PROJECT TITLE: Lettuce Breeding, USDA-ARS
PRINCIPAL INVESTIGATORS: E. J. Ryder, R. C. Grube, & J. D. McCreight
PROJECT TITLE: Breeding Crisphead Lettuce
PRINCIPAL INVESTIGATORS: Richard W. Michelmore & Oswaldo E. Ochoa
PROJECT TITLE: Leaf Lettuce Breeding
PRINCIPAL INVESTIGATORS: Richard W. Michelmore & Oswald E. Ochoa
PROJECT TITLE: Genetic Variation in Lettuce
PRINCIPAL INVESTIGATOR: Richard W. Michelmore
PROJECT TITLE: Basic Approaches to Lettuce Virus Disease Control
PRINCIPAL INVESTIGATOR: Bryce W. Falk
PROJECT TITLE: Examination of the Current Monterey County Seed Testing Protocol and Comparison of Various LMV Antisera and LMV Seed Testing Organizations for Detecting LMV-infected Seed Lots
PRINCIPAL INVESTIGATOR: Robert L. Gilbertson
PROJECT TITLE: Lettuce Mosaic Virus (LMV) Studies - Characterization of a Resistance Breaking Isolate of LMV
PRINCIPAL INVESTIGATOR: Robert L. Gilbertson
PROJECT TITLE: The Etiology, Epidemiology, and Management of a New Soil-Borne Virus Disease of Lettuce in California
PRINCIPAL INVESTIGATOR: Gail C. Wisler
PROJECT TITLE: Biology and Epidemiology of Verticillium Wilt of Lettuce
PRINCIPAL INVESTIGATOR: Krishna V. Subbarao
PROJECT TITLE: Epidemiology and Control of Lettuce Drop Caused by Sclerotina Species
PRINCIPAL INVESTIGATOR: Krishna V. Subbarao
PROJECT TITLE: Fungicide Insensitivity in Lettuce Downy Mildew
PRINCIPAL INVESTIGATORS: Richard Michelmore, Oswaldo Ochoa, & Steven T. Koike
PROJECT TITLE Investigation of Bacterial Leaf Spot of Lettuce
PRINCIPAL INVESTIGATORS: Steven T. Koike, Bob Gilbertson, & Jeri Barak
PROJECT TITLE: Developing an Integrated Disease Management Program for Lettuce Anthracnose
PRINCIPAL INVESTIGATORS: Steven T. Koike & Krishna Subbarao
PROJECT TITLE: Comparison of Fungicide Efficacy Against Powdery Mildew of Lettuce
PRINCIPLE INVESTIGATOR: Thomas Turini
PROJECT TITLE: Crop Tolerance Trials for Actigard
PRINCIPAL INVESTIGATORS: P. Reising, M. Wigglesworth, Jim Dana, & Richard Smith
PROJECT TITLE: Integrated Pest Management of Aphid, Lepidopteran and Whitefly Pests of lettuce
PROJECT LEADER: Nick C. Toscano
PROJECT TITLE: Insect Management for Central Coast Lettuce
PRINCIPLE INVESTIGATOR: William E. Chaney
PROJECT TITLE: Weed Management Systems for Lettuce
PRINCIPAL INVESTIGATORS: Steven A. Fennimore Richard F. Smith
PROJECT TITLE: Efficient N use in Lettuce Production
PRINCIPAL INVESTIGATOR: Tim Hartz
CALIFORNIA LETTUCE RESEARCH BOARD
for the period (April 1. 1999-March 31. 2000)
PROJECT TITLE: Lettuce Breeding, USDA-ARS
PRINCIPAL INVESTIGATORS: E. J. Ryder, R. C. Grube, J. D. McCreight
SUMMARY :
Two cultivars and four PI lines were confirmed as moderately resistant to big vein. In field tests, several cultivars, PI lines and breeding lines showed good field resistance. Numerous selections with quantitative downy mildew resistance, alone or in combination with resistance to corky root or tipburn, were made. Lines with resistance to sclerotinia fwere backcrossed to iceberg cultivars to improve head type. New sources of resistance are being crossed and backcrossed to good heading types. Screening for additional materials resistant to verticillium, as well as screening and selection in segregating generations of crosses to susceptible iceberg types, is continuing.
