Crop

Abstract: Crop pathogens and pests reduce the yield and quality of agricultural production. They cause substantial economic losses and reduce food security at household, national and global levels. Quantitative, standardized information on crop losses is difficult to compile and compare across crops, agroecosystems and regions. Here, we report on an expert-based assessment of crop health, and provide numerical estimates of yield losses on an individual pathogen and pest basis for five major crops globally and in food security hotspots. Our results document losses associated with 137 pathogens and pests associated with wheat, rice, maize, potato and soybean worldwide. Our yield loss (range) estimates at a global level and per hotspot for wheat (21.5% (10.1–28.1%)), rice (30.0% (24.6–40.9%)), maize (22.5% (19.5–41.1%)), potato (17.2% (8.1–21.0%)) and soybean (21.4% (11.0–32.4%)) suggest that the highest losses are associated with food-deficit regions with fast-growing populations, and frequently with emerging or re-emerging pests and diseases. Our assessment highlights differences in impacts among crop pathogens and pests and among food security hotspots. This analysis contributes critical information to prioritize crop health management to improve the sustainability of agroecosystems in delivering services to societies. An expert elicitation survey estimates yield losses for the five major food crops worldwide, suggesting that the highest losses are associated with food-deficit regions with fast-growing populations and frequently with emerging or re-emerging pests and diseases.

Abstract: Crop heterogeneity is a possible solution to the vulnerability of monocultured crops to disease1,2,3. Both theory4 and observation2,3 indicate that genetic heterogeneity provides greater disease suppression when used over large areas, though experimental data are lacking. Here we report a unique cooperation among farmers, researchers and extension personnel in Yunnan Province, China—genetically diversified rice crops were planted in all the rice fields in five townships in 1998 and ten townships in 1999. Control plots of monocultured crops allowed us to calculate the effect of diversity on the severity of rice blast, the major disease of rice5. Disease-susceptible rice varieties planted in mixtures with resistant varieties had 89% greater yield and blast was 94% less severe than when they were grown in monoculture. The experiment was so successful that fungicidal sprays were no longer applied by the end of the two-year programme. Our results support the view that intraspecific crop diversification provides an ecological approach to disease control that can be highly effective over a large area and contribute to the sustainability of crop production.

Abstract: cab can be a devastating disease affecting all classes of wheat and other small grains. This fungal disease, also called Fusarium head blight (FHB), has the ability to completely destroy a potentially high-yielding crop within a few weeks of harvest. Lush, green fields become blighted seemingly overnight (Figs. 1 and 2). Frequent rainfalls, high humidities, and/or heavy dews that coincide with the flowering and early kernel-fill period of the crop favor infection and development of the disease. Damage from head scab is multifold: reduced yields, discolored, shriveled “tombstone” kernels (Figs. 3 to 5), contamination with mycotoxins, and reduction in seed quality. The disease also reduces test weight and lowers market grade. Difficulties in marketing, exporting, processing, and feeding scabby grain are experienced. In North America, Fusarium graminearum Schwabe (teleomorph Gibberella zeae (Schwein.) Petch; synonym = G. saubinetti) predominates among several Fusarium species that can cause scab (4,5,8,40,48,60). Other species may predominate in cooler climates or where crops other than wheat and corn are dominant (8,40,48,60). F. graminearum also is associated with stalk and ear rot of corn and may cause a root rot of cereals. The fungus persists and multiplies on infected crop residues of small grains and corn. The chaff, light-weight kernels, and other infected head debris of wheat and barley, returned to the soil surface during harvest, serve as important sites of overwintering of the fungus. Continued moist weather during the crop growing season favors development of the fungus, and spores are windblown or water-splashed onto heads of cereal crops. Wheat and barley are susceptible to head infection from the flowering (pollination) period up through the soft dough stage of kernel development. Spores of the causal fungus may land on the exposed anthers of the flower and then grow into the kernels, glumes, or other head parts. Excellent descriptions of the disease cycle and spore stages of the causal fungi have been published (4,8,21,40,48). Mycotoxins are frequently associated with the growth and invasion of cereal grains by scab fungi. The most common toxin associated with F. graminearum– infected grain is vomitoxin (deoxynivalenol). Vomitoxin is known to cause vomiting and feed refusal in nonruminant animals and poses a threat to other animals and humans if exposure levels are high (45). The presence of mycotoxins in infected grain further exacerbates the losses that scab can cause. Recent articles have reviewed the epidemiology, management, and history of scab outbreaks in the United States, Canada, Europe, Asia, and South America (5,40,45,48). As these papers indicate, numerous research and survey reports have described the worldwide occurrence and epidemic levels of scab during the past century. Yield loss reports have not always been based on replicated research trials, but extensive surveys of producers’ fields have provided assessments of head blighting severity, which were translated into yield loss estimates. In the United States, scab was found in 31 of 40 states surveyed in 1917, with losses estimated at 288,000 metric tons (10.6 million bushels), primarily in Ohio, Indiana, and Illinois (4). Scab caused an estimated loss of 2.18 million metric tons (80 million bushels) of winter and spring wheat throughout the United States in 1919 (14). Extensive field surveys

Abstract: [1] To support global-scale assessments that are sensitive to agricultural land use, we developed the global data set of monthly irrigated and rainfed crop areas around the year 2000 (MIRCA2000). With a spatial resolution of 5 arc min (about 9.2 km at the equator), MIRCA2000 provides both irrigated and rainfed crop areas of 26 crop classes for each month of the year. The data set covers all major food crops as well as cotton. Other crops are grouped into categories (perennial, annual, and fodder grasses). It represents multicropping systems and maximizes consistency with census-based national and subnational statistics. According to MIRCA2000, 25% of the global harvested areas are irrigated, with a cropping intensity (including fallow land) of 1.12, as compared to 0.84 for the sum of rainfed and irrigated harvested crops. For the dominant crops (rice (1.7 million km2 harvested area), wheat (2.1 million km2), and maize (1.5 million km2)), roughly 60%, 30%, and 20% of the harvested areas are irrigated, respectively, and half of the citrus, sugar cane, and cotton areas. While wheat and maize are the crops with the largest rainfed harvested areas (1.5 million km2 and 1.2 million km2, respectively), rice is clearly the crop with the largest irrigated harvested area (1.0 million km2), followed by wheat (0.7 million km2) and maize (0.3 million km2). Using MIRCA2000, 33% of global crop production and 44% of total cereal production were determined to come from irrigated agriculture.