Wednesday, August 24, 2016

Plant Growth Regulators: Why & How We Use Them

Selective breeding is a powerful tool. It has allowed us to take cotton, a perennial bush, and breed it to be cotton, an annual field crop. Sometimes however, breeding can’t do everything for us. Sometimes we need to rely on other means to achieve a good harvest at the end of the year. That’s why we have tools like plant growth regulators, commonly referred to as PGRs.

Why do we use PGRs?

Different types of PGRs exist, but the PGRs we use on our farm allow us to prevent the excessive vegetative growth of the cotton plant. Despite hundreds of years of selective breeding, cotton still has some tendencies of a perennial bush, and PGRs allow us to control those tendencies, resulting in an overall better harvest. When a cotton plant puts too much focus on growing leaves and branches, it doesn’t produce as many flowers, which will turn into bolls. Those bolls are what we harvest from the cotton plant, which is where the cotton lint is housed. We want our cotton to focus more on producing bolls than producing too many leaves because in the end, we get paid by how much lint is harvested. Under certain conditions, cotton plants will actually cannibalize young bolls to put on more vegetative growth. This is the exact opposite of what we want.

Another factor PGRs let us manage is the maturity of the bolls. Unlike corn which stops growing vegetation once it enters its reproduction cycle (also known as a determinate plant), most cotton varieties are indeterminate plants, meaning they can still put on more leaves and branches even after they have started to set bolls on lower branches. This is a challenge for farmers because the bolls on the bottom of the plant could be ripe weeks in advance of those on the top of the plant without the proper use of PGRs. This can result in bolls that are either 1) ruined by overexposure to the weather for bolls at the bottom of the plant or 2) left in the field because they aren’t ripe at harvest for bolls at the top of the plant. This, again, results in money lost for the farmer.

How do we know if/when to use PGRs?

Cotton will often start to take off growing when the weather is wet and cooler than normal. Throughout the cotton’s life cycle, we monitor closely the length of the main stalk between branches, known as the internode. While the actual length at which farmers determine to use a PGR depends on many factors, the practice of measuring the internodes for excessive growth is common throughout the Cotton Belt. If the length of the internode exceeds the recommended length for our expected yield, geography and length of season, we will administer an application of a PGR.

How do we use PGRs?

Like other chemical applications we make to our cotton, we apply the PGR using our sprayer at the recommended rate. We pay close attention to the amount applied to the cotton so that we don’t waste money on over-applying a chemical that could adversely affect the crop. Spraying too much or too often with PGRs is detrimental to growing cotton because it can result in a plant without enough leaves to fuel the production of flowers and bolls.

As with any chemical application farmers use on a crop, it is a careful balance between not spraying and spraying too much. Farmers monitor their crops very closely to determine if and when a chemical application may be needed to control the loss of yield. They will then have to determine if the loss of yield would result in a greater economic impact than the price of the chemical. It is tricky, but that’s what make farmers great at their job. They don’t just throw money (aka chemical) at crops if the crop doesn’t need it.

Above: Here's an inside view of the sprayer. This monitor controls the autosteer, which allows the operator to make the application without overlapping. Autosteer is controlled through GPS and is accurate within inches! The GPS follows the sprayer through the field, tracking what has been sprayed and what hasn't. As the sprayer reaches a place that has been sprayed, the booms of the sprayer will stop spraying based on what the GPS tells them. This has allowed for much more targeted and precise application of chemicals.

Above: Another photo taken from the cab of the boom applying the PGR to the cotton. Most of the liquid being sprayed is water with just a very small portion of the solution being the actual PGR. 

And here's my adorable husband riding comfortably in the sprayer - no crazy white suit necessary! 

What questions do you have about PGRs, growing cotton, or applying chemicals to crops?