No description available.

No description available.

Thesis (M. Environmental Science))--North-West University, Potchefstroom Campus, 2007.

Commercial sugarcane in South Africa is a monoculture, and therefore lacks vegetation diversity, which is instrumental in increasing associated faunal diversity. Diverse habitats tend to support more stable populations of herbivorous and predacious animals. It is hypothesised that lack of this diversity in sugarcane was partially responsible for the existence of Eldana saccharina infestation levels that are higher than is commercially acceptable. Amongst the available E. saccharina control strategies, is habitat management. This has been developed with the view of increasing and enhancing predator foraging activity. Through increasing arthropod predator abundance and activity, it is believed that E. saccharina control may be enhanced. In this study, habitat diversity was increased through intercropping beans within sugarcane. Arthropod populations were monitored throughout the sugarcane-growing period, to determine what effect this intercropping had on known potential arthropod predator populations of E. saccharina. The study site was divided into two plots: the intercrop (beans planted within sugarcane rows: sugarcane-bean intercrop) and sole sugarcane: control plot. At monthly intervals, epigeal arthropods were sampled with pitfall traps, while foliage associated arthropods were sampled with a suction trap. Predator activity at the base of the sugarcane stalk, where E. saccharina lays its eggs was monitored with sticky traps. Sampling took place in the sugarcane-bean intercrop and control plots as well as in the roadway bordering the study site. Epigeal predator habitat preference was assessed by randomly placing pitfall traps in the sugarcane rows, bean rows, interrows between sugarcane rows, interrows between sugarcane and bean rows and the roadway. Corresponding with monthly trapping, an E. saccharina infestation and damage survey was conducted. Environmental factors such as weather, light intensity, plant (beans and sugarcane) phenology and weed density were measured, and their effect on E. saccharina potential arthropod predators examined. At harvest, sugarcane stalks were sampled for sucrose yield analysis. Potential E. saccharina predators that were captured included species of the orders and/or families Acarina, Blattidae, Formicidae (Pheidole megacephala and Dorylus helvolus) and Araneida (Lycosidae, Oxyopidae, Thomisidae and Salticidae). P. megacephala and species of Acarina were the only predators caught with all three trapping techniques, thus indicating that they occurred both on the ground and foliage. D. helvolus and Acarina were the only predators caught in significantly higher numbers in the intercrop, suggesting that increased habitat management had positively affected their population sizes. D. helvolus were captured both on the ground and length of sugarcane stalk, while species of Acarina were captured on the ground, foliage and at the base of sugarcane stalk, indicating that they forage at the base of the stalk, where E. saccharina activity is concentrated. Specific ground habitats preferred by D. helvolus included the sugarcane rows and bean rows, while Acarina preferred the interrows between sugarcane and bean rows. Despite the generally low E. saccharina infestation levels during this study, significantly higher levels of infestation occurred in the intercrop when compared to sole sugarcane. As expected with high infestation, higher (although not statistically significant) damage occurred in the intercrop. Surprisingly, sucrose yield and sugarcane stalk mass were slightly higher in the intercrop. The implications of the observations made during this study are discussed in the context E. saccharina management. / Thesis (M.Sc.)-University of Durban-Westville, 1998.

No description available.

