Browsing by Author "Alexander, Samuel A."
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- Biology and Control of Pepper AnthracnoseMarvel, Josh K. (Virginia Tech, 2003-12-17)Anthracnose (caused by Colletotrichum capsici or C. gloeosporioides) of bell peppers (Capsicum annum) has become a serious problem in recent years on the Eastern Shore of Virginia. The purpose of this research was to characterize isolates of the fungus from the Eastern United States, to compare them with the type species from the American Type Culture Collection, and to evaluate fungicides for disease management. Two cultivars of pepper were inoculated with a conidial suspension, and held in a dew chamber. Lesions were counted and measured every 48 hours. The type species was either not pathogenic or only mildly virulent; most of the virulent isolates originated in areas of intensive pepper production. In addition to pathogenicity experiments and traditional morphology, the Biolog® system was used to compare the ability of fungi to utilize different carbohydrate combinations in 96-well plates. Plates were read at 96 and 168 hours. Analysis of data, by Ward's statistical method, could reliably distinguish field isolates if based on 15 or more replications, but species-level identification was inconsistent. Standard fungicides and new compounds were compared in a field test with four replications of treatments in a randomized complete block design. Fruits were harvested three times, weighed for yield, and the number of marketable and diseased fruit recorded. Aggressive isolates from green pepper were controlled by applications of maneb, or alternation of maneb and strobilurin fungicides.
- Brown Spot Needle blight of ConifersAlexander, Samuel A.; Skelly, John M. (Virginia Cooperative Extension Service, 1977-04)Discussion of brown spot needle blight on conifers including its range, cause, symptom and disease cycle, and control.
- Fluoride Injury to Forest VegetationSkelly, John M.; Alexander, Samuel A. (Virginia Cooperative Extension Service, 1977-11)Discussion of fluoride injury to forest vegetation including its symptoms, diagnostic methods and mimicking symptoms, and control and reduction of loss.
- Needlecast of ConifersAlexander, Samuel A.; Skelly, John M. (Virginia Cooperative Extension Service, 1977-08)Discussion of needlecast of conifers including its cause, symptoms, and control.
- Ozone and Its Effect on Forest TreesSkelly, John M.; Alexander, Samuel A. (Virginia Cooperative Extension Service, 1977-08)Discussion of the ozone and its effect on forest trees in Virginia including its symptoms, diagnostic methods, and control and reduction of losses
- Pine-Pine Rust of Scotch Pine Christmas TreesSkelly, John M.; Alexander, Samuel A. (Virginia Cooperative Extension Service, 1975-11)Discussion of pine rust of scotch pine Christmas trees including its range, cause, and symptoms and signs
- Procerum root disease physiology and disease interactions with ozoneCarlson, Jodi A. (Virginia Tech, 1994-02-17)Procerum root disease of eastern white pine (Pinus strobus L.), caused by Leptographium procerum (Kendr.) Wingf., has been epidemic in Virginia Christmas tree plantations since 1990. Symptoms of chlorosis, wilt, and decreased apical growth resemble those of water stress. Resin infiltration of the xylem at the stem base may be responsible for vascular occlusion leading to severe water deficits and mortality. The pathogen has been isolated from the roots of ozone-sensitive eastern white pines in the field, although not from nearby tolerant trees, and it may be that ozone sensitivity predisposes the trees to infection. The objectives of my Studies were to investigate the physiology of diseased white pines, and to determine the effects of ozone fumigation on disease development. Impacts of vascular occlusion upon host water relations and gas exchange were investigated in 8-yr-old, plantation-grown, white pine Christmas trees. Disease severity was estimated as the proportion of resin-soaked cross-sectional area at the base of the stem. The linear response of a suite of six physiological variables to disease severity was highly significant. Individually, the variables pre-dawn water potential, daily change in pre-dawn to mid-day water potential, stomatal conductance, and photosynthetic and transpiration rates all decreased significantly with increasing disease severity. Fumigation studies were conducted on white and loblolly (P. taeda L.) pine seedlings to determine if ozone exposure increased the incidence of root disease or the amount of stem tissue colonized by L. procerum. Roots were inoculated by soil drenching with conidial suspension, and stems were wounded at the base and inoculated with mycelium. Beginning 24 h post-inoculation, and for 14 consecutive days, seedlings were fumigated in closed chambers with charcoal-filtered air or 200 ppb ozone for 5 h/day, then removed to a charcoal-filtered greenhouse. Six weeks post-inoculation, root and stem tissue were plated on a medium selective for L. procerum. Ozone treatment did not significantly affect the proportion of diseased roots per seedling or the vertical colonization of stem tissue in seedlings of either species.
