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LETTUCE BREEDING, - USDA-ARS R. C. Grube, B. Mou, J. D. McCreight, & E. J. Ryder, 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 CHARACTERIZATION AND MANAGEMENT OF LETTUCE DIEBACK DISEASE AND LETTUCE TOMBUSVIRUSES - William M. Wintermantel, USDA-ARS, Salinas INVESTIGATION OF A CROWN ROT DISEASE OF LETTUCE: NEW FINDINGS Steven T. Koike & Krishna V. Subbarao, UC Cooperative Extension, Salinas and UC Davis ECOLOGY AND MANAGEMENT OF BACTERIAL LEAF SPOT OF LETTUCE Carolee 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 FUSARIUM WILT OF LETTUCE: MANAGEMENT THROUGH DETECTION, AVOIDANCE, AND DISEASE RESISTANCE Thomas R. Gordon, UC Davis INSECT MANAGEMENT FOR CENTRAL COAST LETTUCE William E. Chaney, UC Cooperative Extension, Salinas INSECT MANAGEMENT FOR LOW DESERT LETTUCE Eric T. Natwick, UC Cooperative Extension, Holtville GREENHOUSE WHITEFLY CONTROL IN ROMAINE LETTUCE Oleg Daugovish, UC Cooperative Extension, Ventura WEED MANAGEMENT SYSTEMS FOR LETTUCE Steven A. Fennimore & Richard F. Smith, UC Davis and UC Cooperative Extension, Salinas -- INFLUENCE OF VARYING NITROGEN AND PHOSPHORUS FERTILIZATION ON POSTHARVEST QUALITY OF LETTUCE Husein Ajwa & Murshidul Hoque, UC Davis MUSTARD COVER CROPS TO OPTIMIZE CROP ROTATION FOR LETTUCE PRODUCTION Richard F. Smith, UC Cooperative Extension, Salinas ABSTRACT CALIFORNIA LETTUCE RESEARCH BOARD for the period (April 1, 2002-March 31, 2003) PROJECT TITLE: Lettuce Breeding, USDA-ARS PROJECT INVESTIGATORS: R. C. Grube, B. Mou, J. D. McCreight, E.J. Ryder SUMMARY: Our objectives are to incorporate resistance to several diseases and insects into crisphead and mixed lettuce cultivars and breeding lines. In 2002, major efforts targeted lettuce big vein (BV), lettuce mosaic virus (LMV), downy mildew/Bremia (DM), lettuce drop/Sclerotinia minor, Verticillium wilt, lettuce dieback/tombusviruses, Fusarium root rot, bacterial leaf spot (BLS), corky root (CR), lettuce aphid and leafminer. Minor programs addressed adaptation to desert conditions, dark green leaf color, nutritional content, resistance to Phoma basal rot and powdery mildew (PM), and combination of multiple resistances. In all programs, horticultural traits, adaptation, and resistance to tipburn are considered essential. In 2002, we screened and identified new candidate sources of resistance to CR, leafminer, Fusarium, Phoma, Verticillium, BLS and BV. In replicated tests, we confirmed resistance of previously identified germplasm to CR, leafminer, BV, dieback, BLS, PM and LMV. Advanced I breeding lines were evaluated for resistances to BV, LMV, CR, and Verticillium (crisphead), dieback (romaine), and dark green color (leaf). Dieback-resistant romaine breeding lines were released. Genetic studies concurrent with breeding programs are being conducted to determine the inheritance of resistances to LBV, LMV, lettuce drop/S. minor, and field resistance to DM. The inheritance of mild and necrotic reactions to LMV were completed and published in 2002. CALIFORNIA LETTUCE RESEARCH PROGRAM April 1, 2002 to March 31, 2003 BREEDING CRISPHEAD LETTUCE Richard W. Michelmore Oswaldo E. Ochoa Department of Vegetable Crops University of California, Davis rwmichelmore@ucdavis.edu ochoa@vegmail.ucdavis.edu SUMMARY: The program continues to emphasize the identification and incorporation of genes for disease resistance, particularly to downy mildew, lettuce mosaic virus, anthracnose, verticillium and corky root, into horticultural types suitable for California. Resistance for downy mildew is being introduced from several new sources 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. We are also introducing delayed bolting from wild lettuce. We are initiating a program for resistance to Verticillium. Advanced lines are trialled at the USDA field station in Salinas. We have continued to monitor variation in the ability of the downy mildew pathogen to overcome resistance genes. There has been a continued increase in variation in the pathogen. Of the known resistance genes, only Dm 17 remained effective against all California isolates. The frequency of isolates in our non-random sample that were capable of overcoming all of the other characterized sources increased in 2002. The advanced breeding lines released in 2002 retained their spectrum of resistance; five were resistant to all isolates tested CALIFORNIA LETTUCE RESEARCH PROGRAM April 1, 2002 to March 31, 2003 LEAF LETTUCE BREEDING Richard W. Michelmore Maria Jose Truco Oswaldo E. Ochoa Department of Vegetable Crops University of