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The variability in both stomatal conductance and shoot Fe concentration was considerably large

As aphid species rely heavily on the endosymbiont Buchnera species to grow and develop, many aphid populations treated with antibiotics will not survive. However, our treatments did not affect aphid microbial communities when treated with antibiotics and other CECs, which is possibly why there were no discernable effects on the aphid population as a whole. While treatments used in our study have previously been demonstrated to have negative effects for at least two other species of insects, this work suggests that aphids are either not exposed to CECs through their host plant, or their bacterial symbionts are not sensitive to, or depleted enough, to alter their basic biology. Plants treated with antibiotics typically have lower levels of intracellular calcium due to chelation. However, in our study we did not notice any obvious signs of calcium stress , possibly due to the use of a hydroponic solution which contains more than enough metal ions to provide adequate nutrients to the plants, even with some chelating. We did notice an overall decrease in mass for plants treated with antibiotics likely due to a slowed growth rate from direct action of the antibiotics on plant growth. Overall, there were no discernible effects of CECs on the aphids’ populations and or microbes. However, there were reductions in plant growth when treated with antibiotics. This could pose a problem to growers, especially as antibiotics tend to be reapplied with each watering especially with manure from antibiotic-treated animals. These antibiotics could also hinder the growth of the plant’s rhizosphere which would add another problem for growers who rotate crops to reintroduce nitrogen into the soil . More studies will need to be performed to determine how CECs will affect root microbial communities in soil,macetas de plastico 30 litros the roots themselves in soil, and degradation of CECs in soil.Drought, rising temperatures and expanding human populations are increasing water demands. Many countries are extending potable water supplies by irrigating crops with wastewater.

Unfortunately, wastewater contains biologically active, long-lived pharmaceuticals, even after treatment. Run-off from farms and wastewater treatment plant overflows contribute high concentrations of pharmaceuticals to the environment. These pharmaceuticals then can be either directly ingested by insects or translocated through plants and then ingested by insects. I have determined the effects of CECs on four different insects, all with different feeding styles and exposure risk. Culex quinquefasciatus larvae reared in water contaminated with environmentally relevant concentrations of common CECs were affected both directly and indirectly. Acetaminophen alone and a mixture of contaminants were found to increase developmental time of larvae. Susceptibility to Bacillus thuringiensis subsp. israelensis toxin increased in larvae exposed to antibiotics, acetaminophen, or a mixture of PPCPs. Overall there were significant differences in the microbial community of C. quinquefasciatus in treated water. Within control groups, the predominant families of bacterial symbionts change with each larval instar despite consistent diets and rearing conditions, an effect that has been described in older life stages but not in larvae. This trend was also seen in hormone treatments, but not in the antibiotic or the mixture treatments. Richness and evenness were reduced in both antibiotic and mixture treatments, suggesting that antibiotics remove certain bacteria or inhibit them from increasing to proportions seen in the control treatment. Interestingly, the mixture treatments had greater richness and evenness compared to antibiotic alone treatments, possibly due to the other contaminants facilitating growth of different bacteria. Megaselia scalaris larvae reared on artificial diets spiked with contaminants of emerging concern at environmentally relevant concentrations displayed no oviposition preference for treated or untreated diets. Larvae exposed to caffeine in diets showed increased mortality, and larvae fed antibiotics and hormones showed signs of slowed development, especially in females. The normal sex ratio observed in M. scalaris from control diets was affected by exposure to caffeine and the pharmaceutical mixture treatments. There was an overall effect of treatment on the flies’ microbial communities; notably, caffeine-fed insects displayed higher microbial variability.