Cruciferous crops comprise one of the major crop divisions and contribute significantly to global crop production. Insect pests associated with cruciferous crops have the potential to destroy harvests. The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) and cabbage aphids, Brevicoryne brassicae (L.) and Lipaphis erysimi (Kaltenbach) (Homoptera: Aphididae) are considered the most important cabbage pests in South Africa. Pest control in cabbage is still heavily reliant on use of insecticides even though insecticide application usually result in increased pest status of P. xylostella. Use of integrated pest management (IPM) strategies may yet prove invaluable as a means of suppressing the more serious cabbage pests. Global interest in cultural control strategies, that includes intercropping of unrelated crop plants, has been rekindled because of problems experienced with pesticide use. A study that involved the planting of two field trials with cabbage and carrot plants in different ratios, as a substitutive intercropping system, was undertaken during the 2002/03 and 2003/04 planting seasons. Field trials had five treatments viz. control (cabbage monoculture sprayed with mercaptothion), cabbage monoculture (without chemical application), 1:1 intercropping (cabbage:carrots), 1:3 intercropping and 1:5 intercropping, replicated six times in a randomized block design. Insects were sampled weekly by removing the third-youngest open leaf, from one plant per plot (six plants per treatment). Feeding damage to cabbage leaves was assessed visually by rating 14 plants per plot according to a numeric scale based on damage severity. P. xylostella and aphid parasitism levels were determined. Prominence values were calculated for P. xylostella larvae and aphids for each treatment per sampling date. P. xylostella infestations and parasitism levels were significantly (P ≤ 0.05) lower in control treatments. Intercropping ratio did not have a significant impact on pest infestations. P. xylostella infestations and parasitism on intercropping treatments did not differ significantly (P > 0.05) from that on monoculture plots (except for 1:5 intercropping during the 2003/04 season). Cotesia plutellae (Hymenoptera: Braconidae) was the dominant parasitoid and parasitism levels were significantly correlated with P. xylostella infestation levels. Prominence values showed a decline in P. xylostella infestations on intercropping treatments towards the last sampling date during both seasons. Feeding damage severity was lowest on the control treatment but similar for other treatments for both seasons. Aphid infestations were significantly (P ≤ 0.05) lower on the control treatment, but did not differ significantly between intercropping treatments. Aphid prominence values indicated possible suppression of infestations at low population levels during the early part of the season. Aphid parasitism was low during both seasons. It seems more likely that the reduction in insect infestation levels reported from the literature are related more to spatial arrangement of plants than cropping ratios. The observed suppression of aphid infestation levels on intercropped plots early in the season may be valuable in reducing the need for early chemical applications. The limiting of early insecticide application against aphids may result in a reduced pest status of P. xylostella, due to the conservation of C. plutellae populations. / Thesis (M. Environmental Science))--North-West University, Potchefstroom Campus, 2007.

Cruciferous crops comprise one of the major crop divisions and contribute significantly to global crop production. Insect pests associated with cruciferous crops have the potential to destroy harvests. The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) and cabbage aphids, Brevicoryne brassicae (L.) and Lipaphis erysimi (Kaltenbach) (Homoptera: Aphididae) are considered the most important cabbage pests in South Africa. Pest control in cabbage is still heavily reliant on use of insecticides even though insecticide application usually result in increased pest status of P. xylostella. Use of integrated pest management (IPM) strategies may yet prove invaluable as a means of suppressing the more serious cabbage pests. Global interest in cultural control strategies, that includes intercropping of unrelated crop plants, has been rekindled because of problems experienced with pesticide use. A study that involved the planting of two field trials with cabbage and carrot plants in different ratios, as a substitutive intercropping system, was undertaken during the 2002/03 and 2003/04 planting seasons. Field trials had five treatments viz. control (cabbage monoculture sprayed with mercaptothion), cabbage monoculture (without chemical application), 1:1 intercropping (cabbage:carrots), 1:3 intercropping and 1:5 intercropping, replicated six times in a randomized block design. Insects were sampled weekly by removing the third-youngest open leaf, from one plant per plot (six plants per treatment). Feeding damage to cabbage leaves was assessed visually by rating 14 plants per plot according to a numeric scale based on damage severity. P. xylostella and aphid parasitism levels were determined. Prominence values were calculated for P. xylostella larvae and aphids for each treatment per sampling date. P. xylostella infestations and parasitism levels were significantly (P ≤ 0.05) lower in control treatments. Intercropping ratio did not have a significant impact on pest infestations. P. xylostella infestations and parasitism on intercropping treatments did not differ significantly (P > 0.05) from that on monoculture plots (except for 1:5 intercropping during the 2003/04 season). Cotesia plutellae (Hymenoptera: Braconidae) was the dominant parasitoid and parasitism levels were significantly correlated with P. xylostella infestation levels. Prominence values showed a decline in P. xylostella infestations on intercropping treatments towards the last sampling date during both seasons. Feeding damage severity was lowest on the control treatment but similar for other treatments for both seasons. Aphid infestations were significantly (P ≤ 0.05) lower on the control treatment, but did not differ significantly between intercropping treatments. Aphid prominence values indicated possible suppression of infestations at low population levels during the early part of the season. Aphid parasitism was low during both seasons. It seems more likely that the reduction in insect infestation levels reported from the literature are related more to spatial arrangement of plants than cropping ratios. The observed suppression of aphid infestation levels on intercropped plots early in the season may be valuable in reducing the need for early chemical applications. The limiting of early insecticide application against aphids may result in a reduced pest status of P. xylostella, due to the conservation of C. plutellae populations. / Thesis (M. Environmental Science))--North-West University, Potchefstroom Campus, 2007.

