Having crops standing at harvest is critical to the successful production of all combinable crops. Perfect standing may not be essential, but it does help the performance of a combine especialy in a broken harvest.

For these reasons, active growth regulation is practiced in many crops. That said, have you ever considered what these products do and how their effect is influenced by the timing of their application? We associate growth regulators with improved standing power and yet they can have the opposite effect. For this reason, it is important to understand what individual products do and how their timing can influence these effects.

What they do

The main effects of plant growth regulators in terms of preventing lodging is to produce some combination of plant shortening or stem strengthening. These are the main ways as to how lodging or lower stem breakage is prevented.

Products differ in respect of their ability to do either or both of these things and knowing the impact of timing is perhaps more important than product choice.

It must also be stated that a number of growth regulators also have other effects on growth. It has long been established that CCC-based products have the potential to affect the apical dominance of tillers during specific periods of growth. This characteristic is used to either help promote tillering by suppressing the dominance of the main stem or to promote tiller survival when applied soon after the end of tillering.

It is important to recognise the reasoning and timing for the application of any of these products. While individual products differ in cost, they all cost money and it is important to know how to get the best from them. It is also equally important to understand what they can do so as to help avoid unexpected consequences.

Let me give a few examples of this. In my years of experimentation, the use of CCC to affect tiller production and survival became high-tech husbandry. The major research was on wheat, which is a more challenging crop on which to either produce or maintain tiller numbers. The technology spilled over by default into barley and a number of CCC-based products appeared in the market for both spring- and winter-sown crops.

On spring barley it was plain to see that these products do increase tillering – they delivered on the theory. They certainly increased tiller production when applied at early tillering during active growth. But when the plant population was good to begin with, forcing a lot of additional tillers generally meant that these treated plots were the first to lodge. Basically, the extra tillers resulted in a level of density that was very difficult to keep standing.

Even before this came the introduction of products like Terpal and Cerone. These were shortening and strengthening products which produced these visible effects in the crop. But because they were relatively expensive at the time it became common practice to wait until the last recommended period to make an application, leaving the products with little chance of strengthening the stem to prevent lodging.

This practice often resulted in lodging where the presence of the growth regulator produced more tillers to result in a dense crop prone to lodging.

Season and growth pattern

So growth regulation should not be just a matter of putting on a product to get an effect – it may not always be the one you want. The slow pace of growth this spring has been frustrating for most people. While actual growth stage may not be that much behind an average year, the fact that crops that had been forward in early spring were forced to become backward brings its own risk.

For many weeks now I have been saying that crops’ growth stages have continued to move along despite the slow growth. This is partly because the development of a plant is partly to do with increasing day length, as well as temperature. So crops realise they should be at a more advanced growth stage and when the growth opportunity comes they tend to move rapidly through the growth stages. But when this pent-up growth is happening during stem extension, it can very easily result in rapid elongation, soft stems and possible lodging.

This is potentially one of those seasons, possibly for all winter cereals at the moment. But for as long as growth is slowed by low temperatures, the same risk could apply in spring cereals. Right now we see that nodes have been around, in the case of oats, for example, since early March. And now these plants want to be pushing out flag leaves as quickly as possible. This means that all winter cereals are likely to experience rapid stem extension and, if they are heavily fertilised and the days are very warm, then this risk is even greater.

Rapid stem growth can give rise to soft and weak stems that may be prone to lodging. And once a stem grows weak and soft it is difficult to undo this characteristic. For this reason it is important to act at early stem extension to prevent this rather than realising that it has happened in a month’s time. This means having one or more plant growth regulators applied during stem extension. The extent of the risk is also influenced by the density of the canopy (and this year many crops’ canopies are no longer very dense), the amount of nitrogen applied, the general fertility of the field and the inherent genetic strength of the variety grown.

The danger of producing soft stems to increase lodging risk is a balance between many different factors (Figure 1) and these must be judged and assessed on a field-by-field basis. But the growth pattern this spring is likely to add to the risk of lodging and made all the greater by the other factors that potentially contribute to risk.