Trichoplusia ni larvae showed increased developmental time and mortality when reared on artificial diets containing antibiotics, hormones, or a mixture of contaminants. Mortality was also increased when T. ni were reared on tomatoes grown hydroponically with the same concentrations of antibiotics. The antibiotic-treated plants translocated ciprofloxacin through their tissues to roots, shoots, and leaves. Microbial communities of T. ni changed substantially between developmental stages and when exposed to CECs in their diets. Myzus persicae reared on bell peppers treated with CECs displayed no effects in population growth over nearly three generations and no effects on the aphids’ microbial communities. The M. persicae retained their proportionately largest family Enterobacteriaceae across all life stages and across all treatment groups. Interestingly, the greatest effect was noticed in the bell peppers themselves, which had decreased root and leaf growth in treatments containing antibiotics. Overall, our findings indicate that at environmentally relevant concentrations, CECs in reclaimed water can have biologically important effects on important insects. They also, illuminate the complexity of the effects CECs can have on insects with different feeding methods. While the research reported in this dissertation suggests that CECs in reclaimed water could have positive effects on certain pests , they could have unintended negative effects on other insects and how humans interact with them. Effects described here have substantial potential consequences for forensics and IPM strategies. The results show increased developmental time and mortality in insects would alter biological time-clocks for forensic entomology and for dosage practices for IPM . Determining whether or not these PPCPs could influence pathogen transmission in insect-plant interactions is also of concern. Because many of the insects studied here are lower trophic level organisms, the potential for bio-magnification or unexpected chemical modification as CECs move through the food webs are serious concerns. There is also the possibility of pharmaceuticals affecting the rhizosphere of plants in soil and influencing plant health, but more research is still needed to determine precise effects.Soybean is an important biotech food, vegetable, and field crop that provides oil , protein , and carbohydrate to millions of people worldwide. Furthermore, soybean is a promising sustainable source of bio-fuels in North America, South America, and Europe . Zinc deficiency has been recognized globally as a major micro-nutrient stress that lowers crop yield and productivity around the world . Zn deficient soils occur in nearly 30% of the world’s arable lands. Selection and breeding of plant genotypes for Zn efficiency , defined as the ability of plants to maintain reasonable yield under Zn deficiency, is considered a sustainable approach to increase plant production on low Zn soils .

Considerable differences in response to low Zn stress are known to exist among genotypes of bread wheat , rye, triticale , rice, tomato , and common bean . Variations in shoot or leaf based parameters together with higher internal Zn utilization can be the principal factors in differential ZE in crop plants . Preliminary studies in common bean indicated that leaf physiological parameters such as leaf area are a useful criteria for ZE screening . Currently, there is little information regarding response of stomatal conductance to low Zn stress. Many earlier studies of low Zn stress focused on economically important cereal species. Few studies have been conducted in soybean,cultivo hidroponico and fewer have tested hydroponics as a growing media. It has been shown that critical Zn deficiency level for soybean leaves was 15 µg g-1 . In a field study in Central Turkey, Zn deficient calcareous soils were shown to reduce yield and cause the development of visual symptoms on young leaves of soybean plants . Many soybean genotypes are being developed in the U.S. but little is known about their reaction to low Zn stress. Therefore, the objectives of this study were to: develop a suitable hydroponics-based method for ZE screening of soybean plants to identify more Zn efficient and less Zn efficient genotypes; and detect genotypic ZE variation in soybean using physiological parameters such as leaf area, chlorophyll contents, stomatal conductance, nutrient concentration, and plant biomass. Available Zn concentrations around 1 to 2 pM has already been shown to induce Zn deficiency in bread wheat and common beans . Accordingly, our experiments successfully induced Zn deficiency at this concentration level in hydroponics. Based on our results, it appears that hydroponics with chelate buffers is feasible for screening soybean ZE trait. The soybean genotypes tested in this study had considerable variability and physiological responses to low Zn stress in hydroponics. Total leaf area, chlorophyll content, and leaf Zn concentration levels were all high in MZE genotypes. At the same time LZE soybean genotypes had various visible symptoms which indicated unfavorable Zn levels. This is consistent with previous findings that soybean plants showed chlorosis and brown leaf patches in calcareous soils . In terms of overall assessment genotypes “Williams” and “Hampton” were the most Zn efficient and inefficient, respectively . Although chlorosis is the most prominent symptom of low Zn stress, there is limited info on the effect of Zn deficiency on chlorophyll content levels. Leaf chlorophyll content was greater for MZE genotypes such as “Williams” and “Pella86” compared with LZE genotypes. Our results suggest that increased chlorosis was the cause of reduced SPAD levels. This is in agreement with the previous findings on wheat and common beans .It is interesting to note that Fe concentrations were considerably high for some genotypes such as “Thomas” . The lack of correlation with ZE trait across the genotypes tested may indicate that stomatal conductance could not be used for early detection of Zn stress in soybean.

