Bradley L. Harmon

Effect of late season insect infestation on yield, yield components and oil quality of Brassica napus , B. rapa , B. juncea and Sinapis alba in the Pacific Northwest region of the United States

The effect of late season insect infestation on seed yield, yield components, oil content and oil quality of two canola species ( Brassica napus L. and B. rapa L.) and two mustard species ( B. juncea L. and Sinapis alba L.) was examined over 2 years. In each year, ten genotypes from each species were evaluated with late season insects controlled with either methyl parathion or endosulfan insecticides, and without insecticides. Major late season insect damage in 1992 was caused by cabbage seedpod weevil ( Ceutorhynchus assimilis Paykull), while diamondback moth ( Plutella xylostella L.) and aphids (primarily cabbage aphids, Brevicoryne brassicae L.) were major insect pests in 1993. Insecticide application was very effective in controlling diamondback moth larvae and adult cabbage seedpod weevils, but only partially effective in controlling aphids. Higher numbers of diamondback moth larvae were observed on mustard species compared to canola species. S. alba was completely resistant to cabbage seedpod weevil and there was no damage due to this pest observed. Aphid colonization was observed on plants from all species, but infestation on S. alba and B. rapa occurred too late to have a major effect on seed yield. Seed oil content of canola species was significantly reduced by insect damage although oil quality (indicated by fatty acid profile) was not affected by insect attack. Uncontrolled insect infestation reduced seed yield of canola species by 37 and 32% in B. napus and B. rapa , respectively. Least yield reduction occurred in S. alba , where average yield reduction from plants in untreated control plots was S. alba , therefore, has good potential as an alternative crop suitable for northern Idaho because it can be grown with reduced late season insecticide application.

Comparative survey of the phytophagous arthropod faunas associated with Lepidium draba in Europe and the western United States, and the potential for biological weed control.

Abstract Hoary cress (Lepidium draba L.) is an invasive perennial mustard (Brassicaceae) introduced to North America from Eurasia. In 2001 we initiated a program to investigate the potential for classical biological control of this weed in the US. Literature and field surveys for the arthropods associated with L. draba were conducted on both continents. Field surveys began in Europe in 2001, and in 2002–2003 standardized surveys were conducted in both Europe and the western US. These field surveys resulted in 80 new host records for L. draba in Europe, and 37 new host records in the US. Although total species richness was nearly four times greater in Europe, there were approximately equal proportions of oligophagous and polyphagous species in each range. Monophagous species were only encountered in the European surveys. The literature surveys revealed that the arthropod fauna associated with L. draba is fairly well known in Europe (175 species), but not in the US (eight species), where the literature was virtually derelict of host records. In both the literature and field surveys, the order Coleoptera contained the most species (>50%) in Europe, whereas the order Hemiptera contained the most species (>40%) in the US. Nearly one-half of the species found in literature and field surveys are flower or seed feeders and the other half are primarily foliage or stem feeders. Ten potential biological control agents were discovered from the surveys, of which four are currently being investigated at the CABI Bioscience Centre in Switzerland. The phenologies of these four species are briefly described.

Assessment of Sinapis alba, Brassica napus and S. alba × B. napus hybrids for resistance to cabbage seedpod weevil, Ceutorhynchus assimilis (Coleoptera: Curculionidae).

Canola (Brassica napus L.), yellow mustard (Sinapis alba L.) and intergeneric crosses of S. alba × B. napus were assessed for resistance (antixenosis) to the cabbage seedpod weevil (Ceutorhynchus assimilis Paykull). Pod trichomes did not appear to be a major factor in the resistance of S. alba to weevils. The number of feeding punctures and eggs per pod in S. alba was not significantly different in pods with trichomes than in those where the trichomes had been removed. Choice and no-choice laboratory tests examining feeding punctures and eggs laid per pod suggested that resistance in S. alba is not conferred in the intergeneric cross, S. alba × B. napus. Similar data on feeding and weevil oviposition were found in field test plots. However, despite many eggs being laid in S. alba × B. napus hybrid plants, fewer cabbage seedpod weevil larvae developed to exit the intergeneric hybrid pods. Glucosinolate analyses of leaves, pods and seeds showed that S. alba plants have a high concentration of p-hydroxybenzyl glucosinolate in all three plant parts, but B. napus has no p-hydroxybenzyl. Interestingly the intergeneric hybrid examined in this study had 62% and 60% of p-hydroxybenzyl concentration in the leaves and seeds, respectively, than was found in the S. alba parent. However, pod tissues contained very little (3 %) compared with the S. alba parent. It is possible, therefore, that the adult cabbage seedpod weevil feeds on the pods of the intergeneric hybrid and lays eggs in the pod, because of the low concentration ofp-hydroxybenzyl glucosinolate, but the larvae then fail to develop as they feed on the seeds containing high concentrations of p-hydroxybenzyl glucosinolate. It should be noted also that this hybrid produced pods that were more similar in physical shape to canola pods and that this may also be a factor determining cabbage seedpod weevil feeding and subsequent egg laying. In addition, both B. napus and the intergeneric hybrid produced 3-butenyl and 4-pentenyl glucosinolates in their pods, and degradation products (3-butenyl, and 4-pentenyl isothiocyanates) from these glucosinolate types, are known to be stimulatory kairomones that attract cabbage seedpod weevil. Further studies are being conducted to examine these factors in more detail.

