| RESEARCH PROJECT REPORTS PROJECT TITLE & PRINCIPAL INVESTIGATOR(S)
2001 - 2002 LETTUCE BREEDING, - USDA-ARS E. J. Ryder, R. C. Grube, B. Q. Mou, & J. D. McCreight, USDA-ARS, Salinas BREEDING CRISPHEAD LETTUCE Richard W. Michelmore, Oswaldo E. Ochoa, & Maria Jose Truco UC Davis LEAF LETTUCE BREEDING Richard W. Michelmore, Maria Jose Truco, & Oswaldo E. Ochoa, UC Davis GENETIC VARIATION IN LETTUCE Richard W. Michelmore, UC Davis THE ETIOLOGY, EPIDEMIOLOGY, AND MANAGEMENT OF A NEW SOIL-BORNE VIRUS DISEASE OF LETTUCE IN CALIFORNIA William M. Wintermantel, USDA-ARS, Salinas INVESTIGATION OF A NEW CROWN ROT DISEASE OF LETTUCE Steven T. Koike, Krishna V. Subbarao, & D. Fogle UC Cooperative Extension, Salinas UC Davis, and CDFA, Sacramento DEVELOPING AN INTEGRATED DISEASE PROGRAM FOR GRAY MOLD OF LETTUCE OF LETTUCE Steven T. Koike & Krishna V. Subbarao UC Cooperative Extension, Salinas and UC Davis LETTUCE POWDERY MILDEW MANAGEMENT Thomas Turini, UC Cooperative Extension, Holtville and Steven T. Koike, UC Cooperative ECOLOGY AND MANAGEMENT OF BACTERIAL LEAF SPOT OF LETTUCE CaroleeT. Bull, USDA-ARS, Salinas INVESTIGATIONS ON BOTTOM ROT OF LETTUCE Frank Martin, USDA-ARS, Salinas EPIDEMIOLOGY AND CONTROL OF LETTUCE DROP CAUSED BY SCLEROTINIA SPECIES Krishna V. Subbarao, UC Davis BIOLOGY AND EPIDEMIOLOGY OF VERTICILLIUM WILT OF LETTUCE Krishna V. Subbarao, UC Davis INSECT MANAGEMENT FOR CENTRAL COAST LETTUCE William E. Chaney, UC Cooperative Extension, Salinas WEED MANAGEMENT SYSTEMS FOR LETTUCE Steven A. Fennimore & Richard F. Smith, UC Davis and UC Cooperative Extension, Salinas — EVALUATION OF CONTROLLED RELEASE FERTILIZERS FOR WINTER LETTUCE PRODUCTION Richard F. Smith, UC Cooperative Extension, Salinas NUTRIENT AND PHYTOCHEMICAL ANALYSIS OF 5 LETTUCES: BUTTERHEAD, GREEN LEAF, RED LEAF, ICEBERG AND ROMAINE Joanne M. Holden & Gary Beecher, USDA-ARS, Beltsville, MD ABSTRACT CALIFORNIA LETTUCE RESEARCH BOARD for the period (April 1, 2001-March 31, 2002) PROJECT TITLE: Lettuce Breeding, USDA-ARS PRINCIPAL INVESTIGATORS: E. J. Ryder, R. C. Grube, B.Q. Mou, J. D. McCreight SUMMARY: Seventeen accessions of Lactuca virosa show high level resistance to big vein. In two plantings, 178 early generation breeding lines from crosses of L. virosa and cultivated lettuce were screened for BV resistance. BV resistance was confirmed in 10 PI accessions, and confirmed in three accessions. Two groups of breeding lines showed good resistance to BV in field tests. Field downy mildew resistance combined with LMV resistance will be selected in romaine crosses. F2 populations from crosses between Second Round selections and Salinas 88 and Iceberg are being reevaluated for field resistance. F2 populations between field resistant lines and romaine, leaf and butter lettuces are being evaluated. Genetic studies on field resistance continue. In lettuce drop work, backcross populations of resistant families to susceptible cultivars and crosses involving new resistant sources are being evaluated. Improvement of the screening technique continues. New sources of resistance to verticillium were identified and selection for resistance and head type continued. Ten cultivars showed apparent resistance to bacterial leaf spot. Numerous crosses were made to transfer corky root resistance to leaf, romaine, and butterhead types. Selection continued for several multiple resistance combinations. Selections for leafminer resistance in various crosses were made and further crosses were made. Crosses have been made with lettuce aphid resistant cultivars and other sources of resistance are being explored. Selection for powdery mildew resistance and other traits were made in fall and mid-winter desert plantings. Families from the cross Vanguard 75 x Salinas were evaluated for tipburn resistance in a spring desert planting. Selection continued for dark green leaf lettuce. Opening iceberg lettuce heads and closing romaine heads reversed the nutrient values for the two types. Studies of the inheritance of resistance to lettuce mosaic, big vein, sclerotinia drop, lettuce infectious yellows and downy mildew resistance continued. Germplasm screenings for resistance to corky root and leafminer were initiated. Screening for resistance to big vein, verticillium, lettuce aphid and sclerotinia drop continued. CALIFORNIA ICEBERG LETTUCE RESEARCH PROGRAM April 1, 2001 to March 31, 2002 BREEDING CRISPHEAD LETTUCE Richard W. Michelmore Oswaldo E. Ochoa Maria Jose Truco Department of Vegetable Crops University of California, Davis rwmichelmore(S),ucdavis.edu