Significant differences between soybean genotypes in shoot Zn and N concentration were observed in low-Zn grown plants in hydroponics. Although there was no significant correlation between shoot nutrient concentration and ZE trait, LZE genotypes were characterized by slightly lower concentration of Zn, Fe, and N . This data are in agreement with previous findings showing that Zn efficient wheat varieties transported more Zn from roots to shoots than Zn inefficient varieties under Zn deficiency in the early field growth stages in bread wheat . Pharmaceuticals have been increasingly prescribed for the past 30 y, and prescription rates have almost tripled in just the past 14 y . In 2013, animals grown for human consumption were treated with 9.1 × 106 kg of antibiotics; of those, 6.6 × 106 kg were used for the purpose of increasing production . Many antibiotics and other common contaminants of emerging concern  can be excreted by both humans and animals with little change in their chemical structure . Not surprisingly, pharmaceuticals have been appearing in wastewater, surface waters, and in some cases tap water, over the past few years . Standard wastewater treatment facilities are not equipped to completely remove pharmaceuticals , resulting in these compounds being found in effluent. In addition, even higher concentrations of many pharmaceuticals are released during heavy storms in the untreated wastewater overflow, which then directly contaminate the environment . These pharmaceuticals have been found at biologically active concentrations in surface waters around the world . There is also an increasing effort to use reclaimed wastewater in drought-affected areas, such as Southern California . In agriculture/livestock operations, pharmaceuticals are found in manure that is used as fertilizer, effectively compounding the pharmaceutical concentrations . Current research shows these chemicals tend to be both pseudopersistent in soil and detrimental to soil and rhizosphere microbes . Our recent studies of the effects of pharmaceuticals on aquatic insects show that, at concentrations found in reclaimed water, these CECs can alter development of the mosquito Culex quinquefasciatus, its susceptibility to a common larvicide, and its larval microbial communities . Watts et al. showed 17α- ethinylestradiol, a common birth control agent, and Bisphenol-A, a common plasticizer, can cause deformities in the midge Chironomus riparius. However, because larval forms of aquatic insects develop directly in the contaminated water, their constant exposure is likely greater than most terrestrial insects. Interestingly, many CECs, which were not designed specifically to impact microbes, have been shown to affect microbial communities. For example, caffeine, a common mental stimulant, can alter biofilm respiration, and diphenhydramine, an antihistamine, has been shown to modify the microbial community of lake biofilms .

Farmers in the past often provided housing in order to attract and retain good workers

The cost of mandatory fringe benefits was $1.67 an hour or nine percent of total compensation, and employers provided voluntary fringe benefits worth $4.33 or 19 percent of total compensation, including $1.42 an hour for paid leave and $1.36 for health and other insurance.Fringe benefits can be expensive for farm workers with low earnings, since benefits such as health insurance for workers and their families that cover off-the-job injuries and illnesses require monthly payments that are independent of earnings. A low-cost $160 a month or $1 an hour health insurance premium for a full time worker adds 16 percent to the cost of a worker earning $6 an hour and 7 percent to the cost of a $14 an hour worker.However, poor farm worker housing led to higher standards and, since farmers are not required to provide housing, many responded to tougher housing rules by closing their housing. Farm workers were thus pushed into cities and towns in agricultural areas, where they competed with other tenants for housing, sometimes living in rented houses or sheds that were no better than the on-farm housing that was closed. However, the cost of living in cities was usually more than what farmers charged—often $50 to $100 a week—and workers living away from the fields must usually pay for rides to work, which adds another $20 to $25 a week to their costs of working. The government, which used to regulate farmer-provided housing, macetas de plastico 30 litros today primarily makes grants and loans to provide subsidized housing for farm workers, often families with children.

