Fruiting issues that occurred last year from shedding of four bract squares in some Mississippi cotton were likely caused by high temperatures rather than insects, says Darrin Dodds, assistant Extension professor of plant and soil sciences at Mississippi State University.
“When we started getting reports of squares on the ground, our first thought was plant bugs,” he said at the annual meeting of the Mississippi Agricultural Consultants Association. “But when we looked more closely, we found the shed squares were mostly four bract squares. Research regarding four bract squares points to high temperatures as the cause, rather than insects.
“If we look back to weather conditions last season, about 60 percent of our cotton was planted when temperatures went from cold to very hot and very dry 9 or 10 days later — and it stayed that way the rest of the summer.
“We started seeing blooms about the first week of July; 40 days prior to that, plants would have been in the stage when squares would in the terminal, and temperatures were 6 degrees to 8 degrees above normal. On average, temperatures were 80 degrees or more daytime, and didn’t cool down that much at night. The number of four bract squares shot up dramatically.”
When squares are differentiating in the terminal, Dodds says, high temperatures can cause the plant to attempt to form an additional leaf, which becomes a fourth bract, generally on lower-most branches. These four bract squares are highly susceptible to shedding.
Growers may think the square loss is due to insects, even when low insect populations were present, he says, but “while four bract squares can be an entry point for multiple insects, more often than not the squares will end up on the ground as a result of having four bracts, and there will be some yield loss as a result.”
In such situations, he says, the crop will need to be managed “a little more aggressively” with plant growth regulators.
“When fruit retention starts to decline, plants want to take off and run, so a PGR should be used to keep height under control. Also, insects need to managed more intensively.
“If you’ve already lost some of your fruiting potential because of four-bract squares, you don’t want to lose additional squares to insects. And you will want to manage other stress factors, particularly irrigation. If you’ve lost some squares and have fruit retention issues, the last thing you want to do is stress cotton by waiting until it has been blooming a week or 10 days before starting irrigation.
“If you have a four bract square situation, you need to be proactive with management in order to reduce the impact.”
Addressing other cotton topics, Dodds says variety selection is becoming “a more complicated decision” for growers.
“There are a lot of choices now, compared to the period from the early 1960s into the early 1980s, when there were only about two to four varieties planted on the majority of the acres in Mississippi.
“Contrast that to 2000, when over 50 varieties were planted in the state — including some conventional varieties, some BXN47, first generation Roundup Ready varieties — a lot of different choices. As we moved on, the conventionals and BXNs all but went away, but in 2010 we still had 36 or 37 varieties.
“While we have fewer varieties today than in 2000, I feel we have better quality choices than ever before. From the early ‘60s through the mid-‘80s, just two to four varieties were planted on 70 percent to 90 percent of the acreage; today there are about seven varieties planted on 50 percent of the acreage.
“If I asked everyone here today, ‘What is the dominant cotton variety you’ve seen in your time?’ it would be Deltapine 555, which has been on the market six or seven years.
“But if you look back through the data, starting in 1964, Stoneville 213 was the predominant variety through the mid-80s — in some years, it was planted on as much as 60 percent of the acreage. That’s 25 or more years that variety was planted widespread. It’s not likely we’ll ever again see a single variety with that kind of dominance and life span.”
New varieties “are coming along more quickly than ever,” Dodds says, “and it puts pressure on the university community to provide research data, and more reliance on private industry to generate management and performance data to help growers choose varieties that will make the best crop possible.”
In evaluating varieties, he notes, “the highest yield doesn’t always make the most money, especially for growers in the upper Delta, where there are issues with pigweed and getting preemerge materials activated.
“If you pick the highest yielding variety and then have to spend a lot of money on hand labor, you may be better off to consider a different technology. Of course, you want to pick a top yielding variety — but you also have to consider which variety will make the most money so you can stay in business.”
Every year, Dodds says, there is a limited interest, usually in northeast Mississippi, in growing conventional cotton.
