Plant Growth Regulators: Does Size Matter?

Plant Growth Regulator’s: Does Size Matter?

Plant growth regulators (PGR’s) are one of the sey new topics to discuss in western Canadian agriculture. I have been at a large number of farm tours with PGR’s this July, talked to many people in the industry and heard a lot of conversations and everyone seems to be talking or asking about “how much did Manipulator shorten the crop?”, or “It’s hardly shorter than the untreated”. We are all drawn to first order implications that are inherently visual, but in order to get the most out of plant growth regulators this shouldn’t be the primary focus and (typically) the addition of PGR’s shouldn’t be the only practice that changes within a field. It’s what this shortening and increase in stem thickness allows you to more intensively manage that is the real golden ticket. The point of applying PGR’s isn’t the fact that your crop is shorter, it’s what that allows you to do for your operation in terms of yield, efficiency and overall profit. Size (shortening) doesn’t matter, it’s how you use and manage within that shortening that truly matters, and there are a few factors that can be managed to take advantage.

 When I mention plant growth regulators, I am specifically talking the gibberellic acid inhibitors that have begun to get a lot more attention now that the maximum residue limit (MRL) has been set for Manipulator (chlormequat chloride) and Moddus (trinexepac ethyl) that will be on the market from Syngenta in the next couple of years.

PGR’s need to be utilized from a holistic agronomic perspective, not in a silo. They are a tool that support the entire management of your crop and can help you make decisions that support other aspects of your agronomic needs.

Here are 3 key areas PGR’s allow you to more intensively manage:

1. Fertilizer rates - This isn’t limited to nitrogen, but without getting overly specific lets focus on nitrogen. Incremental nitrogen can hinder stand ability of cereal crops, which means if you are in search of higher yields, lodging can be a real concern. Knowing you are planning on utilizing a PGR presents a prime opportunity to look at your nitrogen rates and whether they match the uptake unit per bushel of your target yield, or allow you to go back to your target yield and push that for higher output. Now don’t get me wrong, I am not saying put more N down for the sake of putting down N, but knowing you are utilizing a PGR allows you to re-address your fertility rates. If you want to get even more high-tech, you could even get into imagery, zones and look into variable application, but that topic is for another time.
2. Seeding rate is another agronomic piece that a growth regulator allows you to manage. Targeting an optimal number of plants, and therefor heads/tillers for your area can allow you to further enhance your yield. Many cereals still get seeded by the bushel, or a generic pound per acre rate. Not the optimal way of working backwards from your target plant/head per square foot, meter or acre. What I typically see is a lower than optimal seeding rate “to avoid lodging”. This means you could be leaving yield and quality in the field and making timings for fusarium head blight fungicide or insecticidal applications more difficult than they need to be. I’m not saying crank your seeding rate up because you are using a PGR, I am simply saying knowing you will be using one gives you the added confidence to hit those higher target plant stands to maximize yield and quality without the fear your cereal is going to lose it’s legs.
3. Varieties - The variety you select to grow every year is an important decision. Yield, disease resistance, height, lodging resistance, days to maturity are all factors that need to be considered. The reality is that a lot of the time there are varieties that are great fits, but they have one downfall for your area. This is where a tool like a PGR comes in. Maybe there is a variety that has the majority of the qualities you are looking for, such as good disease package and high yield potential, but it always loses it’s legs and is a nightmare to combine. A strategic plant growth regulator can allow you to manage this varietal downfall and increase the output on your farm. A caveat to this is we know certain varieties react differently to PGR’s. However, at the very least applying a PGR gives you the ability to approach your crop plan without pigeon holing yourself into one specific variety.

It’s sexy to be able to show that your PGR shortened your crop by 5”, but you know what’s sexier? Being able to combine your crop at 1.5mph faster while using less fuel to chop through the straw and have less trash for your next years seedlings to grow through. That is another way of measuring “response” to a PGR. Shortening a crop doesn’t make you more money – more bushels, better quality, and increased efficiency do. PGR’s will support that, but let’s just make sure that’s the discussion point vs. simply talking about crop height.

When you roll into your field of PGR’s this fall or begin planning for 2019 crops, be sure to consider all of the above factors when approaching your use decision.