Cultivars with moderate resistance to pea leaf miner have been crossed with commercial cultivars. Screening for lettuce aphid resistance has begun, as well as crossing with known resistant cultivars. Seven accessions with powdery mildew resistance have been identified. Selection in materials with various multiple resistances continues. Five romaine type PI accessions with resistance to lettuce dieback were identified. Selection for improved green color in green leaf lettuce continues. Crosses to transfer various resistances to mixed lettuce types have been made. Selection for improved iceberg type lettuces for the desert continues. Genetic studies on resistance to lettuce mosaic, big vein, lettuce infectious yellows, downy mildew, and sclerotinia continue. Screening germplasm for resistances continues.
CALIFORNIA ICEBERG LETTUCE RESEARCH PROGRAM
April 1, 1999 to March 31, 2000
BREEDING CRISPHEAD LETTUCE
Richard W. Michelmore
Oswaldo E. Ochoa
Department of Vegetable Crops
University of California, Davis
rwmichelmore@ucdavis.edu
oeochoa@ucdavis.edu
SUMMARY:
The program emphasizes the identification and incorporation of genes for disease resistance, particularly to downy mildew, lettuce mosaic 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. However, it now appears that Dm18 and R32 have the same specificity and are rendered ineffective by the same isolates. Advanced lines with resistance to these diseases are trialed in commercial fields. We anticipate releasing another set of advanced breeding lines in the coming year.
CALIFORNIA LETTUCE RESEARCH PROGRAM
April 1, 1999 to March 31, 2000
LEAF LETTUCE BREEDING
Richard W. Michelmore
Sean Fort
Oswald E. Ochoa
Department of Vegetable Crops
University of California, Davis
rwmichelmore@ucdavis.edu
oeochoa@ucdavis.edu
SUMMARY:
Backcross programs have been initiated 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 twenty new sources into cultivated genotypes suitable for California and will ultimately be combined with resistance to LMV 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 all cultivars susceptible simultaneously. Screening of 64 commercial cultivars and 66 breeding lines for resistance to four isolates of downy mildew detected no cultivars and only seven breeding lines that were resistant to all four isolates. Three cultivars and 19 breeding lines were resistant to anthracnose.
CALIFORNIA LETTUCE RESEARCH PROGRAM
April 1, 1999, to March 31, 2000
GENETIC VARIATION IN LETTUCE
Richard W. Michelmore
Department of Vegetable Crops
University of California, Davis
numichelmore@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 biotechnological techniques. We have continued three 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. This year the third component received the greatest emphasis. The map-based cloning of Dm3 has been confirmed and we have initiated studies to clone functional homologs from other genotypes. We are currently analyzing the stability of expression of Dm3 as a transgene. A comprehensive map that integrates data from the major mapping projects completed to date is nearing completion. The map position of corky root resistance, cor has been refined and several linked markers identified that are informative in the breeding germplasm. We have been setting up a database for the Compositae that includes lettuce; this will be accessible on-line in the immediate future.
RESEARCH ABSTRACT TO THE CALIFORNIA LETTUCE RESEARCH BOARD'S RESEARCH PROGRAM
for the Period
April 1, 1999 - March 31, 2000
PROJECT TITLE: Basic Approaches to Lettuce Virus Disease Control
PRINCIPAL INVESTIGATOR: Bryce W. Falk
Department of Plant Pathology
University of California
Davis, CA 95616
SUMMARY:
Our efforts for this past year were concentrated on lettuce big-vein (LBV), caused by a suspected virus that is transmitted by the soilborne fungus, Olpidium brassicae. Efforts were primarily directed towards evaluating lettuce genotypes for LBV resistance/susceptibility, and to develop a consistent and efficient approach to screen lettuce cultivars for LBV. We used a hydroponic system developed previously and two representative 0. brassicae – LBVs (Santa Maria and Yuma). Results were obtained for eleven lettuce cultivars from five experiments and additional cultivars are presently being evaluated. Even though attempts were made to use standard environmental conditions, variation in reactions were observed and a number of factors were seen which affected the ability to reliably interpret results. However, by comparing the percentage of plant, which showed LBV symptoms at the end of the experiment, relative rankings were obtained. LBV is a complex disease and consistent, efficient strategies to control it are unlikely to be developed until a greater understanding of the etiological agent itself is obtained.
