Severe thunderstorms on July 8, 1993, and July 1, 1994 resulted in brittle-snap over a large portion of Nebraska’s corn production area. Brittle-snap is a phenomenon also referred to as greensnap or mid-season stalk breakage. Individual fields also were affected by a storm on July 7, 1996. Breakage was a result of winds ranging up to 100 miles per hour in 1993 and to 80 miles per hour in 1994 and 1996. Some fields had less than 10% standing plants after the storms. Corn ranged from the 10th- to the 14th-leaf stage (Ritchie et al., 1996) at the time of wind damage in all three years. Most breakage occurred at or below the primary ear node. Estimated losses were $200 million in Nebraska from the 1993 storm alone. The destruction in both 1994 and 1996 was more sporadic.
Small occurrences of brittle-snap had been observed before 1993. These incidences were sometimes destructive but were usually confined to a given field or hybrid within a field. In contrast, the 1993 and 1994 storms were widespread in the area of destruction and the hybrids affected. Other crops were not adversely affected.
Rapidly growing corn is subject to breakage from wind as well as other physical phenomenon such as cultivation, hilling, or anhydrous application where stalks are bent by a low tool bar. Corn is most vulnerable during the seven- to ten-day period prior to tasseling (King and Carda, 1993). The “window of susceptibility” varies with hybrids and can be as little as 50 growing degree day units (GDD) to 450 GDD (Paul Carter, Pioneer Hybrids, personal communication, 1993). Preliminary data based on laboratory analyses indicates that hybrids with either higher rates of lignification or higher lignin content of mature plants are more prone to brittle-snap (Blaine Johnson, University of Nebraska, personal communication, 1996).
Little information is published on the impact of brittle-snap on yield of different hybrids. Although, as mentioned, brittle-snap occurred prior to 1993, extensive damage on a large number of diverse hybrids has not been reported.
The effect of stand loss from hail damage has been tabulated (Vorst, 1990) and provides a general idea of the potential impact of brittle-snap. For a given plant density, yield decreases in a curvilinear fashion with reduced plant populations up to the 10th-leaf stage based on the growth staging system used by hail adjustors (Figure 1
, curved line) (Vorst, 1990). This corresponds to the 8th-leaf stage on the staging system used by many agronomists (Ritchie et al., 1996) (Robert Nielsen, personal communication). We use the staging system defined by Ritchie et al. (1996) throughout this presentation. The curvilinear yield response is due to the ability of the surviving corn plants to compensate for missing (or broken) plants. Hail adjustors assume that stand loss after the 8th -leaf stage (V8) (Ritchie et al., 1996) will result in a 1:1 yield loss (Figure 1, straight line).Between V6 and V12, corn plants increase in height rapidly through elongation of internodes (Ritchie et al., 1996). By V12, the number of potential kernels and the number of rows per ear is determined. By V17, the number of kernels per row is determined. Kernel weight is determined after pollination. Timing of a storm in relation to a hybrid’s growth stage can greatly influence a hybrid’s ability to compensate since the potential capacity of the various yield components is determined at different growth stages. Likewise, hybrids may respond differently if a hybrid’s ears are determinate versus indeterminate and whether the indeterminate trait is characterized by changes in girth (rows per ear) or length (kernels per row) (Tom Hoegemeyer, Hoegemeyer Seed Company, personal communication). The storm damage we are reporting occurred mainly after rows per ear were determined. However, the breakage occurred early enough that compensation by standing plants could still occur by increased kernels per row and by increased seed weight.
Row direction, as well as planting dates and other cultural practices, had varying impacts on a hybrid’s ability to withstand the wind. Replicated trials with various treatments imposed on a single hybrid are useful in interpreting the impact of the storm and help us understand the effects of cultural practices on brittle-snap. Effects of organic matter differences, and nitrogen application timing and amounts have not been reported as influencing a hybrid’s ability to withstand strong winds.
