Rat Damage to Coconuts in Fiji Part 1 Assessment of Damage

Abstract

The amount of rat damage to immature coconuts was assessed by two methods. The first involved fortnightly recordings of all coconuts produced, including those rat damaged, at representative sites for up to three years. The second method attempted to utilise decay characteristics of rat damaged coconuts as a basis for projecting spot counts of damaged coconuts to long term estimates of damage.

Damage was concentrated on coconuts aged three to six months with most of the damage being inflicted by Rattus rattus. Damage varied considerably from month to month with seasonal trends in damage being apparent at only one site.

Rats clearly favoured particular palms in all plantations, resulting in over 75% of the damage being confined to 30% of the palms. Those selectively attacked were randomly distributed within the survey plots and did not produce significantly fewer harvestable coconuts than those palms seldom attacked.

Tall palms, i.e. over 15 m incurred less damage than those under 10 m.

Decay characteristics of rat damaged coconuts proved to be of limited value as a basis for projecting spot counts to long term losses, but counts of green damaged coconuts accurately reflected the previous 33–35 days damage.

Overall production losses (derived after adjustments for known palm compensation for damage) were relatively low; being 2.7, 2.0 and 1.3 nuts per palm per year during 1970, 1971 and 1972.     

Population dynamics of Apodemus agrarius Pallas and its economic threshold in the paddy region

Abstract

Investigations were conducted in the double or middle season paddy regions from 1988 to 1990; main results showed that the population of Apodemus agrarius reached maximal reproductive rate between April and May, and between September and October each year. Their maximal population size occurred in July and between October and November each year. At different stages of the rice, mouse density (X) was significantly related to loss rate of the rice (Y). Studies on imitation mouse damage on rice indicated that the rice, damaged by the mice in tillering stage, possessed a certain capacity for compensation. When the mouse damage rate approached yield loss rate in the booting or spiked stage the rice plant lost this compensatory capacity. It will be seen from the above that early spring is the most available, feasible time for mice control. Under the current production level the economic thresholds of mouse density are 3% in spring, 5% for early and middle‐season rice and 7% for later rice.     

Insect pests of pearl millet in West Africa: A review

Abstract

Pearl millet (Pennisetum americanum (L.) K. Schum), a major food crop in the sahelian and savanna regions of West Africa, is attacked by about 100 species of insects. Of these, the only regular pests are stem borers (Acigona ignefusalis Hmps. and Sesamia spp.) and earhead caterpillars (Masalia spp., Raghuva spp.). Sporadic pests such as hairy caterpillars (Amsacta moloneyi Druce), armyworms (Spodoptera spp. and Mythimna spp.) and grasshoppers (Acrididae) may cause severe losses to crops during prolonged droughts early in the season. A grain midge (Geromyia penniseti (Felt)) attacks late millets and causes a considerable loss in yield. Information is presented on the biology, distribution, hosts and natural enemies of these pests, and some methods of control are discussed.     

Rice nematode problems in Nigeria: Their occurrence,distribution and pathogenesis

Abstract

In a survey of plant parasitic nematodes associated with or affecting rice throughout Nigeria, some important nematode pests, especially the white tip disease nematode, Aphelenchoides besseyi and the rice root nematodes Hirschmanniella spinicaudata and H. oryzae were identified from seed, soil and root samples from swamp rice fields respectively. The sugarcane cyst nematode, Heterodera sacchari occurred in swamp rice fields only around the major sugarcane estates in Nigeria. The root‐knot Meloidogyne incognita and the root lesion nematode, Pratylenchus brachyurus were also encountered in upland (rainfed) rice fields. The white tip disease nematode, A. besseyi occurred at low levels in soils and rice seeds throughout the country. High population levels of H. spinicaudata and H. oryzae were encountered especially in areas where monoculture of rice is practised. General chlorosis, poor tillering and significantly reduced yield have been observed due to H. spinicaudata. Rice plants attacked by H. sacchari also showed intense chlorosis, delayed and reduced tillering and reduced grain yield. The roots of attacked plants were twiggy, very necrotic and blackened. The root‐knot M. incognita and the root lesion nematodes P. brachyurus have both been observed to reduce rice yields. Rice cultivars screened for reactions to the nematodes showed varying degrees of susceptibilities. Some varieties were however resistant to the root‐knot nematode, M. incognita.     