RESEARCH ABSTRACT TO THE
CALIFORNIA LETTUCE RESEARCH
BOARD'S RESEARCH PROGRAM
for the period
April 1, 1999 - March 31, 2000
PROJECT TITLE: Examination of the Current Monterey County Seed Testing
Protocol and Comparison of Various LMV Antisera and LMV Seed Testing Organizations for
Detecting LMV-infected Seed Lots
PRINCIPAL INVESTIGATOR: Robert L. Gilbertson
SUMMARY:
There is no single standardized ELISA procedure that has been developed for detecting LMV in lettuce seed. Thus, due to the variability in testing methods used, there is a possibility of different results from different tests/labs. In 1997, there were a number of documented discrepancies in tests performed by different labs, which lead to a concern about reliability of the test and questions regarding the need to standardize the LMV seed assay. We have proposed to better define the 'players in the game' and the methods that are used to detect LMV in lettuce seed. We are planning to carry out a series of experiments aimed at improving our understanding of LMV seed transmission in lettuce and determining the extent to which tests conducted by other major testing organizations give similar results. A long-term goal is to establish a standard testing procedure that could be followed by all organizations involved in testing lettuce seed for LMV.
RESEARCH ABSTRACT TO THE
CALIFORNIA LETTUCE RESEARCH
BOARD'S RESEARCH PROGRAM
for the period
April 1, 1999 - March 31, 2000
PROJECT TITLE: Lettuce Mosaic Virus (LMV) Studies - Characterization of a Resistance Breaking Isolate of LMV
PRINCIPAL INVESTIGATOR: Robert L. Gilbertson
SUMMARY:
Historically, lettuce mosaic virus (LMV) has been the most important and potentially damaging virus disease of Lettuce. Through a series of disease management strategies, most notably the mandatory LMV seed testing program, LMV has not been a problem in California. However, since 1986, LMV has been appearing with greater frequency in the Salinas Valley and other lettuce growing regions and there has been some concern that new strains of LMV have appeared. In work previously carried out by the lab on transgenic lettuce plants, based on the LMV coat protein gene, transgenic plants that showed evidence of resistance in early generations (R2) became susceptible in advanced generations (R3 and R4). In an attempt to determine the basis for the apparent loss of resistance in these transgenic Lines, detailed molecular characterizations were carried out: RNA extractions for Northern blot analyses (gene expression) showed varied RNA expression levels, ranging from low to high levels, and protein expression studies in the form of Western blot analyses illustrated that the CP gene was still being expressed, at least for R2 plants and for some R3 plants.
During the course of these experiments, a severe resistance-breaking LMV isolate was identified that presumably emerged by mutation of an existing strain. To determine if this was indeed the case, the susceptibility of ten different lettuce cultivars (varying in the complement of resistance genes) and the two susceptible host species (Chenopodium quinoa and Nicotiana benthamiana) were inoculated with the new virulent LMV isolate (LMV-R*), the stored isolates LMV-R951 and LMV-R952, and LMV-ER, another typical pathotype II LMV isolate provided by Ed Ryder. The coat protein gene from four different cultivars (LMV-R*, -R, -Rom and -ER) was sequenced and comparisons made. The mechanism of resistance in 'mo' and 'g' gene varieties was investigated by carrying out differential ELISAs. Resistant and susceptible plants were inoculated with LMV-ER or LMV-R*, leaves were harvested at 7, 14, 21 and 28 dpi, and ELISAs were carried out. LMV-R* replicated and moved as well in susceptible and resistant cultivars, whereas LMV-ER did not spread systemically in the Gallega and Salinas 88 cultivars.
Research Abstract
California Lettuce Research Board
April 1, 1999-March 31, 2000
Project Title: The Etiology, Epidemiology, and Management of a New Soil-Borne
Virus Disease of Lettuce in California
Principal investigator: Gail C. Wisler
USDA-ARS
Salinas, California
SUMMARY:
A necrosis-inducing, soil-borne disease of lettuce has caused significant losses in California and Arizona lettuce growing regions in the past several years. The disease has been called "lettuce dieback" and has been shown by research conducted in our laboratory to be caused by a new lettuce strain of Tomato bushy stunt virus (TBSV-L). Lettuce dieback may actually be the same disease that was responsible for an epidemic in the early 1900's throughout California that was then called "brown blight." At that time, the crisphead variety 'New York' was primarily planted in California and was uniformly susceptible to the disease. A selection ('Imperial') was made from 'New York' that was resistant to brown blight and the disease essentially disappeared. Heavy rains and flooded land in the past several years have caused the emergence of a similar disease of lettuce. However, due to the changes in varieties that are currently planted, this disease is has become a problem in romaine and leaf lettuce varieties. The similarity of dieback to brown blight is evidenced by the fact that in variety trials for the past two years, 'New York' has been uniformly susceptible and .Imperial' has been consistently resistant to this disease.
