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SMALL GRAINS

Planting Date and Foliar Fungicide Effects on Yield Components and Grain Traits of Winter Wheat

Kansas State Univ. Southeast Agric. Res. Center, P.O. Box 316, Parsons, KS 67357

Corresponding author (kkelley{at}oznet.ksu.edu)

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
In the eastern Great Plains, winter wheat (Triticum aestivum L.) typically is planted from late September through November. However, grain yield and grain quality often are reduced by variable weather conditions in the spring and foliar disease infections. Field studies were conducted in southeastern Kansas from 1990 through 1995 on a Parsons silt loam soil (fine, mixed, thermic, Mollic Albaqualf) to evaluate effects of planting date, with and without a foliar fungicide (propiconazole: (1-{[2-(2,4-dichloro-phenly)-4-propyl-1,3-dioxolan-2-yl] methyl}-1H-1,2,4-triazole), on grain yield, yield components, and grain quality (test weight and protein) of hard and soft red winter wheats with different maturities and disease resistances. In 2 of 6 yr, grain yields of all cultivars planted in late September were reduced significantly by barley yellow dwarf virus (BYDV) infection. Intermediate planting dates in mid- to late October resulted in the best grain yield and quality in most years. Grain yields and test weights of November-planted wheats were more variable and depended on specific environmental conditions. Grain yield and test weight responses to foliar fungicide depended on severity of specific foliar diseases, cultivar disease resistance, and environmental conditions, but significant yield increase occurred 77% of the time. Planting date had no significant effect on foliar fungicide effectiveness. Foliar fungicide had no effect on grain protein, head density, or kernels per head. Results indicate that a foliar fungicide application could be beneficial in protecting grain yield and test weight potential of both hard and soft winter wheat cultivars when conditions are favorable for foliar disease epidemics in the eastern Great Plains wheat-growing region.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
WINTER WHEAT (Triticum aestivum L.) often is planted over an extended period in the Midwest depending on specific region, intended use, crop rotation, and weather. In the eastern Great Plains, wheat typically is grown for grain and rotated with other crops to diversify cropping systems. Both hard red winter and soft red winter cultivars are adapted to the region and generally planted over a 6-wk period extending from late September through mid-November. However, grain yield and grain quality often are reduced by variable weather conditions in the spring and foliar disease infections.

Numerous research studies have shown that a rather narrow planting period often results in optimum grain yield for a particular wheat-growing region (Witt, 1996; Dahlke et al., 1993; Rocheford et al., 1988). In areas with limited soil moisture, planting too early can cause excessive fall growth that results in depletion of soil moisture for early spring growth (Winter and Musick, 1993). Early planted wheat also breaks winter dormancy earlier in the spring as temperature increases and, thus, has a greater potential for late spring freeze injury (Miller, 1992). Wheat planted at an intermediate date has greater yield potential than late-planted wheat because of increased tillers, heads, and kernel weight (Thill et al., 1978; Darwinkel et al., 1977). Late-planted wheat also develops under different temperature and day-length, has a shortened phyllochron interval (Cao and Moss, 1994), and requires greater seeding rates to compensate partially for reduced tiller development (Shah et al., 1994). Research also has shown the importance of adequate P fertilization with delayed planting (Knapp and Knapp, 1978; Blue et al., 1990).

In the more humid wheat-growing regions of the USA, foliar diseases can significantly reduce yield potential. The most common foliar diseases are powdery mildew (Blumeria graminis f. sp. tritici), leaf rust (Puccinia triticina), septoria blotch (Septoria tritici), and stagonospora blotch (Stagonospora nodorum). These diseases can occur alone, but frequently occur as a complex. Growing resistant cultivars has been the principal means of controlling foliar diseases in the USA. However, in the case of leaf rust, new races can develop quickly and overcome host resistance (Kolmer, 1997). Foliar fungicides have been used as a management tool to control diseases in the soft wheat-growing regions of the USA, although effectiveness often depends on specific environmental conditions and cultivar selection (Guy et al., 1989; Cox et al., 1989; Beuerlein et al., 1989; Guy and Oplinger, 1989; Milus, 1994). Foliar fungicides typically have not been recommended for the drier climate of the central and southern Great Plains where hard winter wheats are grown. However, very little information is available on the effectiveness of foliar fungicides in reducing losses of grain yield and quality from foliar diseases in the transition zone of the eastern Great Plains, where both hard and soft wheat cultivars are planted over a wide range of planting dates.

