Nitrogen (N) status of vegetable crops is often monitored by analysis of dried plant tissues. However, dry tissue analysis often causes a significant delay between sampling and analysis. This study was conducted to examine the accuracy of a portable nitrate meter for determining petiole sap nitrate (NO₃) concentrations in broccoli (Brassica oleracea L. Italica group cv. Claudia) and cauliflower ( Brassica oleracea L. Botrytis group, cv. 'Candid Charm'). The relationship between NO₃-N concentration in fresh petiole sap and in dried petiole tissue was Studied for these crops in southern Arizona during the 1993-94 and 1994-95 winter growing seasons. Experiments were factorial combinations of 3 irrigation rates and 4 N rates, both ranging from deficient to excessive. Petioles were sampled throughout each season, and were split for sap and dry tissue analysis. A linear correlation was obtained between the two measurements in both seasons, with no consistent effect due to irrigation treatment or crop maturity. The regression coefficients did not differ among seasons. Regression equations were derived to convert petiole sap nitrate concentrations to dry tissue nitrate concentrations. These equations can be used to relate sap test measurements to existing guidelines for NO₃-N concentrations in broccoli and caulker petioles. These results suggest that the quick sap test, using the portable nitrate ion meter, is a valuable technique for monitoring N status of broccoli and cauliflower.

Field experiments were conducted during the 1995-96 winter growing season at The University of Arizona's Maricopa Agricultural Center to determine the response of broccoli and cauliflower to a factorial arrangement of water rates and nitrogen (N) fertilizer rates. Both the broccoli and cauliflower experiments were randomized complete block factorial designs with three water levels (deficient, optimum, and excessive), four N fertilizer levels (deficient, suboptimal, supra optimal, excessive), and four replications. Drip tubing was buried at a depth of eight inches along the midline of each planting bed. Irrigation was applied daily as needed to maintain the predetermined target soil water tension levels and N fertilizer (urea ammonium nitrate solution) was applied in 4 or 5 split applications. Broccoli spears and cauliflower curds were harvested weighed and graded according to prevailing commercial practices. The optimum marketable yield of broccoli of 4.6 tons/acre was achieved with a total application of 18.9 inches of water and 267 lbs. N/acre. The optimum marketable yield of cauliflower of 9.5 tons /acre was achieved with a total application of 18.5 inches of water and 178 lbs. N/acre. For both crops a nitrogen deficiency had a greater negative impact on marketable yield than either deficient or excessive water application. Optimum marketable yields, earliness and head quality for both crops were achieved when the average soil water tension level for the entire season was maintained at about 10 cbars (or 13 cbars uncorrected gauge reading).

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Pyrethroid and endosulfan mixtures applied at full and reduced rates with three application methods (air-assisted electrostatic, air-assisted hydraulic, and standard hydraulic sprayers) were evaluated in field studies in 1992 and 1993 for control of sweetpotato whitefly, Bemisia tabaci-strain B (Genn.), also known as silverleaf whitefly, Bemisia argentifolii Bellows and Perring, and spray deposition on caulker, Brassica oleracea L. Based on adult suppression, improved control of whiteflies was achieved with full and reduced rates of the air-assisted electrostatic sprayer following two applications in 1992, but percent reduction of adults did not differ significantly among the application methods when full rates of insecticide were applied in 1993. Control based on immature colonization indicated that the air-assisted electrostatic sprayer was the only spray method to significantly reduce nymph densities when compared with the control in 1992, but differences in numbers of eggs, nymphs and eclosed pupal cases varied among application methods and rates of active ingredient in 1993. Comparisons of cauliflower harvest dates indicated that the air -assisted electrostatic sprayer did not provide significantly better control than the other application methods when used at similar rates. Spray deposition with the air-assisted electrostatic application technique was variable throughout these studies with no clear trends being observed. Our results suggest the air-assisted electrostatic sprayer may offer a means to control sweetpotato whitefly with a 50% reduction in insecticide usage.

Downy mildew of broccoli, cabbage, and cauliflower is caused by the plant pathogenic fungus Peronospora parasitica. Cool damp weather with high humidity is highly favorable for sporulation, dissemination of spores, and infection by this pathogen. The severity of disease is affected by the duration of these weather conditions favorable for disease development. Potential new fungicides were evaluated for disease control in a field trial conducted in the winter of 1992-93. For broccoli, no significant differences in disease severity were detected among treatments. On the other hand, Microthiol and Microthiol + Maneb significantly reduced the number of downy mildew lesions on cabbage and cauliflower compared to nontreated plants. Maneb alone provided significant disease control on cabbage, but not on cauliflower.