Alvardo and Luna found that 13 percent of SJV farm workers in 2001 lived in housing provided by their employers, and 50 percent lived with non-family members; they paid an average $238 a month in rent. Fewer than a third of the workers interviewed had a California drivers’ license, and 70 percent paid an average $5 a day for transportation from the city or town in which they lived to their farm job.The third key labor market function is retention—identifying and keeping the best workers, or encouraging the best seasonal workers to return next year. Most U.S. employers have formal evaluation systems under which supervisors evaluate each worker, and these evaluations are used to determine promotions and wage increases. Few farm employers have formal personnel systems. Instead, there are two methods of recruitment and worker evaluation that illustrate agricultural extremes in personnel practices. Some farmers, especially those who work closely with one or a few year round workers in dairies and similar operations, treat hired workers “as part of the family,” selecting workers carefully and providing them with housing near the farmer’s home . The other extreme is exemplified by a grower who hires a crew of workers through a contractor or a foreman, and never deals directly with workers. Crew-based hiring explains why recruitment and retention are often part of the same labor market function in agriculture. Indeed, an analogy to obtaining irrigation water may be helpful to understand the recruitment and retention options. There are two major ways to supply irrigation water to crops: a field can be “flooded” with water so that some trickles to each tree or vine, or fields can be irrigated with a drip system that involves laying plastic pipes down or under the rows and dripping water and nutrients to each tree or vine. If water is cheap, farmers flood fields with water; if water is expensive, farmers may invest in drip irrigation systems. The analogy to recruitment and retention is clear: farmers more often work collectively to flood the labor market with workers, usually by getting border gates opened or left ajar, instead of recruiting and retaining the best farm workers for their operation, the drip irrigation model.

The best way to ensure plenty of irrigation water is to invest in more dams and canals; the best way to flood the labor market is to invest in politicians willing to ease access to foreign workers.Farm workers were not granted federal collective bargaining rights in the 1935 National Labor Relations Act, and remain excluded from the NLRA. In 1975, California enacted the Agricultural Labor Relations Act to provide state-level organizing and bargaining rights: the purpose of the ALRA was to end a decade of strife in the fields, to “ensure peace in the agricultural fields by guaranteeing justice for all agricultural workers and stability in labor relations.” The ALRA includes three major elements: organizing and bargaining rights for farm workers, unfair labor practices that employers and unions can commit when they interfere with these worker rights, and a state agency, the Agricultural Labor Relations Board , to supervise elections in which farm workers decide if they want to be represented by unions and to remedy ULPs. Between 1975 and 1984, there were over 1000 elections on California farms, and unions were certified by the ALRB to represent workers on 70 percent of these farms . Since then, there have been fewer than 250 elections, and unions were certified on less than 50 percent of the farms on which they requested elections .Farm worker unions were often unable to negotiate first agreements with most of the farms on which they were certified to represent workers, and in many cases, were unable to re-negotiate first agreements. The number of collective bargaining agreements in California agriculture has never exceeded 300 at any time, and in 2002 was about 225—80 percent of the current contracts cover 3-4 workers under Christian Labor Association contracts with dairy and poultry farms. The United Farm Workers , Teamsters, and other unions representing field workers have fewer than 30 contracts covering less than 25,000 workers. Unions such as the UFW charge that farm employers are able to avoid reaching first or subsequent contracts by refusing to bargain toward agreement. In 2002, the UFW led an effort to amend the ALRA to provide for state intervention to ensure contracts on farms on which workers voted for union representation.