The objectives of this study were to evaluate the effects of planting date, with and without a foliar fungicide, on grain yield, yield components, and grain quality for selected cultivars of hard and soft red winter wheats with different maturities and disease resistances. Also, because of likely interactions with environment, treatment effects were evaluated over an extended period of 6 yr.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
This field study was conducted at the Southeast Agricultural Research Center of Kansas State University near Parsons (37°N. lat., 95°W. long.) from 1989 through 1995. The soil was a Parsons silt loam (fine, mixed, thermic, Mollic Albaqualf). The experimental design was a split-split plot arrangement of a randomized complete block with three replications. Main plots consisted of four planting dates, which were meant to be spaced approximately 2 wk apart from late September through mid-November. However, wet fall conditions resulted in cancellation of one planting date and delays in others. Actual dates are shown in Table 1. Subplots consisted of a foliar fungicide application vs. no treatment and were separated by a 1.52-m border. Propiconazole (1-{[2-(2,4-dichloro-phenly)-4-propyl-1,3-dioxolan-2-yl] methyl}-1H-1,2,4-triazole), trade name Tilt, was applied at 126 g a.i. ha^-1 as a foliar spray in 187 L ha^-1 of water with a CO₂-pressurized backpack sprayer with a constant boom pressure of 207 kPa. The application was targeted for Feekes' growth stage 8 (flag leaf visible); however, because of maturity differences within various planting dates, some early maturing cultivars were at Feekes' 9.0 (ligule of flag leaf visible) and Feekes' 10.0 (boot stage) at the time of fungicide application. Sub-subplots consisted of six wheat cultivars (four hard red winter and two soft red winter) with different maturities and disease resistances (Table 2). Cultivar selection was based on regional performance in statewide yield trials as well as percentage of land area when the study was initiated. Seeding rate varied with planting date to approximate Kansas State University recommendations. Cultivars were seeded with a seven-row research plot drill on 18-cm spacing at 344250 seeds ha^-1 for late September planting; 425250 seeds ha^-1 for October planting; and 506250 seeds ha^-1 for November planting. Seeds of all cultivars for each planting date were treated with a systemic fungicide [carboxin: (5,6 dihidro-2 methyl-N-phenyl-1,4oxathiin-3-carboxalinide) 17%; thiram: (tetramethylthiuram disulfide) 17%] before planting to control seed rots and seedling diseases. Individual cultivar plot size was 1.52 m by 12.16 m. Plots were end-trimmed prior to harvest. Grain yields were obtained by harvesting with a modified research plot combine. A subsample was taken to determine grain moisture, test weight, kernel weight, and grain protein. Grain yield was adjusted to a 12.5% moisture basis. Head density was determined by counting the number of head-bearing tillers from a 1-m length of row. Kernels per head were determined by collecting 20 heads at random from each plot before harvest and threshing with a small head thresher. Grain protein was determined by analyzing Kjeldahl digestion of grain N colorimetrically (Crooke and Simpson, 1971) and multiplying by 5.7. Monthly mean temperatures and total rainfall during the growing seasons are shown in Table 3. Cultivar heading differences as affected by planting date and different weather conditions are shown in Table 4.