Even within the hybrids most susceptible to breakage, not all plants were snapped by the wind (Figure 2). Farmers and agronomists alike questioned why. What was different about the standing plants that allowed them to withstand the wind without breaking? Perhaps standing plants were different genetically, developed differently morphologically, developed at different growth rates because of micro environment differences, or may have been subjected to different wind currents during the storm. We are not aware of published answers to this question.
The three wind damage events gave us the opportunity to examine the effects of hybrid, soil, and cultural factors on the susceptibility of corn to wind damage at the V10- to V14-growth stages. This report summarizes data collected in 1993, 1994, and 1996. These data were collected to: A) determine hybrid differences and the impact of brittle-snap on grain yields (Experiment 1); B) determine whether standing plants compensated for broken plants (Experiment 2); C) evaluate the influence of soil and cultural factors on susceptibility to wind damage (Experiments 3 and 4), and D) determine whether standing and broken plants differed morphologically (Experiments 5 and 6).
Hybrid differences
Experiment 1. In order to assess hybrid responses to brittle-snap resulting from high winds, we recorded stalk breakage and yield on 113 hybrids at the University of Nebraska South Central Research and Extension Center (SCREC), Clay Center, NE in 1993 and on 105 hybrids at SCREC and in Merrick County, NE in 1994. These studies were part of the University of Nebraska Corn Hybrid Tests (Nelson et al., 1993, and 1994). Broken stalks were counted within a few days of the storm. Rows in the Clay Center plot were oriented north-south in both years, while rows at the Merrick County site were oriented east-west. Our observations from several locations in south central Nebraska were that north-south rows were damaged more by the storm in 1993 and east-west rows were damaged more in 1994. Winds during the storms were from the west-northwest in 1993 and from the north in 1994.
Yield compensation by standing plants
Experiment 2. Twelve hybrids were chosen at each location described in Experiment 1 listed above to determine whether yield of standing plants compensated for the plants broken by the storms. The hybrids were chosen to represent a range of maturities and broken stalk damage (Table 1).
Effect of soil and cultural factors
Long-term Nitrogen Study - Experiment 3. Stalk breakage from wind was evaluated on plants included in two separate soil fertility studies. The first is a long-term nitrogen study initiated at SCREC in 1986 to evaluate the main and interactive effects of nitrogen (N) fertilizer rate, tillage, application timing and use of the nitrification inhibitor nitrapyrin on nitrogen use efficiency of irrigated corn, and to monitor the accumulation and movement of nitrate in the soil. The influence of existing treatments on stalk breakage was evaluated using linear regression. Hybrids, planting, and fertilizer application dates are presented in Table 2.
Variable rate Nitrogen Study - Experiment 4. A separate evaluation was conducted on the site of a variable rate nitrogen study on a farmer’s field in Clay County. This field was soil sampled on a grid basis (20 ft. by 100 ft. intervals) in the fall of 1993 for several parameters, including organic matter. Following the high winds in 1994, the field was evaluated for broken stalks on the same grid interval. The spatial distribution of organic matter and broken stalks were mapped using SURFER, and correlations were calculated.
Morphological differences between broken and standing plants
Experiment 5. We collected data in two fields in 1996 following the July 7 wind to determine why particular plants within a genotype broke and others did not. The first was a seed production field near Hastings, Nebraska in Adams County. Damage ranged from 20% to 70% in the female rows of this field. No brittle-snap occurred on the male rows. On July 9, 80 pairs of broken and standing detasseled plants growing side-by-side were collected and detailed measurements were recorded on: growth stage, root evaluation for rootworm feeding, corn borer tunnels, and internode lengths. Leaf sheath thickness, leaf sheath length, and stalk diameter were also measured above the node where the upper-most leaf with an exposed leaf collar was attached. We also measured node width and node diameters on five nodes. The five nodes measured were: the node immediately below the point where the stalk was broken (we designated this node 3); the two nodes immediately below node 3 (nodes 1 and 2) and the two nodes above node 3 (nodes 4 and 5). Node 1 was the closest to the soil and node 5 the furthest. ‘Node width’ was the vertical distance from the bottom to the top of the band that circumvents the plant at each node.
