It’s said timing is everything and that is especially true when it comes to the use of plant growth regulators.
Plant growth regulators (PGRs) are hormone-based compounds used primarily as a harvest management aid to modify plant growth and development. They help produce plants with shorter, thicker and stronger stems and reduce the risk of lodging in a number of different crops while also potentially boosting yields.
While PGRs have been in use in Europe and elsewhere for decades, they are still relatively new here in Canada, where they are largely used in cereals crops such as barley, oats and wheat. Two PGRs are approved for use with cereal crops in Western Canada under the brand names Manipulator and Moddus.
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Anne Kirk, a cereals specialist with Manitoba Agriculture, says one of the most important things to be aware of when using PGRs is knowing the right time to apply them.
Right time
PGRs are most often applied as a foliar spray to leaves or as a liquid to the soil around a plant’s base. Kirk explains the best time to apply them is early in the growing season when a plant is between growth stages 31 and 32 and stem elongation has just begun (see photo at top). At that point, the plant should already have developed a tillering node near the root and a second node less than two centimetres further up on the stem.
“In order for (PGRs) to work their best, you want to get them on the plant when the stem is just starting to elongate and not at the end of the plant’s elongation,” she says.
“You want to get them on at the ideal time to prevent the stems from elongating right at the start rather than after the fact because you wouldn’t expect them to have as much of a benefit at that point.”
To ensure they are applying PGRs at the correct time, Kirk recommends growers regularly scout their fields and pull a few sample plants to determine their growth stage. A simple visual inspection isn’t enough, she says.
She suggests cutting the main stems in half and closely examining the distance between the tillering node and the next node up the stem.
“Once the second node is more than two centimetres away from the first node then that ideal timing (for application) has passed,” she says.
One of the most important questions growers should ask themselves when it comes to determining if they should use a PGR, Kirk says, is whether or not their crop is experiencing some form of stress, such as drought, excess moisture, heat, insects or disease. She says growers should avoid applying PGRs if a plant is under stress since they can cause negative consequences for the plant and result in reduced yields or injury to the plant.
Aside from improved yields, one of the primary attractions of PGRs is they can significantly reduce the chances of lodging. That’s why Kirk says it’s important for growers to ask themselves whether or not a crop is at risk of lodging before applying a PGR.
If it has been a particularly dry spring and plants are already shorter than usual or if the variety isn’t prone to lodging, growers may want to think twice about using a PGR. However, if they’re using an intensive management program with a high nitrogen application rate and there is strong potential for high yields and lodging, PGRs are probably a good fit, Kirk explains.
Save time and money
In addition to boosting yields and reducing the risk of lodging, PGRs can save growers time and money. Having plants with shorter, stronger stems can result in faster combining of a crop and using less fuel to do so.
“If you shorten the stem by, say, eight centimetres, you would be putting that much less material through your combine and you would be able to combine the crop faster and maybe have less straw to manage after combining … (and) you wouldn’t have to worry about incorporating so much straw back into the soil,” she says.
Kirk says the tricky thing with PGRs is because they are hormonal compounds, they can respond differently in different environmental conditions. Different plant varieties can also respond to PGRs differently.
That’s why she recommends growers first try using PGRs in on-farm trials with replicated strips before incorporating them into an overall management strategy. Doing so will allow growers to know how plants responded to a PGR and to assess the benefits of the treatment for themselves.
On-farm trials
In addition to conducting their own on-farm testing, growers can also check out the results of PGR trials conducted by the Manitoba Crop Alliance (MCA), which represents wheat, barley, corn, sunflower and flax farmers in the province.
The MCA has been conducting the trials every year since 2018 as part of its Research on the Farm program, which allows farmers to do replicated research on their farms that can be shared with other producers. The plant growth regulator trials have focused on quantifying the effects of PGRs on plant height, lodging, yield and quality.
The MCA’s most recent PGR trial was conducted at eight different test sites in 2022 and focused exclusively on barley.
The 2022 trial results showed a significant difference in terms of plant height at six of the eight test sites. The differences ranged from plant heights shortened by eight to 18 centimetres when comparing treated samples with untreated samples.
MCA whole farm specialist Ashley Ammeter says while there wasn’t lodging pressure at all of the test sites, where lodging was present the PGR did significantly reduce the incidence of it.
Lodging was rated on a scale of one to nine for the purpose of the trials. The lower the number, the lower the incidence of lodging. At four of the eight trial sites, the treated samples had a rating of two or one compared with between four and six for the untreated samples. The other four sites showed no significant differences.
In terms of yield, the MCA barley trial showed no significant difference between plants treated with a PGR and those that were left untreated. Ammeter says even though there was no evidence of a significant yield boost, it’s important to note the trials indicated PGRs can still make a difference in terms of harvest ease.
The 2022 trial results indicated PGRs aren’t likely to affect the quality of barley. In almost every case, the protein levels were nearly identical between the treated and untreated samples. The results are similar to those produced as part of a collaborative study conducted by the MCA in conjunction with Cereals Canada involving wheat.
“Our customers are obviously concerned about what products we’re using on our grain and what impact that might have on the end use of products they’re making,” Ammeter says. “The fact that we can confidently say to them that the use of PGRs doesn’t impact flour and end product quality is good news for farmers.”
Farmers who wish to participate in the MCA trials can contact the organization online at the Manitoba Crop Alliance website.