The UFW’s original goal was binding arbitration, under which a union and employer that cannot negotiate a contract typically go through a three-step procedure. First is mediation, when a neutral third party listens to each party separately and makes suggestions to narrow differences and allow them to reach a voluntary settlement. Second is fact finding, when a neutral party listens to both sides and proposes a non-binding settlement. Third is binding arbitration, when a neutral party proposes either any settlement deemed best or when the arbitrator is required to recommend one of the party’s final offers at the bargaining table. Binding arbitration is normally restricted to public employees such as police and firefighters who cannot strike lawfully. The California Legislature approved binding arbitration in agriculture, but Governor Gray Davis threatened to veto the bill, so a last-minute compromise, “mandatory mediation,” was approved. Mandatory mediation, which went into effect January 1, 2003, requires unions and farm employers to bargain for at least 180 days for a first contract. If they cannot reach agreement, a mediator tries to help the parties to resolve their differences for another 30 days but, if mediation fails to produce an agreement, the mediator must, within 21 days, recommend the terms of a collective bargaining agreement that the ALRB can then impose on the parties. Although mandatory mediation might result in a greater number of collective bargaining agreements, other factors suggest that the new law will not affect a large number of agricultural employers or employees while it is in effect through at least 2007.The hired farm workers of tomorrow are growing up today outside the U.S.,cultivo hidroponico usually in rural Mexico and Central America. A major federal policy issue is what conditions, including what housing provisions, U.S. farm employers should satisfy to get access to these foreign workers. The U.S. has a guest worker program for farm workers, known as the H-2A program. It requires DOL to certify a farmer’s need for H-2A guest workers. In order to obtain certification, a farmer must satisfy certain recruitment, wage, and housing regulations, including applying for certification and trying to recruit U.S. workers at least 45 days before they are needed, offering to pay the higher of the minimum, prevailing, or Adverse Effect Wage Rate, and offering to provide free and approved housing to out-of-area U.S. and H-2A workers.Except for sheep farmers, California farm employers have traditionally not obtained workers through the H-2A program; most admissions have been in eastern states such as North Carolina. But the number of H-2A admissions in these eastern states has been rising, and H-2A workers for non-shepherding jobs were approved in California in March 2002, when a Ventura county custom harvester/FLC brought 38 H-2A workers from Mexico to California to harvest lemons, possibly a precursor to more H-2A farm workers.

If the H-2A program expands, there would likely be an increased demand for barracks or dorm style housing, and inspectors to check it. Instead of expanding the H-2A program, three other concepts are being debated to regulate the access of farmers to foreign farm workers: temporary guest workers, legalization, and earned legalization. Temporary guest workers are non-immigrants, persons in the U.S. to work generally for one employer, who must leave when the work ends—guest workers, under U.S. law, do not generally obtain any preference for admission as immigrants. During the 1990s, the SAWs—unauthorized farm workers legalized in 1987- 88—and their replacement with newly arrived unauthorized workers increased the risk to farmers that they may be fined or lose their workers at critical harvest times. Farmers could avoid such risks by having DOL certify their need for H-2A workers, but certification required offering at least a DOL-set wage and free housing. Many California farmers want an alternative guest worker program that does not require certification, and they do not want to offer free housing to legal guest workers. In July 1998, the U.S. Senate approved one grower proposal, the Agricultural Job Opportunity Benefits and Security Act , which avoided the need for farmers to be certified by creating a registry in each state to enroll legally authorized farm workers. Under AgJOBS, farmers would apply to the registry, for example, requesting 100 workers. If only 60 registry workers were available, the farmer would be automatically “certified” to recruit and have admitted to the U.S. 40 foreign workers. AgJOBS would also end the housing requirement by allowing the governor to certify that there is “sufficient” farm worker housing in the area, and then the farmer could offer a housing allowance equivalent to “the statewide average fair market rental for existing housing for non-metropolitan counties for the State…based on a two bedroom dwelling unit and an assumption of two persons per bedroom,” about $500 a month in the northern Sacramento Valley and $800 a month in San Benito in 2000. However, most California agriculture is in metro counties, where 40th percentile fair market rents in 2000 are about $525 to $1,100 for two-bedroom units. Under AgJOBS, typical housing payments for guest workers would have been $125 to $150 per worker per month in California. President Clinton opposed AgJOBS, and issued a statement: “When these programs were tried in the past, many temporary guest workers stayed permanently and illegally in this country. Hundreds of thousands of immigrants now residing in the U.S. first came as temporary workers, and their presence became a magnet for other illegal immigration.” In 1999, after consultations with worker advocates, a new concept was added to AgJOBS: earned legalization. Legalizing unauthorized farm workers might encourage many of them to leave for non-farm jobs, as SAWs did in the 1990s, so farmers who wanted guest workers and worker advocates who wanted legalization agreed to a program that would grant unauthorized workers a temporary legal status.Under their compromise, unauthorized workers who could prove that they did 100 or 150 days of farm work in the preceding year would get a temporary legal status that permitted them to live and work in the U.S.In order to maintain this temporary legal status, and eventually apply to become a regular U.S. immigrant, the temporary worker would have to do a certain amount of farm work each year for several years, e.g., 80 or 100 days of farm work for three to five years. Thus, after several years and 240 or 500 days of farm work, the temporary legal worker could earn an immigrant status.