oeochoa(S)ucdavis.edu mjtruco(a)vegmail.ucdavis.edu SUMMARY: The program continues to emphasize the identification and incorporation of genes for disease resistance, particularly to downy mildew, lettuce mosaic, anthracnose virus and corky root, into horticultural types suitable for California. Resistance for downy mildew is being introduced from several new sources into cultivated genotypes suitable for California and combined with resistance to LMV and corky root. Utilization of multiple new sources will minimize the chances that changes in the pathogen will render all cultivars susceptible simultaneously. Eight advanced breeding lines are being released this year. CALIFORNIA ICEBERG LETTUCE RESEARCH PROGRAM April 1,2001 to March 31,2002 LEAF LETTUCE BREEDING Richard W. Michelmore Maria Jose Truco Oswaldo E. Ochoa Department of Vegetable Crops University of California, Davis rwmichelmore@ucdavis.edu mjtruco@vegmail.ucdavis.edu oeochoa@ucdavis.edu SUMMARY : Backcross programs are underway that emphasize the identification and introduction of genes for disease resistance, particularly to downy mildew, corky root, lettuce mosaic virus and anthracnose, into the four leaf lettuce types. Resistance for downy mildew is being introduced from eighteen new sources into cultivated genotypes suitable for California and will ultimately be combined with resistance to LMV, anthracnose and corky root. Utilization of multiple new sources and introduction of different resistances into the different types will probably increase the longevity of individual resistances and minimize the chances that changes in the pathogen will render cultivars of different lettuce types susceptible simultaneously. Genetic studies are in progress to determine the genetic basis for the resistance and to increase the efficiency of generating resistant lines. CALIFORNIA LETTUCE RESEARCH PROGRAM April 1, 2000 to March 31, 2001 PROJECT TITLE: GENETIC VARIATION IN LETTUCE PRINCIPAL INVESTIGATOR: COOPERATING PERSONNEL: Richard W. Michelmore Department of Vegetable Crops University of California, Davis rwmichelmore@ucdavis.edu Maria Jose Truco, Kathy Shen, Santiago Moreno, Mireille van Damme Tadeusz Wroblewski, Hanhui Kuang Oswaldo Ochoa Department of Vegetable Crops, University of California, Davis Edward J. Ryder, Rebecca Grube UDSA-ARS, Salinas OBJECTIVES: To develop and apply new methods for detecting, analyzing and manipulating variation in lettuce. We continue to pursue these objectives in four projects: (i) Introduction of genes into lettuce using Agrobacterium tumefaciens and testing transgene activity. (ii) Molecular cloning of disease resistance genes. (iii) Development of a detailed genetic map using a variety of markers and identification of reliable readily-assayed markers linked to disease resistance genes. (iv) A comparative genomics approach to identification of candidate genes controlling horticultural traits. In the first three projects we are emphasizing either novel forms of disease resistance or increasing the efficiency of selection for disease resistant genotypes. Some of these studies are now funded from federal grants. The fourth project includes a wide range of horticultural traits. All projects were initiated with CLRB funds and application of the results to lettuce improvement is supported by CLRB funds. All projects impact both crisphead and leafy improvement. PROJECT REPORT CALIFORNIA LETTUCE RESEARCH BOARD April 1, 2001-March 31, 2002 PROJECT TITLE: THE ETIOLOGY, EPIDEMIOLOGY, AND MANAGEMENT OF A NEW SOIL-BORNE VIRUS DISEASE OF LETTUCE IN CALIFORNIA W.M. Wintermantel1, R.C. Grube1, and S. Koike2 USDA-ARS1 and University of California-Davis2 Salinas, California Lettuce dieback is responsible for losses in Romaine and leaf lettuce production in areas associated with rivers in California and Arizona. Losses vary, ranging from severe in some years to mild in others. Characteristic symptoms include severe stunting, necrosis and dieback of lettuce plants. The disease is caused by isometric viruses in the genus Tombusvirus. Field isolates from lettuce have been identified and characterized as both Tomato bushy stunt virus (TBSV) and the newly described Lettuce necrotic stunt virus (LNSV). Detection of tombusviruses directly from lettuce plants has been difficult. We have now developed a rapid, reliable method for detection of tombusviruses from lettuce tissue. This method decreases the time necessary for confirmation from weeks to a few days. The method involves spin-column purification of