Thesis (Ph.D.) -- University of Rhode Island, 2009. / Typescript. Includes bibliographical references (leaves 178-205).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S. in soil science)--Washington State University, May 2010. / Title from PDF title page (viewed on July 7, 2010). "Department of Crop and Soil Sciences." Includes bibliographical references.

Economic analyses, which indicated a need for reducing lettuce production costs, were the basis for feasibility studies of mechanizing some production processes. These processes are the thinning and weeding operations. Thinning can be eliminated by precision seeding while weeding can be reduced or eliminated by using a suitable mulch layer. Mechanization of these processes requires development of a mulch layer applying machine and a precision seeder capable of seeding through the mulch. A model of the precision seeder was designed, fabricated and tested. Test results were below the minimum acceptable performance level of the machine. Weaknesses in the model were obvious and modifications are recommended. These modifications should bring the model to an acceptable performance level. A model of the mulch layer applier was also designed and fabricated. Field testing was not completed, however, expected problems are discussed and alternatives are recommended. The practical feasibility of both these machines cannot be completely evaluated until the models have been thoroughly field tested. / Land and Food Systems, Faculty of / Graduate

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The use of stylet oil to slow the spread of the whitefly- transmitted vines, lettuce infectious yellows, shows sufficient promise to plan for expanded research efforts. The main positive results were a slower buildup of virus infection and a larger number of marketable heads in the block of lettuce sprayed with oil. Weight (in grams) of individual heads could be correlated with time of infection in that the lowest weights and marketability ratings occurred in plants infected earliest in the season. Whether they were front treated or untreated plots, marketable heads weighed an average of 784 grams; unmarketable heads weighed 491 grams. The key difference is that, on the average, five marketable heads of lettuce were in the oil- treated plots for every three in the untreated plots. A follow-up experiment will be conducted in 1989 to determine if these preliminary positive results indicate that stylet oil treatment may be a practical control method for slowing the spread of L1YV.

Leaf drop of lettuce, caused by Sclerotinia sclerotiorum, is a sporadic, but destructive, disease in Arizona. Field trials were established during 1987 and 1988 to evaluate potential new fungicides for disease control. Ronilan and Rovral, the two materials currently registered for use on lettuce for Sclerotinia leaf drop, were consistently among the most effective fungicides for disease control. Levels of disease control equivalent to that provided by Rovral and Ronilan were observed with CGA-449, SC-0854 SDS-65311, Bay HWG 1608, and Spotless. These field tests have identified several potential new fungicides for control of leaf drop of lettuce caused by S. sclerotionan.