Dicamba is a synthetic auxin herbicide that may be applied over the top of transgenic dicamba-tolerant crops. The increasing prevalence of herbicide-resistant weeds has resulted in increased reliance on dicamba-based herbicides in soybean production systems. Because of the high volatility of dicamba it is prone to off-target movement, and therefore concern exists regarding its drift onto nearby specialty crops. The present study evaluates 12 mid-Atlantic vegetable crops species for sensitivity to sublethal rates of dicamba. Soybean, snap bean, lima bean, tomato, eggplant, bell pepper, cucumber, summer squash, watermelon, pumpkin, sweet basil, lettuce, and kale were grown in a greenhouse and exposed to dicamba at 0, 0.056, 0.11, 0.28, 0.56, 1.12, 2.24 g ae ha−1, which is, respectively, 0, 1/10,000, 1/5,000, 1/2,000, 1/1,000, 1/500, and 1/250 of the maximum recommended label rate for soybean application (560 g ae ha−1). Vegetable crop injury was evaluated 4 wk after treatment using visual rating methods and leaf deformation index measurements. Overall, snap bean was the most sensitive crop, with dicamba rates as low as 0.11 g ae ha−1 resulting in significantly higher leaf deformation levels compared with the nontreated control. Other Fabaceae and Solanaceae species also demonstrated high sensitivity to sublethal rates of dicamba with rates ranging 0.28 to 0.56 g ae ha−1 causing higher leaf deformation compared with the nontreated control. While cucumber, pumpkin, and summer squash were no or moderately sensitive to dicamba, watermelon showed greater sensitivity with unique symptoms at rates as low as 0.056 g ae ha−1 based on visual evaluation. Within the range of tested dicamba rates, sweet basil, lettuce, and kale demonstrated tolerance to dicamba with no injury observed at the maximum rate of 2.24 g ae ha−1.

Sulfentrazone was recently granted food-use tolerance approval for use on Brassica head and stem, as well as Brassica leafy vegetables. To date, one sulfentrazone registrant has listed those crops on its use label. In coastal California multiple crops per year including Brassica vegetables are grown in rapid succession; therefore, to avoid injury to rotational crops, herbicides used in those fields must be carefully selected. Given concerns about the relatively long soil persistence of sulfentrazone, studies were conducted to measure the response of direct-seeded carrot, lettuce, onion, spinach, and seeded tomato planted 3, 6, 9, and 12 mo after sulfentrazone application at 0, 112, 224, and 336 g ai ha−1. Eight plant-back studies were conducted during 2010–11 and 2012–13. Data collected were injury estimates, and stand and dry weights. Results indicate that it is safe to plant carrot and tomato 3 mo after sulfentrazone application at rates up to 336 g ai ha−1. Lettuce and green onion should not be planted within 9 mo of sulfentrazone application. Spinach should not be planted within 12 mo of sulfentrazone application.

Burning nettle is a noxious weed that commonly infests coastal California vegetable fields. Weed control programs for lettuce and fresh spinach grown in this area do not adequately control burning nettle, and escaped weeds that mature are highly problematic during hand weeding and harvesting. Information on the biology and ecology of burning nettle is limited, and work was conducted to develop information about this weed. The objectives of this study were to evaluate the effect of temperature on burning nettle germination and to determine its base temperature value, to characterize the germination pattern of this weed and seedbanks under local California coastal conditions, and to estimate the optimal timing for burning nettle removal by herbicides and physical methods. The upper optimal temperature for burning nettle germination was 22.8 C, but there was no difference in the final germination percentage between 4 and 22.8 C. The base temperature was determined to be 3 6 0.2 C, and this information allowed the development of temperature-based optimal control timing models. In the field, burning nettle emerged throughout the year without any seasonal pattern, and germinable seeds were also found in the seedbank throughout the year. Burning nettle was able to complete a growth cycle throughout the year in coastal California. Burning nettle has a short growth cycle that allows it to set viable seeds within 466 6 13 growing degree days (GDD), and this timing is critical for burning nettle removal by herbicides, cultivation, or hand weeding. The optimal timing for phenmedipham application at 180 g ai ha–1 was estimated to be 205 GDD. The germination and seedbank field studies indicate why burning nettle is so well adapted to the mild climate of coastal California. However, results presented here suggest strategies to reduce the burning nettle seedbank, improve its control, and allow more efficient lettuce and fresh spinach production.