total RNA from lettuce, followed by RT-PCR amplification using primers specific to the 3' end of tombusviruses. Tombusviruses are very stable in nature and do not break down easily. As a result, they can survive in soil and water for long periods of time. We have collected soil samples from adjacent lettuce dieback-infested, as well as disease-free fields, and have compared the soil profile of these related soils. Initial studies suggest poor drainage may lead to high salt concentrations, and that these conditions may lead to increased incidence of infection. Adjacent fields with better drainage may have virus, but may not be exposed to conditions leading to disease development. Field testing continues, and research is currently in progress to identify lettuce varieties with resistance to dieback-inducing tombusviruses. Most crisphead varieties are resistant to dieback inducing tombusviruses, and some butterhead and green leaf varieties are available that exhibit resistance. Several romaine, leaf, and stem PI lines have been identified as resistant. Research Abstract to the California Lettuce Research Board's Research Program April 2001 to March 2002 Project Title: Investigation of a new crown rot disease of lettuce Project Investigators: Steven T. Koike University of California Cooperative Extension Monterey County Krishna Subbarao Department of Plant Pathology University of California at Davis Diana Fogle California Department of Food & Agriculture Sacramento, California Summary: In the spring of 2000, a potentially new crown rot disease of lettuce was discovered in both Monterey and Santa Cruz counties. Early symptoms consisted of yellowing and wilting of lower leaves. Affected plants later had an uneven appearance because one side of the foliage grew normally while the diseased side of the plant was stunted and short. As plants matured, the entire plant became affected and eventually wilted and collapsed. Examination of affected plants revealed distinct, black cavities (sunken areas) on the crown and upper taproot. These cavities extended far into the crowns and roots, resulting in extensive weakening of the plant; these plants could be easily broken off at ground level. The black cavities were characteristically firm and lacked any sign of fungal growth or spores. The disease was most commonly found and most severe on Romaine cultivars. In 2001, the same disease again occurred in both counties, perhaps signally the establishment of a new lettuce disease. Extensive isolations in 2001 resulted in the recovery of the same gray-green fungus that was found in 2000. In a significant development, we were able to induce the fungus to grow some identifying structures and have tentatively identified the pathogen as a species of Phoma. Field surveys indicate that Romaine was the type of lettuce that was mainly infected. Interestingly, a majority of the Romaine crops that were affected were planted in fields where the previous crop was strawberry. The association of crown rot with fumigated soils and strawberry plantings will be explored further. Research Abstract to the California Lettuce Research Board's Research Program April 2001 to March 2002 Project Title: Developing an integrated disease management program for gray mold of lettuce Project Investigators: Steven T. Koike University of California Cooperative Extension Monterey County Krishna Subbarao Department of Plant Pathology University of California at Davis Summary: In years when transplants are widely used in early spring, Botrytis gray mold at times can cause significant stand losses in leaf lettuce plantings. This loss is particularly evident with Romaine cultivars as this lettuce type is very susceptible to the disease. The initial symptom of gray mold is a water-soaked, brownish-gray to brownish-orange rot that occurs on transplant leaves and stems that are damaged during the normal practice of handling and planting. Damaged tissues that are wet or in contact with the soil are especially susceptible. From infected leaves and stems, the pathogen progresses into the crown of the lettuce plant, causing a decay and eventual death of the main stem. A characteristic fuzzy gray growth of the Botrytis cinerea fungus can cover diseased areas. We conducted field trials to evaluate the effectiveness of various fungicides against the B. cinerea pathogen. Fungicides were applied both preplant (to transplants in trays, one day prior to field planting) and postplant (immediately after transplants were placed in the ground) onto Romaine