The widest plant diameter was from plants grown in the peat and perlite system

The primary justification for using this system is that strawberry crops canbe produced without fumigation ; although if the soilless media could be disinfested and recycled, instead of discarded at the end of each cropping cycle, it would, in theory, represent a more sustainable system. Additional advantages include the ease of attracting harvest labor due to the high fruit yield per linear foot of bed row, and the ability to leave the beds in place for several crop cycles. One of the disadvantages is that coir and peat substrates are expensive and of limited quantity. However, composted wood fiber and composted pine bark have shown good results as substrates and are available locally and are generally less expensive . Logistical issues such as substrate costs and the delivery and installation of large amounts of substrate material have yet to be addressed in U.S. systems. Field trials of a raised bed trough system were carried out at Monterey Bay Academy, near Watsonville, and at Mar Vista Berry, near Santa Maria, from fall 2010 to summer 2011. The studies were set up in randomized complete block designs consisting of five treatments replicated four times. The treatments were 100% coir , a 70:30 peat and perlite mixture, an amended soil mix of 50% steamed soil plus 25% rice hulls and 25% coir, a standard fumigation treatment , and an untreated, non-fumigated control. Harvesting was done from April 28 to Sept. 15, 2011 , and April 13 to Oct. 4, 2011 . The fruit was sorted into marketable berries and cull . Periodic collection of substrate samples was done to monitor pH, electrical conductivity , nitrate nitrogen , ammonium nitrogen and available phosphorus . All data were subjected to analysis of variance ,macetas de plastico 30 litros and Fisher’s protected LSD at 0.05 was used to compare means. Table 1 shows the plant diameters and yields of strawberry crops grown in the plots at Monterey Bay Academy and Mar Vista Berry.

There were highly significant differences in plant diameter and yield of strawberries grown at Monterey Bay Academy.The three substrate treatments did not significantly differ in marketable yield. The untreated, non-fumigated control treatment had the smallest plant diameter and lowest marketable yield. The marketable yield of the coir, peat and perlite, and steamed soil with amendments treatments was 27%, 29% and 13% higher, respectively, than the yield from the standard fumigated treatment. At Mar Vista Berry , the widest plant diameters were in the steamed soil with amendments plots and the peat and perlite substrate plots . However, the substrate treatments did not affect the marketable fruit yield. Significant differences were noted only on the cull yield. The highest cull yield was observed in the steamed soil with amendments; this was the case at both Mar Vista Berry and Monterey Bay Academy, and it could be attributed to the very low pH and high EC of this substrate. One of the main concerns in soilless strawberry production is the maintenance of a favorable pH, EC and nutrient supply to the growing plants. For most of the sampling periods at the experimental sites, different substrate and soil treatments had significantly different levels of pH, EC, nitrate nitrogen, ammonium nitrogen and available phosphorus. At both sites, the pH of the coir and the peat and perlite treatments was lower in the early sampling periods but increased with time, reaching the targeted value of 5.7 after 3 to 4 months ; this slow rise in pH to the target value was attributed to the high nutrient adsorptive capacity of the soilless substrates. The pH of the amended soil treatments at both sites was generally low at all sampling periods, and the target value was not reached during the production cycle. With the exception of the initial sampling period, the EC of the substrate treatments at Monterey Bay Academy was generally low . In contrast, the EC in the Mar Vista Berry beds was consistently high, which could be due to the higher amount of salts in the irrigation water.