The allelopathic potential of a plant has been evaluated on the basis of two indicators: specific activity, which is the specific concentration of the allelochemical to exert a half-maximum effect on a receiver plant (EC50), and total activity in a plant, which is the ratio of the concentration of an allelochemical in the producing plant to its EC50. In the present study, a new indicator, total activity in a soil, which takes into account the effects of a soil on the allelopathy activity, is proposed because allelopathic activity is affected by the presence of soils. The total activity in a soil was calculated by multiplying the “total activity in a plant” with a “soil factor.” In this calculation, we assumed simplified cases for comparison, such that the allelopathic plant materials are evenly incorporated in the soils and the allelochemicals are released from the plant materials to the soils at a constant rate. We conducted bioassay experiments in the presence and absence of soils and cited some published data to calculate the specific activities and total activities in a plant and in a soil. The results indicated that the allelopathies of buckwheat caused by (+)-catechin, Leucaena leucocephala by L-mimosine, Xanthium occidentale by trans-cinnamic acid, and Brassica parachinensis by cis-cinnamic acid were not significant in a volcanic ash soil, an alluvial soil, and a calcareous soil, but the allelopathy of sweet vernalgrass caused by coumarin and Spiraea thunbergii by cis-cinnamoyl glucosides was highly effective in those soils. The allelopathies of Juglans species caused by juglone plus juglone precursors and Mucuna pruriens by L-DOPA would depend highly on the soil types. Although some limitations exist for this approach, the total activity approach would allow for a better quantitative estimation of the allelopathic potential of plant materials in soils.

The performance of the Robovator (F. Poulsen Engineering ApS, Hvals⊘, Denmark), a commercial robotic intrarow cultivator, was evaluated in direct-seeded broccoli and transplanted lettuce during 2014 and 2015 in Salinas, CA, and Yuma, AZ. The main objective was to evaluate the crop stand after cultivation, crop yield, and weed control efficacy of the Robovator compared with a standard cultivator. A second objective was to compare hand weeding time after cultivation within a complete integrated weed management (IWM) system. Herbicides were included as a component of the IWM system. The Robovator did not reduce crop stand or marketable yield compared with the standard cultivator. The Robovator removed 18 to 41% more weeds at moderate to high weed densities and reduced hand-weeding times by 20 to 45% compared with the standard cultivator. At low weed densities there was little difference between the cultivators in terms of weed control and hand-weeding times. The lower-hand weeding time with the Robovator treatments suggest that robotic intrarow cultivators can reduce dependency on hand weeding compared with standard cultivators. Technological advancements and price reductions of these types of machines will likely improve their weed removal efficacy and the long-term viability of IWM programs that will use them.

“Buying local״ has become one of the most important trends in food marketing. Despite widespread public attention, the influence of the “local״ attribute on food prices is not well understood. We aim to begin to fill this gap in research by exploring the presence of a price premium for “local״ in actual market transactions. Using scanner data on fresh packaged lettuce in the Honolulu market and hedonic modeling, we investigate consumers’ revealed preferences for the attribute. Contrary to the positive willingness to pay for local food widely reported in previous studies, we find no local premium for fresh lettuce in the Honolulu market.

The following study assesses cold-season hoop house lettuce production in the context of local food systems’ relative environmental effects. For this purpose, we compare the carbon footprints of leaf lettuce production in two climatic zones, one close to the consumer market and one distant, via environmental impact modeling in SimaPro 7.3. A site-specific scenario is first detailed with organic leaf lettuce locally grown in an East Lansing, Michigan hoop house. This is compared to a hypothetical scenario, modeled using average industry data, with leaf lettuce conventionally grown in California then shipped to East Lansing. The system boundaries used in this analysis extend from manufacturing of farm production inputs to a hypothetical retail gate. We assumed that the consumer drove the same distance to the retailer in each case. The functional unit used is 1 kg of leaf lettuce. Results demonstrate that the distant system exhibits 4.3 times the CO2 ‘footprint’ per kg of lettuce. This nonlocal system also resulted in higher resource depletion, health impact and ecological damage potential as demonstrated via the SimaPro simulation. This study concludes that unheated, hoop house lettuce production, given the assumption on within-area travel, has a smaller carbon footprint than outdoor, distant production, and speaks to both the potential value of more localized food systems and the need for a more diverse set of scenario modeling to understand the boundaries of this value.