lettuce transplants. Various fungicide treatments showed some potential in controlling Botrytis crown rot. However, the Botran and BAS 516 products provided the best control. For all materials the preplant drench method of application tended to give better control than postplant field sprays. BAS 516 preplant and Botran preplant and postplant treatments resulted in the highest lettuce yields. RESEARCH ABSTRACT TO THE CALIFORNIA LETTUCE ADVISORY BOARD'S RESEARCH PROGRAM for the period April 1, 2001 - March 31, 2002 PROJECT TITLE: Powdery Mildew Management PRINCIPLE INVESTIGATORS: Thomas Turini University of California Cooperative Extension, Imperial County Steven Koike University of California Cooperative Extension, Monterey County Ed Ryder and Becky Grube USDA Monterey County SUMMARY: Powdery mildew of lettuce, caused by Erysiphe cichoracearum, is a common problem in lettuce grown in the low desert and appears to be an emerging problem in coastal production areas. There are few fungicides registered for control of this disease. To address this problem, fungicide activity and relative susceptibility of common lettuce varieties were compared in Imperial and Monterey Counties. Trials in Imperial and Monterey Counties were initiated to compare activity of fungicides against powdery mildew. Under the conditions of these fungicide efficacy trials, materials that consistently provided excellent powdery mildew control included Flint and Microthiol. Quintec alone and alternated with Rally also provided excellent control, although these treatments were only tested in one trial this season. Both Rally and Quintec also provided excellent control in 2000- 2001 Imperial County trials. In Monterey County, Quadris and Quadris alternated with Actgard also provided excellent control; however, in Imperial, these treatments were no different than the non-treated control. In addition, a trial to compare relative susceptibility of lettuce cultivars was initiated in Imperial County. GL-11 and Two Star green leaf varieties, Conquistador and Green Towers romaine varieties, and Margarita, Optima and Esmeralda butter lettuce types had the lowest disease severity. Powdery mildew was most severe in the iceberg varieties tested. CALIFORNIA LETTUCE RESEARCH BOARD APRIL 1, 2001 - MARCH 31, 2002 Project Title: Ecology and management of bacterial leaf spot of lettuce Principle investigator: Carolee Bull, USDA/ARS Cooperators: Polly Goldman, USDA/ARS Steve Koike, UCCE Ed Ryder, USDA/ARS Summary: Bacterial leaf spot of lettuce caused by Xanthomonas campestris pv. vitians (Xcv) is an important pathogen of lettuce in California's coastal and inland counties. We evaluated 9 commercially available chemical or biological treatments for control of bacterial leaf spot. In trials conducted in Salinas, only a combination of copper and the biological treatment Serenade (AgraQuest, Davis, CA) provided significant reduction in the incidence of disease. None of the treatments tested influenced lettuce yield, however. Additionally, we conducted a preliminary screening of 28 cultivars of lettuce for resistance to bacterial leaf spot. The incidence of bacterial leaf spot was numerically lower on Holborn Standard, Batavia Blonde Paris, Little Gem, Salad Bowl, Iceberg, Batavia Reine Glaces, and Batavia Rossia. Additionally five cultivars (Early Giant, GL65, Bat. Flavia, Vista Verde, and Pybas 251) had disease incidence ratings between 91 and 100% and were considered susceptible. Since this trail did not consist of replicated plots, these results should be considered preliminary. We are further testing these cultivars and the chemical and biological treatments in field trials in Salinas. RESEARCH ABSTRACT TO THE CALIFORNIA LETTUCE RESEARCH BOARD'S RESEARCH PROGRAM For the period April 1,2001 -March 31,2002 PROJECT TITLE: Investigations on Bottom Rot of Lettuce PRINCIPAL INVESTIGATOR: Frank Martin SUMMARY: Attempts to clarify which pathogens are responsible for lettuce bottom rot in California and Arizona production areas is in progress. Of the isolates that have been recovered from diseased plants in the field, 75% were multinucleate Rhizoctonia solani, 14% were binucleate Rhizoctonia and 11% were Pythium species (the predominant species was P. ultimum). Thus far the most common anastomosis group (AG) identified for R. solani is AG 4, a broad host range AG that is capable of attacking a number of the host crops, some of which are commonly grown in rotation with lettuce. From one collection location isolates of this AG were recovered from