Earlier reports have summarized crop yield losses throughout various North American regions if weeds were left uncontrolled. Offered here is a report from the current WSSA Weed Loss Committee on potential yield losses due to weeds based on data collected from various regions of the United States and Canada. Dry bean yield loss estimates were made by comparing dry bean yield in the weedy control with plots that had >95% weed control from research studies conducted in dry bean growing regions of the United States and Canada over a 10-year period (2007 to 2016). Results from these field studies showed that dry bean growers in Idaho, Michigan, Montana, Nebraska, North Dakota, South Dakota, Wyoming, Ontario, and Manitoba would potentially lose an average of 50%, 31%, 36%, 59%, 94%, 31%, 71%, 56%, and 71% of their dry bean yield, respectively. This equates to a monetary loss of US $36, 40, 6, 56, 421, 2, 18, 44, and 44 million, respectively, if the best agronomic practices are used without any weed management tactics. Based on 2016 census data, at an average yield loss of 71.4% for North America due to uncontrolled weeds, dry bean production in the United States and Canada would be reduced by 941,000,000 and 184,000,000 kg, valued at approximately US $622 and US $100 million, respectively. This study documents the dramatic yield and monetary losses in dry beans due to weed interference and the importance of continued funding for weed management research to minimize dry bean yield losses.

Crop losses from weed interference have a significant effect on net returns for producers. Herein, potential corn yield loss because of weed interference across the primary corn-producing regions of the United States and Canada are documented. Yield-loss estimates were determined from comparative, quantitative observations of corn yields between nontreated and treatments providing greater than 95% weed control in studies conducted from 2007 to 2013. Researchers from each state and province provided data from replicated, small-plot studies from at least 3 and up to 10 individual comparisons per year, which were then averaged within a year, and then averaged over the seven years. The resulting percent yield-loss values were used to determine potential total corn yield loss in t ha−1 and bu acre−1 based on average corn yield for each state or province, as well as corn commodity price for each year as summarized by USDA-NASS (2014) and Statistics Canada (2015). Averaged across the seven years, weed interference in corn in the United States and Canada caused an average of 50% yield loss, which equates to a loss of 148 million tonnes of corn valued at over U.S.$26.7 billion annually.

Weeds are one of the most significant, and controllable, threats to crop production in North America. Monetary losses because of reduced soybean yield and decreased quality because of weed interference, as well as costs of controlling weeds, have a significant economic impact on net returns to producers. Previous Weed Science Society of America (WSSA) Weed Loss Committee reports, as chaired by Chandler (1984) and Bridges (1992), provided snapshots of the comparative crop yield losses because of weeds across geographic regions and crops within these regions after the implementation of weed control tactics. This manuscript is a second report from the current WSSA Weed Loss Committee on crop yield losses because of weeds, specifically in soybean. Yield loss estimates were determined from comparative observations of soybean yields between the weedy control and plots with greater than 95% weed control in studies conducted from 2007 to 2013. Researchers from each US state and Canadian province provided at least three and up to ten individual comparisons for each year, which were then averaged within a year, and then averaged over the seven years. These percent yield loss values were used to determine total soybean yield loss in t ha−1 and bu acre−1 based on average soybean yields for each state or province as well as current commodity prices for a given year as summarized by USDA-NASS (2014) and Statistics Canada (2015). Averaged across 2007 to 2013, weed interference in soybean caused a 52.1% yield loss. Based on 2012 census data in the US and Canada soybean was grown on 30,798,512 and 1,679,203 hectares with production of 80 million and 5 million tonnes, respectively. Using an average soybean price across 2007 to 2013 of US $389.81 t−1 ($10.61 bu−1), farm gate value would be reduced by US $16.2 billion in the US and $1.0 billion in Canada annually if no weed management tactics were employed.