In the past research year, we have demonstrated that the new TBSV-L isolates are responsible for the soil-borne lettuce dieback disease. We have identified antisera that reacts to TBSV from lettuce and other TBSV isolates, and have applied both serological and molecular assays to develop diagnostic tests for TBSV directly from lettuce. However, these tests still need to be optimized for direct detection from lettuce due to the low titer of TBSV in infected plants. Diagnosis at this time still requires inoculation of lettuce tissues onto sensitive indicator plants, followed by specific diagnostic tests. We have employed biological and molecular assays to fully characterize these isolates from lettuce, and have found a new group of tombusviruses, which are associated with and responsible for this disease. We have conducted three variety trials, one being a replication of the previous year's trial in Chualar, and an expanded trial in Salinas with additional varieties tested. A third test was performed in collaboration with Dr. W. Waycott with Peto Seed in Santa Maria. In these expanded tests, five romaine accessions were identified with resistance to lettuce dieback. However, they are not ready for commercial release at this time. Fumigation trials on an infested field using methyl bromide and methyl bromide/chloropicrin showed no significant effect on disease incidence for lettuce dieback.
CALIFORNIA LETTUCE RESEARCH PROGRAM
April 1, 1999 - March 31,2000
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) host range determination of several isolates of Verticillium dahliae strains from lettuce and other hosts on all hosts; (2) determine the genetic relatedness of all these isolates using vegetative compatibility tests and DNA polymorphism; (3) continue the breeding program to identify and develop sources of resistance to Verticillium wilt in crisphead, leaf, and other lettuce types. The host range of four isolates each of V dahliae from lettuce and 13 other hosts were determined in all possible combinations. The lettuce isolates were highly pathogenic on artichokes, chili pepper, cotton, eggplant, potato, and watermelon, and pathogenic on strawberry and tomato. Isolates that were pathogenic on lettuce came from artichokes, chili pepper, cotton, potato, strawberry, tomato and watermelon. The lettuce strain, however, was not pathogenic on bell pepper and cauliflower. Alfalfa (V albo-atrum), chili pepper, cabbage, cauliflower, bell pepper, cotton and mint isolates were non-pathogenic on lettuce. Both the vegetative compatibility grouping tests and random amplified polymorphic DNA tests suggested that the lettuce strain was nearly identical to the artichoke and strawberry strains. Identification of sources of resistance and their utilization in breeding programs continued.
CALIFORNIA ICEBERG LETTUCE RESEARCH PROGRAM
April 1, 1999 - March 31, 2000
EPIDEMIOLOGY AND CONTROL OF LETTUCE DROP CAUSED BY SCLEROTINDI
SPECIES
Krishna V. Subbarao
Department of Plant Pathology
University of California, Davis
SUMMARY:
The research objectives for the current year included: (1) to determine the value of existing registered fungicides for lettuce drop control; (2) to continue the evaluation of the effects of soil moisture and temperature on the timing and production of apothecia, and types of germination of Sclerotinia sclerotiorum and S. minor sclerotia; (3) to determine other environmental factors that contribute to the geographical isolation of the two species; and (4) evaluate breeding lines for Sclerotinia minor resistance both in the field and in the greenhouse. We began a long-term study on the evaluation of the existing and potential fungicides for the control of lettuce drop this year. The fungicides included this year were botran, rovral, ronilan, and elevate. Since the experiment was begun in a field with no prior history of lettuce drop, the plots were artificially infested prior to planting lettuce in the summer.
