Mosaic Virus and Leaf Curl Diseases of Okra in Nigeria

Abstract

The etiology and incidence of okra leaf curl and okra mosaic virus diseases observed in Nigeria are reviewed and the difficulty in evolving a control measure for these two diseases is discussed.     

Seasonality of Eurytoma sp.—a parasitoid on okra petiole maggot,Melanagromyza hibisci Spencer

Abstract

Studies on the seasonal abundance of Eurytoma sp. a parasitoid on okra petiole maggot, Melanagromyza hibisci Spencer were conducted for one year. Per cent parasitism ranged from 10 to 68 during the study period. However, there was no significant relationship between percentage parasitism on host density. Data further revealed that parasitoid response to host density was weak.     

Insect Pests of Cotton – Western Herbaceum Region of India

Abstract

Pre-plant and pre-emergence herbicides were tested for effective weed control in a seed crop of okra during 1974–75 and 1975–76. All treatments significantly decreased the weed population and increased the seed yield as compared to the unweeded control. Fluchloralin (0.90 and 1.20 kg a.i./ha pre-plant), alachlor (2.50 kg a.i./ha pre-em) and EPTC plus alachlor (3.75 kg a.i./ha pre-plant and 1.25 kg a.i./ha pre-em) proved to be the most effective and economical treatments. No residual effects were observed with any herbicide on the succeeding crops of radish, carrot, turnips, peas and spinach.     

The floating islands of Rawa Pening

Abstract

The resistance in okra (Abelmoschus esculentus (L) Moench varieties to the leafhopper, Amrasca devastans (Dist.) is governed by nonpreference and antibiosis mechanisms. The variety A.E. 22 was less preferred for oviposition and feeding compared to the susceptible variety Pusa Sawani. The rate of multiplication of the insects on the resistant variety was low compared to the susceptible variety.     

Detection of Ceratitis capitata Wiedemann (Diptera: Tephritidae) using trimedlure versus enriched ginger oil in citrus orchards

Abstract

Successful fruit fly control requires effective monitoring to make pest management decisions. Ceratitis capitata (Medfly) is typically monitored in Tunisia with parapheromone commercialised as trimedlure (TM). Chemical treatment is applied when the economic threshold (3 flies/trap/day) is reached. In this study, C. capitata populations in a commercial citrus orchard captured in McPhail traps baited with TM or enriched ginger oil (EGO) were compared over two seasons (2011 and 2012). Females of C. capitata were not attracted to TM or EGO. Trimedlure was significantly more attractive to C. capitata males than EGO under low and high population densities over sampling dates. The TM used in McPhail traps was adequate to attract male medflies in citrus orchards under a wide range of Medfly population levels. The use of the best attractant can help to make control decisions when population levels of flies are low, thus preventing unnecessary application of insecticides and/or other control methods.     

Promising herbicides for weed control in chickpea

Abstract

Chickpea suffers severe competition due to Chenopodium album L. infestation. Two to three hoeings are generally given to check C. album but increasing labour costs and scarcity of farm labour make the manual weeding difficult. Usage of herbicides appears to be a logical solution. Pre‐emergence applications of pendimethalin or ametryn alone at 1.5 kg ai ha^?1 or one handweeding at 35–40 days after seeding following either 1 kg ai ha^?1 of pendimethalin, ametryn or fluchloralin or metribuzin at 0.3 kg ai ha^?1 applied pre‐emergence gave effective control of C. album and seed yields similar to clean‐weeded chickpeas. There was an 84% reduction in seed yield of chickpea without weeding.     

Control of Spodoptera litura and Scrobipalpa heliopa in Nursery Tobacco

Abstract

Endosulfan and trichlorphon at 0.03% and 0.06%; carbaryl (0.05% and 0.1%) and methomyl (0.025% and 0.05%) were used as treatments to control Spodoptera litura and, with and without sticker, Scrobipalpa heliopa in nursery tobacco. Four treatments were applied; 14, 24, 34 and 44 days after germination. Carbaryl and trichlorphon gave the most effective control of Spodoptera litura and endosulfan was the only effective treatment for Scrobipalpa heliopa.     