Experiment 6. After processing data from the Adams County seed field, we questioned whether the standing plants had changed in their dimensions. If changes had not occurred, we reasoned we could still sample other fields damaged in the July 7 storm to determine morphological differences between standing and broken plants. We returned to the Adams County field on August 20 and sampled 20 plants using the same procedures as before. We found that node widths and diameters at nodes 1 and 2 had not changed from July 9 to August 20.
Consequently, on August 27 and 28 we measured characteristics of nodes 1 and 2 of Pioneer 3394 in a field planted at the South Central Research and Extension Center which had received damage during the July 7 storm. The stalks in this hybrid field generally broke about 3 inches above the node in the bottom half of the internode. This position of breakage contrasts with the inbred in the Adams County field which broke directly above the node. Breakage in the 1993 and 1994 studies usually occurred near a node; this was more similar to the Adams County 1996 findings. In the 1996 SCREC study we sampled 80 pairs of standing and broken plants in a long-term tillage experiment. Average brittle-snap in the field was 5%. Only the portions of stalks containing nodes 1, 2, and 3 were sampled.
Hybrid differences
Experiment 1. Stalk breakage was 48% at SCREC in 1993 averaged over all hybrids, and ranged from 7% to 88%. Yield decreased as stalk breakage increased, r2=0.82 (Figure 2). Stalk breakage averaged 16% at SCREC in 1994 and damage ranged up to 51% (data not shown). Yield and stalk breakage were negatively correlated (R=0.74). Stalk breakage averaged 10% at Merrick County in 1994, and damage ranged up to 35% (data not shown). Yield and stalk breakage were negatively correlated (R=0.63). Grain yields from these studies were from fields with naturally occurring breakage.
Yield compensation by standing plants
Experiment 2. Broken plants contributed little to yield (data not shown). Yield components for standing plants (unbroken) are shown in Figure 3 from SCREC 1993 for the 12 hybrids we studied. All values are relative to those of Hybrid 7, the hybrid with the least breakage. Similar results were obtained from the other two locations (data not shown). Yield components of all hybrids were similar regardless of the frequency of stalk breakage. We expected increases in either ear length or kernel weights in hybrids with the highest breakage levels if compensation by standing plants occurred. Thus, standing plants did not compensate for broken plants. The yield to standing plant relationship is like the straight line shown on Figure 1.
Effect of soil and cultural practices
Experiment 3: Long-term Nitrogen Study . Figure 4 illustrates the effects of fertilizer nitrogen rate, nitrogen application time, and tillage method on the severity of stalk breakage in this study in 1993 and 1994. Breakage increased with nitrogen rate in both years. Damage was reduced with sidedress application and no-till compared to preplant application of N and conventional tillage, respectively. Sidedressed nitrogen was applied at a relatively late date; consequently, plants had not had as much time to respond to applied nitrogen with the sidedress application relative to preplant. Initial crop growth in this study has often been slower with no-till, related possibly to slower mineralization rates early in the season compared to conventional tillage. Both no-till and sidedressed nitrogen apparently resulted in less mature plants that were less susceptible to breakage.
Figure 5 shows the resulting grain yields from this study in both years. In 1993, there was an average of 53% broken stalks on the preplant treatments. These treatments were not harvested. Consequently, means for nitrogen rate and tillage method in 1993 are for sidedress treatments only.
Experiment 4: Variable Rate Nitrogen Study. Organic matter content was 2.68% and broken stalks were 27% at the 1994 variable nitrogen rate study site. Occurrence of broken stalks was related to organic matter level (Pearson correlation coefficient, R = 0.2715, Prob.R = 0.0001). No other soil fertility factors were related statistically to the frequency of broken stalks.