The study was planted on a different site in each year to eliminate any contamination from volunteer wheat. The previous crop was spring oat (Avena sativa L.), and residue was incorporated into the soil with conventional chisel and disk tillage before wheat planting. All wheat plots received 17 kg N ha^-1 and 67 kg ha^-1 of P₂O₅ and K₂O (17–29.3–55.6, N–P–K) as a preplant-incorporated application and 67 kg N ha^-1 as a urea broadcast treatment in early March.

Treatment effects were analyzed across years and by individual years with the MIXED procedure of SAS (SAS Inst., 1988). Analyses across years treated year as a random effect, because the study was planted on a different site each year. Year interactions were tested with the GLM procedure of SAS. Treatment means were compared using Fisher's protected LSD (0.05).

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
Grain Yield Response to Planting Date x Foliar Fungicide x Cultivar Interactions
Grain yield was influenced significantly by planting date, foliar fungicide, cultivar, and treatment interactions (Table 5). Significant year interactions also occurred because of varying environmental conditions during the 6-yr period from 1990 through 1995; thus, grain yield results for individual years are shown in Table 6.

In 1991, temperatures were higher than normal, but precipitation was below normal from February through June (except April), resulting in earlier than normal plant heading (Table 4). However, moist and cool conditions during April were conducive for infections of septoria blotch and powdery mildew, and leaf rust developed in May. Grain yields of all cultivars were significantly higher with October planting and foliar fungicide application (Table 6). However, yield response to propiconazole varied with cultivar. Disease-susceptible cultivars (Chisholm and TAM 107) generally showed the largest yield response, especially in October and November plantings when leaf rust pressure likely was greater. However, yields of several disease-resistant cultivars (2163, Karl, Pioneer 2551) also were increased significantly. Results suggest the development of newer leaf rust races, which overcame the initial leaf rust resistance. Typically, new wheat cultivar releases with good to excellent leaf rust resistance have become susceptible to newer leaf rust races within a few years of release (Kolmer, 1997).

In 1992, subfreezing temperatures in late October resulted in severe losses of seedlings (visual estimate of 50%) for Caldwell and Chisholm planted in mid-October; thus, grain yields of those cultivars were reduced significantly compared with yields of other cultivars for the same planting date. Similar to 1991, wheat headed earlier than normal because of higher than normal temperatures from December through March. However, cooler than normal temperatures from April through June as well as near ideal rainfall were favorable for kernel development and grain filling. Major foliar diseases consisted of septoria blotch and stagonospora blotch, but leaf rust infection again developed late in the season. Research in Arkansas also noted that leaf rust typically develops after septoria blotch (Milus, 1994). Grain yields were relatively high for all planting dates and cultivars, regardless of foliar fungicide treatment. Results suggest that the combined effects of an early heading date and cool conditions during grain filling partially overrode the adverse effects of foliar diseases. However, grain yields of all cultivars, except Karl, were significantly greater when foliar fungicide was applied, regardless of planting date, indicating that foliar diseases were still reducing maximum yield potential. Yield response to propiconazole was lowest for Karl, which likely was due to its greater resistance to stagonospora blotch compared with the other cultivars.

In 1993, wet soil conditions in November and December resulted in cancellation of the last planting date, which is not that uncommon for the eastern Great Plains region. Cooler than normal temperatures from February through April delayed plant development; thus, heading date was later than normal. Extremely wet conditions in May led to severe infections of septoria blotch and leaf rust, and scab infection also appeared near grain maturity in the late September planting. Grain yields of nearly all cultivars were lower with late September planting, regardless of fungicide treatment. Similar to 1990, the effect of scab infection on grain yields in the early planting date was unclear. Yield response to foliar fungicide varied with cultivar. In all planting dates, the most disease-resistant hard wheat cultivars (2163 and Karl 92) had the least yield benefit from propiconazole, whereas the later maturing soft wheat cultivars (Caldwell and Pioneer 2551) showed the most yield increase. However, with propiconazole, disease-susceptible cultivars (TAM 107 and Chisholm) yielded significantly higher than several disease-resistant cultivars (2163 and Karl 92). Results show that with foliar disease protection, some high-yielding cultivars that lack specific disease resistance can produce higher grain yields than more resistant cultivars in specific environmental conditions.