bottom rotted lettuce as well as diseased celery and radicchio in adjacent fields. Pathogenicity tests with isolates of R. solani revealed that these isolates exhibited a range in virulence, with some causing only minor levels of infection while others caused significant rot of the leaf base of the host. Additional pathogenicity tests to confirm the involvement of recovered pathogens on disease expression are in progress. Environmental conditions have been found to influence disease expression in growth chamber trials. While plant infection was observed at temperatures ranging from 23-28 C, symptom expression and disease progress was more pronounced at the higher temperatures. By placing temperature recorders in the field it was found that the temperatures at the base of the head in contact with the soil (where disease occurs) was 8-10 C cooler than ambient temperatures. This data will assist in clarifying the influence of temperature on disease incidence. In an effort to determine if genetic tolerance to the disease exists in the germplasm, growth chamber evaluations of germplasm provided by Ed Ryder are currently in progress. Due to the techniques used in these assays, results are reflective of genetic tolerance and are independent of plant architecture. While none of the cultivars evaluated were completely resistant to the pathogen, definite differences in cultivar susceptibility to disease were observed. For example, all crisphead types were susceptible to R. solani AG-4, while some of the romaine and leaf lettuce types exhibited less susceptibility. Field evaluations were conducted, but due to low disease pressure meaningful results were not obtained. In collaboration with Steve Koike, field trials to evaluate fungicide efficacy for control of bottom rot were conducted. Eight fungicide treatments (plus an untreated control) were under evaluation in two replicated trials in the Huron area. Fungicides currently registered for use on lettuce (Quadris, Rovral, Ronilan and Botran) were included in the trials, as were several fungicides registered for other crops and one experimental unregistered fungicide (BASF 516). Disease pressure was low to moderate for the trials with the 8/17 germination date, but lower for the 9/5 germination date. All three products containing strobilurin fungicides included in these trials (Quadris, Flint and BASF 516) worked well in disease control, as did Rovral and Switch. CALIFORNIA ICEBERG LETTUCE RESEARCH PROGRAM April 1,2001 -March 31, 2002 EPIDEMIOLOGY AND CONTROL OF LETTUCE DROP CAUSED BY SCLEROTINIA SPECIES Krishna V. Subbarao Department of Plant Pathology University of California, Davis SUMMARY: The research objectives for the current year included: (1) to continue the evaluation of the existing and potential fungicides for lettuce drop control; (2) to test Brassica spp. for resistance to Sclerotinia minor; (3) to determine the survival of sclerotia from the two species at different soil temperatures; and (4) to evaluate breeding lines for Sclerotinia minor resistance both in the field and in the greenhouse. We also surveyed over 300 lettuce fields in the Salinas, Santa Maria and Central Valleys and analyzed the data for the relative distribution of fields with lettuce drop caused by S. minor and S. sclerotiorum, effects of lettuce types, irrigation practices and growth stages on lettuce drop incidence. Of the fungicides evaluated, two applications of Rovral did not reduce lettuce drop incidence relative to unsprayed control in either spring or fall. But both two applications of Botran and split applications of Botran and Rovral significantly reduced lettuce drop incidence in spring but not in fall. Fungicides Messenger and Switch reduced lettuce drop by more than 50% during the spring and only BAS 510 gave excellent control of lettuce drop during both seasons. Two week-old seedlings of bok choi, broccoli, brussels sprouts, broccoliraab, cabbage, Chinese cabbage, cauliflower, radish, and rape were all susceptible to both mycelial and sclerotial inoculum from four isolates of S. minor. However, delaying the inoculation by one week reduced infection of broccoli by S. minor by nearly 100% in contrast to lettuce, which was susceptible regardless of the time of inoculation. Field experiments to determine the survival of Sclerotinia minor and S. sclerotiorum sclerotia were repeated in both San Joaquin and Salinas Valleys. Survival of S. minor was greatly reduced in the San Joaquin Valley after 24 weeks of burial but not in the Salinas Valley. Length