Book Review: Pesticides in Zimbabwe: Toxicology and health implications

Book Title: Pesticides in Zimbabwe: Toxicology and health implicationsBook Authors: C.F.B. Nhachi & Ossy M. KasiloUniversity of Zimbabwe Publications, 115 pp. ISBN: 0-908307-49-

Competition of Soybean with Blackjack ( Bidens pilosa L.) and Pigweed ( Amaranthus hybridus L.)

Field studies were conducted to evaluate competitiveness between blackjack or pigweed and soybean using replacement series. Plant height of the three species was not affected by interspecific competition. Branching was reduced in soybean at 75 days after plant emergence (DPE), but increased in the weed species. Soybean, blackjack and pigweed shoot dry weight was reduced in most mixtures. The weed species had higher relative growth rate (RGR) and leaf area index (LAI) than soybean. The highest LAI occurred in monoculture pigweed. Competitive ration (CR) values showed that pigweed was the most competitive of the three species. Soybean pod number per plant, 1000 seed weight and grain yield per plant were significantly less in mixtures with the two weed species. Pigweed caused more reduction in soybean yield components than blackjacks. The number of blackjack seeds per head, seed heads per branch and seeds per plant were significantly reduced in mixtures while seed production by pigweed in mixture increased by 30 to 253%. It is concluded that both weed species reduce soybean vegetative growth except for height and components of yield

Competition of Soybean with Blackjack ( Bidens pilosa L.) and Pigweed ( Amaranthus hybridus L.)

Field studies were conducted to evaluate competitiveness between blackjack or pigweed and soybean using replacement series. Plant height of the three species was not affected by interspecific competition. Branching was reduced in soybean at 75 days after plant emergence (DPE), but increased in the weed species. Soybean, blackjack and pigweed shoot dry weight was reduced in most mixtures. The weed species had higher relative growth rate (RGR) and leaf area index (LAI) than soybean. The highest LAI occurred in monoculture pigweed. Competitive ration (CR) values showed that pigweed was the most competitive of the three species. Soybean pod number per plant, 1000 seed weight and grain yield per plant were significantly less in mixtures with the two weed species. Pigweed caused more reduction in soybean yield components than blackjacks. The number of blackjack seeds per head, seed heads per branch and seeds per plant were significantly reduced in mixtures while seed production by pigweed in mixture increased by 30 to 253%. It is concluded that both weed species reduce soybean vegetative growth except for height and components of yield

Response of Short Season Maize Cultivars to Striga Infestation

A glasshouse experiment was conducted to assess tolerance/resistance of five short season maize cultivars namely, CG4141, CG4538, CG4585, PHB3427 and PHB3435 to Striga ( Striga asiatica (L.) Kuntze) infestation. Striga infested all cultivars but to different levels. Maize ( Zea mays ) height and diameter were only suppressed in cv CH4141. Shoot fresh and dry weights were suppressed in all other infested cultivars except PHB3427. All cultivars but PHB3427 and CG4538 were very susceptible with CG4141 suffering the greatest reductions in most parameters. Striga emerged 12 to 17 days earlier in PHB3435 and CG4141 than in PHB3435 and more plants emerged from CG4141 and CG4538. Striga plants supported by CG4141 and PHB3435 flowered earlier than others. The number of capsules in Striga was lowest in plants which emerged on CG4585 while no capsules were formed on plants growing on PHB3427. Generally, CG cultivars were more susceptible than PHBs. Farmers are recommended to grow cultivars PHB3427 and CG4585 which were relatively more resilient to the weed

The effect of undersowing euca!yptus (Euca/ypfus Camaldulensis L.) with maize (Zea mays L) and cowpeas (Vigna unguiculata L.) on tree growth and crop performance

A journal article on the effect of undersowing Euca!yptus with maize and cow-peas on tree growth and crop performance in Zimbabwe's agricultural sector..Maize (Zea mays L.) hybrid R201 and cowpea (Vigna unguiculata L.) variety IT82D- 875 were separately inter-row interplanted with gum-tree (Eucalyptus camaldulensis L.) during the 1995-96 cropping season at Domboshava Training Centre. Planting E. camaldulensis with cowpeas and maize had no marked effect on the yields of the two annual crops. Sole clean-weeded E. camaldulensis had significantly thicker circumference than the Eucalyptus in the other treatments, but was comparable to Eucalyptus interplanted with the annual crops in terms of branching habit. However, E. camaldulensis interplanted with maize showed a slightly higher performance (branching and circumference) than that interplanted with cowpeas. This was probably related to the fertilizer added to the maize/£. camaldulensis intercrop since no fertilizer was added to the cowpea/£. camaldulensis intercrop. Management factors such as clean weeding in sole Eucalyptus markedly increased tree performance as observed through parameters of stem circumference and branching compared to those of the unweeded sole Eucalyptus situation. Neither tree branching pattern, height growth nor soil moisture were significantly affected by intercropping with annual crops. Undersowing annual crops to E. camaldulensis will facilitate maximum utilization of land and light in the early years of E. camaldulensis woodlot establishment. This approach will also allow better tree growth when compared to the unweeded situation which is common in small-holder farming