The black currant-lettuce aphid, Nasonovia ribisnigri, is an important pest of cultivated lettuce, Lactuca sativa. Since 1982, the control of this aphid on lettuce is largely based on host plant resistance, conferred by the Nr gene, introgressed from Lactuca virosa. The resistance mechanism remains to be identified. N. ribisnigri populations virulent on the Nr-based resistance in lettuce have emerged in several locations in Europe since 2007. The objective of this study was to investigate the resistance mechanism mediated by the Nr gene in lettuce by detailed studies of aphid feeding behaviour and performance. Both avirulent (Nr:0) and virulent (Nr:1) biotypes of N. ribisnigri were studied on five resistant and two susceptible near isogenic lines (NILs). In addition, survival and colony development were quantified. Nr:0 aphids showed a strong decrease in sieve element ingestion and took longer to accept a sieve element on resistant NILs compared with susceptible NILs, and no aphids survived on the resistant NIL. Nr:1 aphids fed and performed equally well on the resistant and susceptible NILs. The resistance mechanism against Nr:0 aphids encoded by the Nr gene seems to be located in the phloem, although we also observed differences in feeding behaviour during the pathway phase to the phloem. Nr:1 aphids were highly virulent to the resistance conferred by the Nr gene. The consequences of the appearance of Nr:1 aphids for control of N. ribisnigri are discussed.

A greenhouse pot culture experiment was conducted to study the effect of graded levels ofwaste mica (0, 10, 20 and 40 g kg-1) on reducing the radiocesium uptake byspinach (Spinacia olerecea L) and lettuce (Lactuca sativaL.) grown in 134Cs-contaminated (at 37 k Bq kg-1 soil)Inceptisols, Vertisols and Ultisols. The biomass yield, and potassium content and itsuptake by crops have been significantly improved by waste mica application. The cropsgrown in Vertisols recorded higher biomass yield, and K content and its uptake as comparedwith Inceptisols and Ultisols. The average 134Cs transfer factor valuesrecorded were : 0.21, 0.17 and 0.26 at the first cutting, 0.15, 0.12 and 0.28 at thesecond cutting and 0.07, 0.05 and 0.23 at the third cutting from Inceptisols, Vertisolsand Ultisols, respectively. Waste mica significantly suppressed radiocesium uptake, theeffect being more pronounced at 40 g mica kg-1soil. There exists an inverserelationship between the 134Cs transfer factors with plant potassium contentand also the K uptake by the crops

Genebanks serve as a rich source of diversity that can be exploited for crop improvement. However, large numbers of accessions usually have to be evaluated to find material with the characters of interest, and therefore, enhanced trait information can facilitate the more efficient selection of accessions by users. In this study, we report on the distribution of resistances to 28 races of downy mildew among 1223 genebank accessions of cultivated lettuce (Lactuca sativa L.) and 14 related wild species. Due to modern plant breeding, the overall level of resistance of cultivars released after 1950 appears to have increased two- to three-fold compared with varieties from earlier periods. Although fully resistant reactions could be observed among the accessions of cultivated lettuce for each of the 28 investigated races, the resistance probability was more than two-fold higher on average for accessions from the wild gene pool. In general, species of the primary gene pool appeared less resistant than those of the secondary or tertiary gene pool. Probabilities for examined Lactuca species ranged from 0.29 for L. serriola to 1.00 for L. perennis compared with 0.19 for cultivated lettuce, with lower overall resistance probabilities observed only for L. altaica, L. dregeana and L. tenerrima. For L. serriola, the closest relative of cultivated lettuce and the wild species with the highest number of examined accessions, resistance probabilities to each of the investigated downy mildew races were relatively high for populations originating from Eastern Europe and Northern Asia.

