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Regulating crop growth without additional red tape

By Mitchell Japp, MSc, PAg, Provincial Specialist, Cereal Crops and Clark Brenzil, PAg, Provincial Specialist, Weed Control

Lodged wheat
Lodged wheat that could have benefited from
a timely PGR.
Plant growth regulators (PGR) piqued the interest of Saskatchewan farmers a few years ago. We were experiencing high amounts of in-season precipitation, high yields and significant problems with lodging.

Also contributing to the interest was the registration of a new product, Manipulator (Belchim), for use on spring wheat and durum. Manipulator offered more application options than other PGRs in the marketplace and was lower risk. Now that Manipulator has an established maximum residue limit in the United States, it is a viable option for managing lodging in spring wheat and durum.

Low precipitation, dry soils and slow growth are not ideal to see the benefits of a PGR, but for areas or years when lodging pressure is higher, using a PGR can be advantageous to reduce lodging and the amount of straw to process at harvest.

The primary goal in using a PGR is to preserve yield. Losses due to lodging come from reduced grain fill, inability to harvest all the production in the field and grade losses — both directly in the lodged crop and indirectly from other fields that may be harvested later due to increased harvest time on the lodged crop.

Generally, PGRs are synthetic compounds that change plant growth by altering plant hormonal balances. PGRs are commonly used in Europe where yields are much higher and the lodging pressure is more consistent. Historically, yields in Saskatchewan were lower and many varieties had good straw strength.

The genetic yield potential of modern varieties is higher and, generally, farmers are applying more fertilizer, which can increase the risk of lodging. Occasionally, farmers will choose varieties that have poorer straw strength in favour of another advantage a variety may offer. The option to use PGRs makes that choice more manageable. The benefits of using a PGR are reduced on a variety that has strong straw.

A PGR will be most useful when there is good moisture, high fertility and a variety that does not have sufficient straw strength for those conditions. High fertility may be direct from fertilizer applied to the crop, or from a recent application of manure, or high residual or mineralization from a previous crop.

Manipulator suppresses gibberellins, a group of plant hormones responsible for stem elongation. Manipulator can lead to reduced plant height, thicker stems and potentially reduced lodging. Many of the AgriARM sites have conducted research on Manipulator that supports these claims, but there are some differences amongst varieties and different wheat classes.

Other PGRs are registered in Canada, such as Ethrel (Bayer) and Cycocel Extra (BASF), but they have not been widely used. In Western Canada, Ethrel is registered on spring wheat. Cyclocel Extra has the same active ingredient as Manipulator (chlormequat chloride), but its registration is for winter wheat only. Syngenta has been evaluating another PGR, which may be available in the future.

PGRs generally require a specific application window to be effective. Application outside of the application window may not only be ineffective, but potentially detrimental to the crop. Manipulator for a single application is best applied at the one to two node stage (Zadoks 31-32) and Ethrel at flag leaf emergence to swollen boot (Zadoks 37-45).

Be certain that your grain buyer will accept grain treated with any new product before applying the product.

For more information, check the Guide to Crop Protection

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