Conservation tillage systems for sorghum production under semi‐arid conditions in India

Abstract

Field research was conducted near Hyderabad, India, during 1981 and 1982 to investigate zero‐tillage and reduced‐tillage systems for production of sorghum (Sorghum bicolor (L.) Moench.) under semi‐arid tropical conditions. Part of the investigation compared post‐seeding hand weeding and herbicide treatments for weed control efficacy. The results showed that shallow pre‐seeding tillage was just as effective as deep cultivations in producing high sorghum fodder and grain yields provided weeds were controlled after crop emergence. Both tillage regimes were more effective than a no tillage regime which received only a mixture of glyphosate and 2,4‐D prior to seeding. Post‐seeding weed control practices were essential to maintain high fodder and grain yields of sorghum. Hand weeding and inter‐row blade harrowing were more effective than atrazine applied pre‐emergence or 2,4‐D applied post‐emergence.     

Seasonal activity of EPTC for Cyperus rotundus L. control in a tropical climate*

Four experiments were conducted at six week intervals to determine the seasonal activity and persistence of soil-incorporated EPTC (5-ethyl N,N-dipropyl(thiocarbamate)) for Cyperus rotundus L. control and tolerance of okra (Hibiscus esculentus L.), cucumber (Cucumis sativus L.), lettuce (Lactuca sativa L.), red beet (Beta vulgaris L.) and carrot (Daucus carota L.) during the dry and wet seasons in Viçosa, Brazil. Satisfactory control of C. rotundus was obtained at 2 kg/ha EPTC during the dry season and 4 kg/ha or more during the wet season. Only red beet and carrot tolerated these doses of EPTC when the crops were planted five days after application. However, selective control of C. rotundus was obtained when the planting date of lettuce was delayed for three or six weeks after EPTC application. EPTC controlled C. rotundus at half the dose that was required to control three species of annual grass that germinated near the soil surface. EPTC persisted longer when applied to air dry soil and incorporated with a rototiller than when incorporated into moist or wet soil.     

Characterization of <Emphasis Type="Italic">Pectobacterium carotovorum</Emphasis> causing a new soft rot disease on okra in Malaysia

Dark brown, necrotic pods with extensive water-soaked lesions caused by plant pathogenic bacteria were found on okra plants in different fields in Malaysia in 2010. PCR amplification of the pectate lyase (pel) gene and amplification of the 16S–23S rRNA (ITS) with G₁ and L₁ primers produced 434-, 535- and 570-bp fragments, respectively. From the similarity between the results of biochemical tests and their equivalency with standard bacteriological sources, PCR-based pel gene, and RFLP analysis of the ITS-PCR products, all isolates were identified as Pectobacterium carotovorum. This is the first report of P. carotovorum in okra from Malaysia.     

Incidence and geographical distribution of downy mildew on maize caused by Peronosclerospora sorghi in Nigeria

Abstract

Incidence and geographical distribution of downy mildew (Peronosclerospora sorghi) on maize (Zea mays) were determined in a systematic survey of 181 maize fields in the major maize‐growing regions and ecological zones of Nigeria. Downy mildew was observed in the forest and Guinea savanna ecologies, but no disease was detected in other ecologies. Highest levels of disease incidence (63%) were observed in the forest zone, and progressively less disease incidence was found at the southern and northern Guinea savanna zones. Spatial pattern analysis indicated an aggregation and randomness of infected plants in the northern Guinea savanna and the forest zone, respectively. Disease incidence was positively correlated with the presence of downy mildew infected sorghum plants and relative amount of sporulation on infected sorghum (Sorghum bicolor) but negatively correlated with plant age and cropping pattern. Relative sporulation on maize plants was negatively correlated with age of maize plants. Higher levels of disease incidence were observed when the previous crop was either maize or sorghum than when previous crops were cassava, okra, tomatoes, or rice.     

Sodium Alginate as an Adjuvant of an Antagonistic Bacterium, Pseudomonas fluorescens Strain A11RN, to Enhance Biocontrol of Turfgrass Snow Mold Caused by Typhula ishikariensis

Pretreatment with sodium alginate (20 g/m²) prior to application of a biocontrol agent, Pseudomonas fluorescens strain A11RN, enhanced the control turfgrass snow mold caused by Typhula ishikariensis biotype B. Disease severities in two fields relative to untreated control plots were 53% and 61% in plots treated with both the strain and sodium alginate, which were significantly lower than 69% and 77% in plots treated only with the strain. The antagonist population remained above the threshold for effective control (ca. 1×10⁷ cfu/cm³) at least for the first month under snow in pretreatment with sodium alginate. The population of the biocontrol agent after snowmelt on turfgrass was five times higher in sodium alginate-amended plots than in unamended plots. Sodium alginate alone did not reduce disease severity. Sodium alginate might have supported the survival of the applied strain. Received 7 June 1999/ Accepted in revised form 20 December 1999     

