Ethephon [(2‐chloroethyl) phosphonic acid] has recently been introduced in North America as a regulator to control lodging in cereals. A 3‐yr study (1983‐1985) was conducted to determine how widely grown spring wheat (Triticum aestivum L.) and spring barley (Hordeum vulgare L.) cultivars in the North Central United States responded to ethephon. Nine randomized complete‐block, split‐plot experiments with wheat, and seven with barley, were conducted at the Crookston (soil classification, Aeric Calciaquoll), Morris (Aeric Calciaquoll), St. Paul (Typic Hapludoll), and Waseca (Aquic Hapludoll) Experiment Stations in Minnesota. Ethephon was applied at a rate of 0.42 kg a.i. ha−1 in all years as well as 0.28 kg a.i. ha−1 in 1985. When lodging occurred, ethephon treatment at either rate lessened its severity. Ethephon shortened crop height, more so when applied at the higher rate. Effects of ethephon on grain yields varied from significant reductions (average 13% for wheat, 9% for barley) to significant increases (average 12% for wheat, 13% for barley). Increases were most common when control plots lodged, although higher yields in response to reduced lodging were not obligatory. When lodging did not occur, ethephon treatment tended to result in reduced yields. Among barley cultivars, ‘Robust’ was most likely to exhibit reduced yields. Genotypic variability for ethephon sensitivity among wheat cultivars was less evident. In most experiments, ethephon treatment lowered kernel numbers per spike or mass per kernel. We conclude that ethephon use is most reasonable when the production practices followed, or environmental conditions, assure the likelihood of significant lodging. Further research investigating cereal responses to lower ethephon rates, as well as interactions between ethephon and plant stress, is needed.

Campbell and Lipps, 1998;Yang et al., 1999). Resistance expression often differs among envi-The development of wheat (Triticum aestivum L.) cultivars resis-

Plants require a continuous supply of iron (Fe) to maintain proper growth. Low rates of Fe chelates applied to reduce Fe deficiency in soybean [Glycine max (L.) Merr.] probably do not satisfy this requirement. Our objective was to evaluate the effectiveness of high rates of Fe‐EDDHA in reducing Fe deficiency when applied to susceptible and resistant cultivars grown on soils where soybean historically has exhibited mild to severe Fe deficiency. Four cultivars (two resistant, two susceptible) and six rates of Fe‐EDDHA (0, 2.24, 4.48, 6.72, 8.96, and 11.20 kg ha−1) were evaluated at one location in 2002 and two locations in 2003. Severity of Fe deficiency varied markedly across environment and cultivars. Unifoliolate relative chlorophyll concentrations indicated that Fe deficiency can occur early in plant development and that planting seed Fe concentration (seed [Fe]) may be insufficient for early growth. Responses to higher rates of Fe‐EDDHA were environment and cultivar specific and occurred over an extended period, manifest at maturity. At lower rates (<6.72 kg Fe‐EDDHA ha−1), resistant cultivars exceeded susceptible cultivars in plant height, seed number, and grain yield, whereas at higher rates, susceptible cultivars often had values similar to resistant cultivars. Both resistant and susceptible cultivars exhibited linear responses to increasing rates when grown in harsh or intermediate environments, suggesting that even at very high rates of Fe‐EDDHA, Fe deficiency limited plant growth and grain yield. Seed [Fe] changed very little in response to added Fe. Plotting relative grain yield versus seed [Fe] for each environment illustrated the narrow range of seed [Fe] associated with wide ranges in relative yield and the large difference between resistant and susceptible cultivars regardless of relative yield.

Lodging can be a limiting factor of hard red spring wheat (HRSW) production. The main objective of this study was to determine the optimum timing and rate of trinexapac‐ethyl (TE) to improve straw strength, resistance to lodging, and related agronomic responses of HRSW. Field experiments arranged in randomized complete blocks were conducted from 2004 to 2006 in Crookston, MN. Five TE rates (0, 62.5, 93.75, 125.0, and 250.0 g a.i. ha−1) and one ethephon rate (280.2 g a.i. ha−1) were applied at Zadoks growth stage (GS) 30, 32, or 37. Measurements included crop injury, plant height, lodging, straw strength, acid detergent lignin (ADL) content, plant maturity, plant density, and yield. Increasing TE rates linearly decreased plant height and increased lodging resistance, straw strength, and ADL content. Lodging resistance was negatively correlated with plant height and positively associated with straw strength and ADL content. The TE rate of 125 g a.i. ha−1 decreased plant height by approximately 6%, and increased plant erectness by 9% and straw strength by 13%, without causing crop injury, delaying maturity, or affecting yield. Applications of TE at GS 37 resulted in less crop injury, shorter stand, and more erect plants than those at GS 30 or 32. These data suggest that the optimum application rate and timing of TE may be 125.0 g a.i. ha−1 at GS 37 for HRSW.