The fungicide treatments were imposed immediately after thinning lettuce. None of the fungicide treatments reduced incidence of lettuce drop during this season. Germination of sclerotia of three isolates each of Sclerotinia minor and S. sclerofiorum was compared under various soil moisture and temperature combinations in two soil types from Huron (HUR), and Salinas (SAL), CA. Ten sclerotia from each isolate in two replications in soil disks equilibrated at 0, -0.03, -0.07, -0.1, -0.15, -0.3 MPa were transferred to petri plates. The plates were sealed, and incubated at 5, 10, 15, 20, 25, and 30"C. Soil type did not affect germination of sclerotia. Mycelial germination of S minor sclerotia occurred at -0.03 to -0.3 MPa and 5 - 25"C. No germination occurred at 30"C, or O MPa. The optimal moisture and temperature were -0.1 MPa and 15"C, respectively. Soil moisture and temperature affected the carpogenic germination of S sclerofiorum. The optimum conditions for carpogenic germination were 15"C and -0.03 or -0.07 MPa.
To determine the extent of carpogenic germination possible in S minor and S. sclerotiorum, sclerotia of three size classes were either placed in soil disks equilibrated at -0.03 MPa as described above or placed on the surface of saturated sail in a petri plate, and incubated at 15"C. Solitary S. minor sclerotia did not form apothecia, but aggregates of sclerotia did. The number of stipes produced by both S. minor and S. sclerofiorum was highly correlated with sclerotial size. These results suggest that there is a threshold sclerotial size below which apothecia are not produced, and explains in part, why production of apothecia in S. minor seldom occurs in nature. Amongst the environmental factors, air temperature and wind speed were significantly different during all seasons between the central and Salinas Valleys, relative humidity was also different in all seasons except winter, but solar radiation was only different during the winter and summer. Breeding efforts to develop lettuce drop resistance continued.
CALIFORNIA LETTUCE RESEARCH PROGRAM
April 1, 1999, to March 31, 2000
FUNGICIDE INSENSITIVITY 1N LETTUCE DOWNY MILDEW
Richard Michelmore, Oswaldo Ochoa, Sarah Brown
Department of Vegetable Crops
University of California, Davis
Steve Koike
University of California Cooperative Extension
Monterey County
1432 Abbot Street. Salinas, CA 93901
SUMMARY:
Over the past year a total of 85 isolates of Bremia lactucae have been characterized for insensitivity to Aliette and Maneb as well as for virulence phenotype and mating type. No differences were detected in sensitivity to Maneb. There are clear differences in sensitivity of isolates of downy mildew to Aliette in tests involving both seedlings and older plants. With heavy inoculum and under ideal conditions for disease development, some isolates caused significant disease, even on plants treated with field rates of Aliette. However, in screens utilizing 6 week-old plants rather than seedlings, disease was reduced compared to Aliette-untreated plants. Therefore, under heavy disease pressure, failures of control can be expected in the field. However, under low inoculum pressure Aliette would be expected to provide some protection. There was no correlation between virulence phenotype and Aliette insensitivity and therefore it is not possible to combine the use of resistance genes and Aliette to provide protection against all isolates, Aliette insensitive isolates were identified from all California regions sampled Pathotype V remained the most common pathotype Novel 18 was the next most common. Dml8 remains the most effective resistance gene. Ten isolates were tested for Ridomil sensitivity; all were insensitive. All 85 isolates were of the B2 mating type.
Research Abstract to the
California Lettuce Research Board's Research Program
April 1999 to March 2000
Project Title: Investigation of Bacterial Leaf Spot of Lettuce
Project Investigators:
Steven T. Koike
University of California
Cooperative Extension
Monterey County
Bob Gilbertson and Jeri Barak
Department of Plant Pathology
University of California
Davis
SUMMARY:
Bacterial leaf spot of lettuce now appears established throughout most of the lettuce growing areas in California's coastal and inland counties. While the pathogen, Xanthomonas campestris pv. vitians (Xcv), can clearly be carried on lettuce seed, our research indicated that commercial lettuce seed lots are rarely infested with this bacterium. Therefore, the main source of initial inoculum was unknown. This prompted our investigation into weed and soil residue sources of Xcv. Our multi-year field study indicated that if Xcv is introduced onto a lettuce crop, the pathogen has the ability to persist on crop residue in the field and infect subsequent lettuce crops.
Hence, Xcv sprayed onto the 1997 lettuce crop has persisted and established a population that has caused disease on three other plantings, the latest one being the fall 1998 crop. If residue in the soil was plentiful (during the one month fallow period between back-to-back lettuce crops), we could readily recover Xcv colonies at high levels. During the four month winter fallow periods, though, lettuce residues were difficult to recover and we found obvious Xcv colonies only during the first, and sometimes second, month into the winter. By the third and fourth months we could see only large numbers of apparently saprobic bacteria (non-pathogens). However, by using molecular methods we confirmed that this extensive bacterial growth did contain Xcv.