Herbicides and the Regulation of Pesticide Usage in Brazil

Abstract

Groundnut rust (Puccinia arachidis Speg.) is widely spread in Zambia and is a new threat to groundnut crops in Africa. Fungicides tested for Cercospora control were also effective when both rust and leafspot occurred and yield increases up to 102% were obtained. The most effective chemicals were chlorothalonil, mancozeb plus benomyl and a mixture of mancozeb, benomyl and fentin.     

Evidence for two predominant viral lineages,recombination and subpopulation structure in begomoviruses associated with yellow vein mosaic disease of okra in India

Yellow vein mosaic disease (YVMD) caused by whitefly‐transmitted begomoviruses is an economically significant viral disease of okra. In this study, a survey of begomoviruses associated with YVMD was carried out in eight states and two union territories of India. A total of 92 full‐length DNA‐A components were sequenced and characterized. Sequence comparisons and population structure analysis revealed the existence of four begomovirus species. Two novel species were detected with several recombinationally derived genome fragments that probably originated from begomoviruses known to infect malvaceous and non‐malvaceous hosts. Among the four species, Bhendi yellow vein Maharastra virus (BYVMaV) and Bhendi yellow vein Madurai virus (BYVMV) were found to be predominant in okra, with BYVMV having a pan‐India distribution. There was evidence for a high degree of genetic variability and subpopulation structure within these four species. Neutrality tests suggested the occurrence of purifying selection acting upon these populations. The results of the current study have uncovered the diversity and genetic structure of okra‐infecting begomoviruses in India and generated potentially useful information for developing management strategies for YVMD.     

Satisfactory Control of Echinochloa crus-galli in Rice Nurseries

Abstract

In field-scale trials at Hamoul in the north of the Nile delta in 1967 and 1968, certain herbicides applied to a soil heavily infested with barnyardgrass (Echinochloa crus-galli) gave very satisfactory results. Taking into account both grass control and increase in rice stand, molinate and propanil at 3-4 Ib/feddan* were shown to be most effective. Molinate used either as a liquid or granular formulation gave excellent results when applied pre-flood (liquid) or post-emergence (liquid and granules). Propanil used post-emergence gave good results provided that the field was drained 24 hours before treatment and flooded again 24 hours after.     

Chemical Control of Phalaris minor and Avena ludoviciana in Wheat

Abstract

In field experiments conducted at the Punjab Agricultural University, Ludhiana during 1973–74 and 1974–75, pre-emergence application (one day after sowing) of methabenzthiazuron (1.05 kg a.i./ha), metoxuron (1.6 kg a.i./ha) and chlortoluron (0.75 kg a.i./ha) gave effective control of Phalaris minor and Avena ludoviciana in wheat without any phytotoxic effect on the crop. Methabenzthiazuron, metoxuron and chlortoluron gave 1410, 1420 and 1090 kg/ha, respectively, more grain than the unweeded crop and 590, 600 and 270 kg/ha more than the crop hand-weeded twice. Nitrofen (1.25 kg a.i./ha) applied pre-emergence was effective against P. minor only and gave substantial increase in grain yield. Terbutryne, dichlormate and linuron, while effective against P. minor, also had a phytotoxic effect on the crop.     

Molecular characterization and phylogeny of phytoplasma associated with bunchy top disease in its new host Okra (<Emphasis Type="Italic">Abelmoschus esculentus</Emphasis>) in India reveal a novel lineage within the 16SrI group