Yield Reduction in Brassica napus, B. rapa, B. juncea, and Sinapis alba Caused by Flea Beetle (Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae)) Infestation in Northern Idaho

Abstract Phyllotreta cruciferae is an important insect pest of spring-planted Brassica crops, especially during the seedling stage. To determine the effect of early season P. cruciferae infestation on seed yield, 10 genotypes from each of two canola species (Brassica napus L. and Brassica rapa L.) and two mustard species (Brassica juncea L. and Sinapis alba L.) were grown in 2 yr under three different P. cruciferae treatments: (1) no insecticide control; (2) foliar applications of endosulfan; and (3) carbofuran with seed at planting plus foliar application of carbaryl. Averaged over 10 genotypes, B. rapa showed most visible P. cruciferae injury and showed greatest yield reduction without insecticide application. Mustard species (S. alba and B. juncea) showed least visible injury and higher yield without insecticide compared with canola species (B. napus and B. rapa). Indeed, average seed yield of S. alba without insecticide was higher than either B. napus or B. rapa with most effective P. cruciferae control. Significant variation occurred within each species. A number of lines from B. napus, B. juncea, and S. alba showed less feeding injury and yield reduction as a result of P. cruciferae infestation compared with other lines from the same species examined, thus having potential genetic background for developing resistant cultivars.

Phenological Synchrony of Eustenopus villosus (Coleoptera: Curculionidae) with Centaurea solstitialis in Idaho

Abstract The phenological synchrony of Eustenopus villosus (Boheman) with its host, yellow starthistle, Centaurea solstitialis L. (Asteraceae: Cardueae), was studied in Idaho in 1995 and 1996. Field plots were observed for adult weevil activity periodically throughout the growing season, and yellow starthistle capitula were examined for adult feeding damage, oviposition damage, and larval development. At the study site, weevil phenology was well synchronized with C. solstitialis. Immature capitula, fed upon by adults, were abundant when E. villosus began to emerge in late May. During both years, the number of weevils and capitula increased throughout June. Adult females fed on capitula for about 2 wk. Weevil ovary dissections revealed that ovaries were mature after a 2-wk period of feeding. The development of mature capitula during late July corresponded to the initiation of oviposition. Eustenopus villosus, unique among the phytophages introduced for C. solstitialis biological control, attacks four plant stages resulting in observable impact to buds. Damaged buds either died or became distorted. Weevil feeding damage on young and mature capitula may make this insect a highly effective control agent.

Phenological Synchrony ofEustenopus villosus(Coleoptera: Curculionidae) withCentaurea solstitialisin Idaho

Abstract The phenological synchrony of Eustenopus villosus (Boheman) with its host, yellow starthistle, Centaurea solstitialis L. (Asteraceae: Cardueae), was studied in Idaho in 1995 and 1996. Field plots were observed for adult weevil activity periodically throughout the growing season, and yellow starthistle capitula were examined for adult feeding damage, oviposition damage, and larval development. At the study site, weevil phenology was well synchronized with C. solstitialis. Immature capitula, fed upon by adults, were abundant when E. villosus began to emerge in late May. During both years, the number of weevils and capitula increased throughout June. Adult females fed on capitula for about 2 wk. Weevil ovary dissections revealed that ovaries were mature after a 2-wk period of feeding. The development of mature capitula during late July corresponded to the initiation of oviposition. Eustenopus villosus, unique among the phytophages introduced for C. solstitialis biological control, attacks four plant stages resulting in observable impact to buds. Damaged buds either died or became distorted. Weevil feeding damage on young and mature capitula may make this insect a highly effective control agent.

Effect of generalist insect herbivores on introduced Lepidium draba (Brassicaceae): implications for the enemy release hypothesis

The enemy release hypothesis (ERH) states that decreased regulation by natural enemies allows plants to increase in distribution, abundance and vigour following their introduction into an exotic range. Invasive plants rarely escape herbivory entirely, and for hoary cress [Lepidium draba L. (Brassicaceae)] it has been demonstrated that generalist insect abundance is greater in its introduced North American range than in the native European range. We assessed the role of increased generalist herbivory on hoary cress using representatives of four important herbivore niches commonly found in the introduced range. We experimentally examined the density dependent impact of these herbivores individually and in combination on hoary cress in a series of greenhouse experiments. We found that defoliation of the oligophagous diamondback moth Plutella xylostella (L.) (Lep., Plutellidae) had the strongest and most consistent impact, while damage by the stem‐mining weevil Ceutorhynchus americanus Buchanan (Col., Curculionidae) tended to have the highest per capita effect. Plant response to feeding by the oligophagous crucifer flea beetle Phyllotreta cruciferae (Goeze) (Col., Chrysomelidae) was minor despite obvious feeding damage, and the impact of the polyphagous tarnished plant bug Lygus hesperus Knight (Het., Miridae) was negligible. In multiple‐species experiments, herbivore impacts were usually additive. In general, we found that hoary cress can tolerate high densities of oligophagous insect herbivory and effectively resisted attack by the polyphagous L. hesperus, but also the oligophagous C. americanus. Our results indicate that a combination of plant resistance and tolerance allows hoary cress to withstand increased generalist herbivore load in its introduced range, consistent with the predictions of the ERH.

