The infestation of the fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) in Africa since 2016 has been a major threat to maize production. Previous studies in Togo and Ghana from 2016 to 2018 did not correlate FAW infestation to yield losses. Thus, the aim of this study which assesses the impact of FAW infestation by inspecting 150 maize farms throughout the five Agro-Ecological Zones (AEZs) of Togo for FAW plant damage, and third instar larvae were used to infest 10-day-old maize plants in netted plots under controlled conditions at an experiment station (Station d'Expérimentations Agronomiques de Lomé) in 2019 and 2020. As control plots at the experiment station, plots were both netted and treated with emamectin benzoate, simply netted, or open to natural infestation. The number of larvae, egg masses, percent damaged plants, and damage proportions of leaves and ears were scored until harvest. Infestations and damages on maize plant throughout Togo were similar between the two years but were higher in the southern part of the county (AEZ5). At the experiment station, the yield losses were significantly considerable and increased from 25% infestation. The losses were 0.37 t ha−1 for 25% infestation, 0.34 t ha−1 for 30%, 0.59 t ha−1 for the open plots, 0.70 t ha−1 for simple netted and 50% infestation, 1.03 t ha−1 for 75%, and 1.27 t ha−1 for 100% infestation. This current study suggested thorough inspection on maize farms to set off management practices from 25% of infestation.

Glyphosate, a widely used preplant herbicide in annual and perennial crops, was introduced to Sri Lanka in 1977. Its use has expanded since 2008 with the phase-out and ban in 2014 of paraquat. In December 2014, glyphosate use in Sri Lanka was regionally restricted. Crop protection and production in the country was severely affected in 2016 and 2017 due to the irrational decisions of the government of Sri Lanka (GoSL). Increased crop production costs due to the absence of effective and economically viable weed control techniques, low crop yields, loss of foreign exchange, and enhanced use of smuggled glyphosate products are the consequences of the glyphosate ban. The ban was imposed without a scientific basis because of sociopolitical pressure. A series of dialogues with the GoSL helped rescind the ban in 2018 for a period of 36 mo, but its use is limited to tea [Camellia sinensis (L.) Kuntz.] and rubber [Hevia brasiliensis (Willd. ex A. Juss.) Müll. Arg.]. In August 2019, the Cabinet of Ministers of the GoSL also decided to allow use of glyphosate to devitalize propagules in the floriculture industry (export oriented) and destroy coconut (Cocos nucifera L.) trees infected by Weligama coconut leaf wilt disease and sugarcane (Saccharum officinarum L.) infected by white leaf disease. However, glyphosate products with the co-formulant polyethoxylated tallow amine are still not permitted in Sri Lanka.

Laboratory and field experiments were conducted to determine whether manipulation of radiation environment during the period of winter wheat establishment can be used to improve wheat yields in Italian ryegrass-infested fields. Percentage of total irradiation and ratio of red (R) light (around 660 ηm) to far-red (FR) light (around 730 ηm) reaching the soil surface were important factors in regulating Italian ryegrass germination, growth, and competitive interactions with wheat. Reducing total irradiation to about 10% of full sunlight while maintaining the normal R/FR ratio of about 1.0 reduced wheat grain production in the presence of Italian ryegrass by about 40% compared with weed-free wheat in full sunlight. Further, reducing total irradiation to 3% of full sunlight plus reducing the R/FR ratio to about 0.2 reduced wheat grain production competing with Italian ryegrass by about 35% compared with production in the control conditions. Wheat production of dry matter, spikes, and seeds in the presence of Italian ryegrass increased more than threefold under both shading treatments compared with production in full sunlight.

The objective of this research was to modify the senior author's previously developed method for predicting yield losses in maize crops attributable to johnsongrass. The new method is based on the following assumptions: a) relative leaf frequency determines relative biomass; b) total biomass is constant despite the crop/weed ratio; and c) biomass, and therefore leaf frequency, are related to grain yield. Experiments in Argentina from 1986 to 1989 supported the above hypotheses, and the new method was more accurate than the old for predicting relative species biomass in johnsongrass/maize mixtures. Maize grain yield reductions associated with weed interference were also more accurately predicted.