California, Davis rwmichelmore(a),ucdavis.edu mitruco@vegmail.ucdavis.edu oeochoa(q),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 varieties. CALIFORNIA LETTUCE RESEARCH PROGRAM April 1, 2002, to March 31, 2003 GENETIC VARIATION IN LETTUCE Richard W. Michelmore Department of Vegetable Crops University of California, Davis rwmichelmore@ucdavis.edu SUMMARY: Novel methods for detecting, analyzing, and manipulating genetic variation are being applied to lettuce. The aim of this project is to ensure that lettuce does not lag behind other crops in benefiting from the application of genomic and biotechnological techniques. We have continued four projects: (i) Introduction of genes into lettuce using Agrobacterium tumefaciens and analysis of their expression, (ii) Cloning and characterization of disease resistance genes, (iii) Genetic mapping using a variety of molecular markers with the goal of locating most of the disease resistance genes known in lettuce. (iv) Comparative genomics to identify candidate genes controlling horticultural traits. We are in the process of cloning functional homologs of DmS with different specificities from other genotypes with an initial focus on Dml8. We have shown using post-transcriptional gene silencing that Dml8 is probably encoded by a homolog of Dm3. Over 66,000 ESTs have been generated representing over 19,000 unigenes and at least a third to a half of all genes in lettuce. QTL analysis has identified chromosomal regions controlling numerous horticulturally important traits. These are being mapped relative to candidate genes. We have developed and are curating a database for the Compositae (http://compositdb.ucdavis.edu/) that includes genetic, molecular marker, cultivar, and sequence data for lettuce as well as information on lettuce researchers. CALIFORNIA LETTUCE RESEARCH BOARD April l, 2002 - March 31, 2003 Project Title: CHARACTERIZATION AND MANAGEMENT OF LETTUCE DIEBACK DISEASE AND LETTUCE TOMBUSVIRUSES W.M. Wintermantel1, R.C. Grube1, and S. Koike2 USDA-ARS' and University of California-Davis2 Salinas, California SUMMARY: 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. The disease is tightly linked to the presence of river water, being found commonly in areas where flooding has recently occurred, where river water is used for irrigation of fields, and where dredge is deposited on fields. 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 Lettuce necrotic stunt virus (LNSV), and Tomato bushy stunt virus (TBSV). We collected soil samples from adjacent lettuce dieback-infested, as well as disease-free fields, and compared the nutrient profiles of these related soils. The studies indicated that poor drainage, such as occur in areas near rivers, may lead to high salt concentrations, and that these conditions may lead to increased incidence of infection. Greenhouse and growth chamber studies were conducted to directly determine the effect of high salt concentrations on infection and development of LNSV symptoms in lettuce. Results indicate that high salt, as measured by elevated electrical conductivity levels in soil, lead to increased LNSV infection and increased incidence of lettuce dieback in two different Salinas Valley soils. Studies suggest other types of plant stress, in addition to salinity stress, may also lead to increased incidence of lettuce dieback disease symptoms, and these are being examined in continuing studies. Confirmation of lettuce dieback disease requires identification of LNSV or TBSV in lettuce. Variability among tombusviruses that exist in lettuce has previously complicated uniform detection, since some cause disease while others do not. Recent studies have focused on optimizing primer sequences to detect specific groups of tombusviruses, and distinguish those responsible for lettuce dieback disease from those that are not. Tombusvirus detection involves purification of total nucleic acid from lettuce, followed by amplification of specific nucleic acid sequences using a technique known as RT-PCR, and primers specific to sequences in the 3' end of tombusviruses. Different primer sets are necessary for detection of divergent tombusvirus isolates, but the universal method of purification facilitates fairly rapid character Research Abstract to the California Lettuce Research Board's Research Program April 2002 to March 2003 Project Title: Investigation of a crown rot disease of lettuce: new findings Project Investigators: Steven T. Koike University of California Cooperative Extension Monterey County Krishna Subbarao Department of Plant Pathology