“In years past, Deltapine 393 filled those acres. More recently, some of the Seed Source Genetics varieties have been planted, and last year UA 48, an Arkansas variety, started getting some traction. UA 48 has really good fiber quality — it will almost qualify as Pima in terms of fiber length.
“If you’re fighting worms already and you’re already applying herbicides to control pigweed, a conventional variety may be an option. But, I don’t think there’s any doubt that varieties with trait technology will continue to dominate in Mississippi cotton production.”
In choosing technology traits, Dodds says, “Don’t just look for the highest yield — also look at insect traits, herbicide traits, and seed treatment. If you’re looking at a Widestrike variety, be aware that you’ll need to manage a bit more aggressively for worms. The benefit that Widestrike brings to the table is being able to make postemerge applications of Liberty, which will be available in 2012. Bollgard II may be a bit more effective against worms, but it’s by no means bulletproof.”
When considering a herbicide trait, Dodds says, “I would urge you to spend your money on a system that will allow you to effectively control your weeds and pay the bills.
“If you’re comfortable with residuals and have irrigation, then pick the best yielding variety. If you’re less comfortable, you may want to consider the LibertyLink system; however, keep in mind that Liberty is not Roundup. If you try to use Liberty like Roundup, you’re going to spend a lot of money and not be very happy.
“It’s important to know which weed species are in the field and their growth stage when making applications. You can’t melt down a six foot tall pigweed with Liberty the way you could with Roundup before resistance showed up.”
Dodds cautions that “we want to be careful not to over-use Liberty. It’s a very valuable tool in cotton, and if resistance develops to this chemistry, it would put us in a very difficult spot, relying heavily on PPOs.
“We’ve already seen resistance in some related weed species in the Midwest, and it could show up here. We need to look at Roundup as an example of how not to use Liberty. Let’s be a bit more judicious in our use of Liberty in order to try to prolong the life of that technology.”
Trait technologies in the development pipeline “will present some unique challenges,” Dodds says. “The dicamba and 2,4-D technologies are very interesting, but certainly the biggest issue with them will be keeping them where they’re sprayed and off neighbors’ fields.”
A grower’s choice of seed treatments should also be carefully made, he says.
“We talk a lot about insecticide traits and herbicide traits, and it’s often easy to overlook what’s on the seed — but that’s certainly not an unimportant decision.
“Over the last decade, seed treatments have become the standard, and there are numerous options available, from insecticide to fungicide to full packages plus a nematicide.” While different varieties may include many of the same treatment components, Dodds says beyond that the question is whether to use a nematicide treatment.
“Several years ago Gabe Sciumbato, plant pathologist at the Delta Research and Extension Center, and others did a survey in the Delta and found about 33 percent of the surveyed acreage infested with reniform nematodes.
“If you have 333 acres infested out of 1,000, figuring a 10 percent yield loss on a 950 lb. state yield average, you’d lose 95 pounds per acre, or 31,000 pounds total. At $1 per pound, that’s $31,000 lost to nematodes.
“If you reduce that loss by 50 percent with a nematicide seed treatment and other management practices, such as irrigation, you’ve just gained almost 16,000 pounds, or $16,000, which is a really great return on your investment.”
Some growers, he says, are not happy that “I spent money on soil sampling and didn’t find any nematodes, so I wasted that money.”
“My argument is that if you didn’t find any nematodes, you can eliminate a nematicide seed treatment, a savings of $6 to $8 per acre, which is a three- or four-fold return on your cost for soil sampling. And knowing whether or not you have yield-limiting levels of nematodes is worth making that investment.
“I would suggest matching seed treatments to the needs you have. If you have no treatable level of nematodes, then just choose an insecticide and fungicide seed treatment. Some of your choices there will be dictated by the brand of seed you choose.
“If we get a season like 2011 that was cold and wet for a long time, and cotton seed sits there in those conditions for a long time, results likely will be less than optimum. A lot of folks weren’t happy with the way their seed treatments performed in those conditions last year.”