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Downy mildew of broccoli, caused by the fungus peronowora parasitica, usually can be found on a yearly basis in broccoli fields in Arizona During the 1988-89 season, four different fungicides were evaluated in the field for disease control. All four materials significantly reduced the number of downy mildew lesions on treated broccoli leaves. Although significant disease control was achieved the average head weight was not significantly different when treated plants were compared with untreated plants. Light to moderate levels of downy mildew or late development of disease, as found in this trial, apparently do not require application of fungicides to prevent yield loss. Ridomil/Bravo and Bravo currently are registered for disease control, while SDS-59891 and Aliette are not registered for use on this crop.

Eleven treatments were applied for sweetpotato whitefly B- biotype control. Best control (62.4%) was evidenced by the Ambush + Thiodan treatment, which had fewest nymph numbers 8 days post treatment and had larger plant sizes (46.3%) 14 days post treatment than the untreated check. Plants in plots receiving treatments including Thiodan and/or Lorsban were also at least 20% larger than the untreated check. Fewest number of adult whiteflies two days post treatments were noted in the Thiodan + M-Pede treatment. Certain treatments increased whitefly numbers.

The new insecticide Imidacloprid (NTN 33893), which is currently being developed for use on vegetable crops, was evaluated on broccoli for control of aphid species. Studies conducted in the spring of 1991 showed that this material applied postemergence as a granular formulation was extremely effective in preventing aphid colonization throughout the season. Aphid control and broccoli yields were significantly greater in plots treated with Imidacloprid. Due to low numbers of aphids in 1992, we were unable to detect differences in aphid numbers between Imidacloprid treatments and the untreated control.

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An exploratory field study provided results of postemergence herbicide weed control efficacy and broccoli tolerance. Pyridate (Tough®), clopyralid (Stinger®), and oxyfluorfen (Goal®) did not cause any crop stand reduction compared to bentazon (Basagran®) that completely reduced the broccoli stand. Tough and Goal at the lower rates tested caused marginally acceptable broccoli injury. Goal effectively controlled pigweed species (Amaranthus sp.), groundcherry (Physalis wrightii), and purslane (Portulacç oleracea). Tough gave good control of pigweed and purslane but not groundcherry. Stinger was safe on broccoli and marginally controlled groundcherry. In a second field study, Tough and Goal were evaluated for cheeseweed control. Goal marginally controlled cheeseweed at all rates tested and caused marginally acceptable injury at the two lowest rates. Tough was relatively safe at the lower rates but did not adequately control the cheeseweed.

Exploratory field studies conducted in broccoli showed that clomazone (Command®) and isoxaben (Gallery®) were extremely phytotoxic to broccoli when applied preemergence (PREE) on the soil surface after planting. Both offered good weed control of the weeds present. Napropamide (Devrinol®) caused moderate crop injury and marginally acceptable weed control.

Downy mildew of broccoli 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 weather conditions favorable for disease development. Potential new fungicides were evaluated for disease management in a field trial conducted in 1996. Disease pressure was moderate and all tested fungicides except Ridomil MZ 72 and one Ciba G + Mancozeb treatment significantly reduced the number of downy mildew lesions on leaves compared to plants not treated with a fungicide. The level of disease reduction provided by all chemical treatments was equivalent to that given by Aliette and Bravo, two fungicides currently available for control of downy mildew on broccoli.

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