Response of canola to simulated diamondback moth (Lepidoptera: Plutellidae) defoliation at different growth stages

Abstract

In field trials conducted during 1995–1998, canola cultivar "Falcon" was subjected to different levels of simulated insect defoliation at four stages of crop growth. Plants were 0, 33, 67 and 100% defoliated at rosette and flowering stages during the 1995–1996 season as well as 2–4 leaf stage during the 1996–1997 and 1997–1998 seasons. Plants were 0, 50 and 100% defoliated at pod filling stage during all seasons. Over all seasons, defoliation did not consistently affect the number of plants per unit area, plant height, 1000 seed weight, and oil content of seeds for most of the defoliation treatments. However, defoliation at the 2–4 leaf and rosette stages made plants more susceptible to cold injury. Generally, canola could withstand a higher level of defoliation as crop development progressed. Maximum yield reductions occurred for defoliations at the 2–4 leaf stage followed by the rosette and flowering stages of the crop. No significant yield losses were recorded for defoliations at the pod filling stage. Results suggest that canola is most sensitive to defoliation in its early stages of growth. Greater amounts of defoliation can be tolerated as crop development progresses. The relationships between defoliation and yield loss were used to establish diamondback moth economic injury levels for canola at different crop growth stages. Key words: Canola, Brassica napus, oilseed rape, simulated defoliation, economic injury level

Yield Response to Early Defoliation in Spring‐Planted Canola

“…For spring-planted canola, removing all leaves at the beginning of flowering caused 20 to 25% yield loss on average (Clarke, 1978;Kirkegaard et al, 2012b), while defoliating during late flowering or pod-filling did not cause significant yield loss (Clarke, 1978;Ramachandran et al, 2000). During vegetative growth, plants suffered greater average yield loss with leaf removal at the two-to fourleaf stage (68%) than at the rosette stage (54%) (Ramachandran et al, 2000). These findings contrast with reports that winter-grown canola may recover completely from defoliation during vegetative growth if sufficient biomass remains (Kirkegaard et al, 2012a,b).…”

“…Yield loss in defoliated canola is influenced by the plant stage when damage occurred (Clarke, 1978;Ramachandran et al, 2000;Kirkegaard et al, 2012a;Seymour et al, 2015), the remaining leaf area or biomass (Ramachandran et al, 2000;Kirkegaard et al, 2012a;Seymour et al, 2015), and environmental conditions following defoliation (Kirkegaard et al, 2012b;McCormick et al, 2012;Seymour et al, 2015). For spring-planted canola, removing all leaves at the beginning of flowering caused 20 to 25% yield loss on average (Clarke, 1978;Kirkegaard et al, 2012b), while defoliating during late flowering or pod-filling did not cause significant yield loss (Clarke, 1978;Ramachandran et al, 2000). During vegetative growth, plants suffered greater average yield loss with leaf removal at the two-to fourleaf stage (68%) than at the rosette stage (54%) (Ramachandran et al, 2000).…”

Biological control of the diamondback moth,Plutella xylostella: A review

“…It occurs throughout the United States (Harcourt 1957) and is one of the major pests of crucifers in various regions including the southeast and Pacific Northwest (Buntin 1990;Brown et al 1999). In southeastern USA, it constitutes /90% of the guild of defoliating lepidopterans of canola and can occur from seedling through crop maturity (Buntin 1990;Ramachandran et al 2000). DBM is also a serious pest of crucifers in Canada.…”

Occurrence of arthropod pests associated with Brassica carinata and impact of defoliation on yield

“…The population density of each species was variable, but these findings indicate that there are several insect species that utilize B. carinata as a host in the southeast U.S. Several pests have been associated with species of Brassica spp. in the southeast U.S. (Loon et al, 2002;Manrique et al, 2012;Ramachandran et al, 2000;Reddy, 2017); however, this is the first report of pests associated with B. carinata. Plutella xylostella is a pest associated with brassica causing annual yield losses and management costs estimated at $2.3 billion (Zalucki et al, 2012).…”