Introduction. In the southern Sudanian zone of Benin, fruit flies are major pests and responsible for considerable yield losses in mango production. The two main species of economic importance affecting mango trees in Benin are Ceratitis cosyra and Bactrocera invadens. During the 2006 crop year and across seven main cultivars, losses stood at 17% in early April and exceeded 70% in mid-June. By the middle of the crop year, over 50% of losses occurred in mango orchards. Materials and methods. The Stone and Pedigo method was used to compute the economic injury level, using variables such as pest control costs, level of losses and mango prices. Results and discussion. The Economic Injury Level (EIL) was highly variable. For the cultivar Kent, for example, it varies from (30 to 75) fruit flies captured per ha and per week, whereas for Keitt the level ranges from (24 to 57) fruit flies·ha–1·week–1. EIL variability depends among other things on market price fluctuation. This method is based on the early introduction of detection traps in mango orchards. A weekly monitoring of trapped fruit flies is used to compute the EIL and make a decision about pest control. Pest control (GF-120 in this case) is recommended if the gross returns exceed production costs. If the number of trapped fruit flies is below the EIL, a treatment is not recommended because pest control will not be profitable. Conclusion. The EIL is an accurate tool to set the optimal (economic) timing of pest control treatment in mango orchards. These preliminary results should lead to the introduction of integrated pest management (IPM) activities to deal with the fruit fly species that are threatening the profitability of mango production in central and northern Benin.

Introduction. The mango tree is of prime importance to the rural economy of central and northern Benin since it provides food and crucial nutriments at the end of the dry season. However, mango producers in Benin are confronted with two problems that are closely connected: deterioration of fruit quality by fruit flies and the inadequacy of postharvest methods. In the Sudanian zone of Benin, fruit flies (Diptera Tephritidae) are highly responsible for major production losses. Materials and methods. An inventory of all present cultivars and yields of main mango cvs. (Gouverneur, Eldon, Dabshar, Kent, Smith, Keitt and Brooks) was carried out in Benin on 7 000 fruits near Parakou (Borgou) during the years 2005 and 2006. Sampling of 3 000 young fruits (length range 13–26 mm) was carried out in 2006 in order to detect some very early tephritid attacks. A loss assessment of pre-ripening and ripening fruits was also carried out on 7 750 fruits in 2006. Results and discussion. We identified 29 cultivars in the district of Borgou where 75% of the mango orchards of Benin are situated. Most of these use the ‘gatherer’ production system. The early Gouverneur cultivar had the lowest yield (1.8 t·ha–1), and the late Brooks cultivar had the highest yield (10.4 t·ha–1). Small and immature young fruits allowed development of both C. cosyra and B. invadens in February and March, i.e., before the mango season itself: this result could be a useful result for pest control. For the pre-ripening and ripening stages, average losses due to tephritid varied from 0.34 t·ha–1 to 6.5 t·ha–1 depending on cultivar type, resulting in considerable loss of income for small planters. Taking all cultivars together, losses stood at 17% in early April and exceeded 70% at mid-June. By the middle of the crop year, over 50% losses were recorded. The seasonal cultivar Eldon and late cultivars (Keitt and Brooks) were the most infested. Conclusion. In the Sudanian zone of Benin, the two main species of Tephritidae that have a high economic impact on mango trees are B. invadens and C. cosyra. Our preliminary observations and calculations will be used in a forthcoming article to calculate the economic injury level of these fruit flies.

Lepidopterous stem borers constitute one of the major constraints to cereal crop production in southern Africa. Chilo partellus Swinhoe, is an economically important stem borer of maize and sorghum. Current research status on C. partellus is reviewed and substantial advances in the distribution, bioecology and control strategies are discussed. Present work on the assessment of crop losses, elucidation of mechanisms of resistance, development of resistant crop cultivare, feasibility of biological control measures and the implementation of other stem borer management methods are reported. Further areas of research into the management of C. partellus are identified.

The special circumstances of plant protection in tropical developing countries, particularly in Africa, are considered within the context of the needs of the preponderant rural farming community, and in respect of food production. The problems are exacerbated by the existence of complex cropping systems (intercropping), the abundance and diversity of pests, the meagre knowledge of the plant-host-pest relationships, and the poor availability of the scientific understanding of the components of pest control and inputs essential for integrated pest management. Institutional innovations, including stepped-up professional training of experts in the field of plant protection, are required to usher in a more sustained effort in efficacious plant protection in these regions. Attempts in this direction are briefly discussed.

The reasons for assessing crop losses due to pests of cereals are reviewed; for making decisions in pest management based on costs and benefits, for allocating resources on the most important pests, and as a guide to how yield is lost. Crop yield is seen as a balanced system, with inputs and output. The methods of quantifying pest attack, measuring losses and the difficulties met are discussed: the interaction of losses, interplot interference, mixed crops, loss distribution and crop compensation. Surveys of loss are described, with examples.