In general, factors which accelerated crop growth early in the season also increased the susceptibility of the crop to stalk breakage. Plants receiving higher nitrogen rates, earlier nitrogen application, or with more nitrogen available due to mineralized organic matter were larger and growing more rapidly, and thus more likely to be damaged.
Morphological differences between broken and standing plants
Experiment 5. Broken and standing inbred plants were similar in height based on the soil to upper-most leaf heights, had similar internode lengths and were at the same stage of growth at the 1996 Adams County site (Table 3). However, several factors were different between broken and standing plants. Stalk diameters at the point of the upper-most leaf attachment and node 4 and 5 diameters were greater for standing than for broken plants. This may be due to desiccation that occurred in broken plants above the break point between the time of breakage and the time of measurement. Node widths above the break point (nodes 4 and 5) and node diameter at node 3 (the first node below the break) were not different between broken and standing plants. More important, node widths of nodes 1, 2, and 3 of the broken plants (below the point of stalk breakage) were wider than those of the standing plants, and diameters of nodes 1 and 2 were greater with broken than with standing plants.
Experiment 6. Broken and standing plants of the hybrid measured at the SCREC 1996 site followed similar trends as in Experiment 5 for widths and diameters of nodes 1 and 2 (Table 3). Nodes 1 and 2 of broken plants were wider and had larger diameters than those of standing plants.
These data from experiments 5 and 6 suggest that although the neighboring broken and standing plants were of similar heights and stages of development at the time of breakage, morphological differences may have contributed to differential breakage within the inbred and hybrid. It is unlikely that the percentage of genetically different (off-type) plants in either field would contribute significantly to the observed differences. ‘Finger printing’ broken and standing plants in subsequent brittle-snap events will be useful. Perhaps during the approximate 40 hours between the storm and the initial sampling at the Adams County site, internodes of broken plants increased in dimensions. Measurements immediately after a storm event will be necessary to determine if this happens. These are difficult to obtain since it takes some time to locate damage in fields (unless the storm is widespread like the July 8, 1993 storm) and most of the storms occur at dusk or at night. Few changes in these measurements occurred between July 9 to August 20.Tools that closely simulate brittle-snap are needed. Such tools would allow us to conduct experiments specifically designed for taking measurements immediately before and after breakage. Microclimate variability between neighboring plants may contribute to these morphological differences.
These data also suggest that simulating brittle-snap by breaking specific percentages of plants in either a planned or a random order may not reflect actual brittle-snap damage. We say this because if broken plants are indeed different morphologically at the time of the storm, any attempt to determine which plants to break will be subject to error due to maturity or morphological differences unless detailed measurements are taken before breakage. Currently there are no documented studies on variation in node diameter and width at the growth stages when corn is most susceptible to brittle- snap.
Brittle-snap occurred in south central Nebraska as a result of winds up to 100 miles per hour on July 8, 1993 and up to 80 miles per hour on July 1, 1994 and July 7, 1996. Growth stages of the corn plants ranged from V10 to V14. We recorded stalk breakage on over 100 corn hybrids at one site in 1993 and at two sites in 1994. Twelve hybrids were chosen at each site and yield components from broken and standing plants were recorded separately to determine if standing plants compensated for broken plants. In 1993 stalk breakage ranged up to 88%, and grain yield was reduced 1.5 bu/acre for every one percent increase in stalk breakage. Breakage in 1994 ranged up to 37% and 51% at the two sites. Grain production of standing plants did not compensate for grain loss from broken plants at any site. We also evaluated stalk breakage on a nitrogen study and a site-specific management/variable rate study. Frequency of stalk breakage increased with nitrogen rate but was reduced with sidedress nitrogen application and no-till. Stalk breakage in the site-specific management study showed a low but significant correlation with soil organic matter content. Factors which accelerated plant growth early in the growing season increased susceptibility to stalk breakage. Differences were also detected in broken stalk node widths and diameters in nodes below the break point in 1996. These may be due to genetic differences, timing of plant sampling relative to the storm, or microclimate differences that affected these plant structures.
