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How to Manage PestsUC Pest Management Guidelines
SYMPTOMSSymptoms of Cercospora leaf spot first appear as individual, circular spots that are tan to light brown with reddish purple borders. As the disease progresses, individual spots coalesce. Heavily infected leaves first become yellow and evenually turn brown and necrotic. Blighted leaves soon collapse and fall to the ground, but remain attached to the crown. Heart leaves are usually less severely affected and remain green. COMMENTS ON THE DISEASEThis disease can occur wherever sugarbeets are grown but is most severe in the southeastern portion of the San Joaquin Valley. In these areas, warm nights combine with high humidity in irrigated fields to provide an ideal environment for disease development. Optimum daytime temperatures for disease development are 77° to 95°F (25°–35°C) with night temperatures above 61°F (16°C) and a relative humidity of 90 to 95%. The primary source of inoculum is residue from a previously infected crop, but the fungus can be carried on seed and is also hosted by numerous weeds. Spores produced by the fungus are dispersed by splashing rain and may also be carried by wind to susceptible sugarbeet leaves. Cercospora is appearing more commonly in late summer in the southern Delta region (spring-planted, spring-harvested areas) because of the widespread use of high-yielding but susceptible varieties. It appears in the summer and may defoliate beets by early winter. Consider using a more resistant variety. MANAGEMENTVarieties vary considerably in resistance, with the highest yielding current varieties having the least resistance. Growers planting sugarbeets in late fall or early spring for an early fall harvest are most likely to be affected by Cercospora and should use a more resistant variety if possible. To effectively eliminate inoculum from a field, plant sugarbeets in a 3-year rotation with nonhosts and plow to incorporate crop residues. Avoid planting a new sugarbeet field adjacent to fields planted to beets the previous season. When sprinkler irrigation is used, run sets so that windblown mist does not keep leaves wet for longer than 24 hours.
Treatment Decisions
PUBLICATION
UC IPM Pest Management Guidelines: Sugarbeet |
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