Within-crop habitat manipulations have the potential to increase the biological control of pests in horticultural field crops. Wildflower strips have been shown to increase the abundance of natural enemies, but there is little evidence to date of an impact on pest populations. The aim of this study was to determine whether within-crop wildflower strips can increase the natural regulation of pests in horticultural field crops. Aphid numbers in plots of lettuce grown adjacent to wildflower strips were compared with those in plots grown in the absence of wildflowers. The presence of wildflower strips led to a decrease in aphid numbers on adjacent lettuce plants during June and July, but had less impact in August and September. The decrease in aphid numbers was greatest close to the wildflower strips and, the decrease in aphid numbers declined with increasing distance from the wildflower strips, with little effect at a distance of ten metres. The main natural enemies found in the crop were those that dispersed aerially, which is consistent with data from previous studies on cereal crops. Analysis and interpretation of natural enemy numbers was difficult due to low recovery of natural enemies, and the numbers appeared to follow changes in aphid abundance rather than being directly linked to the presence of wildflower strips. Cutting the wildflower strips, to remove floral resources, had no impact on the reduction in aphid numbers achieved during June and July, but decreased the effect of the wildflower strips during August and September. The results suggest that wildflower strips can lead to increased natural regulation of pest aphids in outdoor lettuce crops, but more research is required to determine how this is mediated by natural enemies and how the impact of wildflower strips on natural pest regulation changes during the growing season.

A multistate outbreak of Escherichia coli O157:H7 infections occurred in the USA in November–December 2006 in patrons of restaurant chain A. We identified 77 cases with chain A exposure in four states – Delaware, New Jersey, New York, and Pennsylvania. Fifty-one (66%) patients were hospitalized, and seven (9%) developed haemolytic uraemic syndrome; none died. In a matched analysis controlling for age in 31 cases and 55 controls, illness was associated with consumption of shredded iceberg lettuce [matched odds ratio (mOR) 8·0, 95% confidence interval (CI) 1·1–348·1] and shredded cheddar cheese (mOR 6·2, CI 1·7–33·7). Lettuce, an uncooked ingredient, was more commonly consumed (97% of patients) than cheddar cheese (84%) and a single source supplied all affected restaurants. A single source of cheese could not explain the regional distribution of outbreak cases. The outbreak highlights challenges in conducting rapid multistate investigations and the importance of incorporating epidemiological study results with other investigative findings.

Plant to plant gene flow is a route of environmental exposure for GM plants specifically since crosses with wild relatives could lead to the formation of more vigorous hybrids, which could increase the rate of introgression and the environmental impact. Here, we test the first step in the process of potential transgene introgression: whether hybrid vigor can be inherited to the next generation, which could lead to fixation of altered, i.e., elevated, quantitative traits.

The potential for a permanent elevated fitness was tested using individual autogamous progeny lineages of hybrids between the crop Lactuca sativa (Lettuce) and the wild species Lactuca serriola (Prickly Lettuce). We compared progeny from motherplants grown under either greenhouse or field conditions. The survival of young plants depended strongly on maternal environment. Furthermore, we observed that offspring reproductive fitness components were correlated with maternal fitness.

Our study demonstrates that post-zygotic genotypic sorting at the young plants stage reduces the number of genotypes non-randomly, leading to inheritance of high levels of reproductive traits in the surviving hybrid lineages, compared to the pure wild relatives.

Consequently, directional selection could lead to displacement of the pure wild relative and fixation of more vigorous genome segments originating from crops, stabilizing plant traits at elevated levels. Such information can be used to indentify segments which are less likely to introgress into wild relative populations as a target for transgene insertion.

