Several new insecticide was compared to Admire and Provado combinations for management of aphids in head lettuce in Yuma in two trials conducted in 1998. Foliar applications of Provado, Fulllfill, Aphistar and Acetamiprid appear to provide an alternative method of controlling aphids on lettuce comparable to prophylactic applications of Admire. In addition, at planting and side dress soil applications of thimethoxam provided aphid control comparable to Admire. The prevention of aphid colonization in lettuce heads with the foliar alternatives may depend greatly on the timing and frequency of applications before harvest occurs. Residual activity of the new foliar alternatives ranged from at least 7-14 days. These studies suggest that more than one application of the foliar products will be necessary to adequately suppress aphid contamination in heads. Evaluations of thiamethoxam suggest that it is more mobile in the soil than Admire and may be a candidate for side dress applications for aphid management.

For the second year, a large block experiment was conducted at the Yuma Ag Center to compare the field performance of three lettuce management programs for control of lepidopterous larvae. Conventional, experimental and biorational insecticides were sprayed to control beet armyworm, cabbage looper and Heliothis species throughout the growing season. Differences in populations of total larvae among the four treatments, relative to insecticide treatments and timing of application were observed throughout the season. In general, the standard and experimental treatments provided the most consistent control of lepidopterous larvae following each application. Harvest data showed that the spray regimes had a significant influence of head lettuce yield or quality. Maturity and quality were significantly reduced in the untreated control. An economic analysis shows that net returns varied widely among the management programs at different market prices. In conclusion, this study provides preliminary data to support the need for more development of experimental and biorational insecticide products as alternatives to conventional management programs in desert lettuce production.

Bremia lactucae and Erysiphe cichoracearum, respectively, cause downy and powdery mildew of lettuce. Cool moist environmental conditions favor the development of downy mildew, whereas warm and dry weather is conducive for powdery mildew. Several potential new fungicides were evaluated for control of these diseases of lettuce in 1998. The final severity of downy mildew in this trial was low. In addition to the standard compounds maneb, Aliette and Trilogy, several fungicides currently in development significantly reduced the severity of downy mildew compared to nontreated plants. These chemistries included Acrobat, RH -7281, an Unknown, Actigard, EF1295, Curzate, Quadris, BAS 500, QST 153, BAS 505 and BAS 490. Untreated lettuce plants were heavily infected with powdery mildew. In addition to the standard materials Microthiol Special and Trilogy, powdery mildew was significantly reduced on plants treated with BAS 490, BAS 505, EF1295, BAS 500 and Quadris. The possible availability of one or more of these chemistries under development for lettuce could help in efforts to develop and maintain a fungicide resistance management program for plant medicines of importance for this crop.

Sclerotinia leaf drop of lettuce is caused by two different species of this fungal pathogen, Sclerotinia minor and S. sclerotiorum. Cool and moist environmental conditions favor this disease. Some new fungicides in development were evaluated for control of leaf drop on lettuce during the winter vegetable growing seasons of 1996-97 and 1997-98. Sclerotia of each pathogen were applied to plots after thinning and just before the first of two applications of test compounds. The final severity of leaf drop in these trials was high. Significant reduction in disease or increase in marketable heads compared to nontreated plants was usually achieved by application of the standard compounds Ronilan and Rovral as well as the new fungicides BAS 500 and an "unidentified" material. The future registration and subsequent availability of one or both of these new chemistries for lettuce could provide equivalent disease control to that of the current standard materials with 0.2 to 0.25 lb active ingredient (a.i.) per acre instead of the current 1.0 lb a.i. per acre required with the standard compounds.

Mustang 1.5EW, Ammo 2.5EC, Pounce 3,2EC, Scout X-TRA, and three formulations of Karate were compared for efficacy to cabbage loopers infesting head lettuce in Yuma, AZ Karate and Pounce provided the most consistent cabbage looper control followed by Mustang and Scout X-TRA. Ammo appeared slightly inferior to the other pyrethroids tested. There did not appear to be any obvious differences in the efficacy of the three Karate formulations.