of burial had little effect on the survival of S. sclerotiorum sclerotia at either location. These results clearly suggest why we see fewer infections caused by S. minor in the San Joaquin Valley. Our surveys clearly indicated that S. minor infections are dominant in the Salinas Valley, S. sclerotiorum infections were dominant in the San Joaquin Valley, and mixed infections by both species were common in the Santa Maria Valley. Fields with drip irrigation clearly had the lowest lettuce drop incidence compared with either sprinkler or furrow irrigated fields. Crisphead and Romaine lettuce fields had the highest lettuce drop incidence and the leaf lettuce fields had the lowest disease incidence. Lettuce drop appeared as early as 5th leaf stage and progressively increased to maximum at crop maturity. Efforts to identify sources of resistance and using them in the breeding program were continued. Details of this work will be in the report by Ed Ryder and Rebecca Grube. CALIFORNIA LETTUCE RESEARCH PROGRAM April 1,2001-March 31, 2002 BIOLOGY AND EPIDEMIOLOGY OF VERTICILLIUM WILT OF LETTUCE Krishna V. Subbarao Department of Plant Pathology University of California, Davis SUMMARY : The research objectives this year included: (1) to monitor the spread of the pathogen in the Salinas Valley; (2) to collect seed samples from wild Lactuca and other weed species and test them for Verticillium dahliae infestation; (3) to determine the seedborne nature of the pathogen using using GFP-transformed V. dahliae from lettuce; (4) to determine if seedborne inoculum survives prolonged periods of storage at low temperatures; and 5) to continue the breeding program to identify and develop sources of resistance to Verticillium wilt in crisphead, leaf, and other lettuce types. Verticillium wilt was detected in eight additional lettuce fields in the Watsonville and Salinas areas over the past year. Verticillium wilt in these fields varied from a few plants to nearly 80%. The inoculum densities in these fields were typical of those observed in other Verticillium wilt affected lettuce fields and varied from 32 (incidence was very low) to 274 microsclerotia g' soil (incidence approached 80%). Intensive monitoring of a single field over the past two years revealed that populations of microsclerotia exploded from 36 microsclerotia g"1 soil to 631 microsclerotia g"1 soil after an infected lettuce crop was plowed under. A major discovery this year was the recovery of V. dahliae from several infected weed species and their seeds. We are currently evaluating the pathogenicity of these isolates on lettuce. We also successfully transformed an isolate of V. dahliae from lettuce with the GFP marker and compared the pathogenicity of the transformed isolate with that of a wild type isolate. Seed collected from plants inoculated with the transformed isolate further confirmed the seedborne nature of the Verticillium wilt in lettuce. The experiment to evaluate the effect of storage temperatures on the survival of V. dahliae in infested seed was initiated. Results thus far available suggest that storage for 6 months only at room temperature (23 C) significantly reduced V. dahliae recovery from infested seed. The experiment is continuing. Although several germplasm and breeding lines were planted in the field for Verticillium wilt resistance evaluation, high incidence of lettuce drop in the trial interfered with the study and thus, no data on Verticillium wilt resistance could be collected. Research Abstract to the California Lettuce Research Board for the period April 1,2001 to March 31,2002 TITLE: Insect Management for Central Coast Lettuce PRINCIPLE INVESTIGATOR: William E. Chaney Farm Advisor - Entomology U.C. Cooperative Extension - Monterey County 1432 Abbott Street Salinas, CA 93901 The leafminer problem has rebounded in the last two years compared to the two previous years. Lettuce aphid problems continue to be sporadic in the spring, but more consistent in the fall. Several new insecticides aimed at the lettuce aphid were tested and found to be effective, including the existing and new chloronicotinyls, and the material Fulfill, a new selective aphicide. Lab and fieldwork showed that the key leafminer materials, Agrimek, Trigard and the neem-based products are still effective in preventing the emergence of leafminer adults from treated plant material. A method for testing the insecticide susceptibility of field populations of lettuce aphid was developed. This lab test will help track the susceptibility of lettuce aphid