University of California at Davis Collaborators: Becky Grube, Ed Ryder, Gerhard Verkley, Tim O'Neill, Diana Fogle Summary: In 2002, for the third consecutive year, crown rot was again found at numerous sites in Monterey and Santa Cruz counties. In a new development, for the first time clear cases of infected iceberg lettuce were seen, showing that crown rot can no longer be considered only a disease of Romaine. Significant crown rot was also seen in the Santa Maria Valley in Santa Barbara County. Early symptoms on Romaine 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 stunted 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 broken off easily at ground level. The black cavities were characteristically firm and lacked any sign of fungal growth or spores. If a cross-section cut is made at crown level, the typical symptom will be a pie-shaped wedge of black to brown tissue that extends into healthy white tissue. We identified the pathogen as Phoma exigua, which is a soil-borne fungus. It now appears that our California problem is the same disease as the one reported in the United Kingdom. We therefore are calling this problem Phoma basal rot, following the information obtained from the UK. A more consistent pathogenicity test was developed. Several methods were effective: dipping roots into spore suspensions (roots were either clipped or undipped); placing colonized agar blocks at the base of plants; pouring spore suspensions onto the base of potted plants. Inoculation experiments also showed that Romaine isolates were able to consistently cause disease on Romaine and crisphead cultivars, and crisphead isolates consistently caused disease on crisphead and Romaine cultivars. Therefore it appears that the same pathogen affects both lettuce types in California. Results of a field fungicide trial were very promising. Two treatments (BAS 516 and Switch) gave excellent control, and a third treatment (Quadris) provided control that was very close to that achieved by the first two materials. BAS 500, Rovral, and Flint were significantly better than untreated control, but were not as effective as the best three materials. The remaining treatments (Maneb, Botran, Actigard) were not effective. CALIFORNIA LETTUCE RESEARCH BOARD 2002 FINAL REPORT MAY 15, 2003 Project Title: Ecology and management of bacterial leaf spot of lettuce Principle investigator: Carolee Bull, USD A/ ARS Cooperators: Polly Goldman, USD A / ARS Steve Koike, UCCE Ed Ryder, USD A /ARS Summary: During the 2002 funding cycle we conducted seven field experiments and additional greenhouse studies on development and control of, and resistance to, bacterial leaf spot (BLS) of lettuce, caused by Xanthomonas campestris pv. vitians (Xcv). In three experiments we evaluated 4 commercially available chemical and biological products and combinations of these products for control of BLS. In one experiment the combination of Serenade and copper reduced the severity of BLS. In another experiment, all the copper treatments - copper alone and copper in combination with either Maneb or the biological preparation Serenade (AgraQuest, Davis, CA) - resulted in significantly lower disease incidence and severity than that of a water control. This, in addition to results from 2001 suggest that the combination of Serenade and copper may be a useful treatment for BLS reduction. In one of these experiments we also evaluated the influence of these treatments on development of to corky root of lettuce, caused by Rhizomonas suberifaciens. Plants from the Serenade and copper treatment had higher severity ratings for corky root than did the control. These experiments need to be repeated with known quantities of inoculum and appropriate controls. In addition to experiments with chemical management methods, we also evaluated 11 lettuce cultivars for resistance to BLS in three replicated trials. Vista Verde and Pybus 251 were consistently the most susceptible cultivars. Several cultivars including Little Gem, Batavia Reine Glaces, Prizehead, and Iceberg were resistant. We screened additional cultivars and lines in non-replicated trials and identified several new potentially resistant lines. Finally, we developed a greenhouse assay for more rapid screening of lettuce lines for resistance to BLS. The influence of bacterial populations on disease development was evaluated in field and greenhouse trials. Preliminary data suggests that for susceptible lines disease severity increased exponentially with population while for most of the resistant cultivars, the relationship was linear. We