Confirm, Success and Proclaim were evaluated for lepidopterous insect control in lettuce with and without the addition of Mustang 1.5EW. Success and Proclaim used alone were highly efficacious toward cabbage looper and Heliothinae and did not appear to benefit greatly from the addition of Mustang. However, Confirm's activity towards Heliothinae was significantly improved by the addition of Mustang. Additionally, on large framed plants where coverage is difficult, Confirm benefitted from the addition of a pyrethroid for control of loopers.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

Lettuce plants (Lactuca sativa L. var. Ithaca) were transplanted on different beige and black paper mulches and on a coextruded white/black polyethylene mulch in organic soil in 1997 and 1998. Non-weeded and weeded control plots were also used. Plant mortality in 1997 for plants grown on bare soil was 10 to 15% greater than that of mulched plants. Head weight was found to be 3.6 times (1997) and 12 times (1998) greater for lettuce grown on mulch compared with a weeded control. The transmission, reflection and absorption of light of the white/black polyethylene mulch and black paper mulch remained stable over the course of the experiment while those of the other papers changed over time. Paper mulch decomposition occurred during the experiment. Although, black paper mulch was the only mulch that gave complete control of weed growth, weed populations present under the beige papers were too small in terms of the size and number of weeds to cause lettuce yield reduction.

Lettuce mosaic virus (LMV) is an economically important pathogen with worldwide distribution. LMV infection in L. sativa can cause significant yield losses. Resistance to LMV in L. sativa is conferred by the recessive gene mo. We attempted to position the mo gene on the L. sativa map. The ultimate goal is a better understanding of plant-virus interactions. To do so, Random Amplified Polymorphic DNA (RAPD) markers were screened in the near isogenic lines (NILs) Vanguard and Vanguard 75. These NILs differ in the presence of the mo gene in Vanguard 75. Polymorphic markers were screened for linkage to mo in two F$ sb2$ populations segregating for resistance to LMV. The F$ sb2$ populations used were derived from 2 crosses, the first one between the L. sativa cultivars Dwarf 2 (resistant to LMV via the presence of mo) and Saffier and the second one between two breeding lines 87-25M-1 (momo) and 87-1090M-1 (MoMo). In order to develop a highly stringent antibody detection system to phenotype plants infected with LMV, a plasmid construct was developed which overproduces LMV coat protein. This construct will be used in the future to produce enough recombinant LMV coat protein for antibody production. To further characterize mo, a selection of cultivars resistant and susceptible to LMV according to the literature were subjected to various temperature changes to determine the environmental influences on virus movement.

This study was conducted in the experimental unit of the Benson Agriculture and Food Institute, which is located in the Letanias community of the Ingavi province in the department of La Paz. Our objective was to compare the agronomic performance of two baby lettuce varieties (Lactuca sativa L.) at three planting densities in panqar huyus. In order to provide the rural farmer communities of Contorno Letanias and Contorno Medio a possible cost-effective alternative and to employ the use of moderate environments called panqar huyus, we introduced two varieties of baby lettuce: 1) Little Gem in seed form and 2) Tom Thumb already sprouted. These two were planted at densities of 250,000, 333,333, and 500,000 plants/hectare. Statistical analyses performed using the F-test and Duncan’s Multiple Range test found statistical differences between the varieties of baby lettuce and/or planting densities in the following response variables: plant height, number of leaves, root length, total foliage area, green foliage yield, and individual weight of green foliage. The values we obtained for green foliage yield were below those published by the European Union (2004). This was mainly due to the climate of the interior of the panqar huyus. The highest average yield achieved by the baby lettuce varieties was reached by Little gem in seed form with a value of 1.66 kg/m2. As for the planting densities, the highest yield was obtained with the 500,000 plants/hectare density, which had a value of 2.18 kg/m2. As for the quality of the harvested product, the values closest to the parameters established by the European Nations (2004) and the MAG/IICA (2004) were obtained in treatments 5 and 6. Some of these parameters were head diameter, plant height, number of leaves, total foliage area, and individual weight of green foliage. Furthermore, the economic analysis done via the partial budget estimate proposed by CIMMYT (1983) determined that treatment 5 (Little gem in seed form planted at a planting density of 500,000 plants/hectare) is the most profitable when compared to the other treatments in the area of domain.