Genotype × environment interactions in symptom development and yield of cassava genotypes with artificial and natural cassava bacterial blight infections

Thirty-seven cassava genotypes from Benin, including advanced breeding lines, were tested for their reaction to bacterial blight in the forest–savanna transition, wet savanna and dry savanna zones of Benin. Sixteen genotypes were repeated in 12 environments. In year 1998, genotypes RB92164, RB92022, TMS30572, BEN86004, RB92033 and Dangbo2, and in year 2000, genotypes RB92202, RB92151, RB92132 and TMS30572 were resistant in one ecozone. Among the more resistant genotypes, CAP94030, BEN86040, RB89509, RB92132 and TMS30572 showed low interaction across environments and were most stable in disease reaction. Ten genotypes were classified as high yielding across environments. Among the more resistant group of genotypes, only TMS30572 and RB89509 were high yielding, with RB89509 being unstable in yield across environments. Selection of genotypes proved reliable only after artificial inoculation. Comparing environments, artificially inoculated treatments in the wet savanna zone and in the forest–savanna transition zone with stable high symptom severity proved most suitable for screening of genotypes, while the wet savanna zone with low natural infection in year 1998 was suitable for production of propagation material, and the site in the dry savanna zone with natural infection in year 1998 was the best environment for cassava production. The correlation between disease severity and root yield was significant only for the non-inoculated treatment in the dry savanna zone in year 2000 (R = –0.58), but not in any other environment. Among the 37 genotypes tested, several genotypes can be recommended to farmers in specific ecozones, and genotype TMS30572 revealed as relatively stable in disease resistance and in high yield across ecozones.     

First record of the tomato leafminer,Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in Sudan

An outbreak of larvae and adults of a devastating moth was noted to be causing severe damage in tomato grown in greenhouses at Khartoum State, Sudan during June 2010. Symptoms included foliage mining and leaves drying. Photographs of symptoms and larvae and adults of the pest (and subsequently specimens) were sent to Russell IPM, UK and the Finnish Museum of Natural History for identification. The pest was identified as Tuta absoluta (Meyrick), (Lepidoptera: Gelechiidae). This is the first official record of T. absoluta in Sudan, based on surveys in tomato production areas in Khartoum, Gezira, Red Sea and North Kordofan States and eggplant and potato in Khartoum State. Severe yield loss due to the serious feeding damage on foliage and fruits infestation was reported on tomato and eggplant fields at Khartoum State.     

Distribution and biology of the yellow‐spotted longicorn beetle Psacothea hilaris hilaris (Pascoe) in Italy

The Asiatic yellow‐spotted longicorn beetle, Psacothea hilaris hilaris, was found for the first time in Northern Italy in 2005. As this xylophagous insect is considered one of the most important pests of Morus spp. and of Ficus carica in its countries of origin, a multi‐year study was carried out to determine the spread of the pest in Northern Italy, to evaluate its establishment potential and to improve knowledge on its biology in the new habitat. The survey confirmed that P. hilaris hilaris has established in Italy and has colonized an area of about 60 km². The species overwinters as eggs or larvae. Adults are present from June to October. Damage has been recorded mostly on Ficus carica plants, and very rarely on Morus alba. Both young and older plants, healthy and weakened hosts can be attacked by the pest. Severely attacked plants become weakened and eventually die.     

Comparison of empirical models depicting density of Amaranthus retroflexus L. and relative leaf area as predictors of yield loss in maize (Zea mays L.)

The outcome of crop-weed competition should be predicted as early as possible in order to allow time for weed control measures. Maize grain yield losses caused by interference from Amaranthus retroflexus L. (redroot pigweed) were determined in 1991 and 1992. The performance of three empirical models of crop-weed competition were evaluated. Damage functions were calculated based on the weed density or relative leaf area of the weed. In the yield loss-weed density model, values of I (percentage yield loss at low weed density) were relatively stable for similar emergence dates of A. retroflexus across years and locations. Estimated maximum yield loss (A) was more variable between locations and may reflect environmental variation and its effect on crop-weed competition, at least in 1991. The two-parameter yield loss-relative leaf area model, based on m (maximum yield loss caused by weeds) and q (the relative damage coefficient) gave a better fit than the single-parameter version of the model (which includes only q). In both relative leaf area models, the values of q varied between years and locations. Attempts to stabilize the value of q by using the relative growth rate of the leaves of the crop and weed were successful; however, the practical application of such relative leaf area models may still be limited owing to the lack of a method to estimate leaf area index quickly and accurately.     