are repeating all three groups of experiments - the cultivar trial, the chemical and biological field applications, and the greenhouse population biology studies. RESEARCH ABSTRACT TO THE CALIFORNIA LETTUCE RESEARCH BOARD'S RESEARCH PROGRAM For the period April 1, 200March 31, 2003 PROJECT TITLE: Investigations on bottom rot of lettuce PRINCIPAL INVESTIGATOR: Frank Martin, USDA-ARS, Salinas, CA SUMMARY: Rhizoctonia solani has been consistently associated with disease symptoms from field grown plants in the Huron, Stockton, and Santa Maria areas; it has also been recovered from the Yuma production area as well. Unlike other lettuce production areas of the world where anastomosis group (AG) 1 and 2 have been attributed to causing the disease, in the California production areas AG 4 has been consistently isolated. This is a broad host range pathogen that is capable of infecting a number of the host crops commonly grown in rotation with lettuce. In addition to ft solani, there are several other fungal pathogens commonly recovered from diseased lettuce. Some fields in the Huron area have had several Pythium spp. consistently recovered from diseased plants; growth chamber tests indicate these pathogens are capable of infecting lettuce and causing symptoms similar to ft solani. Botrytis cinerea also is consistently recovered from diseased plants in the spring, but not in the fall. Growth chamber tests indicate this fungal pathogen is capable of infecting lettuce but differs from ft solani and Pythium spp. in that infection appears to be confined to the inoculated leaf. Environmental conditions can have important effects on disease expression in the field. From reviewing historical weather data from the Huron area it was found that temperatures ranged from 11.4 to 16.5 C from mid March through mid April, which was 6.3 to 10.4 C cooler than the temperatures observed in mid September through mid October (19.7 to 22.8 C). Based on the results from the growth chamber trials, the lower temperatures in mid March through mid April are likely the reason for the lower recovery of ft solani and higher recovery of B. cinerea from diseased plants during this time period. 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 ft solani AG-4, while some of the romaine and leaf lettuce types exhibited less susceptibility. 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, and Botran) were included in the trials, as were several fungicides registered for other crops and one experimental unregistered fungicide (BAS 516). Drip lines were installed in the center of the beds to enhance disease severity. All three products containing strobilurin fungicides included in these trials (Quadris, Flint and BAS 516) worked well in disease control, as did Rovral and Switch. CALIFORNIA ICEBERG LETTUCE RESEARCH PROGRAM April 1, 2002 - March 31, 2003 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 evaluate chloropicrin, telone+chloropicrin, and methyl bromide+chloropicrin for reduction of S. minor sclerotia in soil; (3) to determine the potential production of apothecia by Sclerotinia sclerotiorum in Salinas; (4) to determine the efficacy of biocontrol agents in Imperial Valley for lettuce drop control; and (5) to evaluate breeding lines for resistance to Sclerotinia minor. We evaluated Rovral, Botran, BAS 510, two rates of Switch, and Messenger during both spring and fall seasons in 2002. As before, two applications of Rovral did not reduce lettuce drop incidence during either season. Two applications of Botran and split applications of Rovral and Botran significantly reduced lettuce drop incidence only during the spring season. Similarly, weekly applications of Messenger four times after thinning reduced lettuce drop incidence during the spring but not in fall. During both spring and fall, however, the experimental fungicide BAS 510 consistently provided the best control of lettuce drop as also the unregistered fungicide, Switch. All fumigation treatments listed in objective 2 reduced the number of S. minor sclerotia and the numbers remained low even at the end of strawberry harvest. During the coming year, we will be following up the lettuce drop incidence on lettuce in these plots. We continued our studies to evaluate the potential production of apothecia by S. sclerotiorum in the Salinas Valley. As a part of these studies, we again 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. These results confirmed our previous conclusions on the relative distribution of the two species in the three valleys, the effects of lettuce