Onions treated at the 2-leaf stage of growth with the 3rd leaf just beginning to emerge with postemergence herbicides bromoxynil (Buctril®) and oxyfluorfen (Goal®) exhibited slight injury at 11 days after treatment (DAT) but had recovered to show no injury at 1 month after treatment (MAT). Annual yellow sweetclover (Melilotus officinalis) was the predominat weed in the test site and early ratings showed that Goal at 0.25 lb a.i. /A and Goal plus Buctril gave marginally acceptable control at 80 %. Buctril alone did not control clover. At 1 MAT, the clovers had recovered from the initial injury and the level of control had declined to become unacceptable.

Thesis (M. Sc.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references (leaves 115-130). Also available via the World Wide Web.

Thesis (MTech (Agriculture))--Cape Technikon, 2001. / Onion seeds (cultivar Caledon Globe), and soil into which the seedlings were planted, were treated with various adjuvants including fungicides, a seed disinfectant and a soil sterilant, as well as soil-applied growth stimulants to determine the effect of these on germination of seed, the growth of plants and the storage life of onions obtained. Three sets of germination trials were undertaken in petri dishes, and sets of seed was also sown in deep seed trays. A trial planting was made and the crop graded and stored. Seed was also sown in pots in soil obtained from a commercial undertaking where poor germination had been obtained. A portion of this soil was pasteurised and a portion inoculated with Fusarium spp. Growth of these seedlings was then followed by re-sowing in the same pots using seed of additional cultivars.

Using a micro-potometric method, it was ,found that X-irradiation (400 R - 18 Kr) of the shoots of the onion plant Allium cepa will produce an immediate, pronounced (200%) and reversible enhancement of the water uptake by the shielded roots. Unfiltered X-irradiation.(1200 R/min., 120 KVP, 5 ma) was delivered at right angles to the shoot. Readings were taken at 10-minute intervals before, and immediately following X-irradiation. The greatest enhancement occurred at dosages between 4.8 Kr (150%) and 6.0 Kr (190%). The data indicate that the irradiation effect on water uptake was a physical rather than a metabolic one.

Difficulties in pollen transfer have adversely affected seed production of hybrid onion (Allium cepa L.) in the United States. Six onion cultivars were examined for differential attractiveness to the honey bee (Apis mellifera L.). Honey bees clearly discriminated between the onion cultivars in both open plots and caged plots. Nectar secretion, nectar sugar concentration, nectar sugar composition, mectar potassium content, and flower phenology were correlated with honey bee visitation. Nectar secretion rates ranged from 0.54 to 0.84 ul per floret per day. Onion cultivars also demonstrated differential flowering potential. The cultivars produced from 176 to 359 flowers per umbel with 32 to 74 umbels per 30 onions. All onion cultivars examinaed contained viscous nectar with sugar concentrations ranging from 51 to 65% of total dissolved solids. Onion nectar was analyzed by gas chromatography to determine qualitative sugar differences among onion cultivars. All cultivars were hexose dominant with an approximately 1:1 fructose:glucose ratio. However, fructose was slightly more abundant than glucose. Sucrose was much less abundant than the hexose sugars. Atomic absorption spectrophotometry revealed little difference in potassium content among the A. cepa cultivars. Nectar potassium levels ranged from 5,300 ppm to 6,900 ppm. Cultivars with higher nectar potassium levels had fewer honey bee visits. Two honey bee bioassays were conducted. The first bioassay simulated the sugar and potassium composition of each onion cultivar. The honey bees selectively foraged on simulated nectars with low potassium and high sugar concentrations. The second bioassay was designed to test honey bee response to "phenolic-rich" solutions. The natural compounds tested were dilutions of salt cedar (Tamarix pentandra Pall.) honey, almond (Prunus dulcis Mill.) honey, and aloe (Aloe littoralis L.) nectar. The pure synthetic compounds tested were caffeic acid and genestic acid. Generally, honey bees foraged preferentially on the lower phenolic concentrations, indicating that compounds high in phenolic composition inhibit honey bee foraging. Finally, seed yields of each of the cultivars were compared. Wide variations in yields were correlated with honey bee visitation, sugar composition, potassium levels, and flower phenology.

No description available.

