Experimental In-Field Transfer and Survival of Escherichia coli from Animal Feces to Romaine Lettuce in Salinas Valley, California.

This randomized controlled trial characterized the transfer of E. coli from animal feces and/or furrow water onto adjacent heads of lettuce during foliar irrigation, and the subsequent survival of bacteria on the adaxial surface of lettuce leaves. Two experiments were conducted in Salinas Valley, California: (1) to quantify the transfer of indicator E. coli from chicken and rabbit fecal deposits placed in furrows to surrounding lettuce heads on raised beds, and (2) to quantify the survival of inoculated E. coli on Romaine lettuce over 10 days. E. coli was recovered from 97% (174/180) of lettuce heads to a maximal distance of 162.56 cm (5.33 ft) from feces. Distance from sprinklers to feces, cumulative foliar irrigation, and lettuce being located downwind of the fecal deposit were positively associated, while distance from fecal deposit to lettuce was negatively associated with E. coli transference. E. coli exhibited decimal reduction times of 2.2 and 2.5 days when applied on the adaxial surface of leaves within a chicken or rabbit fecal slurry, respectively. Foliar irrigation can transfer E. coli from feces located in a furrow onto adjacent heads of lettuce, likely due to the kinetic energy of irrigation droplets impacting the fecal surface and/or impacting furrow water contaminated with feces, with the magnitude of E. coli enumerated per head of lettuce influenced by the distance between lettuce and the fecal deposit, cumulative application of foliar irrigation, wind aspect of lettuce relative to feces, and time since final irrigation. Extending the time period between foliar irrigation and harvest, along with a 152.4 cm (5 ft) no-harvest buffer zone when animal fecal material is present, may substantially reduce the level of bacterial contamination on harvested lettuce

Microbiological quality of lettuce (Lactuca sativa) consumed on the streets of Maroua (Cameroon: Effect of disinfecting agents used by some vendors

This study was carried out to determine and compare the microbiological quality of lettuce (Lactuca sativa) from market (unwashed) and those ready to eat in Maroua. The results revealed that 92.3% of lettuce vendors in Maroua, used Chlorine and 7.7% used potassium permanganate as cleaning method. The microbial concentration of lettuce varied from one vendor to another. Total flora ranged from 2.3 to 4.9 Log CFU/g for unwashed samples and from 2 to 4.51 Log CFU/g for washed samples; fungi counts were comprised between 0.76 to 2.65 Log CFU/g for unwashed samples and 0.26 to 2.17 Log CFU/g for washed samples; total coliforms ranged from 2.84 to 3.60 Log CFU/g for unwashed, and 0.26 to 3.00 Log CFU/g for washed lettuce; fecal coliforms ranged from 1.29 to 3.60 Log CFU/g for unwashed samples and 1.70 to 3Log CFU/g for washed samples. These results show also that Vibrio spp. was found amongst the 69% of unwashed samples, but was absent in all the washed samples. Salmonella spp. was present in 85% samples of unwashed lettuce, but absent in washed samples. The results revealed also that; there was a significant difference between the bacterial concentration of unwashed and washed lettuce samples (P<0.05). Most of the analysed samples (92%) composed of washed and unwashed samples were not satisfactory for consumption. (Résumé d'auteur

An Evaluation of the Economic, Environmental and Social Impacts of NSW DPI Investments in IPM Research in Lettuce

Research into IPM technologies has been conducted by NSW DPI for over 20 years. Evaluating the returns from investment in specific research and development projects is an important component of the NSW DPI science and research program. An economic evaluation has been conducted of IPM in managing invertebrate pests in lettuce in NSW. We found that there has been widespread adoption of IPM practices amongst NSW lettuce growers leading to a flow of economic benefits to the lettuce industry and the community. Important environmental and human health benefits were also identified. A benefit-cost ratio of 2 was calculated for the return to NSW DPI investment in lettuce IPM research which while satisfactory, is lower than returns calculated for other agricultural R&D. It does not include ‘spillover’ benefits to other States nor have human health or environmental benefits been valued.research, benefit-cost, evaluation, IPM (Integrated Pest Management), lettuce, Crop Production/Industries, Environmental Economics and Policy, Farm Management, Production Economics, Q160,

Returns to investment in IPM research in lettuce by NSW DPI

Research into IPM technologies has been conducted by NSW DPI for over 20 years. Evaluating the returns from investment in specific research and development projects is an important component of the NSW DPI science and research program. An economic evaluation has been conducted of IPM in managing invertebrate pests in lettuce in NSW. We found that there has been widespread adoption of IPM practices amongst NSW lettuce growers leading to a flow of economic benefits to the lettuce industry and the community. Important environmental and human health benefits were also identified. A benefit-cost ratio of 2 was calculated for the return to NSW DPI investment in lettuce IPM research which while satisfactory, is lower than returns calculated for other agricultural R&D evaluations. It does not include ‘spillover’ benefits to other States nor have human health or environmental benefits been valued.research, benefit-cost, evaluation, IPM (Integrated Pest Management), lettuce, Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,

