Abstract

HERNANDEZ-SANCHEZ, Elias et al. Effect of initial disease intensity of cactus black spot (Opuntia ficus-indica) in the temporal and spatial characterization. Rev. mex. fitopatol [online]. 2014, vol.32, n.2, pp.132-146. ISSN 2007-8080.

Black spot caused by Pseudocercospora opuntiae is a major nopal fungus disease in Tlalnepantla, Morelos. The objective of this research was to characterize the temporal and spatial progress of the disease and evaluate the efficacy of six systemic fungicides. The epidemics intensity in the autum did not depend on the initial disease severity (r2=0.49), which suggested the occurrence of a major infection cycle in the summer. Final incidence (Yf ) of the disease ranged from 85 to 88 %. From 20.9 to 52.3 % cladodes per plant were damaged and from 37 to 56.4 % plants showed severity levels higher than 20 %. It started with 46 % initial severity (Yo ) and developed to a higher epidemic intensity (Yf = 90.5 spots and ABCPE = 8.6 number of spots per day-1), which led to the development of 3.1 spots per day-1 in a 29-day period. However, this severity level was statistically similar to the type of epidemics induced by Yo =20.7 y 73.5 % (p=0.05). Low relative humidity (<60 %) was associated with a large stage of new lesions. High relative humidity (>80 %) was associated with a short period for the spot to mature. Minimum temperature had a similar association with values from 8 to 12 °C and lower values for the same events. Changes in the expression of symptoms defined the epidemics speed. Aggregate formation was detected through geostatistical interpolation and aggregation indexes (I. Morisita from 1.6 to 1.9) in direction to rows and border effect, which suggested the effect of agronomic management of disease spreading.

Two benzimidazoles achieved the highest biological efficacy against fungus reducing ABCPE by 85.7 % in average compared to the tester (p=0.05). These systemic fungicides are an option to reduce epidemic expression in autum caused by infections in summer.

Keywords : Pseudocercospora sp; epidemiology; fungicides.

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