HEARNE, Sask. – An overlap during spraying will apply a double rate of chemical on part of the field. That might be OK with a fungicide or insecticide, but herbicides are a different story.
A double rate of Sencor, for example, can severely damage or kill young lentil and chickpea seedlings.
Darren Watson grows lentils and chickpeas in a farming partnership with his parents Ron and Carol Watson near Avonlea, Sask. With the limited weed control options in those two crops, Watson is aware of the damage a Sencor overlap can do to his pulse crops.
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Watson doesn’t want to double up his herbicide application, but he
also wants to ensure complete weed control.
His solution for the past few years has been to use half rate nozzles on each end of the spray boom, which ensures enough overlap to eliminate misses but not enough to double up on his rate.
“Some people are naturally gifted at driving straight, but I’m not,” said Watson, who sprays with a John Deere high clearance unit.
In previous years, using GPS guidance but without autosteer, Watson would set a two-foot overlap, running an 88 foot swath with a 90 foot boom. This year, with an upgrade to an autosteer option, he sets the swath to 89 feet, for a one-foot overlap.
He has also started using five-nozzle rotary bodies on his spray boom: 11001.5; 11002.5; 11005; 11008 twin jet and 11010 nozzles.
“The 1.5s are used for good conditions burnoffs,” he said.
“It’s about 3.5 gallons an acre. You need really good conditions to use those. The 2.5s are a more general burnoff tip. You’ve got to fill up more often, but you get much better coverage with them. That’s about a 5.5 gallon tip. The 05 is about a 9.5 gallon general tip that we use to spray grassy weeds.”
Watson said the first three are air induction nozzles.
“The 08 twin jets are good for spraying fungicides in more calm conditions. You use more pressure and get a finer mist. The 10s are for spraying high water volume herbicide so it doesn’t drift as much,” he said.
“If it’s a bit windy and you want to put on fungicides, you can use it as well. But the most I can get out of my sprayer is a medium sized droplet out of those tips, so you don’t get as good a coverage on fungicides.”
Setting the GPS at 89 feet provides a one foot crossover. Sometimes the math doesn’t work out exactly when Watson switches to a half sized tip, but if he ends up with a 1.2 rate it’s fairly close and he can live with it.
He does that when he’s spraying a herbicide that might damage a sensitive crop. For fungicides he said there’s no point. He would prefer to have a bit of overlap to avoid applying only a half rate.
“With Sencor, you’re just as well off to miss as to overlap. You’re better off to have a couple of weeds and all the plants,” he said.
“Sencor is labelled at 110 (grams per acre) but none of us use 110. A double 110 is really toxic. Generally we spray at 75 or 80. And Sencor is registered for a double application, so you could put on two 50s.”
Ratios used
When spraying Sencor, Watson usually applies it at 18 gallons of water per acre. By using the 08 and 05 nozzles, he gets about 18 gallons on the main boom and nine gallons on each of the overlap passes.
While he doesn’t use residual herbicides, Watson said his system might also help reduce carryover from soil residual products, where an overlap could cause carryover issues the next year in sensitive crops.
“That might also work on some wild oat herbicides. Some of them, if you have an overlap you might have a problem, but we don’t really use wild oat herbicides because we don’t grow wheat.”
Watson said some farmers use low rates of Puma on canaryseed, even though it’s not registered. He said his system might also work for them.
This spring, Watson tried another idea when spraying Sencor on his pulse crops.
“We grow some chickpeas and Sencor is just a horrible product on chickpeas. It’s labelled on the one to three above ground node stage, which is like nothing. That window is about four days long. By the time you get all of them up, your smallest are at one node and your biggest at three. If you get a little rain you’ve got a problem,” he said.
“So this year, we sprayed chickpeas at one node – just coming through the ground, so the plants hardly got any Sencor on them. Theoretically, it doesn’t do as good of a job of weed control, but there was a bit of rain forecast. And if you leach Sencor into the ground, it will kill some small weeds.
He said the Sencor damaged the chickpeas that had two nodes, but the plants without nodes at the time of spraying were not damaged.
This year Watson discovered that if he got out at ground pop with Sencor, sprayed it at 10 gallons rather than 17 and put on the high rate of chemical – 100 grams per acre rather than 60 or 70 – it was better for the health of his chickpea crop.
