Understanding the chemistry and the reasons behind lodging can help you interpret some of this years advice on growth regulators. Tom Allen-Stevens reports.
YOU may have found theres a lot of conflicting advice on growth regulators milling around this year. Perhaps the best way to help make an informed decision on product choice is to arm yourself with the facts and unravel some of the jargon. What is the difference between a 3C and a 5C chlormequat, for example?
"As far as the plant is concerned, there is no difference," states Morley Research Centres Doug Stevens. "The original plant growth regulator is chlormequat chloride, known as 3C. 5C is chlormequat chloride with cholene chloride added. The addition is purely there to improve the safety of the product."
5C chlormequat, in formulations such as New 5C Cycocel, has benefited over 3C from greater investment, however: "Manufacturers have put in the trials work to allow growers a wider range of tank mixes on the label and, in some cases, a wider range of timings," continues Mr Stevens.
Lodging can be caused by either a weak stem or poor root anchorage. Chlormequat works by checking the forward growth of the plant, allowing it to develop a stronger root, even up the tillers or build in strength to developing stems, depending on when it is applied.
Mr Stevens advice is to use it early for best effect – from mid-tillering through to second node. Cold conditions can be a problem, however, which is where products like Moddus and Meteor come in.
"Meteor is Cycocel with a small additive, imazaquin, intended to improve activity in certain situations – when its cold, for example. It also claims better persistence than straight chlormequat. Moddus (trinexapac-ethyl) has a wider application window – from tillering through to flag leaf, although its best used in early to mid-tillering through to second node."
These are all initial forms of lodging control that can sometimes be used to help crop potential. Later on, its largely down to the ethephones, like Cerone and Terpal. Used at flag leaf timing these can be effective at keeping the straw short, says Mr Stevens.
The bare minimum or the full monty?
ITS a gamble – just an insurance dose of growth regulator may do, but the belt-and-braces approach of two or even three applications could be more appropriate. The decision has to be made by GS32, says Mr Stevens. Although there are no clear-cut answers, he identifies a number of factors that have an influence on how likely crops are to lodge:
• Drilling date. Early drilled wheat is more likely to lodge, yet strangely later drilled barleys are more at risk. In both cases, this is exacerbated if the seed rate was too high.
• Varietal choice. Its not just a case of straw strength rating, some varieties are better than others at building strong root systems.
• Soil type. More fertile soils tend to produce a more lush crop. Texture can also have a bearing: puffy or loose sandy or organic soils may not hold together as well as a solid clay, leading to poor root anchorage.
• Cultivations. Rolling after the drill can help consolidate the seedbed. Minimum cultivations can also bring about firmer conditions.
• Nitrogen application and timing. If its gone on early, or too much is applied, youre more likely to suffer flattened crops. Early nitrogen tends to feed straw growth, making a tall, weak plant.
• Past cropping. Nitrogen residues depend on previous cropping. Potatoes and vegetable crops leave high residues that are utilised in the following cereal crop early in the year to produce more stem growth.
• Use of organic manures. Again residues, often from applications to previous crops can still be potent enough to give the cereal crop a kick start in the early spring. Poultry manure is a real culprit here.
• Density of crops. According to ADAS Rosemaunds John Spink, dense crops tend to etiolate – reach upwards towards the light, bringing about weak roots and stems.
• Disease levels. Eyespot leads to damage of the stem wall, often resulting in lodging. Unix (cyprodinil) is fairly effective, but Mr Stevens points out there is a difficulty knowing whether the cost is justified because the decision must be made at second node. If eyespot is likely to be a problem and no growth regulator has yet been applied, he advises it may be an idea to apply Unix, even though control may not be complete.
• Weather. The factor most difficult to anticipate or control. If its a moist, good growing season, youll probably have a lush, soft crop. Mr Stevens advises a good, robust growth regulator program in this case. If its dry and you have a less dense crop, you may be able to get away with a cheap insurance dose.