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Herbicide Application Methods – Re-thinking Delta T

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Video Transcript

Herbicide Application Using Delta T

I was going to talk about Delta T. It’s a measure that farmers use for deciding when to do their spraying particularly out of the summertime. Mostly it’s a number that’s generated as a relationship between temperatures and relative humidity and farmers use a rough guide of spraying when that number’s between 2 and 10.

And what that is tending to mean is that in the summertime farmers are spraying quite often evening and early mornings to be able to achieve that. Cause often the numbers will get over, the delta t number get over ten quite quickly during the day. Now one of the unintended consequences of this is that we’ve seen incidences of sprayed drift because when you’re spraying at low delta T’s  particularly in the early mornings you have calm conditions that produce inversion layers which can move herbicide droplets long distances, so this has caused problems in areas where you have vineyards and etc.

Application Trials Over Three Seasons

So what we decided to look at was whether we had some scope to go outside that, through the ten range, to be on the high side where growing conditions are good. So we did trials over three seasons. The first two seasons we did it with, it was excellent soil moisture and young actively growing weeds. And what we found was in both of those seasons we could get up to quite high delta t’s.

Around 16 and 17 and found that we still have very good weed control Those weeds managed to be actively growing. The third trial we did was just this last summer. We had the opposite conditions where it was very dry soil, larger weeds that were under stress. And we looked at whether spraying a different strains of Delta T’s made a difference and it made a slight difference in that we used paraquat and glyphosate and that it’ll make Occasion and there was a drop off in the performance of paraquat at very high delta T. I remember the situation.

The temperature was about 39 degrees and the Delta T was over 17, so really stressful situations, especially the guy had the spray. And there was a bit of a drop off in the performance of the paraquat and actually the round up we applied.perhaps the rate wasn’t as is could of been  but there was just poor performance at any time because the weeds were stressed.

Flexibility in Spray Application

So we learned a bit out of that so we think there’s a lot more flexibility in what you can do when the weeds actively growing, we can probably spray atlonger times during day and probably one of the best guides is to just look at the plant. If they don’t look stressed and the delta t might be thirteen, fourteen I think you can keep keep spraying.

But, if they’re highly stressed, maybe that when you stop. So, delta T’s, a guide but there’s other factors to look at, I think.

Delta T is the relationship between temperature and relative humidity that gives a score for deciding the best times to apply sprays on crops.

John Both from NuFarm at the Eyre Peninsula Agricultural Research Foundation (EPARF) members day held at the Minnipa Agricultural Centre discusses Delta T for making decisions about your herbicide application methods. In the summer Delta T can often be high during the day, resulting in spraying occurring in the morning or evening. These are times when inversion layers are most likely resulting in drift issues.

Research has shown that high Delta T’s in summer can still give good weed control so long as the weeds are actively growing. Delta T is a good guide but you can consider other factors when making spraying decisions to reduce the risk of drift and achieve good weed control.

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