Onion production in the United States is seriously affected by the tospovirus Iris Yellow Spot (IYSV), whose symptoms include lenticular-shaped lesions that reduce photosynthesis and bulb yield. Thrips tabacai Lindeman, onion thrips (OT), is the only known vector of the disease and a primary arthropod pest of onion. Frequent insecticide applications, increasing resistance in OT populations to insecticides, high nitrogen (N) fertilization rates and loss of yield to disease and insect pressure threaten sustainable onion production. The objectives of this study were to identify crop management strategies to enhance onion productivity while suppressing OT and IYSV. Three fertilizer rates and two crop rotations were assigned to replicated plots to assess effects on onion growth, yield, bulb storage quality, soil quality, thrips populations and IYSV incidence. Trap crops of carrot, buckwheat and lacey phacelia were established in commercial fields to evaluate impact on thrips populations and IYSV occurence. Reduced nitrogen (N) rates, one-third the standard grower rate (133.8 kg N ha-1), resulted in no yield loss as compared with the standard N rate, despite slower crop maturation. Onions treated with a standard N rate(401.8 kg N ha-1) had greater numbers of adult and immature OT than other treatments. Soil nitrate levels were lower and microbial activity measured as dehydrogenase and biomass were greater in reduced N treatments. Plots with buckwheat and phacelia had greater numbers of both adult and immature OT when trap crop apparancy was high (i.e. when onion plants were relatively smaller). There was no observed effect of trap crops on IYSV levels. Results suggest that reduced rate N applications lower numbers of OT while enhancing the microbial population, reducing potential for nitrate leaching while still maintaining yields. Potential for trap crops of buckwheat and lacey phacelia to attract onion thrips from onions exists with successive stands of highly apparent trap crops.

Trap crops were evaluated for harlequin bug control in broccoli field plots in 1994 and 1995. Mustard and rape prevented low densities of harlequin bug from reaching broccoli, but at high densities the insect moved from the trap plants into the broccoli. This indicates that harlequin bugs that are attracted to trap plants may damage the protected broccoli if their numbers are not prevented from increasing. Harlequin bugs were shown to have two and a partial third generation a year. Trissolcus murgantiae Ashmead and Ooencyrtus johnsoni Howard, were identified as egg parasitoids. Their combined parasitization levels for the two years were 8% and 37%. T. murgantiae accounted for 87% and 96% of the parasitization, respectively.. When 19.6 cm and 11.9 cm broccoli plants were exposed to five densities of harlequin bug adults a negative correlation between plant mortality and insect density was observed (y = 38.00 - 2.32x, r2 = 0.95 and y = 22.17 - 1.17x, r2 = 0.99, respectively). No correlation was observed in broccoli plants 11.9 tall.. Host plants affected harlequin bug development. Nymphs developed faster when reared on rape in comparison with mustard. The preoviposition time for rape reared nymphs was shorter than mustard reared insects. Fecundity and viability of eggs were not different for harlequin bugs reared at different sex ratios. / Master of Science

Four trap crops were tested for their ability to intercept stinkbugs (Heteroptera pentatomidae) in a cucurbit field crop at Waterpoort, Limpopo Province. The experimental trap crops were: Sunnhemp (Crotolaria juncea), okra (Abelmoschus esculentum), mustard mixture (Brassica hirta and Brassica juncea) and cowpea (Vigna unguiculata). The surveys were based on visual counts of stinkbugs from all the trap crops. Stinkbugs were collected from trap crops in a field crop trial of cantaloupe (Cucumis melo). The correlation between Brassica hirta and Brassica juncea with other trap crops had a great variance. The repeated B. hirta and B. juncea inner row experiment in 2012 interestingly lured the green stinkbug (Nezara viridula) into the cantaloupe field. Amongst the entire trap crops, stinkbugs recovered from Brassica hirta and Bassica juncea, exceeded the average of the other three trap crops. The number of adult N. viridula captured had significantly increased in March 2012 and started to drop on the B. hirta and B. juncea mixture in the first week of April. During this increase, the crops were at the seeding stage. The perimeter trap-cropping system practiced for all four trap crops varied in the attraction of stinkbugs along the perimeter of the field and inner row. B. hirta and B. juncea attracted a high number of N. viridula along the perimeter but fewer in the inner row. The B. hirta and B. juncea recorded the highest number of N. viridula in the inner rows and outer rows, compared to the other four trap crops, followed by V. ungiuculata. This study has demonstrated a significant potential of using trap crops as biological alternative for managing stinkbug pests in cucurbit crops. / Agriculture and  Animal Health / M. Sc. (Agriculture)