Response of Short Season Maize Cultivars to Striga Infestation

A glasshouse experiment was conducted to assess tolerance/resistance of five short season maize cultivars namely, CG4141, CG4538, CG4585, PHB3427 and PHB3435 to Striga ( Striga asiatica (L.) Kuntze) infestation. Striga infested all cultivars but to different levels. Maize ( Zea mays ) height and diameter were only suppressed in cv CH4141. Shoot fresh and dry weights were suppressed in all other infested cultivars except PHB3427. All cultivars but PHB3427 and CG4538 were very susceptible with CG4141 suffering the greatest reductions in most parameters. Striga emerged 12 to 17 days earlier in PHB3435 and CG4141 than in PHB3435 and more plants emerged from CG4141 and CG4538. Striga plants supported by CG4141 and PHB3435 flowered earlier than others. The number of capsules in Striga was lowest in plants which emerged on CG4585 while no capsules were formed on plants growing on PHB3427. Generally, CG cultivars were more susceptible than PHBs. Farmers are recommended to grow cultivars PHB3427 and CG4585 which were relatively more resilient to the weed

Upright Starbur Weed Competition with Soybean

The effect of upright starbur (Acanthospermum hispidum DC) time of emergence and duration on its competition with soybean (Glycine max (L.) was studied under field conditions during the 1991/92 and 1992/93 rainy season at Chegutu in Zimbabwe on a Rhodic Nitisols. Soybean grain yield under weedfare conditions was 3.6 t ha-1, but full season competition from the weed reduced soybean grain yield by 1.84 t ha-1 and extended the flowering period by 30 days. Upright starbur that emerged 2-3 weeks after soybean emergence delayed flowering by 14 days. Competition from soybean reduced upright starbur growth, stem diameter by 2.4 to 4.8 mm and seed yield by 910-960 kg ha-1. Flowering and seed set in upright starbur was delayed by 14 days when the plants emerged 2 and 3 weeks after soybean emergence. Upright starbur plants which emerged with soybean and competed for the full season reduced growth and grain yield of the crop. Upright starbur plants that emerged 2 and 3 weeks later were less competitive and produced fewer seeds.L'effet du temps de germination de l'Acanthospermum hispidum DC et de sa duree de competition avec le soja (Glycine max (L.) etait etudie en champ au cours des saisons de pluies 1991/92 et 1992/93 a Chegutu au Zimbabwe sur un nitisol rhodique ayant un pH de 6,5. Le rendement de soja-graines en champ sarclee etait de 3,6 t/ha, mais sa culture non sarclee pendant route la saison reduisait la croissance du soja et son rendement en graines a 1,84 t/ha tout en prolongeant sa periode de floraison a 30 jours. L'Acanthospermum hispidum qui levait 2 a 3 semaines apres le soja, retardait sa floraison de 14 jour. La competition du soja reduisait la croissance de l'Acanthospermum, son diametre de tige par 2,4 a 4,8 mm et son rendement en grains de 910 a 960 kg/ha. La floraison et formation de semences de l'Acanthospermum etaient retardees de 14 jours lorsque les plants levaient 2 a 3 semaines apres le soja. L'Acanthospermum qui levait avec le soja et entrait en competition pour toute la saison, reduisait la croissance et le rendement en graines de la culture de la culture. Les plants de l'Acanthospermum qui levaient 2 a 3 semaines plus tard etaient moins competitifs et produisaient peu de semences

The Effect of 2,4-D, Dicamba and Hand Weeding on Witchweed Density and Maize Yield

An on-farm experiment was conducted in Chinyika resettlement area during the 1994/95 and 1995/96 rainy seasons to determine the effects of 2,4-D, dicamba and hand weeding on Striga asiatica density and maize grain yield. Three sites were established during the 1994/95 season while an extra site was added during the 1995/96 season. Dicamba suppressed S. asiatica more than the other treatments at 8 and 10 weeks after crop emergence (wace) while 2,4-D was as effective as dicamba at 12 wace. In a drier season like the 1994/95, handweeding two times was more economic than applying the herbicides. Dicamba gave a marginal rate of return of 91% over 2,4-D during the wetter 1995/96 season. When the data were combined over sites, maize grain yields were lower in plots treated with dicamba and highest in plots hand weeded at 2 and 5 wace during the 1994/95 season. However, maize grain yields were similar in all the weeding treatments during the 1995/96 season.Un essai en milieu r\ue9el a \ue9t\ue9 conduit dans la zone de repeuplement de Chinyika pendant les saisons pluvieuses de 1994/95 et 1995/96 pour d\ue9terminer des effets de 2, 4D, dicamba et du sarclage \ue0 la main sur la densit\ue9 de Striga asiatica et du rendement du ma\uefs. Les sites ont \ue9t\ue9 \ue9tablis durant la saison 1994/95 et des sites additionnels ont \ue9t\ue9 \ue9tablis pendant la saison 95/96. Dicamba a supprim\ue9 le Striga asiatica plus que d\u2019autres traitement \ue0 8 et 10 semaines apr\ue8s \ue9mergence (SAE) alors que 2, D-D a \ue9t\ue9 efficace comme dicamba \ue0 12 SAE. Pendant la saison s\ue8che de 1994/95, le sarclage \ue0 la main a \ue9t\ue9 plus \ue9conomique plus que l\u2019application des herbicides. Dicamba a donn\ue9 un revenu marginal de 91% plus que 2, 4-D pendant la saison pluvieuse de 1995/96. Quand les donn\ue9es des sites ont \ue9t\ue9 combin\ue9es, le rendement en grains du ma\uefs a \ue9t\ue9 bas dans les parcelles trait\ue9es au dicamba, plus \ue9lev\ue9 dans les parcelles sarcl\ue9es \ue0 la main \ue0 2 et 5 SAE en saison 94/95. Cependant les rendements du ma\uefs ont \ue9t\ue9 les m\ueames dans les traitements au sarchage pendant la saison 95/96