Plant growth regulators (PGR) are not a new technology. They are commonly used in other areas of the world with high intensity cereal management systems, where high levels of nitrogen fertilizer are being used and lodging is a threat to yield and quality.
Data from the U.K. Department for the Environment, Food and Rural Affairs indicates that 89 per cent of winter wheat acres have a PGR applied at an average of 1.7 times per crop. For winter barley and winter oats, use is a little lower at 77 and 78 per cent respectively.
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PGRs shorten plant stems and increase resistance to lodging. “Research in the EU and by Alberta Agriculture shows that small changes in plant height can have a strong influence on lodging resistance,” explains Phil Bernardin, technical representative with Engage Agro, a supplier of pest control products for horticultural, specialty, and other unique markets in Canada. “We see an opportunity for PGRs on the Prairies and that is why we are pursuing registration of our PGR product, Manipulator.”
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In cereals, PGRs reduce stem elongation, and so plant height. There is also evidence that stem wall thickness is increased as a result. There are two types of PGRs that can impact plant height — those that work on ethylene and those that inhibit gibberellin biosynthesis. “Our product, Manipulator, is an anti-gibberellin,” says Bernardin. “By reducing gibberellin biosynthesis it interrupts plant signals involved in stem elongation. That then results in reduced crop height of four to six inches.”
The hypothesis is that when crop height is reduced, more nutrients, water and energy are available for grain production and the shorter, stronger stem is more resistant to lodging. “If farmers can reduce lodging in their crops, then they are increasing yield potential,” says Bernadin. “They are also reducing their risks of uneven maturity and loss of grain quality as well as making harvesting a lot easier.”
“The key to getting effective control of stem elongation with a PGR is having the right PGR formulation,” says Bernardin. “It’s not simply a matter of running the EU formulations through some trials and hoping to get them registered. Conditions in western Canada are substantially different — temperature in particular.” Formulations have to be developed that will work at temperatures down to 1 C. “Another issue with PGRs has been crop safety. By having various softeners in the formulation the window of application is opened up and crop safety has been improved,” explains Bernardin.
Importance of application timing
Application timing depends on the active ingredient and the type of PGR. Manipulator is best applied at the start of stem elongation (five- to six-leaf stage) for excellent results but very good results are also achieved at typical herbicide timing or the three- to four-leaf stage with one tiller. Research results from Indian Head Agricultural Research Foundation in Saskatchewan and from various sites in Alberta are showing consistent height reductions in wheat as well as reduced incidence of lodging. Additionally, research co-operators have found that yield is increased even if lodging isn’t a factor.
Bayer CropScience has a PGR registered for use on cereals in Western Canada called Ethrel. Timing of application of Ethrel is so critical that cereal producers are required to sign a liability waiver before they can access the product. “Ethrel has a very narrow window of application in cereals which is why we require the liability waiver,” explains Al Eadie, market development manager with Bayer CropScience in Calgary. “It is primarily used in horticultural crops in Canada.”
Syngenta is working on a product for cereals in Canada. “We are collecting information now on our product in Canada,” says Allen Terry, biological assessment manager with Syngenta. “We have used a product called Moddus globally for a number of years but a product fit in Canada will need to be better suited to the Canadian climate, as well as ensure the window of application is optimal for crop shortening.” Syngenta expects it will have a product registered in the next three to five years. †
Many plant functions, like many human functions, are controlled by hormones, more properly called phytohormones. Phytohormones operate in a complex but organized way to ensure that the growth, development and functioning of plants is regulated by responding to various signals from both the plant itself and its environment. We are all familiar with the way sunflowers follow the sun throughout the day. This is called phototropism and is a result of phytohormone activity, auxin in this case. Another obvious example of phytohormones at work is leaf drop in deciduous trees in the fall in response to shortening day length and cooler temperatures.
There are five major phytohormones: auxin, cytokinin, gibberellin, abscisic acid and ethylene. The auxins, gibberellins and cytokinins act as growth stimulators whereas abscisic acid and ethylene act as growth inhibitors.
PGRs work by interrupting or altering the balance of phytohormones to change the plant structure or architecture. PGRs exploit phytohormones and plant biology to modify plants to strengthen stems, alter plant architecture and manage ripening of fruits.