types, irrigation, and growth stage on lettuce drop incidence. A unique conclusion borne out by the data was the higher incidence of lettuce drop in 80" beds compared with that on 40" beds. Furthermore, we also observed the apothecia of S. sclerotiorum on 80" beds. Greenhouse and field studies revealed that the production of apothecia was facilitated by at least 30 consecutive days of soil moisture at field capacity. Such conditions rarely occur during lettuce production in the Salinas Valley, but a largescale adoption of 80" bed configuration may provide optimal conditions the production of apothecia. Of all the biocontrol agents evaluated against both S. sclerotiorum and S. minor, none were effective against S. minor and only Contans was effective against S. sclerotiorum. Efforts to identify sources of resistance and using them in the breeding program were continued. Details of this work are in the report by Ed Ryder and Rebecca Grube. CALIFORNIA LETTUCE RESEARCH PROGRAM April 1, 2002 - March 31, 2003 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 survey weed species susceptible to Verticillium wilt, test seed for Verticillium dahliae infestation, and test isolates for pathogenicity on lettuce; (3) to determine if seedborne inoculum survives prolonged periods of storage at low temperatures; (4) to evaluate chloropicrin, telone+chloropicrin, and methyl bromide+chloropicrin for reduction of microsclerotia in soil; (5) develop rapid detection of V. dahliae in soil; and (6) 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 three new ranches in the Watsonville and Salinas area over the past year. Verticillium wilt in these fields varied from a 5% to nearly 94% yield losses varied from 5-80%. The inoculum densities in these fields were typical of those observed in other Verticillium wilt affected lettuce fields and varied from 16 (incidence was very low) to 932 microsclerotia g-1 soil (incidence and yield losses were 80%). We further confirmed several infected weed species as hosts and the pathogen in these weeds was also seedborne. Isolates from hairy nightshade, sonchus, and shepherd's purse were highly pathogenic to lettuce. The experiment to evaluate the effect of storage temperatures on the survival of V. dahliae in infested seed was continued. Results suggest that storage of infested seed at room temperature (23 °C) for 12 months significantly reduces V. dahliae recovery from seed. All other storage temperature treatments failed to reduce V. dahliae recovery from infested seed. All fumigation treatments significantly reduced the number of microsclerotia immediately after fumigation. However, by the final harvest of the strawberry crop, the numbers had increased significantly. The baiting technique tested for rapid detection of V. dahliae from lettuce in soil failed to provide a quantitative estimation of the microsclerotia in soil but was able to detect the presence of the lettuce strain in soil. Evaluation of resistance in germplasm and breeding lines in the field was successful during the fall and a number of lines with resistance were identified and selected. Abstract Project title: Fusarium wilt of lettuce: management through detection, avoidance and disease resistance Principal investigator: Thomas R. Gordon Department of Plant Pathology University of California Davis, CA 95616 Summary: This project was initiated in 2002 with the objectives of clarifying the relative importance of the various factors that influence disease severity. The primary emphasis is on those factors most likely to contribute to disease management: susceptibility of the host and the abundance of the pathogen in soil. A meaningful test of susceptibility requires the use of an isolate that is representative of the prevalent strains causing disease. Consequently, we have collected isolates from diseased plants and from soil, and we continue to test these to assess their relative virulence to a standard set of cultivars. In addition, we have conducted preliminary tests to determine the appropriate levels of inoculum to use in evaluating cultivar susceptibility. The results indicate that two levels (1,000,000 and 10,000,000 spores/ml) should serve to differentiate cultivars that are resistant and susceptible. Using this method, 49 cultivars have been tested for susceptibility. The results were not clear cut because disease development was more limited than in previous experiments. The most likely explanation for this outcome is the lower temperatures that prevailed in the greenhouse during the fall, as compared to summer and spring when