Four trap crops were tested for their ability to intercept stinkbugs (Heteroptera pentatomidae) in a cucurbit field crop at Waterpoort, Limpopo Province. The experimental trap crops were: Sunnhemp (Crotolaria juncea), okra (Abelmoschus esculentum), mustard mixture (Brassica hirta and Brassica juncea) and cowpea (Vigna unguiculata). The surveys were based on visual counts of stinkbugs from all the trap crops. Stinkbugs were collected from trap crops in a field crop trial of cantaloupe (Cucumis melo). The correlation between Brassica hirta and Brassica juncea with other trap crops had a great variance. The repeated B. hirta and B. juncea inner row experiment in 2012 interestingly lured the green stinkbug (Nezara viridula) into the cantaloupe field. Amongst the entire trap crops, stinkbugs recovered from Brassica hirta and Bassica juncea, exceeded the average of the other three trap crops. The number of adult N. viridula captured had significantly increased in March 2012 and started to drop on the B. hirta and B. juncea mixture in the first week of April. During this increase, the crops were at the seeding stage. The perimeter trap-cropping system practiced for all four trap crops varied in the attraction of stinkbugs along the perimeter of the field and inner row. B. hirta and B. juncea attracted a high number of N. viridula along the perimeter but fewer in the inner row. The B. hirta and B. juncea recorded the highest number of N. viridula in the inner rows and outer rows, compared to the other four trap crops, followed by V. ungiuculata. This study has demonstrated a significant potential of using trap crops as biological alternative for managing stinkbug pests in cucurbit crops. / Agriculture and  Animal Health / M. Sc. (Agriculture)

Department of Ecology and Resource Management / PhDENV / The main aim of the research was to contribute means for converting conventional, high-input production systems to more sustainable ecological systems, thereby improving the sustainability of macadamia production and ultimately contributing to food security. This was achieved by a) investigating the potential use of cover crops and compost to enhance soil quality in macadamia orchards and b) investigating the potential use of use of cover crops and orchard heterogeneity to control stinkbug pests that target macadamia crops. Field experiments were conducted in three phases: phase one tested the potential of six cover crops for crop protection (as trap crops) and simultaneously for soil restoration or fertility enhancement purposes in macadamia orchards. Phase two repeated the trials of phase one (both soil restoration and trap crops) but with modifications to both categories. Soil restoration treatments were conducted with trees which were growing in what appeared to be healthy soils, and then repeated with trees in the same orchard where the topsoil had been degraded (totally removed) by agricultural operations. The third phase repeated the trap crop trials only, but this time on three different study areas (all commercial farms) with the single cover crop which performed the best as a trap crop during phase two. Trials were modified from the first to the last phase to overcome practical implementation problems encountered along the way and to adapt to local conditions experienced in the commercial macadamia farming systems which served as research sites. Diversity of natural orchard vegetation was enhanced in phase three to improve conditions for natural predators as part of the trap crop treatments in the last phase and cover crops were finally first composted and then returned to the root zones of the macadamia trees as part of the soil quality enhancement treatments in the second phase. The results from the trap crop trials shows a significant effect of trap crops combined with increased orchard diversity in reducing unsound kernel percentages caused by stinkbug pests and demonstrate that trap crops combined with an increase in orchard diversity could be utilized in macadamia orchards as a more sustainable alternative to inorganic pesticides against the stinkbug complex. The most notable changes in the soil that took place with soil quality enhancement treatments were the significant increases in soil phosphorous content and pH which resulted not in an improvement in soil quality in terms of these two indicators but revealed an important issue about the use of compost containing animal manure originating from dairies or feedlots. In summary however, it was clear that although not all the soil quality indicators that were employed to assess changes in the soil with compost treatments improved significantly, a holistic consideration of all indicators portrays an overall improvement which was particularly significant in the degraded soil plots where the topsoil had been removed by prior agricultural activities. / NRF