New Zealand Journal of Crop and Horticultural Science abstracts
Aspects of microclimate variation within apple tree canopies
and between sites in relation to potential
Venturia inaequalis infection
L. J. PENROSE
H. I. NICOL
NSW Agriculture
Agricultural Research & Veterinary Centre
Forest Road
Orange, NSW 2800
Australia
Abstract The microclimate variables of major consideration
for infection by Venturia inaequalis are surface wetness, temperature,
and humidity. Because infection risk criteria tend to assume that there is
uniformity of microclimate within a tree, and between sites within a district,
the parameters are usually monitored with one or a few sensors at each site. To
examine this uniformity, studies were made of the occurrence of wetness on four
electrical grid sensors within an apple (Malus domestica Borkh.) tree
canopy at each of seven sites, and of dry bulb (DB) temperature and relative
humidity (RH) at the seven sites within an apple growing district. Wetness
observations were made on days when a Reuter-Stokes "Apple Scab Predictor"
registered wetness at one site. Temperature and RH observations were made at
0300, 0900, 1500, and 2100 h on the same days. The probability of one wetness
sensor detecting wetness was c. 0.6 and the spatial location of the sensors
within the canopy did not in most instances affect wetness detection. On only
c. 5% of occasions were all sites wet at the same time. On two thirds of
occasions, within a tree, the start of the wet period varied by >1 h across
the four sensors, and on one third of occasions by >2 h. The length of the
wet period varied by >1 h on 97% of occasions and was >5 h on almost two
thirds of occasions. When the length of the wet period was extended by the time
the RH remained >90%, as is used in some V. inaequalis infection risk
criteria, almost 50% of occasions varied by >5 h between the four sensors.
The range in DB temperature across the seven sites was c. 2deg.C in December to
6deg.C in February. The range of RH across the district was c. 15% in December
to 23% in February. Our results question the reliability of a single wetness
sensor on a single weather station to provide accurate data on infection
conditions across an apple growing district. Leaf wetness detection reliability
could be substantially improved by the provision of at least three wetness
sensors at each site. Provision of a disease warning service across a district
may require weather stations to be located at multiple sites, depending on the
topography of the district, to provide accurate information.
Keywords surface wetness; temperature; Venturia
inaequalis; microclimate
New Zealand Journal of Crop and Horticultural Science, 1996, Vol. 24:
259-266
0114-0671/96/2403-0259 $2.50/0 (c) The Royal Society of New Zealand
1996
PDF file of entire paper: medium quality (626K); (scanned from paper original: notes about this process)
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