It features pulse-width modulation that regulates flow.

“It is the top piece of technology for drift control, in my opinion,” says Wolf. “The nozzles have flexibility when speed changes. The valve opens up, which allows for more flow. Since pressure does not change, droplet size is not affected. This does not happen in a conventional sprayer.” 

Nozzle Body Turrets

Another way to get flexibility in nozzle selection is nozzle turrets that offer various nozzle options.

“When you use combinations of herbicides, you need flexibility,” says Wolf. “These enable you to have different application volumes and meet droplet size needs.”

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