Resistance of canola-quality cultivars of yellow mustard, Sinapis alba L., to the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham)

Oilseed Bassica is susceptible to attack by the cabbage seedpod weevil while commercial yellow mustard, Sinapis alba L., is resistant. The objective of this study was to determine if canola-quality S. alba would maintain its resistance traits. In laboratory choice and nochoice tests we found the number of eggs laid by the weevil to be low or non-existent in all S. alba genotypes. Key words: Ceutorhynchus obstrictus, Ceutorhynchus assimilis, Sinapis alba, plant resistance

Native and Exotic Grass Competition with Invasive Hoary Cress (Cardaria draba)

Abstract The Eurasian perennial mustard, hoary cress, Cardaria draba (Brassicaceae), is an invasive weed in western North America that can displace native plants and other desirable forage species in pastures and rangelands. This study investigated the competitive ability of 11 grasses representing nine species in the genera Festuca and Poa from either North America (NA) or Europe (EU) against hoary cress. Hoary cress was grown alone and with four different grass densities under controlled conditions with ample water and nutrient supply, typical for riparian and disturbed habitats, in which hoary cress infestations are commonly found. Of the five Festuca grasses tested, only Schedonorus phoenix ( =  F. arundinacea) decreased hoary cress biomass. Four of the six Poa grasses tested decreased hoary cress biomass and were ranked by decreasing competitive effects as follows: P. annua > P. compressa (EU) > P. pratensis (EU) > P. compressa (NA). The most competitive grass species also experienced higher intraspecific competition. Within both grass genera, Eurasian species were more competitive against hoary cress than their North American congeners, which suggests that hoary cress establishment may be facilitated by lower biotic resistance in the invaded range. Regardless of origin, sod-forming Poa species were competitive at low densities, while Festuca species only had significant effects at high densities if at all. Based on our results we recommend the use of Poa species for restoration of riparian and disturbed sites following the control of hoary cress infestations to restrict recolonization. Nomenclature: Annual bluegrass, Poa annua L. POAAN; Canada bluegrass, Poa compressa L. POACO; hoary cress, Cardaria draba (L.) Desv. [ =  Lepidium draba L.] CADDR; Idaho fescue, Festuca idahoensis Elmer; Kentucky bluegrass, Poa pratensis L. POAPR; red fescue, Festuca rubra L. FESRU; rough fescue, Festuca campestris Rydb.; Sandberg bluegrass, Poa secunda J. Presl.; sheep fescue, Festuca ovina L. FESOV; tall fescue, Schedonorus phoenix (Scop.) Holub [ =  Festuca arundinacea Schreb.] FESAR Interpretive Summary: Hoary cress is an exotic clonal perennial mustard that invades disturbed rangeland and riparian areas in the western United States This study compared the competitive ability of 11 native and exotic grass species with regard to hoary cress in a greenhouse experiment that mimicked environmental conditions typically found at habitats highly suitable to hoary cress invasion (abundant nutrients and moisture). We used some of the grass species most commonly used in revegetation and found that three out of six Poa species tested decreased hoary cress plant biomass during its initial establishment phase, whereas only one of five Festuca species tested affected hoary cress growth. European grasses generally were more competitive than grasses of North American origin. The lower competitive ability of North American species suggests that there is a lower level of biotic resistance to hoary cress invasion in our native communities. We recommend planting of Poa species for restoration of nutrient-rich, riparian habitats, following chemical or mechanical control of hoary cress to limit recolonization of these susceptible habitats.

Cabbage seedpod weevil resistance in canola (Brassica Napus L.) yellow mustard (Sinapis alba L.) and canola × yellow mustard hybrids

Canola, yellow mustard and yellow mustard × canola hybrids were screened for resistance to Ceutorhynchus obstrictus (Marsham) in a series of greenhouse and laboratory choice tests. Tests were conducted using small and large cages designed to hold Brassica pods or whole plants, respectively, with ovipositing female C. obstrictus. Pods were examined for feeding punctures, eggs laid and exit holes that resulted from emerging larvae. All yellow mustard cultivars examined were highly resistant to C. obstrictus feeding and egg laying. In addition, hybrid lines were found with significantly reduced feeding punctures, oviposition, and exit holes compared with canola. A negative relationship was observed between total glucosinolate content of seed and C. obstrictus resistance; however, in both detached pod and whole plant choice tests, hybrids were identified with high seed glucosinolate content that were more susceptible than the most susceptible canola. The relatively poor association between total seed meal glu...