Therefore, it appears that very low populations of Xcv were present in soil on small lettuce fragments and that these low numbers are able to initiate disease on subsequent crops in the spring. Longer fallow periods (e.g., seven months or greater) may result in elimination of Xcv from soil, and should be used in fields having bacterial leafspot outbreaks. Eleven weed species, growing around commercial lettuce fields infected with Xcv, were found to be colonized with epiphytic populations of Xcv, indicating that Xcv can survive as an epiphyte on weed species found in lettuce fields. New Xcv primers were developed that are specific for Xcv and do not react with other Xanthomonad bacteria. These primers detected all Xcv strains tested. The primers should be useful detection and identification tools for assaying Xcv.
Research Abstract to the
California Lettuce Research Board’s Research Program
April 1999 to March 2000
Project Title: Developing an integrated disease management program for lettuce anthracnose
Project Investigators:
Steven T. Koike
University of California Cooperative Extension
Monterey County
Krishna Subbarao
Department of Plant Pathology
University of California at Davis
Oswaldo Ochoa and Richard Michelmore
Department of Vegetable Crops
University of California at Davis
SUMMARY:
Anthracnose disease (also known as ringspot and shothole) can be a serious, damaging disease of lettuce when spring weather is cool and rainy in California. As a result of field and greenhouse trials in 1998, a Section 18 registration was approved for Quadris on lettuce for the 1999 and 2000 seasons.
The goals of our continuing project were to further refine fungicide spray programs, develop detection methods for finding the Microdochium panattonianum pathogen in soils, obtain information on how the disease develops, and test cultivars for possible resistance. The compilation of all this information would help us assemble an integrated disease management program for lettuce anthracnose. Rainfall was limited in the spring of 1999, and anthracnose failed to develop in commercial fields and in our trials. Therefore, experiments will be implemented in the spring of year 2000.
RESEARCH ABSTRACT
TO THE CALIFORNIA LETTUCE ADVISORY
BOARD'S RESEARCH PROGRAM
for the period
April 1, 1999 - March 31, 2000
PROJECT TITLE: Comparison of Fungicide Efficacy Against Powdery Mildew of
Lettuce
PRINCIPLE INVESTIGATOR (S):
Thomas Turini
University of California Cooperative
Extension, Imperial County
Albert Paulus, Miguel Vilchez
University of California, Riverside,
Department of Plant Pathology
Powdery mildew of lettuce, caused by Erysiphe chiroracearum, commonly occurs in low desert production areas and there are currently very few materials registered for control of this disease on lettuce. A field experiment was conducted in Imperial County at the Desert Research and Extension Center, in which eight fungicides were applied to Green Towers romaine and Winterhaven iceberg lettuce varieties. The first applications were made before the appearance of the disease and applications were repeated al 7- or I0-day intervals. In the iceberg lettuce, powdery mildew appeared in late January. The disease was detected two weeks later on the romaine.
SUMMARY:
In both the head lettuce and the romaine, all fungicide treatments significantly reduced disease severity as compared to the non-treated control. Lettuce treated with Flint, quinoxyfen, Rally at 2 and 4 oz./acre with the spreader Latron CS7, DAS 500 at 12.3 and 15.4 oz/acre rates, and Quadris applied at 7- and l0-day intervals and Microthiol had the lowest disease severity in both lettuce types on both sides of the leaf. Lettuce treated with Quadris or Serenade in alternating applications only differed from the treatments with the lowest disease incidence on the upper surface of the iceberg lettuce. In general the disease incidence on lettuce treated with Trilogy applied at 7-day and Serenade at 2 and 4 lb/acre rates had slightly higher disease severity than lettuce treated with the other materials tested.
ABSTRACT
CALIFORNIA LETTUCE RESEARCH BOARD
for the period
(April 1, 1999 - March 31,2000)
ROJECT TITLE: Crop Tolerance Trials for Actigard
PRINCIPAL INVESTIGATORS: P. Reising and M. Wigglesworth - Novartis Crop Protection, Inc., Sanger, CA; J. Dana - Western Farm Service, Santa Maria, CA; and R. Smith University of California Cooperative Extension, Salinas, CA.
