Integrating Spring Wheat Sowing Density with Variety Selection to Manage Wheat Stem Sawfly

Abstract

The wheat stem sawfly [Cephus cinctus Norton (Hymenoptera: Cephidae)] (WSS) has been a serious pest of wheat (Triticum aestivum L.) since the late 19th century. Adoption of solid‐stemmed cultivars, which are available only in the spring bread wheat class in Canada, can mitigate damage but the trait that confers resistance tends to be variable. Five other classes of wheat are grown within the geographical range of C. cinctus and are vulnerable to WSS infestation, and the entire production area for durum (T. turgidum L.) in western Canada, Montana, and western North Dakota lies within the geographic range of C. cinctus. Our objective was to test the hypothesis that the response of hollow‐ and solid‐stemmed cultivars to sowing density (150, 250, 350, or 450 seeds m−2) would differ and subsequently affect infestation patterns of WSS and an endemic parasitoids. The lowest rates of infestation occurred in the hollow‐stemmed durum cultivar AC Avonlea and declined with increased sowing density. Wheat pith expression was optimized at the lowest sowing density but the same level produced low and variable grain yield. In the solid‐stemmed cultivar Lillian, pith expression was most stable at 250 or 350 seeds m−2. For all cultivars, grain yield was optimized at the higher seeding rates of 350 and 450 seeds m−2. Solid‐stemmed wheat should be seeded at low to moderate density to maximize resistance to WSS, but hollow‐stemmed cultivars should be seeded at higher seeding rates to optimize yield, lower WSS infestation, and to increase overall crop competitiveness.

Effects of Seeding Rate on Durum Crop Production and Physiological Responses

“…Our results shows that a high yield can be achieved in a particular environment by adjusting SR within that environment as was previously demonstrated in barley (Hordeum vulgare L.) and bread wheat (Faris and DePauw, 1980;Van Den Boogaard et al, 1996). The higher SR resulted in the highest yields in each environment, which also agrees with durum and bread wheat SR responses reported by Beres et al (2011). There were not statistically yield difference between the 217 to 272 seed m -2 SR and 272 to 380 seed m -2 , although the latter showed the highest grain yield.…”

“…Yield Within the range of SRs used, grain yield increased with increasing SR, which is consistent with Nilsen et al (2016) and Beres et al (2011). Figure 1 shows that yield response to plant density was more linear rather than the quadratic response cited by (Pan et al, 1994).…”

“…S1 and Table S2). These findings and results reported from recent reports (Beres et al, 2011;Nilsen et al, 2016) are an indication that the yield potential of modern durum cultivars can only be achieved if higher sowing densities are used compared to the lower SR practices of earlier eras.…”

Winter Wheat Cropping System Response to Seed Treatments, Seed Size, and Sowing Density

“…The variable costs, fixed costs, and estimated crop value based on historical prices were sourced from the Saskatchewan Ministry of Agriculture Crop Planning Guide 2015 (Anonymous, 2015c). The seed input costs were increased slightly to reflect the average selling price of CDC Buteo during the period of the study as it was a newly released cultivar ($10 bushel -1 or $0.367 kg -1 ; Wes Woods, personal communication, 2015).…”

“…If this added input cost is factored into the variable costs of the low seeding rate system, which also is inherently more variable across environments, the net returns become less appealing (Table 8). An additional negative compensatory feature of low seeding rates is that thinner winter wheat stands lead to increased tillering, which creates variations in crop uniformity, delays crop maturity and subsequent harvest dates (Beres et al, 2010(Beres et al, , 2011. The inclusion of the dual seed treatment in the high seeding rate system did not improve grain yield and therefore lowers overall net returns by $11 ha -1 (Table 8).…”