previous experiments were conducted. To further explore this question and to ensure that tests of susceptibility are reproducible, we are now conducting experiments in a controlled environment chamber. Once the temperature regime has been optimized, we will repeat the cultivar evaluations. An important component of managing Fusarium wilt diseases is minimizing the abundance of inoculum in soil. To obtain the information required for effective management of soilbome inoculum, it is necessary to have a reliable quantitative assay for the presence of the pathogen in soil. We have developed such an assay and we are using it to test soils for the presence of the pathogen. Preliminary indications are that where the disease is most severe, the pathogen is present at very high levels. Thus, the abundance of the pathogen, rather than differences in pathogen virulence, may be the most important determinant of disease severity. Our tests also showed that the Fusarium wilt pathogen is still present in the field where the disease was originally identified in 1990. Research Abstract to the California Lettuce Research Board April 1, 2002 to March 31, 2003 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 Lettuce aphid continues to be the key insect concern for most lettuce growers in coastal production areas. Research on potential lettuce aphid management practices yielded interesting pieces of information for use in an overall management program. Field insecticide trials demonstrated that the neo-nicotinoids were all effective as foliar materials except dinotefuran. Fullfil, which was just registered for use in California, showed good efficacy, and offers a new class of chemistry for use in resistance management programs. It should be a good tank mix partner for many of the other aphidicides. The older insecticides for lettuce aphid control still show good activity if applied at a time and in a manner that affords excellent coverage. Tests to look for changes in susceptibility of lettuce aphid populations to Provado still show no clear signs that this insect is becoming less susceptible to this product. Tests with the foxglove aphid, which became a problem in some lettuce fields last season, did show reduced mortality at some of the lower concentrations of Provado tested. This may be due to the fact that this is a larger aphid than lettuce aphid, to which it was compared, and the lower dose was simply too little material per unit of body weight to effect control. Three trials to look at the impact of insectary plantings showed that flowering plants in lettuce fields increases the activity of syrphid fly larvae and reduce aphid populations. The exact amount of land that must be dedicated to these plantings has not been determined and likely varies with many factors. Leafminer populations continue to build in the fall, but still do not approach those seen in previous years. The standard leafminer materials continue to provide excellent control for about 7 days. The addition of buffering agents did not significantly improve the activity of neem-based insecticides against leafminers. Future work will include examining management techniques for soil pests, namely springtials and garden centipedes (symphylans) as well as continuning lettuce aphid and leafminer control tests. Research Abstract to the California Lettuce Research Board's Research Program April 1, 2002 to March 31, 2003 TITLE: Insect Management for Low Desert Lettuce PRINCIPAL INVESTIGATOR: Eric T Natwick Farm Advisor - Entomology University of California Cooperative Extension - Imperial County 1050 East Holton Road Holtville, CA 92250 SUMMARY: The silverleaf whitefly, Bemisia argentifofii, became a severe pest of lettuce in 1991 and has continued to cost low desert lettuce growers approximately $6.5 million annually for insecticidal control. Admire is now used for silverleaf whitefly control prophylactically through pre-plant soil treatments. Several insecticides aimed at silverleaf whitefly control in lettuce were compared to Admire and found to be effective, including two neonicotinoid compounds (Assail and Platinum) and a nitroguanadine compound, dinotefuron (V10112 20 SG). Fieldwork showed that Admire 2F, Assail 70 WP, Platinum 2 SC and dinotefuron are effective in protecting lettuce from silverleaf whiteflies. Pest control advisors and growers have reported an inability to adequately control beet armyworm and cabbage loopers in low desert lettuce production over the past several years with currently registered insecticides. Several new insecticides aimed at