On-farm evaluation of measures to monitor and control soybean pod-borer Etiella zinckenella in East Java,Indonesia

The incidence levels of moths and larvae of Etiella zinckenella were studied in the reproductive stage of soybean at eight farmers' field sites. A positive relationship was found between moths, caught by sweeping during flowering and pod-formation, and seed damage. Hence, rough predictions of damage can be made based on moth catches. Damage incidence was recorded in unsprayed plots and in plots sprayed with deltamethrin during flowering and pod-formation. Spraying did not affect the densities of moths and larvae or damage to pods and seeds. Larvae of H. armigera, Spodoptera litura and Plusiinae were not affected by spraying, but the pod-sucking bug Riptorus linearis, and two groups of predators, spiders and coccinellids, were reduced.     

Estimation of rice yield losses due to the African rice gall midge,Orseolia oryzivora Harris and Gagne

Abstract

The African rice gall midge, Orseolia oryzivora Harris and Gagne (Diptera: Cecidomyiidae), is an important pest of rice, Oryza sativa, in Burkina Faso as well as other countries in West and East Africa. In spite of its importance, little is known regarding the relationship between gall midge populations and grain yield losses. To determine yield losses the gall midge was reared in cages and adult midges were placed on caged plants of the rice variety ITA 123 at different population levels. The seven treatments consisted of different numbers of insects infested on the plants; 0 insect pairs (non‐infested check), and 1, 5, 10, 15, 20 or 25 midge pairs/cage. The loss in yield in relation to the non‐infested control was highly positively correlated (R² = 0.81) with the percentage of gall midge damaged tillers. The infestation by the insect on the plants resulted in the compensatory production of tillers which developed in response to the gall midge damage but the compensation was not sufficient to make up for the loss of yield due to the damaged tillers. Yield loss ranged from 0% in the control to 65.3% in the treatment with 25 pairs of adults. One per cent of tillers damaged resulted in 2% grain yield loss.     

Simulation modelling of yield losses caused by wheat stem rust

Stem rust, or black rust, of wheat, caused by Puccinia graminis f. sp. tritici, has recently re-emerged in several parts of the world, with epidemics occurring in eastern Africa, as well as northern and southern Europe. Damage mechanisms from disease dynamically affect the physiology of the crop as it grows and develops, and as the epidemic progresses, leading to yield losses in the stem rust-diseased wheat stand. Process-based agrophysiological models that include disease-induced damage mechanisms can help to better understand the physiological processes leading to yield losses, and to inform strategic decisions such as breeding strategies. Such models have not been developed for wheat stem rust so far. Two damage mechanisms for stem rust, light stealing and assimilate diversion, were incorporated in the agrophysiological simulation model WHEATPEST. The model, tested from experimental field data retrieved from the literature, provides a satisfactory representation of the system, although consistently underestimates relative yield losses by about 6.9%, resulting in relative yield losses between 17% and 56%. Analyses highlight the importance of the diversion of assimilates toward the pathogen in the magnitude of yield loss. Considering only the reduction of green leaf area would underestimate damage from stem rust by at least threefold. The analysis also shows the importance of the dynamic interplay between disease and crop growth, especially the dynamics of leaf area, on yield loss. Directions to consider additional damage mechanisms are proposed, and perspectives for future research, especially in relation to plant breeding strategies under climate change, are offered.     

Presowing Hardening of the Host with Phenolic Acids Reduces Induction of Seed Germination in the Root Parasite Striga asiatica

Abstract

Striga asiatica (L.) Kuntze, a root parasite, causes severe loss of yield in sorghum and several other crops. The seeds of the parasite are induced to germinate by a stimulant in the host root exudate. Presowing hardening of the host with vanillic acid, caffeic acid and ferulic acid (25 ppm) reduces the induction of seed germination in the parasite by the host root exudate. The treatment causes a slight improvement in the dry matter production in the host and in addition, increases the phenolics level in the host root exudate. The latter effect might be responsible for reducing germination in Striga. If the treatment remains effective under field conditions also, it reduces significantly the incidence of Striga in cultivated fields.     

Notices

Abstract

Seed‐bed types, fertilizers, cassava stem portions, planting time and yam cultivars were studied for the incidence of termites in cassava and yam fields. Planting cassava on ridges reduced the incidence of termites and significantly (P<0.05) increased tuber yield. The bottom stem portion of cassava stick was the least attacked by termites. Planting cuttings when rains became steady reduced termite incidence. NPKMg (12:12:17:2) suppressed termites in yam and improved yield significantly. Delay in harvesting yam tubers increased termite infestation. Yield loss was highest for Dioscorea rotundata cv. Nwopoko, with losses of more than 5 metric tonnes/ha when harvest was done after December in termite infested soil. Chinese yam showed the greatest resistance to termites.     