Greenhouse and field studies were conducted in 1992 and 1993 in Manitoba and Saskatchewan to determine the effect of simulated sprayer contamination with thifensulfuron and thifensulfuron:tribenuron (2:1) on canola. In greenhouse studies, canola was more sensitive to tribenuron and thifensulfuron:tribenuron (2:1) than thifensulfuron. Thifensulfuron was more phytotoxic to canola when applied with Merge (50% surfactant blend and 50% petroleum hydrocarbon solvents) than with Agral 90 (non-ionic spreader and activator) at recommended adjuvant concentrations {1% and 0.2% (v/v), respectively}. In the field, canola injury tended to be more severe when thifensulfuron was applied with Merge than with Agral 90, but yields did not differ significantly between adjuvants, Thifensulfuron and thifensulfuron:tribenuron (2:1) at rates as low as 0.1 g ai/ha severely injured canola, delayed flowering, and reduced yield and subsequent seed germination. Thifensulfuron at 0.1 to 0.15 g/ha in mixtures with sethoxydim plus Merge reduced yields up to 61%.

Studies on losses in yield of rapeseed, Brassica campestris cv. Brown Sarson, caused by the mustard aphid, Lipaphis erysimi (Kalt.) were conducted under natural and artificial conditions. Based on the experiments on the influence of aphid exposure to the crop on aphid number and seed yield and the effect of varied aphid population at flowering/pod initiation stage and artificial release of aphids at 10-day intervals starting from 40 days of sowing on the plant height, number of siliquae per plant, number of primary branches, seed yield per plant and 1000-grain weight, a positive correlation between length of aphid exposure to the crop and aphid population was found. A negative relationship between aphid population, length of aphid exposure and seed yield was observed. An inverse and significant relationship existed between parameters contributing to yield loss and losses in seed yield. However, this relationship was not significant in siliquae per plant and 1000-grain weight. A similar relationship was observed in artificial infestation.

Studies were conducted in several ecological regions of Côte d'lvoire from 1986 to 1990 to monitor maize cob-borer populations and to investigate losses in maize grain yield due to this pest. The relationship between borer abundance and crop losses was studied using regression analyses, in which two regression models were developed. One model related yield loss to number of damaged grains and the other related yield loss to grain weight. Mussidia nigrivenella Ragonot (Lepidoptera: Pyralidae) was the dominant pest in most localities. Its population density was particularly high in the semi-deciduous rain forest and decreased westwards and northwards. The models explained 85.6% (yield loss vs damaged grains) and 72.5% (yield loss vs loss in grain weight) of the observed variation. Moreover, they showed that the weight loss due to cob-borers was much lower than that due to stem borers and also that the number of damaged grains increased rapidly with borer density.

The economic injury level (EIL) of the maize stem borer, Chilo partellus (Swinhoe) was determined by artificially infesting maize (cv. Katumani) plants at three different growth stages; viz, 20, 40 and 60 days old plants with varying densities of newly hatched larvae; viz, 2, 4, 6, 8, 10 and 12 per plant constituting the borer population. The grain yield data obtained from the infested and the protected plants showed that maximum yield reduction and stalk damage occurred to the 20-day old crop, while there was insignificant larval effect on yields for the 60-day old crop. Regression analyses gave a significant linear equation (y = a + bx) which estimated the yields per plant at different infestation levels and these were used to calculate the economic injury level at each stage. The resultant EIL was 3.2 and 3.9 larvae/plant for 20- and 40-day old plants, respectively.