Very high infestation levels of Thrips tabaci Lindeman were observed on onions at Ste-Clotilde (Quebec) with seasonal means of 149 and 161 thrips/plant for 1988 and 1989 respectively. No significant differences in thrips densities were detected among six yellow onion cultivars (Capable, Flame, Norstar, Progress, Rocket, Taurus) through weekly comparisons in 1988 and biweekly comparisons in 1989. / A new variable, the cumulative number of thrips-days/plant, was used to model the impact of T. tabaci on onion yields. This variable allowed for better-fitted models, especially in 1989 where greater variability of the onion yields was observed. A modified Gompertz equation gave the best fit for 1988. No yield reduction due to T. tabaci was observed up to the 1000 cumulative thrips-days/plant point, beyond which the thrips impact first increased with the feeding pressure and then gradually decreased to a minimal level corresponding to a yield loss of 43%. In 1989, thrips impact was immediate and best described by an exponential model with a maximal yield loss of 34,5%. / Economic thresholds of 964 and 251 cumulative thrips-days/plant were calculated for 1988 and 1989 respectively. Converted to thrips/leaf these correspond to 2,2 and 0,9 thrips/leaf. This conversion could facilitate their use in a field situation. / Spatial distribution of T. tabaci was analyzed in ten commercial onion fields. Within field, density was homogeneous in the majority of cases. In some fields, higher thrips densities were temporary (two consecutive weeks at most) in one or two field margins. / The Iwao method was used to calculate the acceptance boundaries of sequential sampling plans for the economic thresholds of 0,9 and 2,2 thrips/leaf and onion growth stages of 6, 7, 8, 9 and 10 green leaves. (Abstract shortened by UMI.)

Two fungi that cause disease on onion in the Mid Murray region of South Australia were investigated. These were Fusarium oxysporum f. sp. cepae, the cause of damping off of seedlings, wilting in the field, and basal rot in storage, and Phoma terrestris, which causes pink root. The aim of the study was to investigate resistant or tolerant cultivars and crop rotations as possible management strategies for these diseases. Several Fusarium spp. were isolated from onion roots and bulbs in the field, onion bulbs in storage, soil, and onion seed. All isolates were tested for pathogenicity by various means, however, none caused disease and therefore could not be identified conclusively as F. oxysporum f. sp. cepae. As a result research on Fusarium was discontinued. Pink discolouration was detected on onion roots in commercial crops at Bowhill, South Australia, and isolation of P. terrestris from roots was attempted. Several published and novel methods were employed with variable success. Only one of the published methods yielded P. terrestris, but results were inconsistent. Two methods developed in this study permitted isolation of P. terrestris. In both cases, infested plant material was incubated on wheat straw agar (WSA), which turns pink in the presence of P. terrestris. One method involved soaking surface sterilised pink-pigmented wheat straw in solution, at approximately 24ºC for 2 days, and then spreading 1 ml of the resulting suspension on acidified potato dextrose agar (APDA) and incubating for a further 7 to 10 days. The second method involved dispensing warm sterile water into a plate of pink-pigmented WSA, agitating the plate, and spreading 1 ml aliquots onto APDA, and incubating for 7 to 10 days. One isolate of P. terrestris, shown to be pathogenic to onion was used in subsequent experiments. Several brown onion cultivars commonly grown in the Mid Murray region of South Australia, or marketed as tolerant to pink root, were examined for susceptibility to infection by P. terrestris. Seven cultivars were tested in vitro, and seedlings of eight cultivars were grown in a greenhouse for 4 months in soil naturally infested with P. terrestris. Selected cultivars were also evaluated in the field. Of the cultivars tested, none was significantly less susceptible to infection by P. terrestris than any other as indicated by pink pigment on WSA. Cereals such as wheat, oat and barley, as well as lucerne and canola, are grown in rotation with onion to provide ground cover, to minimise soil erosion and reduce inoculum of pathogens between onion crops. As the susceptibility of these rotation crops to P. terrestris was not known, several were tested in the field and in the greenhouse for their ability to act as hosts for P. terrestris. Likewise, the potential of weeds commonly found in onion fields to act as hosts of P. terrestris was investigated. Less P. terrestris was detected in the roots of plants of oat cultivars Marloo and Swan, as well as barley cultivars Galleon and Schooner than of most other crops tested and, thus, these cvs were considered less likely to act as hosts of P. terrestris. Weeds such as Brassica tournefortii, Portulaca oleracea and Oxalis pes-caprae collected from the field were infected by P. terrestris, whereas P. terrestris was not detected in the roots of Chenopodium album. In summary, new methods for isolation of P. terrestris were identified and may, with further development, aid in research on pink root. The onion cultivars tested in this study did not differ in susceptibility to pink root, but more cultivars should be tested. P. terrestris infected a range of other crops and weeds, and it is recommended that further work is conducted in this area to facilitate cultural management of onion crops to minimise build up of inoculum in the soil. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1473377 / Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 2009

Thesis (Ph. D.)--University of Wisconsin--Madison, 1928. / Typescript. With this is bound: Purple blotch of onion (Macrosporium porri Ell.), [by] H.R. Angell, reprinted from Journal of Agricultural research, v. 38, no. 9 (May 1, 1929), p. 467-487. Includes bibliographical references ([4] leaves after numbered leaves).

No description available.