草地贪夜蛾对不同生育期玉米产量的影响及防治指标

为明确草地贪夜蛾Spodoptera frugiperda对我国玉米产量造成的损失,并制订相应的防治指标,在玉米不同生育期分别接入不同数量的草地贪夜蛾3龄幼虫,研究其为害玉米后对产量和其他相关指标造成的影响,建立不同生育期产量损失与不同为害率之间的回归方程。结果显示,大喇叭口期接虫对玉米成株期株高有显著影响,玉米各生长时期接入不同数量草地贪夜蛾后对产量损失均有显著影响。根据防治成本及玉米产量等指标计算出国内玉米的经济危害允许水平为5.56%。利用回归方程计算出玉米小喇叭口期、大喇叭口期以及吐丝期的防治指标分别是为害率达8.72%、7.99%和6.17%。     

Evaluation of three empirical models depicting Ambrosia artemisiifolia competition in white bean

The performance of three empirical models describing white bean yield loss (Y_L) from common ragweed competition was compared using field experiments from Staffa and Woodstock, both in Ontario, Canada, in 1991 and 1992. One model was based upon both weed density and relative time of emergence. The other two models described yield loss as a function of weed leaf area relative to the crop. The model based on both weed density and relative time of emergence best described the data sets. The predicted maximum yield loss (A) and the parameter for relative time of weed emergence (C) varied across locations and years whereas the yield loss at low weed density (I) was relatively more consistent across locations and years. Use of thermal time (base temperature=10^oC) rather than calendar days did not change the overall fit of the model, but reduced the value of the parameter for the relative time of weed emergence (C). The two parameter leaf area model accounting for maximum yield loss (m) gave a better fit to the data compared with the one parameter model. The relative damage coefficient (q) varied with time of leaf area assessment, location and year. Values of q calculated from relative leaf area growth rates of the crop and weed were similar to observed values. The relationship between q and accumulated thermal time was linear but varied with location and year. As management tools, models based upon relative leaf area have advantages over models based on density and relative time of emergence since the level of weed infestation needs only to be assessed once, whereas density and emergence time require frequent observations. The ability to assess accurately and quickly both the crop and weed leaf area, however, may limit the practical application of models based on leaf area. The inability of empirical models to account for year–to–year variation in environmental conditions was observed.     

Crop damage and yield loss caused by two species of rodents in irrigated fields in northern Nigeria

We investigated the damage and yield loss caused by two rodent species, Arvicanthis niloticus and Mastomys (Praomys) natalensis, in cereal crops in fields near Kano, northern Nigeria from August, 1990 to April, 1992. Using the random cluster technique, we selected 100 clusters of 30 hills in each rice and wheat field, and assessed damage fortnightly, using the Cut Tiller Count method. In premature crops, damage increased from tillering stages to the dough stages. Differences in the percentages of damage (yield loss) in mature rice (4.8% in 1990 and 12.6% in 1991) and in wheat (30.0% in 1991 and 21.7% in 1992) were statistically significant between years. Severe yield losses in wheat, compared to low and moderate levels in rice (grown for the most part during the rains), were probably a result of greater consumption of the wheat, grown entirely by irrigation during the dry season when other rodent food sources were less abundant. Results of ANOVA showed significant effects of developmental stage of the crop, year of cultivation, and their interactions on the magnitude of crop damage.     

Some effects of single and split applications of carbofuran on the incidence of and damage by Locris Maculata,Busseola Fusca and Sesamia Calamistis on maize

Abstract

Studies have been carried out on the efficacy of carbofuran (Furadan 5G) in reducing the incidence of the major insect pests of maize in Nigeria. A single dose of 1.5 kg a.i./ha applied in the planting hole was found to reduce the incidence of spittle bug (Locris Maculata F.) and stem borers (Busseola fusca (Fuller) and Sesamia calamistis (Hmps.)) when compared with split applications of the same dose applied at planting and 40 days after planting. The number of damaged plants was reduced from 40% in the control to 11.7% in the treated plots. Yields of fresh maize cobs were also increased significantly in treated plots. A significant positive correlation was established between the mean number of stem borer larvae and mean percentage damage, and significant negative correlations between the mean yield and mean percentage damage and between the mean yield and mean number of stem borer larvae.     

