Potential Crop Losses Research Articles

Borer damage and estimation of losses caused by Sesamia grisescens Walker (Lepidoptera: Noctuidae) in sugarcane in Papua New Guinea

Sesamia grisescens Walker (Lepidoptera: Noctuidae) is a serious pest of sugarcane in Papua New Guinea. Field studies on borer damage and potential crop losses were carried out at Ramu Sugar estate between 1986 and 1996. Apart from the direct losses in cane weight (cane yield) due to boring from the larvae, cane juice quality is also adversely affected, resulting in lower recovery of sucrose in the factory. Estimated cane losses were 0.82 tonnes cane ha- 1 and sugar losses were 0.13 tonnes sugar ha- 1 for every 1% bored and rotting stalks. In 1987 losses of up to 32 tonnes cane or 3 tonnes sugar ha- 1 valued at more than US$ 1800 were observed. Other indirect losses are also discussed.

Global crop production and the efficacy of crop protection - current situation and future trends

Actual and potential crop losses of eight major food and cash crops have been estimated by evaluating data from literature and field experiments. Total losses were calculated from yield reductions due to pathogens, animal pests and weeds on a regional, continental and global level. Since 1965, worldwide production of most crops has increased considerably. Simultaneously, crop losses in wheat, potatoes, barley and rice increased by 4 to 10 percent, in maize, soybean, cotton and coffee losses remained unchanged or slightly decreased. The efficacy of crop protection practices was calculated as the percentage of potential losses prevented by control. The efficacy is highest in cotton (55 percent), it reaches only 34 to 38 percent in the food crops rice, wheat and maize. The variability among cropping areas is high: In Western Europe, 61 percent of potential crop losses is prevented, in North America and Oceania 44, in all other regions 38 percent. Due to the small share of Western Europe in worldwide production of 8 percent, the efficacy of actual crop protection worldwide is only 40 percent. In view of population growth and rising food demand crop production has to be increased substantially. As potential loss rates often increase with attainable yields high productivity largely depends on effective crop protection management. Scenarios for the production of food crops by the year 2025 in developed and in developing countries are given. Recent and future developments in crop protection can contribute to establish sustainability in agriculture and to preserve natural resources. However, although effective control methods have been developed for most biotic yield constraints, the use of crop protection products is regulated by economic considerations rather than by food demand.

THE RESPONSE OF FLAX TO DIFFERENT POPULATION DENSITIES OF THE RED-BACKED CUTWORM, EUXOA OCHROGASTER (GN.) (LEPIDOPTERA: NOCTUIDAE)

AbstractControlled field studies carried out in plots within a field of NorMan flax, Linum usitatissum L., showed that the loss of flax plants caused by the red-backed cutworm was proportional to the number of cutworm larvae present. A density of 16 larvae per 0.5 m2 destroyed most plants by severing the plant stems at the soil surface. The loss of only some plants at larval densities lower than 16 larvae per 0.5 m2 resulted in a small but significant increase in per plant yield but the increase did not completely compensate for the yield reductions caused by plant loss. The larvae removed plants in blocks with the result that the density of the remaining plants was unchanged and the opportunity for compensating plant growth was limited. An equation defining this relationship between larval densities and yield is presented. Ancillary experiments in which the population of cutworm larvae was sequentially sampled showed that, after an initial loss of about 20% when the plots were established in the field, the larval population remained constant. The proportion of the larvae found around damaged plants also remained constant until the larvae became immobile through preparation for pupation. Because of this stable relationship, reliable estimates of potential crop loss from cutworm larvae in flax should be possible by sampling for cutworms only around damaged plants within a specified row length.

Crop loss assessment for California: Modeling losses with different ozone standard scenarios

Crop yield losses were estimated for ambient O 3 concentrations and for a series of potential O 3 air quality standards for California, including the current statewide 1-h oxidant (O 3) standard of 0·10 ppm (196 μg m −3), 12-h growing season averages, and other models. A model for statewide losses was developed using hourly O 3 data for all sites in the State, county crop productivity data, and available O 3 concentration-yield loss equations to determine potential yield losses for each crop in each county in California for 1984. Losses were based on comparison to an estimated background filtered air concentration of 0·025 or 0·027 ppm, for 12 or 7 h, respectively. Potential losses due to ambient air in 1984 were estimated at 19% to 25% for dry beans, cotton, grapes, lemons, onions, and oranges. Losses of 5% to 9% were estimated for alfalfa and sweet corn. Losses of 4% or less were estimated for barley, field corn, lettuce, grain sorghum, rice, corn silage, spinach, strawberries, sugar beets, fresh tomatoes, processing tomatoes, and wheat. Implementation of either a modified rollback to meet the current 1 h California O 3 standard (0·10 ppm) or a three-month, 12-h growing season average of 0·045 ppm was necessary to produce large reductions in potential crop losses.

Crop loss due to ambient ozone in the Tennessee valley

Rural and urban ozone (O 3) monitoring data for the Tennessee Valley and crop loss models developed under the National Crop Loss Assessment Network (NCLAN) were used to estimate potential yield reductions for winter wheat, corn, soybean, cotton, and tobacco during the 1982 to 1984 growing seasons. Reductions from 0 to 20% of potential crop yields were estimated due to ambient O 3. Rural O 3 exposures measured in the Tennessee Valley were significantly higher than the measured urban exposures, suggesting that spatial interpolation from urban O 3 records may underestimate rural O 3 and thereby potential crop loss. Seasonal mean O 3 exposures were highest in summer 1983, and similar in 1982 and 1984. Although a consistent inverse relationship was found between measured crop yields in the Tennessee Valley and seasonal O 3 exposures, annual variation in yields was much greater than attributable to the annual variation in O 3. Moisture stress, as indicated by the Palmer Drought Severity Indices, is likely the major determinant for yields of nonirrigated crops. This is consistent with field studies that demonstrate that ambient O 3 levels can reduce crop yields under ideal soil moisture conditions, but cause little to no detectable yield reduction for nonirrigated crops. These models could be improved if crop response to O 3 were allowed to vary as a function of environmental factors such as moisture stress.

Modeling the Relationship Between Transient Vector Densities and Plant Disease Incidence with Special Reference to Bemisia tabaci (Homoptera: Aleyrodidae) and Lettuce Infectious Virus Yellows

Transient vectors (those that do not reproduce on the disease-affected crop) can cause difficulties in assessing potential crop losses to disease. A probability model is presented that relates density of transient vectors (over time) to disease incidence in the crop at harvest. The application of the model is illustrated with reference to Bemisia tabaci (Gennadius), an insect that vectors infectious virus yellow in lettuce in the Imperial Valley of California.