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Growth Staging Wheat for Plant Growth Regulator Applications (05/25/17)

The recent cool weather has prolonged the emergence of recently planted corn and soybeans and slowed the development of small grains.

Growth Staging Wheat for Plant Growth Regulator Applications

The recent cool weather has prolonged thransome emergence of recently planted corn and soybeans and slowed the development of small grains. Nevertheless, this weather has been favorable for yield potential development in the small grains, particularly in the earlier planted crops. Cool weather in the absence of other stresses, enables the development of more and larger spikes. There has been growing interest in the use of plant growth regulators (PGR) in recent years, particularly in the high yielding environments where lodging can be a problem.

PGRs are not as commonly used in our region as they are in Europe and other regions of the Americas (Chile, for example), where yields are typically considerably higher than ours. PGRs are synthetic compounds that either mimic plant hormones or interrupt biosynthesis of plant hormones, thereby altering the growth and development of the plant. They reduce overall plant height, thereby making the plant less prone to lodging. PGRs do not increase yield potential in wheat, barley, or oats but rather allow yield potential to be maintained by reducing the risk of lodging. PGRs will be profitable only if they reduce lodging and thereby reduce yield losses that might occur from lodging. Dr. Jochum Wiersma, UMN Extension Agronomist, put together a decision tree to help growers determine the likelihood that a PGR might be profitable (see article at http://blog-crop-news.extension.umn.edu/2016/05/can-i-reduce-risk-of-lodging.html).

In a dataset from five locations in North West Minnesota in 2016, a 3.0 bu/ac yield increase was found with an application of 12 oz /acre of Palisade at the Feekes 7 timing, compared with no treatment. The environment for these locations was low to medium lodging. Considering $5 wheat and application costs of $28.40 per acre ($12 chemical, $8.40 sprayer tracks lost wheat, $8 time and machinery), this application lost $14 per acre.

Many factors in these calculations could change, but given a more lodging prone environment where greater yield differences might occur between treated and untreated, this application could become break even or profitable. These calculations also don’t take into consideration potential lost time by slower combining of lodged wheat, which could impact the profitability of a PGR application.

Currently, the only registered PGR in North Dakota is trinexapac-ethyl which is sold as Palisade EC™. Research in HRSW has demonstrated that Palisade has good crop safety, a relative wide window of application, and reduces plant height and lodging. The improvement in lodging scores have been about 1 to 2 points on the 1 to 9 scale commonly used by breeders. Palisade can be applied as a single application any time between Feekes growth stage 4 and before Feekes 8, or as a split application with the first application at Feekes 4 to 5 and the second at Feekes 7.

In some of the earliest planted fields we are not far away from the first potential application timing. Feekes 4 occurs as the plant is completing tillering, the leaf sheaths begin to thicken and the plant begins to grow upright. Since the growing point is below the soil surface at this point, the stem of the plant is just a pseudo-stem formed by the leaf sheaves holding the plant upright. At Feekes 5 the pseudo-stem becomes more erect and at Feekes 6 the first node appears, and the true stem begins to elongate. Feekes 7 occurs when there are two visible nodes above ground, and Feekes 8 when the flag leaf (the last leaf) begins to emerge from the whorl.

 

Joel Ransom

Extension Agronomist for Cereal Crops

Grant Mehring

Assistant Research Professor

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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