Summoning the wind: Hydrodynamic cooperation of forcibly ejected fungal spores

The forcibly launched spores of the crop pathogen \emph{Sclerotinia sclerotiorum} must eject through many centimeters of nearly still air to reach the flowers of the plants that the fungus infects. Because of their microscopic size, individually ejected spores are quickly brought to rest by drag. In the accompanying fluid dynamics video we show experimental and numerical simulations that demonstrate how, by coordinating the nearly simultaneous ejection of hundreds of thousands of spores,\emph{Sclerotinia} and other species of apothecial fungus are able to sculpt a flow of air that carries spores across the boundary layer and around intervening obstacles. Many spores are sacrificed to create this flow of air. Although high speed imaging of spore launch in a wild isolate of the dung fungus \emph{Ascobolus} shows that the synchronization of spore ejections is self-organized, which could lead to spores delaying their ejection to avoid being sacrificed, simulations and asymptotic analysis show that, close the fruit body, ejected spores form a sheet-like jet that advances across the fruit body as more spores are ejected. By ejecting on the arrival of the sheet spores maximize \emph{both} their range and their contribution to the cooperative wind.Comment: Submission to the DFD 2009 Gallery of Fluid Motio

Seasonal and Spatial Dynamics of Alate Aphid Dispersal in Snap Bean Fields in Proximity to Alfalfa and Implications for Virus Management

Alfalfa is a source for viruses that may be acquired by aphids and transmitted to snap bean, Phaseolus vulgaris L. Snap bean fields in proximity to alfalfa could have an increased risk of virus infection. Knowledge of the abundance and temporal and spatial dispersal patterns of commonly encountered aphids in commercial snap bean fields, varying in distance from alfalfa, could provide insight into this risk. Alate aphids were monitored using water pan traps in snap bean and alfalfa fields that were adjacent to or >1 km away from each other. The pea aphid, Acyrthosiphon pisum (Harris), was the most common aphid species captured in early-planted snap bean fields in 2002 and 2003 (56 and 23% of total, respectively), whereas the corn leaf aphid, Rhopalosiphum maidis (Fitch), also was common in 2003 (15% of total). In contrast, the yellow clover aphid, Therioaphis trifolii (Monell), and soybean aphid, Aphis glycines Matsumura, were the most abundant species trapped in late-planted snap bean fields in 2002 (77% of total) and 2003 (64% of total), respectively. These species were prevalent in traps in alfalfa as well. The abundance and temporal dispersal patterns of these species in snap beans adjacent to and >1 km away from alfalfa were similar, suggesting that the risk for virus infection may not be affected by proximity to alfalfa. A similar number of alate aphids also were captured along snap bean field edges and field centers, regardless of their proximity to alfalfa. This suggests that the aphids dispersed into snap bean randomly rather than directionally from the field edge. The implication of these results is that separating snap bean fields from alfalfa or using crop borders/barriers are not likely to be successful virus management strategie

Modeling Temporal Trends in Aphid Vector Dispersal and Cucumber Mosaic Virus Epidemics in Snap Bean

Cucumber mosaic virus (CMV) has become a major limiting factor in snap bean production in the Great Lakes region of North America, and epidemics have occurred more frequently since the soybean aphid, Aphis glycines Matsumura, was introduced. Major aphid vectors of CMV epidemics were identified by statistically relating their temporal dispersal trends to the incidence of CMV. Alates were monitored weekly using water pan traps in 74 snap bean fields in New York and Pennsylvania from 2002 to 2006. Plants were tested for CMV by ELISA one time during late bloom in 2002 and 2003 and weekly over the season from 2004 to 2006. Principal vectors of CMV included Acyrthosiphon pisum (Harris), A. glycines, Aphis gossypii Glover, and Therioaphis trifolii (Monell). Among these, A. glycines and T. trifolii were likely responsible for severe CMV epidemics because they were among the most abundant species captured, they efficiently transmit CMV, and their dispersal activity was positively correlated with periods when CMV incidence was highest. Moreover, because high numbers of A. glycines and T. trifolii disperse during July and August, snap bean fields planted beyond late June are at risk for infection during early vegetative stages and are subsequently more at risk for yield loss. In contrast, plantings up to late June are less likely to become infected during early developmental stages and should escape yield loss because major vectors are dispersing infrequently. CMV-resistant or tolerant snap bean varieties should be planted after late June to reduce the risk of yield los

Sclerotinia Rot of Cabbage

NYS IPM Type: Vegetables IPM Fact SheetSclerotinia rot of cabbage (sometimes referred to as white mold) affects cabbage cultivars grown for sauerkraut, storage, and fresh market. The disease is caused by the fungus Sclerotinia sclerotiorum. This fungus can cause serious losses in the field, in storage, and under transit and market conditions. S. sclerotiorum is widely distributed in relatively cool and moist areas throughout the world. The fungus has a wide host range and is known to attack over 360 species of plants. In the Cruciferae family alone, it has been recorded on 18 genera and 32 species. In New York State the fungus is capable of infecting many types of vegetables and is particularly serious on snap beans. It also infects weeds such as ragweed, dandelion, and wild clover