SUMMARY:
Crop Tolerance trials were conducted on iceberg and leaf lettuce in the coastal lettuce production regions of Salinas, and Santa Maria. Replicated experiments involving multiple applications of two rates of Actigard were conducted in two iceberg and two leaf lettuce fields in each production region. There were 8 iceberg and 8 leaf lettuce cultivars included in each experiment. Observations made on crop tolerance indicated no crop injury associated with the Actigard treatments on either the iceberg or leaf lettuce cultivars included in these trials
RESEARCH PROJECT REPORT TO THE CALIFORNIA
LETTUCE ADVISORY BOARD'S RESEARCH PROGRAM
April 1, 1999 - March 31, 2000
PROJECT TITLE: Integrated Pest Management of Aphid, Lepidopteran
and Whitefly pests of lettuce
PROJECT LEADER:
Nick C. Toscano, Department of Entomology,
University of California, Riverside, CA 92521
COOPERATING PERSONNEL:
Greg Ballmer, Nilima Prabhaker Castle, and
Jian Bi, Department of Entomology,
University of California, Riverside, CA 92521
SUMMARY:
Our on going research is focused on the development of an integrated insect pest management program on lettuce. The main objectives of current studies are: 1) to determine the efficacy of beet armyworm (BAW), cabbage looper (CL), an Tobacco Budworm (TB) to insecticides available to growers and new products for registration. 2) to determine the field efficacy of whitefly insecticides available to growers and new products for registration, 3) to determine the efficacy of new and available insecticides against leaf lettuce insect pests in Coachella Valley 4) to develop an aphid management program for this pest on lettuce in southern California. This includes efficacy trails and species determination. Synthetic insecticides generally reduced aphid and lepidopterous larval populations more effectively than did natural products. No consistent improvement in aphid control was apparent with release of Chrysoperla. The insecticide growth regulators Applaud and Knack prove to be excellent whitefly insecticides.
Insect Management for Central Coast Lettuce
Research Abstract to the California Lettuce
Research Board
for the period
April 1, 1999 to March 31, 2000
PRINCIPLEINVESTIGATOR:
William E. Chaney
Farm Advisor - Entomology
U.C. Cooperative Extension - Monterey County
1432 Abbott Street
Salinas. CA 93901
SUMMARY:
The pea leafminer problem seems to have become less important in recent years, both due to a reduction in pest pressure and because of the new lettuce aphid problem. Growers continue to seek new methods for dealing with this pest. Although the research program for this period dealt largely with the lettuce aphid, work did continue on pea leafminer management. In the pea leafminer trials the data showed that the three registered larvacides, Agrimek, Neemix and Trigard are all still effective although the residual period of control seems to be lessening. The effect of temperature on the growth rate of the lettuce aphid demonstrated limits to the temperature range the lettuce aphid could tolerate. It was also shown that the lettuce aphid population can have explosive growth under ideal conditions. At a temperature of 68 to 72 degrees Fahrenheit, one newly deposited live lettuce aphid nymph can produce 125 aphids in just three weeks.
Control of the lettuce aphid using chemical insecticides was studied extensively in both field trials and in laboratory bioassays. The results are consistent with many PCA observations; most aphicides will kill lettuce aphid if the aphids can be contacted. In field conditions however, systemic materials such as MSR, Provado, or Aphistar may be necessary for good control. Aphistar is not currently registered in California for use on lettuce. The effectiveness of Admire under field conditions was studied in conjunction with the Central Coast Vegetable IPM (CCVIPM) Program in field-scale plots and showed varying levels of success in meeting PCA and grower expectations. Work on reflective mulches for lettuce aphid management showed them ineffective in field tests. Laboratory colonies of lettuce aphid allowed for quick and accurate tests of lines of lettuce for lettuce aphid resistance. Some varieties showed complete resistance to lettuce aphid. Seed of these varieties came from Europe and was primarily non-heading types. Work to transfer this resistance to head varieties is underway.