Okra plants with bunchy top disease were found to be prevalent during the period of August–October 2009 in New Delhi, India. The common symptoms observed were shortening of internodes, aggregation of leaves at the apical region, reduced leaf lamina, stem reddening, fruit bending, phyllody and stunting of plants. The disease incidence ranged from 2–60% accompanied by significant reductions in production of both flowers and seeds. Nested polymerase chain reaction targeting phytoplasma specific 16S rDNA and rp genes revealed all symptomatic plants to be positive for phytoplasma. Homology searches depicted its closest identity to phytoplasmas of 16SrI ‘Candidatus Phytoplasma asteris’, like the Sugarcane yellows and Periwinkle phyllody phytoplasmas. Profiles for 16S rDNA obtained with 10 restriction endonucleases, differed in TaqI sites for two phytoplasma isolates (BHND5 & 10) from the standard pattern of 16SrI-B subgroup, the latter was seen in the case of isolate BHND1. Restriction fragment analysis of rp genes with AluI, Tsp509I matched with patterns of the rpI-B phytoplasmas. Phylogenetic reconstruction of rp genes revealed okra bunchy top phytoplasma (BHND1) as a divergent isolate, the subsequent sequence analysis of which showed the presence of a novel BslI site. These significant differences suggest that multiple phytoplasma strains are affecting okra, one of which is a diverging lineage within the 16SrI-B group while others represent a new 16SrI subgroup not reported so far. Additionally, this is the first report of a phytoplasma associated disease in okra plants worldwide.     

Short Communications

Abstract

As part of a continuing programme to aid in the development of new acaricides, the efficacy in the field of four different pour‐on formulations was tested against four economically important tick species in Kenya. Synthetic pyrethroids flumethrin², cypermethrin (mixed isomers)³, and alpha cypermethrin⁴ were compared together with an organophosphate, phosmet⁵. All the acaricides were applied along the dorsal midline of the animals except where Porect was applied onto the ears, neck and face of the animals as an alternative treatment. Bayticol was significantly more effective than all the others tested (P < 0.05) for the duration of the trial of 14 days and would be of immense benefit to farmers who are dipping once or even twice a week and still experience losses from Theileria parva infection or East Coast Fever (ECF). Porect, SF06666 and SF06646 were found inadequate to be used in situations where susceptible cattle are reared in ECF endemic areas. However, they can be used where farmers rear resistant cattle and where the priority is to reduce tick worry without trekking animals for long distances to the dip. SF06666 had poor control over body ticks particularly the Amblyornma species. Porect at special application rates to the ears, face and neck is too cumbersome to be practicable. There was a significant rub‐off effect on to the synthetic pyrethroid control animals, especially Bayticol, which contributed to the low numbers of total ticks in the controls relative to total ticks pre‐treatment.     

The Ant Mosaic - Tropical Tree Crops and the Limiting of Pests and Diseases

Abstract

Field experiments were conducted to determine the effectiveness of herbicides in controlling Rottboellia cochinchinensis (Lour.) W. D. Clayton and Cyperus rotundus L. in upland rice (Oryza sativa L.) at different moisture regimes as imposed by a line source sprinkler system. Preemergence application of pendimethalin [N‐(1‐ethylpropyl)‐3,4‐dimethyl‐2,6‐dinitrobenzenamine] was highly effective in controlling R. cochinchinensis irrespective of soil moisture after herbicide application. Bentazon [3‐(1‐methylethyl)‐(1H)‐2,1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide] and 2,4‐D [(2,4‐dichlorophenoxy)acetic acid] applied at postemergence effectively controlled C. rotundus when moisture supply was well above pan evaporation. These herbicides also had no adverse effect on rice stand and resulted in higher yield over the control. Water application rates above upland pan evaporation for a season‐long period was essential to obtain a high response to weed control either by herbicides or hand weeding. The data suggest that proper weed control by herbicides or hand weeding will not result in high upland rice grain yields if moisture level from rains fall below the critical level.     

The use of dyes to mark populations of beneficial insects in the field

Dyes and dusts have been used to mark insects internally and externally for decades, the majority of examples coming from laboratory-reared pest species used in mark-release-recapture studies. Using dyes or dusts to mark populations of pests and beneficial insects simultaneously in the field has received less attention. We evaluated a water-soluble fluorescent dye and a resin-based fluorescent pigment sprayed on crops to mark beneficial and pest insects, and monitored the dispersal of marked insects. Our results show that resin-based dyes provide an effective mark on several species of insects among several orders. The resin-based dye is also relatively inexpensive, non-toxic, UV-stable and water resistant, unlike a water-soluble dye. Using the resin-based dye in a broccoli production system, we were able to monitor simultaneously the movement of field populations of the parasitoids, Diadegma semiclausum (Hellén) (Hymenoptera: Ichneumonidae), and Apanteles ippeus (Nixon) (Hymenoptera: Braconidae) and the adult stage of the host, diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). Resin-based dye applied on a crop is an effective way to mark and monitor the dispersal of populations of beneficial and pest insects in relation to agricultural practices, integrated pest management and conservation biological control.