Bean Anthracnose

NYS IPM Type: Vegetables IPM Fact SheetBean anthracnose, caused by the fungus Colletotrichum lindemuthianum, is a major disease of beans (Phaseolus vulgaris L.), causing serious crop loss in many parts of the world. In 1921, M. F. Barrus of Cornell University demonstrated that bean anthracnose is seedborne. This information resulted in the widespread use of anthracnose-free seed and a subsequent decline in the occurrence of bean anthracnose in the United States. In bean-growing areas that receive frequent rainfall, however, such as central and western New York State, epidemics of the disease may develop. Production is reduced because of poor seed germination, poor seedling vigor, and low yields. Marketing losses are attributed to seed spots and blemishes, which lower their quality rating and salability. The disease is most common and severe on dry and snap beans (P. vulgaris) but may also affect lima bean (P. lunatus L.), scarlet runner bean (P. multiflorus Willd.), mung bean (P. aureus Roxb.), cowpea (Vigna sinensis Savi ), and broad bean (Vicia faba L.)

Tomato Anthracnose

NYS IPM Type: Vegetables IPM Fact SheetTomato anthracnose is a serious disease of processing tomatoes caused by the fungus Colletotrichum coccodes and is a threat to tomatoes grown in New York State. To minimize the mold count in processed tomato products, processors impose a strict limit on the amount of anthracnose acceptable on the raw product. The most recently published United States Standards for Grades of Tomatoes for Processing exemplifies the low tolerance level for anthracnose: a tomato is classified as a cull when it has more than two anthracnose lesions or lesion(s) aggregating more than a circle three-eighths inch in diameter

Developing Management Strategies for Bacterial Canker on Tomatoes

ReportThe objective of this study was to identify sources of on-farm inoculum of Clavibacter michiganensis subsp. michiganensis (CMM), the causal agent of bacterial canker of tomatoes. Two hundred ninety seven samples from inanimate (swabbing from walls, floor, wood, hoses, etc.) and animate sources (weeds, other plants, tomatoes) from 3 commercial greenhouses were tested to see if they carried the CMM pathogen. A wide variety of methods were utilized in attempts to conclusively identify the bacteria, including an agglutination kit and a commercial diagnostic testing service that used a quick ELISA test. Any bacteria isolated that were likely to be the pathogen were further tested to see if they could cause disease on tomatoes. The various isolation procedures were cumbersome, slow, expensive, and difficult to interpret since none were diagnostic alone. The disease organism is difficult to isolate, identify conclusively, and even more difficult to prove to cause disease

Tomato Late Blight Forecasts: True Forecasting with Adaptation to Disease Management Practices

NYS IPM Type: Project ReportAs a result of the growing concern about exotic genotypes of the late blight fungus and recent availability of 48-hr weather forecasts linked to a revised BLITECAST, we proposed to evaluate tomato late blight management for fresh market tomatoes. A new algorithm for late blight was developed and adapted for use with E-Weather, a weather forecasting product from SkyBit, Inc. We evaluated this product at four locations in western New York in conjunction with another NYS IPM project on TOMCAST, a tomato early blight forecast system. The 1998 project was limited to the comparison of forecast periods of late blight infection and actual disease observations

Bacterial Diseases of Beans

NYS IPM Type: Vegetables IPM Fact SheetThere are three distinct bacterial diseases found on snap and dry beans in New York State: Bacterial brown spot, caused by Pseudomonas syringae pv. syringae, common bacterial blight, caused by Xanthomonas campestris pv. phaseoli, and halo blight, caused by Pseudomonas syringae pv. phaseolicola

Flea Beetle Pests of Vegetables

NYS IPM Type: Vegetables IPM Fact SheetFlea beetles are common pests and frequently do serious damage to vegetable crops. Excessive feeding damage by flea beetles can stress and kill young plants. On maturing crops, feeding may scar leaves or fruit, resulting in cosmetic damage and reduced crop value at harvest. Some species are important vectors of crop disease. Flea beetles rapidly colonize crops at the onset of warm spring weather and serious damage can occur quickly. Species occurring in the northeastern United States include the corn, potato, crucifer, eggplant, striped, horseradish, palestriped, and tobacco flea beetle. Some of these are consistent pests, whereas others only occasionally cause serious damage. As the names imply, there is a certain degree of crop specificity associated with the various species of flea beetles, although many feed on several crops and numerous weeds. On occasion, other species of flea beetles may be present and cause damage to vegetables