Cotton growers probably wonder how they ever got along without Roundup Ready varieties. But some may say the same about plant growth regulators.

Applications of Pix — mepiquat chloride — shorten future cell growth and promote fruiting and boll development. Before Pix and now Pix Plus, both from BASF, it was like a jungle in some fields under irrigation or in heavy rainfall areas.

And if proper applications aren't made early enough, growers may face a “too little, too late” situation with rank, out-of-control growth.

“I don't think we could do a good job of raising a crop without applying it,” says Doug Martin, who farms in the Kress, TX, area.

Mepiquat chloride suppresses the size of newly formed plant cells, says Charles Stichler, Texas A&M University extension agronomist at Uvalde. “As a result, stem length is shortened and leaves are smaller but thicker, so photosynthesis is not reduced.

“Shortened internodes allow sunlight to penetrate the canopy. There is generally increased early boll set, better insecticide penetration and the crop is mature five to seven days earlier. Yields are typically increased by 10% or more,” Stichler says.

Knowing when to apply Pix Plus has never been a detailed science for Martin and others. Most applications are made during vigorous plant growth in midsummer.

“It's field by field,” says Martin, whose dependence on the product is even greater since he started planting ultra-narrow rows a few years ago.

He plants primarily Roundup Ready varieties about May 1 under both furrow and center-pivot irrigation. Initial Pix Plus applications are normally made in early July, with subsequent applications completed within three to four weeks. Application rates per field vary as much as — or more than — the timing.

Fields with quick growth receive up to 8 oz/acre of the growth regulator. Less vegetative fields get as low as 3 oz/acre. An additional application is then made a week to 10 days later. A third goes on in another week to 10 days.

“We just monitor the fields to determine the lowest possible level of application,” he says. “But if you don't get enough applied and it starts growing through it, it's hard to shut down the plant.”

Randy Boman, Texas A&M extension agronomist at Lubbock, notes that some growers “have a tendency to overapply,” which can have a reverse impact on boll production.

“We normally have good early season fruit retention on the southern High Plains,” says Boman. “But if the fruit retention is not there, there is more of a chance for the plant to go vegetative and get into a growth cycle. That's when the values of a growth regulator come in.”

Pix Plus costs about 75¢/oz, excluding application costs. If needed, the initial application should be made at the first matchhead-sized square. As plant growth continues through bloom, up to 20 oz may be needed.

There can be problems if hot, dry weather strikes. “That is my greatest concern,” says Boman. “Sometimes we have good growing conditions early with strong fruit retention. But then we can go into a stress period. If too much mepiquat chloride has been applied, the mainstream node growth potential and thus yield potential may be reduced.

“If we encounter too much water stress too early after mepiquat chloride application, we may limit subsequent growth and possibly yield potential if the rate is too high,” he says.

Stichler says by using the Mepert ruler or the Pix Plus Stick, growers can determine approximately when to apply the chemical.