King, J. and J. Carda. 1993. Green-snap. Western corn belt Agronomic Insights. J. C. Robinson Seed Co. July 1993.
Nelson. L. A., D. L. Holshouser, R. W. Elmore, P.T. Nordquist, R. N. Klein, and D. D. Baltensperger. 1993. Nebraska Corn Hybrid Tests. Univ. of NE. Coop. Extension E.C.93-105.
Nelson. L. A., D. L. Holshouser, R. W. Elmore, P.T. Nordquist, R. N. Klein, and D. D. Baltensperger. 1994. Nebraska Corn Hybrid Tests. Univ. of NE. Coop. Extension E.C.94-105.
Ritchie, S. W., J. J. Hanway, and G. O. Benson. 1996. How a corn plant develops. Cooperative Extension Service, Special Report 48. Iowa State University.
Vorst, J.V. 1991. Assessing hail damage to corn. Purdue Univ. Extension Service, National Corn Handbook, NCH1.
| Brand | Hybrid | Entry Number | Brittle-snap(%) | Yield (bu/acre) |
| Asgrow | RX699 | 1 | 70 | 76 |
| Asgrow | RX801 | 2 | 49 | 128 |
| Cargill | 7697 | 3 | 61 | 115 |
| Ciba | 4494 | 5 | 45 | 118 |
| DeKalb | DK652 | 7 | 7 | 151 |
| Golden Harvest | H-2493 | 9 | 33 | 129 |
| Northrup King | N6330 | 10 | 34 | 149 |
| Pioneer | 3394 | 12 | 71 | 80 |
| Golden Harvest | H2544 | 13 | 20 | 148 |
| DeKalb | DK657 | 14 | 66 | 86 |
| Pioneer | 3417 | 15 | 88 | 37 |
| Pioneer | 3162 | 16 | 58 | 119 |
Table 2. SCREC long-term nitrogen study
| Year | Hybrid | Planting Date | Preplant Application |
Sidedress Application |
| 1993 | Pioneer 3417 | May 18 | May 4 | June 29 |
| 1994 | Golden Harvest 2530 | May 5 | April 1 | June 11 |
Table 3. Broken and standing plant measurements. (Adams County, 1996; SCREC, 1996)
| Variables Measured | July 9 | 26-27 August |
||
| Broken Plants | Standing Plants | Broken Plants | Standing Plants | |
| Root rating | 1.01 a* | 1.01 a | ||
| Leaf sheath length (in) | 5.51 a | 5.55 a | ||
| Crown to flag leaf collar length (in) | 15.0 a | 15.0 a | ||
| Stalk and sheath diameter (in) | 0.48 b | 0.52 a | ||
| Stalk diameter (in) | 0.39 b | 0.43 a | ||
| Sheath thickness (in) | 0.090 a | 0.086 a | ||
| Node width (in) | ||||
| 1 | 3.60 a | 0.310 b | 0.495 a | 0.477 b |
| 2 | 0.324 a | 0.311 b | 0.472 a | 0.472 b |
| 3 | 0.330 a | 0.300 b | ||
| 4 | 0.267 a | 0.273 a | ||
| 5 | 0.239 a | 0.242 a | ||
| Node diameter (in) | ||||
| 1 | 0.95 a | 0.90 b | 1.03 a | 1.00 b |
| 2 | 0.85 a | 0.82 b | 1.00 a | 0.97 b |
| 3 | 0.66 a | 0.67 a | ||
| 4 | 0.49 b | 0.55 a | ||
| 5 | 0.43 b | 0.48 a | Internode length (in) | |
| 1 | 0.86 a | 0.89 a | 6.73 a | 6.89 a |
| 2 | 2.50 a | 2.40 a | 7.48 b | 7.80 a |
| 3 | 3.51 a | 3.40 a | ||
| 4 | 2.80 a | 3.00 a | ||
| 5 | 1.40 b | 1.70 a | ||
| Growth Stage | 9.6 a | 9.50 a | ||
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