Armyworm, Spodoptera exempta (Wlk.) feed on cereals and grassland in eastern and southern Africa. Data on the yield losses and economic effects of an attack on cereals is sparse. They can be an indirect cause of cattle deaths. The need to examine the situation at the farm level has been recognized. A national survey was conducted in 1987, and is currently being analysed. The work entails identifying representative areas and farmers, completing a questionnaire with each farmer, noting the frequency of outbreaks experienced, the farmers' response, the level of government support, the effectiveness of control measures and the costs incurred. Proposals are outlined for future work within the region to determine the reduction in cereal yields due to this insect and to set up action thresholds for control activities. A major difficulty with the survey approach is the disaggregation of various loss-causing factors. At a sub-sample of survey sites, where outbreaks are present, the damage to the crop and the subsequent yield of the damaged crop or the planting of a replacement crop would be recorded to build up data from which action thresholds might be determined.

Soil pests are defined as those in which the damaging stage of the life cycle lives in the soil. In Africa the most important soil insect pests are termites, followed by the larvae of various beetles (particularly scarabs), and by millipedes which are included here as they damage plants in a similar way to some insects.

The most important cereals in Africa are maize, sorghum and millet, with wheat and rice increasing in importance. Attack by soil pests usually begins on the root system and yield losses result from plant mortality, lowered translocation of water and nutrients, increased susceptibility to pathogens, or lodging with subsequent damage to grain on the ground from various vertebrates, invertebrates and saprophytes.

Data have often been presented as ‘percentage of plants damaged’ or ‘infested’ and bear little relationship to yield loss, as this depends on the severity and timing of attack. A succession of soil pests can attack the plants from seedling to maturity. Early season attacks can result in compensatory growth by remaining plants leading to overestimation of yield loss by simple estimates of plants damaged. Direct estimation of yield loss is time-consuming and few such studies have been made. However, methods are presented here for termites and maize which could be adapted for other pests and crops. Indirect estimates using pesticides are more common and, in general, indicate that an integrated pest management approach to soil pests is required.

The present article considers quantitative assessment of crop losses in relation to attack by three trophic levels of insect pests on maize, cowpea and sorghum intercropping systems. The trophic levels considered are (i) specialist feeders subsisting only on one crop within the intercropping systems, e.g. Maruca testulalis (Geyer) on cowpea, and Atherigona soccata (Rondani) on sorghum; (ii) the relative specialist feeders subsisting on two out of the three crops e.g. Busseola fusca (Fuller), Chilo partellus (Swinh.) Sesamia calamistis (Hmps.) and Eldana saccharina (Wlk.) feeding on maize and sorghum cereal plants; and (iii) the generalist feeders e.g. Heliothis armigera (Hbn.) which feeds on all three plant species. Tests for loss assessment were done under natural field conditions within maize, cowpea, sorghum monocropping patterns; maize–cowpea, maize–sorghum, sorghum–cowpea dicropping patterns; and the maize–cowpea–sorghum tricrop intercropping patterns. The authors discuss in detail their modified analytical methods based on the comparison of yield of sets of plants growing under identical conditions except that one set is unattacked by the stem-/pod-borers and the other set attacked, to generate economic losses. The comparative advantages of the planting systems on crop turnover is further discussed. The biomass and plant population fluctuations caused by pest attacks and ‘dead hearts’ at differential time scales in indices of yield have also been discussed. Yield per unit area of monocrop and intercropping patterns have been contrasted using the yield turnover of monocrop plant equivalence as the baseline for comparisons. Maize–cowpea–sorghum mixed intercrop of 1.45 land equivalent ratio (LER), and that for the sorghum–cowpea dicrop with 1.3 LER are considered the most advantageous cropping patterns. Yield losses significantly higher (P < 0.05) within maize-sorghum intercropping combinations with 0.89 LER further suggests that stem-borer colonisation which occurs at an earlier stage of crop establishment resulting in ‘dead hearts’ and significant reduction on plant population per unit area within the two cereal combinations contribute significantly to the overall reduction in crop turnover within such mixtures.