In 1994, the early planting date was delayed until early October because September rainfall was nearly three times above normal (Table 3). April precipitation also was more than three times the average, but May and June rainfall was below average. Because of the extremely wet conditions in April, environmental conditions were conducive for the septoria leaf disease complex (septoria blotch and stagonospora blotch). Higher than normal temperatures in early June also reduced the grain fill period of late-planted wheat, although grain yield of Pioneer 2551, the latest maturing cultivar, was reduced the most. Significant yield differences occurred among cultivars, with and without fungicide treatment. With no fungicide application, Karl 92 yielded significantly higher than other cultivars in the intermediate and later plantings. Similar yield responses with Karl occurred in 1992 when stagonospora blotch infected wheat heads. However, foliar fungicide increased grain yield of most cultivars by 30 to 40%, regardless of planting date. Grain yield losses from the septoria disease complex were greater than normal, because conditions were favorable for an early spring infection and apparently continued through the soft dough stage.

In 1995, the late September planting was infected severely with BYDV, which was similar to the situation in 1990. Excessive rainfall in the fall delayed the last planting until late November. More heavy rainfall in late spring resulted in water-saturated soil and premature death of wheat plants before harvest; however, grain yield of late-planted wheat was reduced the most by water-saturated soil. A severe leaf rust infection also developed near heading because of wet conditions in April and May. Grain yields of all cultivars planted in late September were reduced significantly by the BYDV infection. Although no cultivars were resistant to BYDV, some (Caldwell, 2163, and Pioneer 2551) appeared to be more tolerant than others (Chisholm, Karl 92, and TAM 107). Grain yields of all cultivars were greater with October planting and foliar fungicide application. Results indicate that new races of leaf rust likely had overcome initial host resistance for all cultivars. Grain yield of late-planted wheat was reduced significantly by the water-saturated soil. However, other research in Kansas (Witt, 1996) has shown that wheat grain yields typically decline nearly 25% when planting is delayed into November compared with the more optimum October planting date.

Grain yields were affected by numerous interactions of cultivar x planting date x foliar fungicide x year. However, 77% (106 of 138) of the cultivar x planting date x year combinations resulted in a significant increase in grain yield from use of foliar fungicide. Of the 32 instances where the foliar fungicide did not increase yield significantly, 13 (40%) were with Karl, the cultivar with the highest combined resistance to the four diseases being controlled by the fungicide. However, even with Karl, a significant yield increase with fungicide occurred in 10 of 23 instances. Therefore, cultivars with excellent disease resistance ratings for these diseases occasionally will show significant grain yield increases from foliar fungicide application. The more susceptible a cultivar is to the disease present, the higher the probability will be of a significant yield response. Finally, lack of a planting date x fungicide interaction indicated that planting date did not influence responsiveness to the foliar fungicide.

Although grain yields often are correlated to disease incidence in winter wheat (Guy and Oplinger, 1989; Milus, 1994), cultivars can respond differently because of such factors as yield potential, disease tolerance (Spadafora et al., 1987), and specific environment. Other researchers have noted that visual disease ratings may not be the best indicators of fungicide effectiveness, because cultivars with similar ratings sometimes have different yield responses (Guy et al., 1989). In addition, research in Arkansas found that predicting yield losses from individual diseases becomes much more complex when wheat is infected by two or more foliar diseases, (Milus, 1994).

Yield Component Responses
Yield components (kernel weight, kernels per head, and head density) were affected significantly by interactions of planting date, foliar fungicide, and cultivar (Table 5). Foliar fungicide treatment did not significantly influence head density or number of kernels per head, because these yield components already were determined before application. Yield components also were influenced by environment, resulting in year x treatment interactions (Table 7).