The overall hypothesis of this research was that silage biomass and protein yields would be higher in corn-soybean intercrops than in monocrops on the same land area. Yields, European corn borer infestation and N transfer were tested over tall and dwarf corn hybrids, nodulating and nonnodulating soybean genotypes and at 0, 60 and 120 kg N ha$ sp{-1}$. Land Equivalent Ratios ranged from 0.97 to 1.23, but most were higher than 1.10. Protein concentrations of corn-soybean silage, up to 10.76%, were on average 9.24% vs. 7.41% in corn silage. A general trend of higher protein yield ha$ sp{-1}$ in intercrops compared to corn monocrops was significant in 1986. Corn-soybean intercrops at 60 kg N ha$ sp{-1}$ and three population densities were $132 to $261 ha$ sp{-1}$ more cost effective than monocropped tall corn at 120 kg N ha$ sp{-1}$. European corn borer infestation was reduced by intercropping and was higher at 120 kg N ha$ sp{-1}$ than at 60 or 0 kg N ha$ sp{-1}$. Under normal rainfall, dwarf corn had higher protein and yield levels when intercropped with nodulating rather than nonnodulating soybean. On N-depleted soil, N transfer was detected from nodulating soybean to nonnodulating soybean and to corn by the $ sp{15}$N dilution method, and to corn by direct $ sp{15}$N labelling of nodulating soybean.

An experiment was carried out at Redland Bay on the south-eastern coast of Queensland from (16/2/1991 to 27/6/1991) in an attempt to relate the performance of maize (Zea mays L.)/cowpea (Vigna unguiculata (L) Walp.) intercrops to radiation interception and to radiation availability to cowpea and to ascertain the effects of cowpea morphological characteristics. A quick maturing maize cultivar (DK529) and two cowpea cultivars (Red Caloona and 672330) were used. Changes in light availability to cowpea in intercrops were made by varying maize density. Three plant population densities were used: 22,000 plants ha^-1, 44,000 plants ha^-1, and 67,000 plants ha^-1. Both cowpea cultivars were very vegetative and vigorous in growth with little difference in their morphological characteristics. Cowpea cultivar 1 (Red Caloona) was however a better climber and retained green leaves for a longer duration. Increasing maize plant population density effectively reduced the amount of light reaching the cowpea canopy. Light availability was reduced to a minimum of 13% and 15% in the high maize plant population density and to a minimum of 47% and 42% in the low maize plant population density in cowpea cultivar 1 and 2 respectively. Intercropping reduced growth and yield of both cowpea cultivars through reductions in cowpea leaf area index (LAI), light interception and pod number. It also caused reductions in seed size in cowpea cultivar 2 (67233). Increasing maize plant population density further reduced all the above parameters. Maize growth and yield was affected by intercropping but to a lesser extent. Maize yields were reduced by 16% and 14% under cowpea cultivar 1 and cowpea cultivar 2 respectively, compared to an average reduction of 68% and 82% in cowpea cultivars 1 and 2 across the 3 maize plant population density. Radiation use efficiency (RUE) of the intercrops was lower than that of maize sole crop but higher than that of cowpea sole crop. Intercropping proved to be more advantageous in the vegetative stages of growth than in the reproductive stage except in the medium maize plant population density treatment. This was attributed to better light use efficiency in the early growth in intercrops than sole crops which was estimated to be between 1.1 and 2.9 time higher in intercrops than in sole maize in the first 20 days after sowing (DAMS) . Results indicated that LAI and leaf longevity had a large effect on radiation interception and use in cowpea. Cowpea cultivar 2 was better yielding in sole crop that cowpea cultivar 1 (954 Vs 621 Kgha^-1) but was more affected by intercrop (157 Vs Kgha^-1). An advantage of intercropping was only obtained in the medium maize plant population density intercrops. These were however small advantages (13% and 11%) in cowpea cultivar 2 and cultivar 1 respectively. Intercropping maize with these two cowpea cultivars would therefore be of advantage only, where the interest of the farmer is in the production of maize grain and cowpea leaf, wither for consumption, livestock feed or as green manure.