over time and can be used to investigate field control failures to determine if reduced sensitivity was a factor. The limited testing completed so far has not found significant differences in the susceptibility of the tested populations. Studies looking at the biological control of the lettuce aphid showed that relatively low populations of hoverfly larvae (around 2 per plant) can completely eliminate even large populations of lettuce aphid (approaching 100 aphids per plant). The dependability and timing of this natural control are too unreliable for most growers. Sometimes the hoverfly larval populations never develop or they may develop too late to clean up the lettuce before harvest. The problem of hoverfly larvae remaining in the lettuce plant at harvest is also an issue. Field and lab trials demonstrated that Success, a material used primarily for worms and adult leafminer management, had negative impacts on hoverfly larvae, allowing lettuce aphid populations to surpass those in untreated areas. This is not highly significant at this time, since few if any conventional growers are relying on this form of biological control. This material is not currently registered for use in organic fields where hoverfly larvae are important. CALIFORNIA LETTUCE RSEARCH BOARD April 1, 2001 - March 31, 2002 WEED MANAGEMENT SYSTEMS FOR LETTUCE Steven A. Fennimore Dept. of Vegetable Crops and Weed Science University of California, Davis Salinas, CA Richard F. Smith University of California Cooperative Extension Monterey County Salinas, CA SUMMARY Weed management activities in 2001 were focused on improved management strategies for common sowthistle, and improvement of herbicide use efficiency on 80-inch beds. Specific objectives were: (1) to develop improved management systems for common sowthistle; (2) to compare herbicide use efficiencies in lettuce 80-inch bed production systems. We have found that sowthistle seed does not deteriorate rapidly in soil, and that it needs to be buried for more than one year to die. Sowthistle sets seeds in about 8 weeks after emergence, so it is unlikely that much so,wthistle seed is being set in lettuce fields. It is more likely that sowthistle seed is blowing in from areas surrounding fields such as ditches and fence rows. Cultural practices, such as preirrigation of flat beds that can be prepared for planting with very shallow tillage, appear to slightly improve control of sowthistle, compared to the standard practice, preirrigation of peaked beds. Prefar in mixture with Kerb appears to improve the control of sowthistle soon after lettuce planting, compared to Kerb alone. But this sowthistle control does not hold through the crop cycle. We have completed three years of comparisons of the cost-effectiveness of band vs. bed top applications on 80-inch beds. We conclude that in fields with a history of light weed infestations, that band herbicide applications are more cost-effective than bed top applications. Only in fields where heavy weed infestations are expected can bed top applications be justified in spring and summer plantings. California Lettuce Research Board April 1, 2001 - March 12, 2002 Project Title: Evaluation of Controlled Release Fertilizers for Winter Lettuce Production Principle investigator: Richard Smith University of California Cooperative Extension, Salinas Cooperating personnel: Tim Hartz Dept. of Vegetable Crops, University of California, Davis SUMMARY : Slow release fertilizer trials were conducted in 5 commercial head lettuce fields in the Salinas Valley from 2000-2002. Early planted fields on light soils were selected for these trials to provide the greatest potential for exposure to the high rainfall months and greatest potential for nitrogen movement from the root zone. 200 pounds of nitrogen was applied as all slow release fertilizer or as combinations of slow release fertilizer and sidedress applications of conventional fertilizer. These treatments were compared with a standard treatment of 200 lbs N/A and an untreated control. Slow release fertilizers gave yields comparable to the standard fertilizer in the Romaine trial, but the standard fertilizer treatment had higher yield than slow release treatments in the head lettuce trial in 2002. In summary, over the past three years, slow release fertilizers in combination with standard fertilizers gave comparable yields to the standard fertilizer treatment in 4 trials, and the standard fertilizer treatment gave higher yields than slow release fertilizers in one trial. The combination