beet armyworm and cabbage looper control [Intrepid, Avaunt, Proclaim, gama-cyhalothrin (XDE 225 0.497 CS) and resolved zeta-cypermethrin (F0570 0 8 EW)] were compared to industry standards (Success, Warrior, Lannate and Kryocide) and were found to be effective in lettuce Fieldwork showed that all insecticide treatments are effective against cabbage loopers and that all insecticide treatments except the 0.018 lb(AI)/acre rate of resolved zeta-cypermethrin are effective in protecting lettuce from beet armyworms. Several aphid species, such as the green peach aphid and the potato aphid, are continual problems for lettuce production in Southern California, particularly in leaf lettuce In recent years, the lettuce aphid and the foxglove aphid have become problems, particularly for organic production of leaf lettuce, but these species were not found in this experiment Several neonicotinoid insecticides (Assail, Actara, and Platinum) were compared to Admire for aphid control in lettuce, and were found to be efficacious. Foliar sprays comparing Dimethoate and Orthene to a neonicotinoid, flonicamid (Fl 785 50 DF), dinotefuron and Hexacide (rosemary oil) showed that with the exception of dinotefuron and Hexacide, these insecticides are efficacious against potato aphid on lettuce. Greenhouse whitefly {Trialeurodes vaporariorum; Westwood) control in romaine lettuce (Lactuca sativa). Principal Investigator (PI): Oleg Daugovish Farm Advisor, Ventura County University of California Cooperative Extension (UCCE) 669 County Square Drive, Suite 100 Ventura, CA 93003. Phone: (805) 645-1454, Fax: (805) 645-1474 E-mail: odaugovish@ucdavis.edu Collaborator: Martin Ford Tri-Tech Ag. Products Oxnard, CA (805) 388-9855, Fax (805)388-2953 Cooperator: James Gill Oxnard, CA (805) 488-3074 Summary: Vegetable growers in Ventura County, CA identified greenhouse whitefly control as a priority in insect management. Lack of new insecticides and new modes of action make control efforts particularly difficult. Rotation of modes of action in an the insecticide program is essential for pest resistance management. This study examined five foliar application programs for greenhouse whitefly control, four of which combined materials with alternative modes of action. Two new materials that are not currently registered but are pursued for registration on lettuce by manufacturers were tested to broaden the spectrum of potential control options. Two applications in each program were targeting primarily adults (first application) and nymphs (second) of the greenhouse whitefly in romaine lettuce. Population of whitefly adults was low (0.3 adults per leaf) and increased to moderate (3 adults per leaf) by the end of growing season. Relatively low adult population resulted in low number of eggs and insufficient population of nymphs to assess the effect of treatments on nymphs. However, two applications of V-10112 (dinotefuran) at 0.67 lb/a reduced average whitefly adult number throughout the post-application period 49% compared to control, while Assail (acetamiprid) at 1.5 oz/a followed by Oberon (spiromesifen) at 8 oz/acre reduced adult number 36%. The results suggest that new materials V-10112 and Oberon, having different mode of action have potential for controlling whitefly adults and may be used in rotation for resistance management. Additionally, Assail, a neonecatenoid family insecticide recently registered on lettuce, applied after Mustang +Dimethoate E267 provided significant reduction (47% less than untreated control) in whitefly adult population. CALIFORNIA LETTUCE RESEARCH BOARD April 1, 2002 - March 31, 2003 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: Field studies were undertaken to evaluate the tolerance of lettuce to Muster (Ethanmetsulfuron) herbicide. Muster was applied postemergence at 0.0047, 0.0094, 0.0141, 0.0188 and 0.0376 lb ai/A at the 2- and 4-leaf stages of iceberg and romaine lettuce varieties. While Muster provides control of little mallow, lettuce was not tolerant to Muster at rates necessary for control of this weed. Additional studies were conducted to determine if Dacthal could be used in combination with Kerb on difficult-to-control lettuce weeds such as common sowthistle. Lettuce was not tolerant of Dacthal at rates necessary to control common sowthistle. RESEARCH ABSTRACT CALIFORNIA LETTUCE RESEARCH BOARD For the period (April 1, 2002-March 31, 2003) PROJECT TITLE: PROJECT INVESTIGATORS: INFLUENCE OF VARYING NITROGEN AND PHOSPHORUS FERTILIZATION ON POSTHARVEST QUALITY OF LETTUCE Husein Ajwa Department of Vegetable