The importance of rapid, nondestructive, and accurate measurements of leaf area for agronomic and physiological studies is well known. Several mathematical formulas have been derived for estimating leaf areas for numerous crops, but there is little information available for soybeans [Glycine max (L.) Merr.]. The purpose of this study, therefore, was to develop prediction equations for estimating leaflet, trifoliolate, and total leaf areas of soybeans. Statistical analyses of soybean leaf areas were divided into three levels: leaflet, trifoliolate, and total leaf area. At each level, we compared the predictive abilities of three regression equations, each involving a different independent variable. On the basis of these results, we chose one independent variable at each level for subsequent regression analyses of various hypotheses. Prediction equations derived from independent variables involving measurements of length and width were superior at each level to those involving measurements of only length or width. Our data indicate, however, that considerable savings of time, with little loss of predictive ability, could be possible by measuring only length or width in each instance. With the use of independent variables involving measurements of length and width, regression analyses were performed to assess the effects of cultivars at each level and also the effects of leaflet orientation on the trifoliolate and the trifoliolate position on the plant at their respective levels. In general, these analyses indicated that a single regression equation could be used at each level. Leaflet, trifoliolate, and total leaf areas of the 12 cultivars we studied could be estimated by the following equations, respectively: A = 0.624 + 0.723LW (R2 = 0.985); A = 0.411 + 2.008LW (terminal leaflet) (R2 = 0.983); A = 6.532 + 2.045 (∑L1W1 terminal leaflets) (R2 = 0.965).

Increasing kernel weight has been proposed as a method to increase flour extraction in spring wheat (Triticum aestivum L.). Recurrent selection was initiated to increase kernel weight while maintaining genetic variation for the unselected traits. Our objectives were to determine (i) genetic gain for kernel weight after eight cycles of selection, (ii) the indirect effects of the selection for kernel weight on other agronomic traits, kernel morphology, milling fractions, and grain protein concentration, and (iii) the level of genetic variability among lines within selection cycles for kernel weight and unselected traits. Ten lines, selected for high kernel weight, were originally intermated to form the base population. About 20 F2 plants with the highest kernel weight were selected (∼2% of the population), and about three of their F3 progeny were intermated to form the next cycle. This procedure was repeated for eight cycles, with an average of 60 crosses per cycle. Forty random lines from each cycle were used to evaluate agronomic traits in three environments. Kernel weight increased linearly at about 4.5% cycle−1 Cycle means did not differ for plant height and grain yield, but tillers per square meter and kernels per spike decreased 2.4 and 1.6% per cycle, respectively. Spikelets per spike, kernels per spikelet, test weight, and days to heading decreased, whereas spike length increased in response to selection for kernel weight. The proportion of bran and shorts decreased, and flour extraction and grain protein concentration increased 0.58 and 0.16% cycle−1, respectively. No clear trend towards decreased genetic variance for kernel weight was observed since gain was linear over eight cycles. The observed gain from selection and heritability estimates point to kernel weight being controlled by several genes with small effects. Selection for increased kernel size in this population resulted in increased flour yield.

Wheat straw is a potential cellulosic feedstock for bioethanol. This study was conducted to evaluate straw yield potential and its relationship with grain yield for wheat (Triticum spp.) grown in the United States. The specific objective was to determine if differences in straw yield and harvest index (HI) exist between and within regions and/or wheat classes. Using ongoing variety performance trials in eight states, a total of 255 varietal trial entriess from five classes of wheat were surveyed for above-ground biomass. Averaged over all wheat classes and regions the HI was 0.45. Soft red winter wheat in Kentucky had, on average, the highest HI and lowest straw yield among regions and wheat classes. Soft white winter wheat under irrigation in the Pacific Northwest produced the highest straw yield. Hard red winter wheat in the southern plain states of Texas and Oklahoma had, on average, the lowest HI. Differences in the amount of precipitation and cultivars were the major contributors to the variation detected within wheat classes. The amount of wheat straw available as cellulosic feedstock in a state or wheat class can be estimated using the grain yield estimates provided by the National Agricultural Statistics Service and the class specific HI.

Wild oat is an economically important annual weed throughout small grain producing regions of the United States and Canada. Timely and more accurate control of wild oat may be developed if there is a better understanding of its emergence patterns. The objectives of this research were to evaluate the emergence pattern of wild oat and determine if emergence could be predicted using soil growing degree days (GDD) and/or hydrothermal time (HTT). Research plots were established at Crookston, MN, and Fargo, ND, in 2002 and 2003. On a weekly basis, naturally emerging seedlings were counted and removed from six 0.37-m2permanent quadrats randomly distributed in a wild oat–infested area. This process was repeated until no additional emergence was observed. Wild oat emergence began between May 1 and May 15 at both locations and in both years and continued for 4 to 6 wk. Base soil temperature and soil water potential associated with wild oat emergence were determined to be 1 C and −0.6 MPa, respectively. Seedling emergence was correlated with GDD and HTT but not calendar days (P = 0.15). A Weibull function was fitted to cumulative wild oat emergence and GDD and HTT. The models for GDD (n= 22,r2= 0.93, root mean square error [RMSE] = 10.7) and HTT (n= 22,r2= 0.92, RMSE = 11.2) closely fit observed emergence patterns. The latter model is the first to use HTT to predict wild oat emergence under field conditions. Both models can aid in the future study of wild oat emergence and assist growers and agricultural professionals with planning timely and more accurate wild oat control.