As cotton harvest nears, preparations are being made across Arkansas. “Moisture levels around the state are low but still high enough that plants are fairly active,” says Bill Robertson, Extension cotton specialist. “Temperatures aren't really high.
“In years when soil is so dry that plants wilt during the day, plant activity is low and harvest aids don't work well. That's not the case here. Activity is good, boll load is heavy — we've got a top crop nearly everywhere — and plant nitrogen status is low. All that points to harvest aid products working well.”
The big concern, says Robertson, is getting defoliants to cover plants properly. “With Dropp, Aim, Finish or CottonQuick we can get better plant-bottom coverage with high volumes of water. We inhibit regrowth much better by doing that.”
Ten gallons of water by ground application is Robertson's minimum. Five gallons is a minimum for air application. He likes to use even more water than that, though.
“It doesn't seem 12 gallons would make much difference over 10 gallons. But if droplet size remains the same, 12 gallons does a much better job.”
And if 12 gallons is good, 15 gallons is the best. “I hate to admit that, though,” says Robertson laughing. “Producers I tell that to say, ‘I'm not in the water-hauling business, man.’ I understand the reluctance — it takes longer to get finished.
“One time, a grower told me, ‘Son, if I use 15 gallons of water, my pickers will pass my sprayer. Just tell me how to get the best out of what I'm using. Forget the 15 gallons!’”
With 10 gallons, Robertson suggests using large droplet sizes. Producers need to use enough pressure to get a good pattern out of tips, but not too much pressure — maintain the larger droplets.
“(Arkansas Extension engineer) Dennis Gardisser says double the size of a spray droplet and it's eight times heavier and will get down into the canopy better. If a producer is having a problem with harvest aids, it may be partly due to application.
“Say he's doing 7- or 8-gallon work with his insecticide rig. He hears me say to use 10 gallons. Well, the easiest way to do that is increase the pressure.”
That's the wrong way to go about it, though. By increasing the pressure, the droplet size decreases and “he'll be fogging the spray in. That will lead to too much activity at the plant tops. Top leaves will be fried and stick while leaves at the bottom remain green.”
Two times through
Much of Arkansas works a two-shot harvest aid program. Robertson says this is good: if things don't work just right the first time, the situation is still salvageable.
“With the first pass, we can knock the young, tender stuff off the tops and expose the green bolls. With our second shot, we can get boll openers where they need to be. Also, the more-mature, hardened leaves at the bottom can be dealt with more harshly without fear of sticking them.”
At this time of year, Robertson gets regular questions about the use of Dropp. “I know some producers aren't using Dropp this year. That surprises me a little. Right now, even though our moisture and fertility status is low, we still have the potential to accumulate some heat units and have some good re-growth. I'd be leery of not using Dropp or a similar product.”
Robertson has also gotten questions about waiting for the second application before applying Dropp. “When I put Dropp out without leaf area to take it up, re-growth inhibition was lacking. Say you don't put Dropp in your first application and knock off 60 percent of your leaves. Then, when you put Dropp out later, it won't work as well as it should. It will help some on defoliation, but Dropp works best on juvenile leaves. Make sure you're getting the full re-growth inhibition you're paying for.”
Arkansas cotton, especially in the northern half of the state, may be more mature than many suspect. With 750 heat units after cut-out, Robertson expects open bolls to be at 33 percent to 35 percent. When the crop gets to 850 heat units, open bolls should be at 50 percent.
However, this year, “The further north of I-40 (a highway that divides Arkansas in half) we get, the more out of sync those numbers. In some fields with 850 heat units, percent open boll is barely 35 percent. Some fields I've seen sure look more mature up close than they do on paper. In some cases, we may be off 100 heat units.”
Robertson points to the season's odd weather as a major reason for the discrepancy. “Some years, when we have high temperatures regularly, a crop can accumulate 24 heat units daily.
“If the plant is wilting down during the day, there's no way all those heat units will be effective.
“Conversely, this year we had a lot of days with single digit heat unit accumulation. I think plants were growing better than the heat units indicated. Anyway, we've got a nice crop out there — in a few weeks we'll know just how nice.”
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