- Qualitative Determination of Cellulose in the Cell Walls of Verticicladiella proceraHorner, W. Elliott; Alexander, Samuel A.; Julian, Maureen M. (Mycological Society of America, 1986)The presence of cellulose-containing cell walls has been proposed as a taxonomic character in the genus Ceratocystis Ellis and Halsted (Jewell, 1974; Upadhyay, 1981; De Hoog, 1974; De Hoog and Scheffer, 1984; Benny and Kimbrough, 1980; Harrington, 1981; von Arx, 1974). The significance of this trait derives from its scarcity among the fungi. Among the Eumycota sensu von Arx (1974), cellulose is known to occur only in certain species of Ceratocystis s.l (Bartnicki-Garcia, 1968; Barr, 1983; Upadhyay, 1981). With few exceptions, within Ceratocystis s.l, cellulosic cell walls occur in the same species that have holoblastic conidiogeny, cycloheximide tolerance, and cell walls with rhamnose (Harrington, 1981; Jewell, 1974; Spencer and Gorin, 1971; Upadhyay, 1981). De Hoog and Scheffer (1984) summarize the evidence supporting the disposition of these species in Ophiostoma H. & P. Sydow while retaining species with enteroblastic conidiogeny, sensitivity to cycloheximide and neither cellulose nor rhamnose in their cell walls, in Ceratocystis s.s. This suite of characters' biochemical, developmental/morphological, and metabolic-argue strongly for the segregation of these species into Ceratocystis s.s. and Ophiostoma as accepted by recent treatments (De Hoog, 1974; De Hoog and Scheffer, 1984; Benny and Kimbrough, 1980; von Arx, 1974), supported by Harrington (1981) and used herein.
- Reducing copper and chlorothalonil in staked tomato production on Virginia's Eastern ShoreGraves, Arthur S. (Virginia Tech, 2001-06-28)Virginia ranks third in fresh market staked tomato (Lycopersicon esculentum Mill.) production with approximately 1,659 hectares on the Eastern Shore. Estimated annual gross value is $30,800,000. Copper and chlorothalonil have long been considered essential to control bacterial and fungal diseases in fresh market tomatoes. High rates of these fungicides on tomatoes grown under plastic mulch have led to concerns about their potential adverse effect on water quality in estuaries adjacent to fields. The development of new fungicides, such as azoxystrobin and acibenzolar-S-methyl, which have more favorable environmental fate characteristics and are used at much lower rates, may provide viable alternatives to copper and chlorothalonil. Using a disease forecasting system, such as Tomcast, may reduce the number of applications of fungicides. The research objectives of this study were to reduce the amount of copper and chlorothalonil used in fresh market tomato production and to evaluate the effectiveness of the Tomcast disease forecasting system for controlling fungal leaf diseases on the Eastern Shore. Field studies compared copper to acibenzolar-S- methyl for bacterial diseases caused by Xanthomonas campestris pv. vesicatoria and Pseudomonas syringae pv. tomato. Research plots were established in a randomized complete block design with four replications in grower fields and at the Eastern Shore Agricultural Research & Extension Center. Acibenzolar proved to be as effective as the standard copper bactericides in controlling bacterial spot. Acibenzolar provided better control than the standard copper bactericides when bacterial speck was the target disease. Azoxystrobin application alternated with maneb was evaluated as a replacement for chlorothalonil. Azoxystrobin and Tomcast were studied as tools to reduce chlorothalonil use for control of Alternaria solani. Tomcast can reduce the number of applications by 40-70 % per year and provide adequate control of early blight. Azoxystrobin provides better control of early blight than chlorothalonil. Use of these new, more environmentally compatible, plant-protection products , along with the Tomcast disease forecasting system, can significantly reduce or eliminate the need to use copper and chlorothalonil for tomato disease management and therefore eliminate them as potential pollutants of the Chesapeake Bay and Atlantic Ocean estuaries.
- Salt (De-icing) Injury to Roadside TreesSkelly, John M.; Alexander, Samuel A. (Virginia Cooperative Extension Service, 1977-11)Discussion of salt injury to roadside trees including its mechanism of injury, symptoms, and control and alleviation of losses.
- Sulphur Dioxide (SO₂) and Its Effect on Forest TreesSkelly, John M.; Alexander, Samuel A. (Virginia Cooperative Extension Service, 1977-08)Discussion of sulphur dioxide and its effect on forest trees in Virginia including its symptoms, diagnostic methods, and control and reduction of loss.
- Tomato Spotted Wilt VirusKuhar, Thomas P.; Alexander, Samuel A. (Virginia Cooperative Extension, 2009-07-24)Describes tomato spotted wilt virus, their damage to crops, and notes methods of control.
- White Pine Root DeclineSkelly, John M.; Alexander, Samuel A. (Virginia Cooperative Extension Service, 1977-04)Discussion of white pine root decline including its cause, symptoms, range, and control.