Crops University of California, Davis M. Murshidul Hoque Department of Vegetable Crops University of California, Davis COOPERATING PERSONNEL: Richard Smith UC Cooperative Extension Monterey County, California Michael Cahn UC Cooperative Extension Monterey County, California SUMMARY: The production of high quality lettuce depends on soil fertility. This study was conducted to evaluate the effect of nitrogen (N) and phosphorus (P) fertilizer application rates on yield and postharvest quality of lettuce, and to determine relationships between lettuce tissue composition, yield, postharvest parameters, and soil nutrients. Two types of lettuce [Lactuca sativa L., romaine (var. Green Tower) and iceberg (var. Sharp Shooter)] were evaluated in factorial experiments with four application rates of fertilizers N (0, 100, 200, and 300 lb/ac) and P (0, 100, 150 and 200 lbs/ac). For both lettuce types, no significant differences were found in yields between treatments that received N fertilization. Postharvest quality of lettuce stored in a cooler (at 4 °C) was evaluated weekly for three weeks after harvest. Parameters used to evaluate postharvest quality of romaine were wilting, decaying, brittleness, glossiness, and high saltbum. Parameters for iceberg were defects, fringeburn, turgidity, color, and cleanliness. Deterioration in postharvest quality of stored lettuce was more noticeable in romaine than in iceberg for all treatments. Our results suggest that iceberg lettuce can be stored up to 21 days without reduction in postharvest quality parameters. High N had a negative effect on most of the postharvest quality parameters, especially when stored for more than 14 days. CALIFORNIA LETTUCE RESEARCH BOARD April 1, 2002 - March 31, 2003 Title: Mustard Cover Crops to Optimize Crop Rotations for Lettuce Production Investigators: Richard Smith and Steve Koike, UCCE, Monterey County Krishna Subbarao and Steve Fennimore, University of California Cooperating Investigator: Laura Tourte, UCCE, Santa Cruz County SUMMARY: Effective rotations are an essential part of lettuce production for managing soil borne diseases and weeds. There are fewer options for economically viable rotational crops for lettuce producers; however mustard cover crops (Brassica spp.) offer a new and promising rotational crop for lettuce. They have been shown to be useful in other parts of the U.S. and the world and may have potential to control soil borne diseases and weeds that negatively impact lettuce production. These preliminary studies were conducted to examine potential negative aspects of mustard cover crops, such as their susceptibility to Lettuce Head Drop {Sclerotinia minor), their potential to persist in production fields as weeds, and to examine their relative productivity at different times of the year, as well as their costs of production. Lettuce Head Drop Studies: White mustards {Brassica hirta, Sinapis alba) were susceptible to S. minor while the Indian mustard (Brassica juncea) variety, Pacific Gold, was less susceptible. These two cover crop species are the most important cover crops that are currently being utilized by lettuce growers. Ideally, mustard cover crops should not be susceptible to S. minor, however these results do not indicate the subsequent impact of the cover crop residues on S. minor populations under field conditions. The canola types (Brassica napus) and radish (Raphanus sativus) varieties appear to be less susceptible to S. minor. However, these cover crop species are currently of less interest to growers in the coastal lettuce production districts. The plan for year two of these studies is to examine the impact of white and Indian mustards on S. minor in the lettuce production fields. Weed Persistence Studies: There does not appear to be a significant amount of dormancy in the mustard cover crops seeds and they do not appear to pose a problem as a long-term weed in production fields. Summer plantings of mustard cover crops set seed in as little as 55 days after planting, whereas spring and fall plantings set seed significantly later. Summer plantings of mustard cover crops should be incorporated quickly after the onset of flowering to avoid seed set. Productivity of Mustard Cover Crops: Mustard cover crops had higher productivity in the cooler months of the year (i.e. spring planting), but even in the warmest part of the Salinas Valley in mid-summer, white and Indian mustards produced over 2 tons of biomass per acre. Total cash costs to produce mustard cover crops are S168/A and total costs, including over head, are $625/A. |