Evaluating the impact of turf-care products on soil biological health.

Golf courses require extensive use of inputs to meet the needs of playability and aesthetics. The impact of these inputs on soil biological health is largely unknown. Two field trials were conducted at a golf course in Georgia to evaluate short-term effects of wetting agents (Cascade Plus and Duplex [C+D], Revolution [Rev]), plant growth regulators (PrimoMaxx [PM] and Cutless [CL]), and a product called PlantHelper (PH) on soil biological health by measuring microbial abundance and function. Quantitative polymerase chain reaction was used to measure microbial abundance, which included total bacteria, total fungi, and ammonia-oxidizing prokaryotes. Soil respiration and enzyme assays were used as additional indicators of soil health. In bentgrass putting green, total bacteria and ammonia-oxidizing bacteria decreased in abundance in response to the wetting agents and PH, indicating their sensitivity to the products. Whereas C+D stimulated urease activity, Rev and PH caused a short-lived but immediate increase in respiration, indicating that they acted as labile carbon sources. In a bermudagrass fairway, PM was the only product that caused an increase in total bacteria abundance. PrimoMaxx and CL caused a delayed increase in respiration, suggesting that they may have affected the microorganisms indirectly through their impact on root growth and exudate production later. Although CL caused a decrease in urease activity, none of the products significantly affected phosphatase activity. Overall, the products did not seem to have a lasting impact on soil biological health, although long-term studies are needed to confirm these observations.

Isolating the impact of septic systems on fecal pollution in streams of suburban watersheds in Georgia, United States.

The presence of multiple sources of fecal pollution at the watershed level presents challenges to efforts aimed at identifying the influence of septic systems. In this study multiple approaches including targeted sampling and monitoring of host-specific Bacteroidales markers were used to identify the impact of septic systems on microbial water quality. Twenty four watersheds with septic density ranging from 8 to 373 septic units/km2 were monitored for water quality under baseflow conditions over a 3-year period. The levels of the human-associated HF183 marker, as well as total and ruminant Bacteroidales, were quantified using quantitative polymerase chain reaction. Human-associated Bacteroidales yield was significantly higher in high density watersheds compared to low density areas and was negatively correlated (r = -0.64) with the average distance of septic systems to streams in the spring season. The human marker was also positively correlated with the total Bacteroidales marker, suggesting that the human source input was a significant contributor to total fecal pollution in the study area. Multivariable regression analysis indicates that septic systems, along with forest cover, impervious area and specific conductance could explain up to 74% of the variation in human fecal pollution in the spring season. The results suggest septic system impact through contributions to groundwater recharge during baseflow or failing septic system input, especially in areas with >87 septic units/km2. This study supports the use of microbial source tracking approaches along with traditional fecal indicator bacteria monitoring and land use characterization in a tiered approach to isolate the influence of septic systems on water quality in mixed-use watersheds.

A Multivirus Epidemic of Tomatoes in Alabama.

During 1992, a multivirus epidemic reduced tomato production by as much as 25% in the major tomato-growing region of Alabama. Estimated yield losses of 100% resulted from the epidemic in over 250 ha in two counties of North Alabama. Cucumber mosaic cucumovirus (CMV), alone or in combination with potato potyvirus Y (PVY) and/or tobacco etch potyvirus (TEV), was responsible for the crop failure. CMV was detected alone or in combination with PVY and/or TEV in over 70% of the samples tested and was present in 90% of the fields surveyed. In 1993, 21 tomato fields were monitored weekly from transplanting through harvest for CMV, PVY, TEV, tobacco mosaic tobamovirus, and tomato spotted wilt tospovirus. All 5 viruses were detected, with CMV occurring most frequently. Incidence of CMV at the 61% level or higher was found in 16 of the 21 fields surveyed. Tomatoes transplanted in April and May were least effected and had relatively low virus incidence until late in their development. Tomatoes transplanted in June and July were infected at an earlier age, had the highest virus incidence, were the most severely affected, and suffered the greatest loss in yield. In 1994,Aphis gossypii, the cotton aphid, was the most common virus vector found during an aphid monitoring/virus spread study. Populations of A. gossypii peaked in late June, immediately preceding a period of rapid CMV incidence and spread.

Yield Loss Assessment of Barley Yellow Dwarf Disease on Spring Oat in Illinois.

The quantitative relationship between yield of spring oat cvs. Ogle and Noble and incidence of barley yellow dwarf (BYD) disease caused by barley yellow dwarf virus (BYDV-PAV-IL) was studied. Field plots were infested with Rhopalosiphum padi vectoring BYDV-PAV-IL. A linear critical point regression model was developed that related percentage of maximum yield to BYD incidence, assessed by estimating the percentage of plants with BYD symptoms at Feekes growth stage 10.5 in each plot. The model y = 96.9 - 0.45x (r2 = 0.53) best explained the relationship. Test weight was unaffected by BYD. Although Noble consistently sustained higher disease incidence than Ogle, covariate analysis indicated that the effect of BYD on yield was similar for both cultivars. Studies of random versus focus inoculation of Noble oat, designed to determine the importance of compensation in reducing yield loss associated with BYD, indicated that compensation did not play an important role.