LIBRO-CONGRESO-CITRUS

S15O01
The arrival of Citrus Black Spot (Guignardia citricarpa) in Florida and current research questions
Dewdney M.M. 1 , Peres N.A. 2 , Schubert T.S. 3 , Mondal S.N. 1 , Hu J. 1 , and Hincapie Caputo M. 2
1 Citrus Research and Education Center University of Florida (CREC UF), Plant Pathology, USA; 2 Gulf Coast Research and Education
Center University of Florida (GCREC UF), Plant Pathology, USA; and 3 Department of Plant Industries, Florida Department of Agriculture
and Consumer Services (DPI FDACS), Plant Pathology, USA. mmdewdney@ufl.edu
In March 2010, the Florida Citrus Health Response Program discovered Citrus Black Spot (CBS) in juice blocks
of ‘Valencia’ sweet orange in southwest Florida. In the last two years, the area where the disease has been
found expanded from 14 km2 to 57 km2. In most of the affected blocks, disease incidence has been low,
with one to a few symptomatic trees. In blocks where a few trees were symptomatic, most growers chose
to remove trees but wide scale eradication was not a reasonable option. A successful eradication program
would require the removal of all infected trees, yet the CBS life cycle, as presently understood, offers no
protocol to ensure success. Upon discovery, quarantine measures were immediately applied to reduce
further spread including covering fruit loads, safe debris disposal, fruit surface decontamination and fruit
movement restrictions. Fungicide programs of copper and strobilurins were promptly initiated in affected
groves. To enable better disease management in the humid subtropical climate of Florida, several research
questions are being explored: 1) if methods of enhanced leaf litter decomposition reduce the number of
Guignardia citricarpa pseudothecia in leaf litter; 2) the optimal wetting and temperature regimens to mature
pseudothecia; and 3) the baseline sensitivity of G. citricarpa isolates to strobilurin fungicides for resistance
management. Highlights from these projects will be presented.
S15O02
Predictive model for ascospore release of Guignardia citricarpa using climatological data
Dummel D.M. 1 , Agostini J.P. 1 , and Moschini R. 2
1 Instituto Nacional de Tecnología Agropecuaria (INTA), Plant Pathology. EEA Montecarlo, Misiones. Argentina; and 2 Instituto Nacional
de Tecnología Agropecuaria (INTA), Instituto de Clima y Suelo, Castelar. Argentina. jpagostini@montecarlo.inta.gov.ar
Citrus Black Spot, caused by Guignardia citricarpa, is a cosmetic disease that affects fruit appearance for
export. A predictive model for ascospore release was developed using climatological data. Ascospore release
was monitored in a ‘Valencia’ sweet orange grove in Misiones, Argentina on a weekly basis using a Burkard
spore trap while climatological data was obtained from a Davis GroWeather station during the 2008/09
season. The daily variables considered in the model were maximum and minimum temperature (°C), rain
(mm), and days with more than 10 hours of leaf wetness (DMojt). Cumulative data were calculated for the
7 days prior to the weekly ascospore count for 28 weeks and categorized as high, medium or low. Using
stepwise regression of SAS, two models were defined for ascospore release. The first model had only one
variable (LogitPrS= – 4,553 1,6015* DMojt) with a correlation coefficient of 67.9% whereas, the second model
had one more variable included, viz. the number of days with temperatures between 20 and 29° C (DT)
(LogitPrS= –6, 1318 1,8108*DMojt 3,4829*DT) which had a correlation coefficient of 82.1%.
S15O03
Assessment of retention and persistence of copper fungicides on sweet orange fruit and leaves
using fluorometry and copper residue analyses
Schutte G.C. 1 , Kotze C. 1 , Van Zyl J.G .2,3 , and Fourie P.H. 2,3
1 Citrus Research International (CRI), Nelspruit, South Africa; 2 Department of Plant Pathology (US), Stellenbosch, South Africa; and
3 Citrus Research International (CRI), Stellenbosch, South Africa. ts@cri.co.za
High volumes of copper hydroxide, cuprous oxide and copper oxychloride were sprayed under natural conditions
onto mature sweet orange trees to compare the retention on leaves and fruit over a period of 56 days by means
of copper residue analyses and a spray deposition assessment protocol using fluorometry, photomacrography
and digital image analyses. Rainfall and increase in fruit size were recorded to determine if it had an influence on
weathering of copper residues. Applications with cuprous oxide retained significantly more copper residue and
XII INTERNATIONAL CITRUS CONGRESS 2012 - 255
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