Extended Abstract (20K)P4.11
Heterogeneity of dew-period duration within apple tree canopies and comparison to site-specific wetness estimates
Jean C. Batzer, Iowa State University, Ames, IA; and M. L. Gleason, S. E. Taylor, and K. J. Koehler
The growth and spread of fungal pathogens are influenced by the duration of wetness periods. For this reason, leaf wetness duration (LWD) is a key input to many disease-warning systems (decision aids that help growers to efficiently time disease management practices). On-site monitoring of LWD is unacceptable to many apple growers because it is inconvenient, laborious, and often unreliable. An alternative source of LWD data is commercially available, site-specific LWD estimation (e.g. SkyBit, Inc.). These remote estimates do not consider effects of crop canopy microenvironment, however, which may result in erroneous within-canopy LWD estimates. There is a need to calibrate site-specific estimates of LWD to microenvironments in an apple-tree canopy with acceptable accuracy. Hourly averages of LWD at 12 canopy positions were taken in three mature, semi-dwarf apple trees (3.7 to 4.2 m tall, north-south row orientation, cv. Golden Delicious) in an Iowa orchard from mid-July to September 2000 and in four trees from late May to mid-September 2001. Painted electronic wetness sensors (Model 237, Campbell Scientific, Inc.) were mounted at a 45-degree angle from horizontal and facing north at four lateral, east-west positions within the canopy at each of three heights (3.7 m, 2.4 m, 1.2 m.). Four identical sensors were also erected 1 m above mowed turfgrass on an unobstructed site 100 m north of the apple orchard. LWD for nightly periods from noon to 11 am was analyzed using a SAS Mixed Models procedure. During nights with no precipitation, LWD varied within a canopy from west to east (P=0.00075) and LWD was 197% longer in upper eastern than lower western portions of canopies. LWD over the turfgrass area did not differ significantly from the upper canopy of the apple trees. On-site data from both apple canopies and turfgrass was used to evaluate the accuracy of SkyBit estimates of LWD for microenvironments within the apple canopy.
Poster Session 4, Poster Session: Plants, Phenology, and Drought
Thursday, 31 October 2002, 12:30 PM-1:30 PM
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