Nitrogen and Fungicide Effects on Yield Components and Disease Severity in Wheat

Abstract

Spring N applications increase wheat (Triticum aestivum L.) grain yields in the Mid‐South. The interactive effect of increased N rates and foliar fungicide applications on the common Mid‐South winter wheat foliar diseases—leaf blotch (Septoria tritici Rob. in Desm.), glume blotch and leaf spot [S. nodorum (Berk.) Berk.], and leaf rust (Puccinia recondita Rob. ex Desm. f. sp. tritici)—is not clearly understood. Research was initiated in 1984 on a Collins silt loam soil (coarse‐silty, mixed, acid, thermic Aquic Udifluvents) and continued each year through 1987 to evaluate the effect of N rates and fungicide applications on disease severity in wheat. Spring N rates of 0, 30, 45, 60, 90, and 120 lb/acre were applied at Feekes' growth stage (GS) 3. Fungicides were applied twice during the spring at GS 8 to 9 and GS 10.1 to 10.5. The research was continued between 1988 and 1990 on a Loring silt loam soil (fine‐silty, mixed, thermic Typic Fragiudalfs), but with a reduced number of N treatments. Experimental sites were changed each year on these two soils. The effects of N rates and fungicide applications to wheat were evaluated through grain yields, kernel weights, test weights, and estimated percentage plant foliage and heads infected by diseases. The applied N rates did not have the same effect on increasing yields during the years of the experiment. Generally, yields were increased to a level and then decreased with higher N rates. Fungicide applications had a greater effect on yields produced at the higher N rates. Severity of diseases differed with year, N rate, and fungicides. The severity of the three diseases was increased with N rate, especially when fungicides were not applied, but fungicides reduced disease severity. Yield reductions could not be attributed to any single disease but to a combination of diseases, and reductions could not be ascertained from kernel weights or test weights. Research Question Throughout the Mid‐South, wheat yields may be reduced by one or more plant diseases that may incraese with incraesed N fertilization. This study evaluates spring N and foliar fungicide effects on grain components and disease severity of wheat. Literature Summary Diseases have had a negative but inconsistent effect on grain yields. Not only is severity inconsistent with years, but the predominate disease may differ. In this region, one or more diseases may affect wheat during the growing season. High N rates tend to increase infection by increasing plant susceptibility to these diseases. The disease severity increases with applied N when fungicides are not applied. Study Description Spring N rates and fungicides were applied over 7 yr, evaluating their effect on wheat. Experiment Design: Main‐plots, spring N rates of 0, 30, 45, 60, 90, and 120 lb/acre plus a split N rate (45 lb applied at Feekes’ GS 3 + 45 lb applied 3 to 4 wk later) were applied to a Collins silt loam soil for 1984 through 1987. Main plot N rates plus the split‐rate were applied to a Loring silt loam soil. Sub‐plots, fungicides, Bayleton p...

Synergism of Nitrogen Rate and Foliar Fungicides in Soft Red Winter Wheat

“…This result contrasted with similar comparisons in the literature; several have reported high concentrations of N in the canopy favored leaf rust (Walters and Bingham, 2007), powdery mildew (Olesen et al, 2003a), and septoria (Howard et al, 1994; Lovell et al, Table 10. UTC, untreated check no fungicide; T3, fungicide at Zadoks Growth Stage (GS) 65; T123, fungicide at approximately GS 30, GS 39, and GS 65.…”

The role of sugar signaling in plant defense responses against fungal pathogens

“…Rice blast (Kürschner et al 1992;Long et al 2000) is the best-known example of such a disease. Among wheat diseases, powdery mildew (Last 1953;Teich et al 1987), leaf rust (Howard et al 1994;Teich et al 1987), stripe rust or yellow rust (Ash and Brown 1991;Danial and Parlevliet 1995) and several other diseases (Howard et al 1994) have been reported to increase in severity as the rate of nitrogen application is increased. Transcription analyses show that sugar and inorganic nitrogen act as both metabolites and signaling molecules.…”

Recent Advances on Integrated Foliar Disease Management with Special Emphasis in Argentina Wheat Production

“…Management practices such as N fertilization can also affect the expression of wheat foliar diseases [82,84] and the effectiveness of foliar fungicide application [72,82,84,85]. Increasing N rates may cause negative, positive or neutral effect on foliar disease severity, depending on the geographic location [86] and the type of disease.…”

“…Increasing N rates may cause negative, positive or neutral effect on foliar disease severity, depending on the geographic location [86] and the type of disease. The magnitude and direction of the influence of N supply on Septoria leaf blotch severity has been studied with contrasting results [85,87,88,89]. Simón et al [82,84,90] found that in conducive conditions, N fertilization increases the severity of Septoria leaf blotch and discussed the effect of different factors affecting the influence of N supply.…”

“…Increasing N rates retarded tan spot development [66,69,73,91,92,93,94]. However, Bockus and Davis [95] suggested that N applications do not directly affect tan spot severity, but rather appear to reduce disease impact through delayed leaf senescence or that high N rates increase Septoria leaf blotch or tan spot severity due to an increase in crop biomass production, which creates a microenvironment conducive to fungal development in humid regions [82,84,85,96,97]. In addition, experiments carried out in Argentina indicated that yield increase and increase in yield components due to application of tebuconazole was similar in fertilized and non fertilized conditions, despite the increase in the area under disease progress curve under N fertilization [82].…”