CALIFORNIA LETTUCE RESEARCH BOARD
April 1, 1999 - March 31, 2000
WEED MANAGEMENT SYSTEMS FOR LETTUCE
Steven A. Fennimore
Department of Vegetable Crops
University of California, Davis
Richard F. Smith
U. C. Cooperative Extension
Salinas, CA
SUMMARY:
Investigations into several aspects of weed management in lettuce were conducted in 1999. Specific objectives were: (I) to evaluate new potential herbicides for lettuce; (2) to evaluate the herbicide Affinity for weed control in lettuce; (3) to evaluate the tolerance of major lettuce varieties to Affinity; (4) to evaluate weed control options in 80-inch bed production systems; and (5) to compare purslane control using 5-inch bands and 22-inch bed-top treatments. Nine herbicides were evaluated in lettuce for preemergence selectivity and nine were evaluated for postemergence selectivity. Raptor was identified as a potential postemergence lettuce herbicide. A follow up evaluation confirmed lettuce tolerance to Raptor at 0.008 lb ai/A. In 1998 Affinity was identified as a potential preemergence lettuce herbicide. To further characterize the tolerance of lettuce to Affinity, six studies were conducted in the Salinas Valley and two in Santa Maria, CA. Additionally, a study was conducted to evaluate the tolerance of 10 lettuce varieties to Affinity. The results of these evaluations suggest that the selectivity of Affinity in lettuce is marginal.
Therefore, no further evaluation of Affinity in lettuce is recommended. Most lettuce produced on 80-inch beds either receives a bed-top herbicide application across the 60-inch bed-top, or receives a narrow herbicide band directly over each seed line. Herbicide costs are cheaper with the narrow bands, but labor costs associated with thinning and hand weeding the rows in the bed center may be higher where narrow bands are used. A combination approach was utilized where a wide herbicide band was applied in the bed center and narrow bands were applied to the outside rows. This combination sprayer conformation was compared to narrow band and bed-top sprayer conformations. In one site at Salinas, no differences in thinning or hand weeding times were found between the three sprayer conformations. In a second study near King City, we found that the combination sprayer conformation reduced weed control costs $33 to $100 per acre. Purslane is a difficult weed to kill by uprooting since it is very tolerant to desiccation. The use of narrow herbicide bands was compared to a bed-top application, for efficiency in reducing purslane emergence. Bed-top herbicide treatments were effective at reducing both purslane emergence and labor inputs required for thinning and hand weeding.
Research Project Report
California Lettuce Research Board
April 1, 1999 to March 31, 2000
Project title: Efficient N use in lettuce production
Project leader: Tim Hartz
Extension Specialist
Department of Vegetable Crops
University of California – Davis
Objective: Demonstrate the utility of field-specific N management in improving Fertilizer use efficiency
SUMMARY:
A series of 11 replicated trials in commercial lettuce fields conducted in 1996-97 showed that side dressing could be delayed as long as residual soil NO3-N in the top foot of soil exceeded 20 PPM. Four subsequent trials in 1998 showed that maximum yields could be achieved in fields with lower soil NO3-N levels by side dressing only enough to raise soil NO3-N concentration to 20 PPM. Collectively, these trials demonstrated an average seasonal reduction in N application of approximately 70 lb N/acre compared to the cooperating growers' N regime, with no loss of crop productivity or quality. Eleven additional field demonstrations were conducted in 1999 on commercial farms in the Salinas Valley to demonstrate the reliability of the PSNT approach in determining side dress N requirements of lettuce on a field-specific basis
Ten of the field demonstrations were conducted with iceberg lettuce, and one with romaine. The majority of each field received the growers' standard N management program . A 36 row-wide plot the full length of the field was established at each site, in which side dress N was applied based on residual nitrate-nitrogen (NO,-N) in the top foot of soil prior to each side dress application the grower made. In these PSNT plots no side dress N was applied as long as soil NO3-N was >20 PPM; whenever soil NO3-N was < 20 PPM the N application rate at that side dressing was calibrated to raise soil NO3-N up to the 20 PPM threshold. Both the PSNT plots, and adjacent portions of the field receiving the grower standard N treatment, were harvested by commercial crews.
The cooperating growers applied an average of 247 lb N/acre, 189 lb/acre of which was applied as side dress or water-run. Following the PSNT approach reduced seasonal N application by 45%, to an average of 135 lb/acre; side dress N application in PSNT plots averaged only 77 lb/acre. Evaluations made after 10-14 days of cold storage showed that N treatment had no effect on postharvest quality. Plant N monitoring showed that all plots remained above established tissue critical levels throughout the season. Less than 10% of the N applied by the growers above that applied in the PSNT plots was even taken up by the crop; soil sampling showed that the majority of this extra fertilizer N remained, in NO3-N form, in the soil profile after harvest.