Aerosol smoke and smoke-water can break dormancy and promote seed germination of many plant species. In this study we investigated changes in gene expression after imbibition of light-sensitive Lactuca sativa L. cv. ‘Grand Rapids’ achenes with dilute smoke-water compared to water control samples kept in the dark or continuous light, using the fluorescent differential display technique. Although no difference was detected in the smoke-water versus water control samples germinated in light, smoke-water treatment resulted in the differential display of several expressed sequence tags (ESTs) when compared to water control samples kept in the dark. The most pronounced fragments isolated correspond to known genes related to germination, with functions in cell wall expansion, regulation of translation, the cell division cycle, carbohydrate metabolism and abscisic acid (ABA) regulation. Real-time polymerase chain reaction (PCR) validation revealed that the transcript abundance of the genes, HVA22, short-chain dehydrogenase/reductase and late embryogenesis abundant protein, are upregulated after smoke treatment when compared to control achenes kept in the light. The results indicate that smoke has a dual effect. On the one hand, the smoke can induce genes that may be linked to ABA action, whereas, on the other hand, it elicits a faster germination rate by inducing a similar pattern in gene expression as light treatment. Smoke effects could be manifested mainly through the induction of the cell division cycle, cell wall extension and storage mobilization.

Prolonged imbibition and incubation of lettuce seeds at a supraoptimal temperature induces secondary dormancy. Such seeds no longer germinate when returned to conditions optimal for germination of non-dormant seeds. The possibility that inhibitors are involved in the induction of thermodormancy was investigated.

Washing of thermodormant seeds restored germination to a small extent. However, continuous leaching of seeds during high-temperature treatment with distilled water, largely prevented the induction of thermodormancy. Such seeds were qualitatively similar to nondormant seeds, i.e. they required only light to germinate at a lower temperature and germinated in the dark if given GA3. The germination water from thermodormant seeds inhibited the germination of non-dormant lettuce seeds. The inhibition was not an osmotic effect. Absorbance in the ultraviolet region was higher in germination water from thermodormant seeds than that of non-dormant seeds. It is concluded that inhibitors are involved in the induction of thermodormancy of lettuce seeds.

Lettuce (Lactuca sativa L.) seeds are inhibited from germinating above an upper temperature limit that is dependent upon cultivar, growing conditions and seed treatments. Thermoinhibition is accompanied by an increasing sensitivity of germination to reduced water potentials (ψ). We have employed a water relations analysis (hydrotime model) of seed germination rates to investigate the basis of thermoinhibition. Germination rates can be characterized by the distribution of base water potentials among seeds in the population (ψb(g)) and a hydrotime constant indicating the total accumulated hydrotime (MPa · h) above the base required for radicle emergence. The hydrotime model adequately described germination time courses across a range of ψ at both high and low temperatures. Increasing temperature caused the ψb(g) distributions to become more positive, accounting for the greater sensitivity to ψ and inhibition of germination. Increases in embryo osmotic potential and in the turgor yield thresholds of both the radicle and the endosperm/pericarp envelope contributed to this change. Seed priming (prehydration and drying) treatments speeded germination by reducing the hydrotime requirement. Priming also resulted in smaller increases in ψb(g) at high temperature, alleviating thermoinhibition by lowering the embryo yield threshold sufficiently to compensate for the increased endosperm resistance. The beneficial effects of priming in lettuce appear to occur primarily in the embryo, rather than in the surrounding envelope tissues.

The effect of temperature on the Pfr level required to induce germination in lettuce cv. Grand Rapids was investigated. Various Pfr levels were established in seeds, by irradiation with different fluences of red light, or by saturating irradiations with narrow bandwidth light. Both approaches indicated that increasing Pfr levels caused a progressive increase in the upper temperature limit for germination. The Pfr level required to induce 50% germination after a single light pulse increased from about 11% at 15° and 20°C to 86% at 30.5°C. Repeated red light irradiations raised the GT50 (temperature giving 50% germination) by about 2°C, suggesting that Pfr reversion limited germination at high temperatures. However, a large increase in Pfr level required to induce 50% germination was still apparent at high temperatures, even when relatively constant levels of Pfr were maintained by repeated irradiations with narrow bandwidth light. These results indicate that following a single light pulse, germination at high temperatures is limited solely by the availability of Pfr. The precise position of the upper temperature limit for germination is influenced by reversion; however, the underlying cause of thermoinhibition relates to an increasing requirement for Pfr at elevated temperatures.