An experiment was carried out at Redland Bay on the south-eastern coast of Queensland from (16/2/1991 to 27/6/1991) in an attempt to relate the performance of maize (Zea mays L.)/cowpea (Vigna unguiculata (L) Walp.) intercrops to radiation interception and to radiation availability to cowpea and to ascertain the effects of cowpea morphological characteristics. A quick maturing maize cultivar (DK529) and two cowpea cultivars (Red Caloona and 672330) were used. Changes in light availability to cowpea in intercrops were made by varying maize density. Three plant population densities were used: 22,000 plants ha^-1, 44,000 plants ha^-1, and 67,000 plants ha^-1. Both cowpea cultivars were very vegetative and vigorous in growth with little difference in their morphological characteristics. Cowpea cultivar 1 (Red Caloona) was however a better climber and retained green leaves for a longer duration. Increasing maize plant population density effectively reduced the amount of light reaching the cowpea canopy. Light availability was reduced to a minimum of 13% and 15% in the high maize plant population density and to a minimum of 47% and 42% in the low maize plant population density in cowpea cultivar 1 and 2 respectively. Intercropping reduced growth and yield of both cowpea cultivars through reductions in cowpea leaf area index (LAI), light interception and pod number. It also caused reductions in seed size in cowpea cultivar 2 (67233). Increasing maize plant population density further reduced all the above parameters. Maize growth and yield was affected by intercropping but to a lesser extent. Maize yields were reduced by 16% and 14% under cowpea cultivar 1 and cowpea cultivar 2 respectively, compared to an average reduction of 68% and 82% in cowpea cultivars 1 and 2 across the 3 maize plant population density. Radiation use efficiency (RUE) of the intercrops was lower than that of maize sole crop but higher than that of cowpea sole crop. Intercropping proved to be more advantageous in the vegetative stages of growth than in the reproductive stage except in the medium maize plant population density treatment. This was attributed to better light use efficiency in the early growth in intercrops than sole crops which was estimated to be between 1.1 and 2.9 time higher in intercrops than in sole maize in the first 20 days after sowing (DAMS) . Results indicated that LAI and leaf longevity had a large effect on radiation interception and use in cowpea. Cowpea cultivar 2 was better yielding in sole crop that cowpea cultivar 1 (954 Vs 621 Kgha^-1) but was more affected by intercrop (157 Vs Kgha^-1). An advantage of intercropping was only obtained in the medium maize plant population density intercrops. These were however small advantages (13% and 11%) in cowpea cultivar 2 and cultivar 1 respectively. Intercropping maize with these two cowpea cultivars would therefore be of advantage only, where the interest of the farmer is in the production of maize grain and cowpea leaf, wither for consumption, livestock feed or as green manure.