Foliar fungicide significantly increased kernel weight of nearly all cultivars, regardless of planting date and year. However, because of varying environmental conditions, the magnitude of increase differed with cultivar and year. Foliar fungicide provided approximately 3 wk of disease protection to the upper leaf canopy compared with untreated plots. Because the flag leaf makes up nearly 75% of the effective leaf area that contributes to grain fill (Miller, 1992), keeping it free of diseases with foliar fungicide application can be beneficial for kernel development.

Grain Quality and Grain Protein Responses
Significant interactions occurred between planting date, foliar fungicide, and cultivar for test weight (Table 5). Also, because of environmental effects, significant year x treatment interactions occurred. Results for grain test weight and protein are shown in Table 8.

Several different environmental factors reduced test weights in certain years. In 1990, test weights for early planting dates were reduced significantly for cultivars affected by the late spring freeze. In 1995, test weights of late planted wheat were reduced by water-logged soil conditions. Although severe BYDV infections were present in early planted wheat in both years, they had smaller effects on test weight than on grain yield. In 1991, when late spring temperatures were higher than normal, test weights of late maturing cultivars planted in November were reduced. Gibson and Paulsen (1999) recently showed in a greenhouse study that high temperatures imposed from 20 d after anthesis until grain ripened decreased kernel weight by 18%.

Foliar fungicide had a greater impact on test weight than did planting date in most years. However, the magnitude of response for individual cultivars sometimes varied with planting date. Absolute test weights were highest for all cultivars with foliar fungicide, regardless of year, even though yields and test weights were sometimes not significantly different. Karl 92 generally showed the smallest test weight response to foliar fungicide. Test weight results indicate that foliar fungicide applications would be most valuable where large seed of high test weight are valued, such as for seed wheat. However, foliar fungicide cannot prevent low test weights caused by the wheat genotype, weather conditions, or delayed harvest.

Grain protein was affected significantly by interactions of planting date x cultivar x year. Karl 92 generally had the highest grain protein in most planting dates. Foliar fungicide had no beneficial effect on grain protein, even though the upper leaf canopy was noticeably greener for the 3-wk period after application. These results confirm previous findings, which showed that foliar fungicide had no effect, but applying additional topdressed N significantly increased grain protein (Kelley, 1993).

	SUMMARY AND CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
Where wheat is grown primarily for grain use, early planting dates in late September and early October should be avoided in the eastern Great Plains because of the potential yield reductions associated with BYDV infection. Intermediate planting dates in mid- to late October resulted in the best grain yield and grain quality in most years, whereas grain yield and grain quality of late-planted wheat were more variable and depended on specific environmental conditions.

Grain yield responses to foliar fungicide depended on severity of specific foliar diseases and cultivar disease resistance. However, results also showed that with foliar disease protection, some high-yielding cultivars that lack specific disease resistance can produce higher yields of grain with better quality than more resistant cultivars. Thus, foliar fungicide application could be beneficial in extending the use of some high-yielding cultivars that have lost leaf rust resistance. In addition, foliar fungicide application could be an important management practice for wheat seed producers in regions where foliar diseases typically reduce overall grain quality. Finally, the effectiveness of foliar fungicide use was not influenced significantly by planting date; however, foliar fungicides are most likely to be economical in fields where wheat has been planted at an optimum time and has relatively high yield potential.

	ACKNOWLEDGMENTS

 
The author express appreciation to Michael Dean for his technical assistance during the study; to Dr. Thomas Loughin for assistance in statistical analyses; and to Dr. Robert Bowden for assisting with plant disease nomenclature.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
Contribution no. 00-416-J of the Kansas Agric. Exp. Stn., Manhattan, KS 66506.

Received for publication May 12, 2000.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 

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This Article Abstract Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (13) Citing Articles via Google Scholar Google Scholar Articles by Kelley, K. W. Search for Related Content PubMed Articles by Kelley, K. W. Agricola Articles by Kelley, K. W. Related Collections Weed Management Agricultural Pesticides Wheat