A water relations (hydrotime) model was employed to characterize the responses of lettuce (Lactuca sativa L.) seed germination to temperature, water potential (ψ), endosperm disruption, and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). The base water potentials (ψb), standard deviations of base water potential and hydrotime constants (θH) estimated by the model were used to predict the germination rates at reduced ψ and supraoptimal temperatures in the presence or absence of ACC. The distribution of ψb values among seeds in the population (ψb(g)) increased (became more positive) as the imbibition temperature increased, indicating a greater sensitivity of seeds to reduced ψ at thermoinhibitory temperatures. Slitting the seeds at the cotyledonary end to disrupt the integrity of the endosperm extended the high temperature range for germination and maintained lower ψb(g) distributions compared with intact seeds as temperature increased. ACC (10 mm) in the imbibition solution raised the upper temperature limit for germination by about 2°C, and also lowered ψb(g) values by 0.1 to 0.2 MPa. The effect of ACC on ψb(g) was more pronounced at higher imbibition temperatures and in slit seeds. ACC (via conversion to ethylene) extends the high temperature limit for lettuce seed germination by acting in the embryo to maintain a lower ψ threshold for the initiation of growth as temperature increases. Evidence from other species as well suggests that this may be a general mechanism for the action of ethylene in promoting seed germination.

On the premise that seed ageing may be largely a result of free-radical lipid autoxidation, a study was made of the relationship between lipid stability and longevity in seeds of soybean (Glycine max), lentil (Lens culinaris), mungbean (Vigna radiata), chickpea (Cicer arietinum), broadbean (Vicia faba), pea (Pisum sativum), lettuce (Lactuca sativa), and tomato (Lycopersicon esculentum). Seed lipids were examined for α-, γ- and δ-tocopherols, and levels of unsaturated and saturated fatty acids. Using this information, analysis was attempted using linear, multiplicative or exponential models to correlate aspects of lipid stability with seed longevity values from the published literature. No statistically significant correlations could be found between longevity and total lipid unsaturation, tocopherol levels or two protection formulae obtained from the oil chemistry literature. When values for tomato were excluded, a good correlation (r = 0.89, P = 0.007) was obtained using a multiplicative regression model for levels of linolenic acid per unit of total tocopherols in relation to longevity. Possible factors contributing to a lessening of the relationship between lipid stability and seed longevity are discussed.

Brassicaceae seed meals produced through the oil extraction process release biologically active glucosinolate secondary products and may be useful as a part of biological weed control systems. Before meal can be used most efficiently, recommendations for suitable planting dates that maximize weed control but reduce crop injury must be determined. Our objectives were to determine the impact of 1 and 3% (w/w) meal applications of Brassica napus L. (canola), Brassica juncea L. (oriental mustard) and Sinapis alba L. (yellow mustard) on crop emergence and weed biomass in a growth chamber and field study. Results from the growth chamber experiment indicated that lettuce emergence was reduced by at least 75% when planted into 3% S. alba-amended soil earlier than 5 weeks after meal application. After 5 weeks, emergence was not different among treatments. Crop emergence was not reduced by any meal treatment as compared to the no-meal treatment in year 1 of the field study. In year 2, crop emergence in each 1.2-m row was inhibited by all meal treatments and ranged from 16 plants in the 3% B. juncea treatment to 81 plants in the no-meal treatment. The difference between emergence results in year 1 and year 2 is likely due to differing climatic conditions early in the season prior to irrigation, and the method of irrigation used. Redroot pigweed (Amaranthus retroflexus L.) biomass was 72–93% lower in 1% B. juncea and 3% treatments relative to the no-meal control in the first weed harvest of year 1. These same treatments had 87–99% less common lambsquarters (Chenopodium album L.) biomass. By the second weed harvest, redroot pigweed biomass in meal treatments (0.02–1.6 g m−2) was not different from that in the no-meal treatment (0.97 g m−2). Redroot pigweed biomass in 3% B. juncea plots was reduced by 74% relative to the no-meal treatment in the first harvest of year 2. This treatment also reduced common chickweed [Stellaria media (L.) Vill.] biomass by 99% relative to the 1% meal treatments. While pigweed biomass was reduced by 3% B. juncea in the early part of the season, by the second harvest this same treatment had the greatest pigweed biomass. Despite significant variability between years, 3% B. juncea did provide early season weed control in both years. Repeated meal applications, however, may be necessary to control late season weeds. Inhibition of crop emergence appears to be highly dependent on the amount and distribution of water and needs to be further studied in field settings.