Browsing Vegetable Report 2005 by Title
Now showing items 11-14 of 14
Management of Downy Mildew of Broccoli in 2005Downy mildew of broccoli, cauliflower and cabbage is caused by the oomycete pathogen Peronospora parasitica. Cool moist environmental conditions favor the development of downy mildew on these crops. Several fungicides were evaluated individually or combined with another material (applied as a mixture or in a rotational program) for control of this disease on broccoli in the 2004- 05 growing season. Several treatments provided the most efficacious degree of disease control, including Maneb, Reason+Bond alternated with Aliette, Ranman+Maneb+Silwet L-77, Ranman+Silwet L-77, Forum+Maneb, Forum+Penetrator Plus, Reason+Bond alternated with Maneb, PREV-AM +Formula 1, Ranman+Aliette+Silwet L-77, Acrobat+Maneb, Aliette and Phostrol.
Microbial Quality of Iceberg Lettuce is Affected by Moisture at Harvest - 2nd Year EvaluationIn a continuing work, the effect of moisture conditions on yield and microbial quality of Iceberg lettuce was investigated. Iceberg lettuce cv. Sahara grown at the University of Arizona Yuma Agricultural Center was evaluated for yield, microbial population and postharvest quality either following different irrigation termination schedules or before/after a rainfall event. We report here microbial population data with treatments including early (16 days before harvest), middle (8 days before harvest) and late (4 days before harvest) irrigation termination. Lettuce receiving the last irrigation 4 days before harvest showed increased weight but had higher microbial population than other treatments. The effect of moisture prior to harvest on quality was further evaluated with lettuce harvested before and after a rainfall event. Increased aerobic bacteria population of over 1 log CFU/g for outer leaves and over 2 log CFU/g for head leaves was observed after rain. The results from this study suggest that managing moisture conditions at harvest is important to enhance quality of lettuce.
New Challenges to Management of Whitefly Resistance to Insecticides in ArizonaWe report on susceptibility to insecticides of whiteflies (Bemisia tabaci) collected from cotton, melons and ornamental plants during the 2004 season. No major problems with field performance of insecticides against whiteflies were observed or reported in 2004 in Arizona cotton, vegetables, or melons. However, monitoring revealed further statewide reduction in susceptibility to pyriproxyfen (Knack®) and showed that whiteflies possessing pyriproxyfen resistance could be detected in all low desert areas of the state. Susceptibility to buprofezin (Applaud®/Courier®) has not changed significantly since 1997. Mean susceptibility to synergized pyrethroids (e.g., Danitol® + Orthene®) has increased strikingly on a statewide basis since 1995 though highly resistant whiteflies were detected in some collections from cotton, melons and ornamentals. Whiteflies from throughout Arizona continued to be highly susceptible to imidacloprid (Admire®/Provado®). However, susceptibility to the related neonicotinoid insecticide, acetamiprid (Intruder®) varied widely and was lowest in collections from melons and greenhouse plants. Whiteflies from cotton that were least susceptibile to acetamiprid were significantly less susceptible to a second neonicotinoid, thiamethoxam (Actara®/Centric®/Platinum®). The most worrisome findings of our 2004 studies stemmed from detection of a strain of B. tabaci, at a retail nursery, that was essentially unaffected by pyriproxyfen in egg bioassays. It also possessed strikingly reduced susceptibility to acetamiprid, buprofezin, mixtures of fenpropathrin and acephate, imidacloprid, and thiamethoxam. This strain was found to be a biotype of B. tabaci previously undescribed in the US, the Q biotype. We cannot predict with accuracy the timecourse of future resistance problems or the spread and impact of this new whitefly biotype. However, our findings point to the need to formulate contingency plans for management of resistance, in order to insure that Arizona agriculture does not revisit the severe whitefly control problems experienced in the past.
Yield and Postharvest Quality of Cantaloupe Melons as Affected by Calcium Foliar ApplicationsThe effect of pre-harvest foliar application of calcium on yield and postharvest quality of whole and fresh-cut cantaloupe melons was investigated. The calcium product (Nutrical®) was applied five times before harvest to a melon field at 2 quarts/acre with a volume of 50 gallons/acre. The supplemented calcium increased by over 10% the weight of melons and increased external firmness at harvest but soluble solids was lower in treated melons than in the control. After 21 days of storage at 40 - 45 °F however, there was not difference in quality factors. Melons were processed in cubes and packaged in plastic lidded containers. The overall quality of calcium treated cubes was better after 5 and 10 days of storage. Juice leakage was also higher in the control than in the treated fruits after 5 days. After 10 days the L* values were lower in the control than in the treated fruits indicating that the tissue was darker in the control, which was an indicative of more water soaked tissue. In further trials conducted the following Spring the results obtained at harvest showed differences only in weight of melons that underwent water stress. The overall results in different experiments in the Yuma area indicate that application of foliar calcium can increase yield of melon crops, notably, when the plants undergo environmental stress.