The EC of the steamed soil with amendments treatment at Mar Vista Berry was also consistently high throughout the growing season. The soilless substrates are low in nutrients; thus, fertilization is one of the key issues in these systems. Surprisingly, the initial nitrate nitrogen of the coir and the peat and perlite mixture was higher at both sites, and the target value of 100 ppm was maintained in the beds through the season except for the latter stages of plant growth . The standard fumigated beds had generally low nitrate nitrogen. At all sampling periods, the ammonium nitrate was lower than the RABETS target value of 14 ppm . The RABETS target of 30 ppm available phosphorus was maintained in all of the media treatments at both sites .Anaerobic soil disinfestation , a nonchemical alternative to methyl bromide, was developed in Japan and the Netherlands to control soil borne pathogens and nematodes in strawberries and vegetables. Anaerobic soil disinfestation integrates the principles of solarization and flooding in situations where neither method alone is effective or feasible. Anaerobic soil conditions are created by incorporating readily available carbon sources into topsoil, covering the soil with plastic tarp and irrigating to field capacity. The tarp is left in place to maintain soil moisture above field capacity and to sustain anaerobic conditions. Anaerobic decomposers respire using the added carbon, which results in a buildup of anaerobic byproducts that are toxic to pathogens . These byproducts degrade rapidly once the tarp is removed or holes are punched through the tarp for planting. Studies were conducted during 2008 to 2011 in an attempt to optimize anaerobic soil disinfestation for California strawberry and Florida vegetable production systems. Overall, it was very effective in suppressing Verticillium dahliae in soils, and it resulted in 85% to 100% of the marketable fruit yield observed with fumigated controls in coastal California strawberries when 9 tons per acre of rice bran was preplant incorporated and 3 to 4 acre-inches of irrigation was applied in sandy loam to clay loam soils . In the semitropical climate of Florida, when composted broiler litter and heavy black strap molasses were incorporated as substrate, anaerobic soil disinfestation treatments provided good control of nutsedge and excellent control of grasses, broad leaf weeds, Phytophthora capsici and Fusarium oxysporum f. sp. lycopersici .

In the cooler conditions of the Central Coast, however, anaerobic soil disinfestation may not provide effective control of many weed species . To ensure consistency of pest suppression across varying locations, the effects of soil temperatures and treatment length and the mechanisms of pest suppression by anaerobic soil disinfestation are being further elucidated. Its integration with other non-fumigant approaches may also have promise. For example, a combination of anaerobic soil disinfestation and mustard seed meal application is currently being tested .Heat treatment with steam can be used for soil sterilization or pasteurization . Studies have shown that most plant pathogens, insects and weeds will die when moist soils are heated to temperatures higher than 150°F for 30 minutes . The duration and amount of steam needed to raise the soil temperature to 150°F depend on various soil factors, including texture,cultivo hidroponico type and moisture content. Minuto et al. found that soil could be heated most rapidly at a moisture content between 8.5% and 12% in a sandy loam and between 6% and 7% in a sandy soil. Steam applied to field soil that raised the temperature to 158°F for 20 minutes resulted in weed control comparable to methyl bromide . In addition to pest control, an advantage of steaming is that it lacks the negative environmental and worker health issues associated with chemical fumigants. Some have reported that steaming has little or no lasting negative impact on soil quality or soil microbial communities as opposed to the known potential impact of methyl bromide fumigation on both soil quality and microbes . Other studies have reported a more significant change in soil microbial activity due to steam sterilization . Differences among steam studies may be related to duration of steam application and soil temperatures attained during steam treatments as well as the soil organic matter content. Steam has also been shown to increase crop growth and yields . Previous work found that strawberry fruit yields from steam-treated soils were similar to those from soils fumigated with methyl bromide plus chloropicrin .Natural products such as mustard seed are being evaluated as biofumigants. Recent studies found that mustard seed meal amendment can suppress root infection by Rhizoctonia solani . We have been testing mustard seed meal in strawberry beds at rates of 500 to 4,000 pounds per acre incorporated into the soil. Mustard meal alone does not consistently produce high fruit yields or control weeds . One possible method to enhance solarization is to use combinations of mustard meal, chloropicrin, and metam sodium treatments . By heating the soil with solarization or steam, the pest control activity of metam sodium, chloropicrin or mustard meal may be higher than at ambient soil temperatures.

