Effect of Fungicide Spray Cover on Botrytis Cinerea Infection in Grape Bunches

Abstract

The effect of fungicide spray cover on Botrytis cinerea infection in grape bunches was determined. Bunches were sprayed at pea size and bunch closure with different volumes of a mixture of fenhexamid and a yellow fluorescent pigment, and the percentage fluorescent pigment coverage on pedicels was determined. Bunches were subsequently dusted with dry airborne conidia of B. cinerea in a settling tower and incubated for 24 h at high relative humidity (98%). Infection was determined by estimating the amount of B. cinerea infections on susceptible bunch parts (pedicel, receptacle and rachis) with isolations onto paraquat (herbicide) and Kerssies (B. cinerea selective) mediums. Linear regressions for the part × stage combinations of percentage B. cinerea incidence on different bunch parts were fitted on mean coverage levels. An increase in spray cover caused linear reductions in levels of B. cinerea on bunch parts. Higher B. cinerea incidences were recorded at pea size. Furthermore, higher B. cinerea incidences were found on paraquat medium for both stages, than on Kerssies medium. The information gathered from this study will be used to facilitate future determination of minimum effective coverage levels for effective B. cinerea control in grape bunches.

Spray Deposition and Control of Botrytis cinerea on Grape Leaves and Bunches: Part 1 (Table Grapes)

“…Practical management of these diseases relies almost exclusively on well-timed and/or routine fungicide applications; therefore producers invest heavily in chemical products and spray equipment. Laboratory studies showed that B. cinerea was effectively controlled with the available botryticides, provided that sufficient deposition on susceptible tissue was obtained (Van Rooi, 2001;Van Rooi & Holz, 2003;Brink et al, 2006). Similar efficiency was, however, not achieved when the same fungicides were applied in the vineyards, using conventional spraying methods .…”

“…Brink et al (2004) developed and validated a spray deposition assessment protocol using fluorometry, photomicrography and digital image analyses to assess spray deposition on susceptible grape bunch parts. Brink et al (2006) used this spray assessment technique in developing a protocol that could be used to determine the effect of different spray deposition levels on B. cinerea incidence. However, they could not determine the minimum effective deposition levels needed for effective control of B. cinerea in grape bunches to be used as spray deposition benchmarks to evaluate spray application in vineyards for the control of this and other important grapevine diseases.…”

“…However, they could not determine the minimum effective deposition levels needed for effective control of B. cinerea in grape bunches to be used as spray deposition benchmarks to evaluate spray application in vineyards for the control of this and other important grapevine diseases. Sufficient spray deposition levels were not attained to ensure adequate control of Botrytis infections and Brink et al (2006) indicated several factors resulting in insufficient infections, such as too low spray volumes (or spray deposition), as well as inconsistent conidium and fungicide spray deposition on the structural bunch parts. This inconsistent conidium and fungicide spray deposition on the structural bunch parts was largely due to the 3-dimensional structure of bunches and bunch compactness, which led to variation in conidium and fungicide spray deposition to determine minimum effective deposition values.…”

“…This inconsistent conidium and fungicide spray deposition on the structural bunch parts was largely due to the 3-dimensional structure of bunches and bunch compactness, which led to variation in conidium and fungicide spray deposition to determine minimum effective deposition values. Brink et al (2006) recommended that variation in conidium and spray deposition might be minimised by cutting bunches into a two dimensional shape, which would subsequently lead to better linear relations between spray cover and B. cinerea infection levels.…”

“…Furthermore, the Brink et al (2006) protocol did not address deposition quality measurements nor did it include deposition studies on grapevine leaves. Grape leaf blades carry high amounts of B. cinerea and it was hypothesised that pre-blossom leaf infection is an important primary infection event playing an important role in the epidemiology of the pathogen on grapevines .…”