Thesis (M.Sc.(Agric.))(Horticulture)--University of Pretoria, 2005. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

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In response to the request for alternative crop production information, 92 varieties of long-day onions were planted on the Safford Agricultural Center. Many varieties performed well, with the top variety yielding almost 480 cwt per acre. It appears that onions can be a viable alternative crop for some farmers in the upper Gila valley.

Twenty onion varieties were planted on two different dates in March at the Safford Agricultural Center. Yields up to 780 50-pound sacks per acre were harvested, with the early planting generally yielding slightly more than the later planting. The earlier planting generally had more jumbo and large onions and fewer medium and small onions than the later planting. The highest yielding onions were yellow varieties compared to the two white and one red varieties, but premiums for the non-yellow onions at harvest compensated for the lower yields. Three intermediate-day onions were included in the test; they were out-yielded by many of the long-day varieties at both planting dates. Spring - planted, long-day onions can be successfully grown in the Safford valley with yields that are economically feasible.

Successful seed production of open pollinated onion (Allium cepa L.) is difficult in Arizona. Providing adequate pollen transfer by honey bees (Apis mellifera) to ensure adequate seed set is a problem often encountered. Honey bees discriminate between onion cultivars. Onion flowers appear to be less attractive to honey bees than flowers of most competing plants. Bees may neglect the crop, particularly if another highly attractive plant species is in bloom. This honey bee discrimination has led to poor onion seed yields. This report compares seed production among five onion cultivars in Tucson, Arizona.

As a followup to the previous years onion variety trial (1), 23 of the more promising long-day varieties were retested along with 5 new intermediate-day varieties. The soluble salts and exchangeable sodium percentage were high (4340 and 28.1%, respectively) in the field where the onions were grown. This suppressed the yields significantly from the previous year. The top yielder produced 386 sacks (50 lbs) compared with 956 sacks in 1985. The top yielders from 1985, Durango and Inca, performed well again this year. The new intermediate-day varieties produced well also and seem quite promising.

Forty-five different dry bulb onion varieties were grown and evaluated to provide a comparison of varietal characteristics including firmness, size, shape, and maturity.

DCPA (Dacthal®) herbicide was applied preemergence (PE) to the soil surface after onion planting and no crop injury was observed for rates of 5.3, 7.5, and 10.5 lb. a.i. /A at one of two locations. Dacthal® gave good control of London rocket and cheeseweed (90 -94 %) at one location and marginal control at the second location (79 -85 %). Dacthal® did not exhibit a rate response to control the two weeds common to both locations. The lower rate of Dacthal® did not differ in efficacy compared to higher rates to completely control lambsquarters and nettleleaf goosefoot. All rates of Dacthal® marginally controlled yellow sweetclover and other mustard weeds present. Dacthal® provided adequate weed control to allow onion stand establishment.

Oxyfluorfen (Goal®) herbicide at 0.125 to 0.25 lb. a.i./A applied postemergence (POST) to onions at the 3-leaf stage of growth effectively controlled London rocket, yellow sweetclover, and prostrate pigweed with marginal injury to onions. Earlier POST applications on 1- and 2-leaf onions caused injury and some stand reduction. Bromoxynil (Buctril®) herbicide at 0.25 lb. a.i./A applied early POST gave generally good weed control but did not adequately control sweetclover. Buctril® applied in clear weather did not injure 1-leaf onions but caused severe injury on 2- and 3-leaf onions when applied during cloudy weather conditions. Buctril® plus pendimethalin (Prowl®) tank-mix combination applied POST provided good control of London rocket, sweetclover, and prostrate pigweed; however, onion injury was severe due to applying Buctril® in cloudy weather. Buctril® and Goal® effectively controlled weeds present in the onions but timing of POST applications was critical with respect to onion size and weather conditions to minimize injury.