A field study was conducted at Monterey Bay Academy from October 2010 to September 2011 to evaluate anaerobic soil disinfestation and steam with and without mustard seed meal application prior to planting strawberry beds. Treatments included a control; Pic-Clor 60 at 300 pounds per acre as a standard; mustard seed meal at 3,000 pounds per acre; anaerobic soil disinfestation with rice bran at 9 tons per acre; anaerobic soil disinfestation with rice bran at 7.5 tons per acre and mustard seed meal at 3,000 pounds per acre; steam; and steam plus mustard seed meal at 3,000 pounds per acre. The trial was arranged in a randomized complete block design with four replicates. Anaerobic soil disinfestation was initiated Oct. 7 to create a saturated condition. The plots were maintained above field capacity with intermittently applied irrigation water from Oct. 8 to Nov. 3, 2010. Steam was applied via spike injection from a stationary steam generator for a sufficient time to raise the soil temperature to 158˚F for 20 minutes on Oct. 13 and 14, 2010. Weed densities were measured in 25-square-foot sample areas covered with clear tarp, on Dec. 15, 2010, Jan. 21, Feb. 23 and April 6, 2011. Strawberry fruit was harvested weekly from April 28 to Sept. 15, 2011. Fruit was sorted as marketable and cull at each harvest date. Data were subjected to analysis of variance and means were separated using Fisher’s protected LSD.Overall, the steam treatment and the steam treatment with mustard seed meal were as effective as Pic-Clor 60 in providing weed control . Anaerobic soil disinfestation plus rice bran suppressed weed densities, but it was less effective than Pic-Clor 60. No strawberry plant injury was observed in any of the treatments . Marketable yields data collected from April 28 to Sept. 15, 2011, indicate that strawberry fruit yields in the steam treatments and the anaerobic soil disinfestation treatments were comparable to those in the Pic-Clor 60 application . These data, along with data from our prior studies, show that steam is as effective as chemical fumigation; and that anaerobic soil disinfestation also produces yields equivalent to Pic-Clor 60 but may need to be combined with herbicide use in severely weed-infested sites. The costs of the anaerobic soil disinfestation treatments with rice bran, and with rice bran plus mustard seed meal, were $1,632 and $3,093 per acre, respectively, including material, spreading, incorporation and irrigation . The cost of steam was $10,440 per acre, compared to $1900 per acre for Pic-Clor 60. Therefore, although the yields and gross revenues were comparable across treatments, the net returns after treatment and harvest costs were highest for the Pic-Clor treatment, followed by the anaerobic soil disinfestation with rice bran. The lowest net revenue was for the steam plus mustard seed meal treatments due to the high cost of the steam treatment. The cost data showed a critical need for more-efficient steam injection systems before steam can be adopted commercially. Recent advances with steam application equipment can reduce the cost of steam treatment to less than $5,500 per acre with the potential for further cost reductions . Since 2011 we have used an automatic mobile steam applicator in our research, which lowers the labor costs relative to those reported here by approximately 50% to 70%. It mixes steam with soil, allowing soil to be heated from 60˚F to 160˚F in 90 seconds — much more rapidly than the steam application system used here .