Tackling soft stems

While many growers will already have growth regulators applied to winter barley and winter wheat, it is important to consider what these have done and what risk remains. Crops may be regarded as very short for the time of year but this can, and will, quickly change. It is always worth considering growth regulation in terms of what the crops need and what the tools offer.

CCC

CCC is active against both strengthening and shortening of the plant stem and it can also be used to manipulate the dominance of the main stem relative to its tillers. It is perhaps better at shortening than strengthening and it works more efficiently when growing conditions are good. The latest application timing for CCC is GS32 for most cereals, but check the label. Because of the importance of growth to its efficacy, this active may not be the best choice during periods of slow to no growth.

All chemicals are broken down in the plant over time and growth itself dilutes the concentration within the plant tissue. However, in times of slow growth it would appear that the rate of breakdown over time can be greater than the rate of growth so that you may not produce the desired effect. CCC can also have difficulties with plant uptake in cold conditions.

CCC with adjuvants – Ceraide/K2

These products are broadly similar to CCC, but they contain different adjuvants and compounds to help penetration into the leaf during cold weather. They also appear to have the advantage of being longer-living in the plant than straight CCC. This could be either slower breakdown or controlled uptake over a longer period which may leave more of the product in situ when growth does get under way.

These individual products differ both in terms of the crops they can be used on and the latest timing of application, so read the label.

Moddus

There are now a number of Moddus lookalikes in the market containing Trinexapac-ethyl, but at least one has a different concentration of active ingredient so take care with rates. This active is now widely used and it is certainly a good straw strengthener, with shortening effects also. It is frequently used with a low rate of CCC to enhance the shortening effects.

Ethephon based – Cerone

This is an old active with shortening and strengthening activity. It is normally applied later in the season up to GS47. When applied late it has a very visible shortening effect. Where treatment is delayed until just before earing out it is not uncommon to have ears remaining partially in the leaf sheath. Cerone reduces the extension of the upper internode, which pushes up the head.

Because it can be used late it was common in the past to leave its application until the 11th hour when lodging looked inevitable. But when a crop is allowed to grow weak at its base it is virtually impossible for a shortener to guarantee lodging prevention. Over the past two decades it has become more common to have growth regulator applied early in the life of a plant to help strengthen the base of the stem. Where this was done, late treatment with Cerone is likely to be much more effective.

Terpal

Terpal is another old product which has a shortening and strengthening effect, but shortening is its forte. Traditionally, this product was applied late on barley around when the awns were emerging. Like with Cerone, treated crops would often have heads still caught in the leaf sheath following a late treatment, as elongation of the final head internode is inhibited.

One of the features associated with both Terpal and Cerone was their potential to re-initiate tillering late in the season, resulting in additional green tillers at harvest. And this effect was even more in situations where lodging occurred post-treatment. So, while these products can be applied late (depends on crops and product) they are better used earlier to help strengthen the stem base and shorten the crop to prevent lodging. That said, where an initial PGR treatment may not be sufficient to prevent lodging, these products can provide a very useful top-up to the programme.

Canopy

This is another CCC-based product for use as a straw shortener/strengthener on all cereal crops. It can be applied at any time during stem extension, but must be applied before the leaf sheaths of the flag leaf begins to extend (GS41). It can be a bit hot on a crop if it is under stress and overlaps are to be avoided.

Straw for composting

A number of PGR products, including Canopy and Terpal, should not be used where straw is destined for composting. Actives can carry though in the straw to the compost and end up in food like mushrooms.

Understanding is critical

Understanding how these products work and how they interact with your crop is key to making the best use of any of these products. Remember, your chemical use records must provide justification for each ingredient in the sprayer tank and suggesting that a product is applied to increase tillering long after tillering is finished could leave you with further questions to answer.

To have a chance of increasing tiller production, CCC-based products must be applied while the plant is still tillering. Where lodging prevention is the major objective, use PGRs to strengthen the base of the crop at early stem extension. This means treatment around GS31 to GS33, depending on the crop and the product, with a possible follow-up spray depending on the risk.

Allowing rapid stem extension to take place in a year like this can only predispose a crop to lodging.