The Basis of Predictive Modelling for Estimating Yield Loss and Planning Potato Cyst Nematode Management

The basis of modelling yield loss and population dynamics relations of potato cyst nematodes is that both are strongly density-dependent. Potato cyst nematodes (PCN; Globodera pallida and G. rostochiensis) are particularly suitable for analysing such relationships because they have only one generation per year, potato is their only field host, the juvenile nematodes within the egg are very durable (up to 20 years persistence), and they hatch mainly in response to specific chemicals exuded from host roots. Small populations increase the most, up to 50-fold, when a potato crop is grown. Multiplication rates decrease as the population density increases because damage decreases root system size and increases competition so that very large populations may actually be decreased when potatoes are grown. The newly formed eggs have a ‘half-life’ of c.two years when non-host, rotational crops are being grown. Control is achieved largely by the use of rotation, the application of nematicidal chemicals, and growing resistant cultivars. As rotations are shortened, so PCN populations will be increased, and crop damage becomes more likely. Thresholds for damage vary with both soil type (greatest on sandy soils) and potato cultivar. Cultivars differ in their tolerance of PCN damage depending on how vigorously they grow, on their root sensitivity to damage from the PCN juveniles which invade close to root tips, on cultivar resistance which decreases the parasitic effect by reducing the numbers of developing PCN females, and on various environmental factors such as the amounts of fertiliser applied. The dependence of the yield-loss relationship on population density, soil type and cultivar effects has been described in a simple equation and assessed using field-trial data. Effects on yield are described in proportion to the PCN-free yield but the addition of information on expected yield (in tonnes ha⁻¹) in the absence of PCN renders this equation predictive. Nematicides are widely applied to infestations of potato cyst nematodes, both to prevent the crop from being damaged and to prevent population increase which could hazard the next potato crop in the rotation, but they are generally more effective at preventing the former than the latter. A complex equation has also been developed to model the population dynamics of PCN. This equation incorporates a factor for host-crop growth and tolerance (from the yield-loss equation) and also the effects of host resistance. This latter is particularly relevant to G. pallida, where all the resistance currently available is determined by minor genes and hence is ‘quantitative’ or ‘partial’. Effects of rotation and of nematicides can also be incorporated into this model. To provide a realistic prediction also requires accurate information on PCN population densities, species composition and distributions, and rates of PCN population decline between potato crops.     

Nitrogen fertilization and yield losses of tea to red crevice mite (Brevipalpus phoenicis geijskes) in the Eastern Highlands of Kenya

A field trial using a mite-susceptible clone 11/4 of tea whose yield potential is over 3 t ha^-1 year^-1 was conducted to determine how yield losses due to infestation by red crevice mite (Brevipalpus phoenicis Geijskes) relate to nitrogen nutrition. This was done over a 3 year period in plots either receiving 0, 100, or 200 kg N ha^-1 year^-1. For determining the losses due to mites, an acaricide check method of yield loss assessment was used. Mites were controlled in the plots by spraying flucythrinate. The yield varied considerably between seasons with mean yields in the 3 year period ranging from 2.0 to 2.4 t ha ^-1 without fertilizer and 2.4 to 2.6 t ha^-1 year^-1 at 100 kg N and 2.5 to 2.7 t ha^-1 year^-1 at 200 kg N. Application of the acaricide decreased the mite population by 60-74%. Yield loss between sprayed and unsprayed treatments was 12-22% without fertilizer but this was reduced to 5-6% when fertilizer was supplied at 100-200 kg N ha^-1. The reduction in yield losses in fertilized plots indicate the beneficial effects of nitrogen in inducing tolerance to mites and possibly increasing plant vigour. Protecting the tea from mite attack resulted in yield advantage and a net benefit of $US 0.3, 0.2 and 0.2 per kg made tea at 0, 100 and 200 kg N ha^-1 respectively. Application of 100 kg N ha^-1 had higher net cost benefit than the 200 kg N application rate. The strategy for control of mites would be to integrate spraying with use of fertilizer.     

Prediction of yield loss caused by Orobanche spp. in carrot and pea crops based on the soil seedbank

Root parasites of the genus Orobanche cause serious losses in many subtropical crops. Direct control options are very limited and crop yield loss can reach 100%. Prediction of potential damage in a crop before sowing or planting would support farmers in their choice of crop. This paper discusses the relationship between the number of Orobanche spp. seeds in the field and yield loss in peas (Pisum sativum L.) and carrots (Daucus carota L.) in Israel. Yield loss due to Orobanche crenata Forsk. in peas was 100% at high infestations, whereas in carrots when O. crenata and O. aegyptiaca were present it stabilized at about 50% for moderate infestations of 200 seeds per kg of soil. Statistical analyses related the yield loss from parasitism in peas and carrots to the numbers of Orobanche seeds remaining in the soil. A rectangular hyperbolic model, previously applied to competition data, fitted the data well. Confidence intervals for per cent yield loss were calculated using the bootstrap method. The practical applications of these models in predicting yield loss are discussed.