of slow release with conventional fertilizer appears to give improved performance over a large initial application of slow release fertilizer at the beginning of the season. There were high residual levels of nitrate-nitrogen in the top foot of soil at the initiation of the trials in 2002. Over the course of the trials most of the initial nitrogen was taken up or leached to deeper levels in the soil profile. We did not see evidence of reduced leaching of nitrate in the slow release fertilizer treatments in these trials, however this observation could have been influenced by the high initial levels on nitrate nitrogen in the soil at the beginning of the trial. Slow release fertilizers generally maintained nitrate-nitrogen levels in the top foot of the soil over the course of the season, which were comparable with or higher than the standard fertilizer treatment. In addition, the levels of tissue nitrogen were also adequate in the slow release treatments. Slow release fertilizers cost were more expensive than the standard fertilizer program. No yield advantage was observed for slow release fertilizers over standard fertilization practices in any of the five trials conducted. As a result, there appears to be no short-term economic advantage to the use of slow release fertilizers in lettuce. These trials were conducted during low rainfall years and the benefits of slow release fertilizers may be more apparent in years with higher rainfall and greater potential for leaching nitrogen from the root zone. RESEARCH ABSTRACT TO THE CALIFORNIA LETTUCE RESEARCH BOARD FOR THE PERIOD APRIL 1, 2001 TO MARCH 31, 2002 Project Title: Nutrient and Phytochemical Analysis of 5 Lettuces: Butterhead, Green Leaf, Red Leaf, Iceberg, and Romaine Principal Investigators: Joanne M. Holden Research Leader Nutrient Data Laboratory Gary Beecher, Retired Research Chemist Food Composition Laboratory Beltsville Human Nutrition Research Center USDA-ARS, Beltsville, MD 20705 iholden@rbhnrc.usda.gov Summary : The analysis of traditional nutrients and phytochemicals in lettuce is important for the promotion of lettuce as part of a healthful diet, support of research to determine the impact of diet on health, and development of Dietary Reference Intakes for carotenoids and flavonoids. As part of a study conducted by Agriculture Research Service of USDA that included 53 vegetables, fruits and nuts, samples of the lettuces were taken in two seasonal passes from supermarkets across the U.S. The nationwide sampling scheme was designed to ensure that data represent, to the greatest extent possible, what is eaten by consumers in the continental U.S. Analyses were done for the nutrients used in USDA's Nutrient Database for Standard Reference, 8 carotenoids, 17 flavonoids and ORAC. Data on traditional nutrients and carotenoid data will be used to update the current USDA Databases in the fall of 2002, and flavonoid data will be part of a new USDA Flavonoid Database in 2003. The Produce for Better Health Foundation, who partnered with USDA on the project, will develop and disseminate information on the nutrient and phytonutrient content of all 53 commodities in the study, and will promote the health benefits of a diet high in a variety of vegetables and fruits. Results showed that values for most traditional nutrients confirm previous data generated more than 10 years ago and provide additional data points for those databases. Beta-carotene for romaine, and the value for vitamin A computed from it, is significantly higher than the value that was published in 1999 and based on limited numbers of samples. No values for B-carotene in butterhead, red leaf, and green leaf lettuce were previously available. Vitamin A values for butterhead, romaine, red leaf and green leaf lettuces were three to four times higher than previous values. The new data, when adjusted to the 85g FDA serving size, approach or exceed the 5000 IU of vitamin A currently being used as the Reference Daily Intake for food labeling. Although a large body of observational epidemiological evidence suggests that higher blood concentrations of beta-carotene and other carotenoids obtained from foods are associated with lower risk of several chronic diseases, nutrient content claims cannot be made because Dietary Reference Intakes for carotenoids have not yet been established. Quercetin is the major flavonoid component detected in various lettuces. Determinations of ORAC have been made for only a limited number of samples and are, therefore, not reported at this time. |