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Researching and Managing Grain Lodging Lodging, quite simply, is the permanent displacement of a stalk or stem from its vertical upright position. Defining and recognizing the problem is easy enough, but researching and managing it are quite another. Lodging affects all cereals and is a major limiting factor on grain production worldwide. In general, the introduction of the semi-dwarf stature in several cereals has greatly reduced the risk of lodging. However, even among semi-dwarf varieties large differences in resistance to lodging are found. The risk of lodging can be reduced through variety selection and specific agronomic practices, such as reduction in initial stand, delay of planting, reduced or delay of nitrogen fertilization, and/or the use of plant growth regulators. But even these steps aren’t foolproof. Understanding the mechanics of lodging Recent research in the United Kingdom has shown that both forms of lodging occur in UK’s winter wheat varieties. It is likely that the same is true for the hard red spring wheat (HRSW) varieties in our region. The same research group reported that wet soils and high plant populations can increase the risk of root lodging, while high levels of available nitrogen weaken stem strength and increase the potential for stem lodging. Wet soils increase the risk for root lodging, because the wet soils have less shear strength, allowing roots to move or shift easier in the soil. Consequently, wet soils increase the risk for root lodging. In addition, higher plant populations increase this risk, because higher plant populations result in fewer tillers per plant. In the first three to four weeks of development, rooting depth of wheat is shallow. Not until tillers are initiated do crown roots form. The number of crown roots is correlated with the number of tillers a plant initiates. These crown roots not only provide the primary means of water and nutrient uptake, but also anchor the plant. This means that fewer tillers result in fewer crown roots – and as a result, make the plant more prone to root lodging. The UK research group recognized that there are genetic differences that varieties have for both root and stem lodging. The authors also found a poor correlation between a variety’s ability to withstand root and stem lodging. These latter findings may explain some of the inconsistencies in the observations I (and probably others) have made over the years among different varieties. If hard red spring wheat varieties differ in their ability to withstand root and stem lodging, then the lodging observed under natural conditions can be the result of either. Thus, in some environments we may have observed and evaluated root lodging, while in other locations we may have observed and evaluated stem lodging, resulting in different and inconsistent scores for varieties. As already mentioned, the introduction of the semi-dwarf genes has reduced the overall potential for lodging, but marked differences can still be found among cultivars, regardless of their height. These genetic differences mean that breeders can select plants to better withstand both root and stem lodging to improve overall standability. Data from the Minnesota Variety Trials Bulletin supports research findings and observations that plant height and straw strength do not necessarily correlate. For example, varieties like Parshall and Granite have much better resistance to lodging than shorter varieties like Oklee and Briggs. You can see how it can be difficult to evaluate and score varieties for straw strength when both root and stem lodging influence standability. This difficulty in evaluating stands can be compounded further when weather conditions are not conducive to lodging. Thus, rather than observing lodging under field conditions, the research group in the UK used mechanical engineering methods to determine and evaluate the resistance to stem and root lodging for different winter wheat varieties. The methods developed allowed for an objective estimate of lodging risk for every variety in every year. A huge advantage is that no natural lodging has to occur to adequately evaluate the varieties. One of these methods included the use of a portable wind tunnel to simulate natural wind gusts (view it online at www.iem.bham.ac.uk/environmental/wind/sterling.htm ). Interestingly, it’s noted that this novel approach might also be a valuable research tool for investigating the effect of wind on crop spraying and the movement of pollen/seeds www.adas.co.uk/crops/lodging.html?topid=3 ). Another method the UK researchers used to measure both stem and root lodging was a load-sensing device that measured the resistance a row of wheat plant exuded when bent (Figure 1 illustrates this devise). Figure 1. The lodging instrument (Source: Spink et al. 2003) to establish separate standing power ratings for stem and root lodging in the UK recommended lists for wheat. Project Report 305. Home-Grown Cereal Authority, Caledonia House, 223 Pentonville Road, London.
This past summer, I replicated the basic design of the lodging instrument and used a slightly modified version of the protocol described by the research group in the UK to measure resistance to bending of entries in the Minnesota Variety Trials in Crookston and Roseau. Preliminary data analysis indicates that: 1) The lodging instrument provides a fairly repeatable measure of straw strength for individual varieties across replications and locations. Significant differences were detected among varieties (Table 1). Further adaptation of the protocol should improve the accuracy and repeatability of evaluation and the collected data. Table 1. The average straw strength as measured by the lodging instrument and straw strength rating reported in the Minnesota Variety Trials bulletin of the 25 HRSW varieties entered in the Minnesota Variety Trials.
2) No correlation was detected between plant height and straw strength as measured by the lodging instrument or the straw strength rating reported in the Minnesota Variety Trials bulletin. In other words, this mechanical devise indicates further that we cannot assume that just because a wheat line is shorter it will have greater straw strength, or conversely, that if a wheat line is taller it will be weaker. 3) A significant correlation was detected between the straw strength as measured by the lodging instrument and straw strength rating reported in the Minnesota Variety Trials bulletin. What does this tell us? That this tool can help us to accurately evaluate lodging scores, even in years when the growing season is not conducive to lodging, and yet we still need to generate straw strength ratings. Management options to reduce lodging A 15% reduction of the initial stand is feasible if planting is not delayed and the crop has ample opportunity to tiller. However, a delay of the nitrogen application or splitting the total nitrogen application in two or three smaller applications not only is time consuming, but has not shown a yield advantage, and increases risks that the nitrogen is not available in the root zone when needed. At this time, only ethephon (brand name Cerone) is labeled as a plant growth regulator in hard red spring wheat (label online: www.cdms .net/ldat/ld3NH005.pdf ). The University of Maryland points out in their online bulletin on maximizing wheat yield (www.agnr.umd.edu/MCE/Publications/PDFs/FS446.pdf ) that growth regulators such as ethephon will not increase yield; that it functions by shortening the plants, and stiffening the straw, thus reducing lodging and protecting yield. Also, that growth regulators are advisable if grain producers have experienced lodging under conventional management systems, or have reason to believe that lodging may be a problem under high fertility. The bulletin further advises: “Do not use growth regulators when the wheat crop is under any sort of stress and lodging is not an anticipated problem. In these instances, growth regulators have occasionally decreased yields. Some wheat varieties are more sensitive to damage by Cerone than others.” Of course, Maryland is not Minnesota. Previous research has shown inconsistent responses of ethephon in HRSW. One also has to weigh the time and cost involved in an application. Your best bet to minimize lodging is with varietal selection. If you have experienced lodging problems, consider varieties with improved straw strength that also promise to perform well agronomically in your locale. Further, you may wish to plant several varieties so all your eggs (wheat) isn’t in one genetic basket, so to speak. Then, hope the weather cooperates. Wiersma’s research and outreach efforts are supported in part through the Minnesota wheat checkoff administered by the Minnesota Wheat Research and Promotion Council. |
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