CERTIFICATION AND SUPPLY RESPONSE IN THE ORGANIC LETTUCE MARKET

The impact of supply relationships and certification programs on the organic lettuce market is examined using an integrated partial adjustment and asymmetric supply response model. Costs associated with organic certification, production, and marketing have not restricted producersÂ’' abilities to respond to price signals. Organic growers allocate output between certified and noncertified markets in response to changing price premiums. Estimates of short-run supply elasticities indicate that organic lettuce growers are more responsive to price changes than producers of nonorganic lettuce. Long-run elasticity has increased since 1988, a change that coincides with the market entry of larger producers.Crop Production/Industries, Industrial Organization,

AN IMPERFECTLY COMPETITIVE MARKET MODEL OF THE U.S. LETTUCE INDUSTRY

An econometric model was specified to represent the U.S. lettuce industry. Cursory examination of the industry structure suggests that imperfect competition may prevail in the lettuce market. Therefore, relations were specified that allowed for the possibility of imperfectly competitive behavior to affect market equilibrium outcomes. Specifically, a supply price equation was specified to account for the influence of market power of large growers, particularly during seasons of geographically concentrated production. Results do not contradict the hypothesis that imperfect competition exists in the lettuce market.Industrial Organization,

Effect of weed management strategies on the risk of enteric pathogen transfer into the food chain and lettuce quality

The hygienic quality of raw edible vegetables such as lettuce may be influenced by pathogen transfer from soil to plant, which might occur during weed control by hoeing or as splash-effects during rainfall. The hygienic quality is often discussed when farmyard manures are applied during production, as e.g. in organic farming systems. In a field experiment, the effects of weed control on pathogen transfer from soil fertilised with farmyard manure to lettuce (Lactuca sativa, var. capitata) were evaluated. First results do not confirm pathogen transfer by mechanical weeding or splash effects during rainfall

A comparison of Olpidium isolates from a range of host plants using internal transcribed spacer sequence analysis and host range studies

Olpidium brassicae is a ubiquitous obligate root-infecting fungal pathogen. It is an important vector of a wide range of plant viruses. Olpidium isolates that infected brassica plants did not infect lettuce plants and vice-versa. Host range tests, PCR amplification and sequencing of the internal transcribed spacer (ITS) and 5.8S regions of 25 Olpidium isolates from brassica, carrot, cucumber and lettuce originating from four continents revealed differences between isolates. Based on their ability to infect lettuce and brassicas and the differences between their ITS1, 5.8S and ITS2 regions they could be separated into a number of distinct groups. Comparisons with other published sequences revealed two distinct genetic groups of brassica-infecting isolates, two distinct groups of lettuce-infecting isolates, one of which contained a carrot-infecting isolate and a distinct group comprising a cucumber-infecting isolate and a melon-infecting isolate. The possibility of the isolates belonging to three distinct species is discussed

Root growth and soil nitrogen depletion by onion, lettuce, early cabbage and carrot

Experiments examining root growth, the utilization of N and the effect of green manures were carried out on four vegetable crops. Large differences were observed both in rooting depth penetration rates, and in final rooting depth and distribution. Onion had a very low depth penetration rate, carrot an intermediate rate, and lettuce and cabbage showed high rates. A combination of depth penetration rates and duration of growth determined rooting depth at harvest. Therefore, lettuce, which had a very short growing season, had a shallow root system at harvest, whereas carrot with a lower depth penetration rate but a long growing season had deep rooting at harvest. The final rooting depth of the vegetables varied from approximately 0.3 m for onion to more than 1.0 m for carrot and early cabbage. Carrot and cabbage were able to utilize N from deeper soil layers, not available to onion and lettuce. The ability of green manure crops to concentrate available N in the upper soil layers was especially valuable when they were grown before the two shallow rooted crops

Nutrient supply from organic amendments applied to unvegetated soil, lettuce and orchardgrass

Organic sources of nutrients are increasingly being used in horticultural and certified organic production. The nutrient-supplying potentials of poultry manure compost (PM), feather meal (FM), alfalfa meal (AA) and vermicastings (VC) and an unamended control were measured in a growth room experiment. The amendments were applied at rates equivalent to 200, 400 and 800 kg total N ha-1 to a soil of low fertility. Nitrogen supply rates and concentrations were measured over 6 mo in unvegetated pots using PRS™ probes and KCl extraction, respectively. Biomass of lettuce (Lactuca sativa L.) and orchardgrass (Dactylis glomerata L.) and N uptake of orchardgrass were measured. Repeated measures analysis revealed significant amendment × rate × time interaction effects for N supply rate and concentration. Of total N applied, available N was 50 to 70% in the FM and PM treatments, 10 to 40% in the AA treatments, and 10% in the VC treatments. High rates of FM and PM were toxic to lettuce but produced good orchardgrass yields. VC was safe for lettuce but low N availability limited long-term orchardgrass growth. Higher application rates did not result in corresponding increases in nutrient supply. Consideration should be given to balancing the ratio of available nutrients in amendments with plant requirements