Spatial heterogeneity of leaf wetness duration in winter wheat canopy and its influence on plant disease epidemiology

Leaf wetness duration (LWD) is an important factor influencing the occurrence of plant disease
<br />epidemiology. Despite considerable efforts to determine LWD, little attention has been given to
<br />study its variability within the canopy. The objective of this study was to evaluate its
<br />spatiotemporal variability in wheat fields in a heterogeneous landscape. The spatiotemporal
<br />variability of LWD was evaluated in a site close to Arlon (Belgium) during the period May to July
<br />2006 and 2007. LWD measurements were made using a set of flat plate sensors deployed at
<br />five different distances from a 18 m high hedge (5, 10, 20, 50, 100 m). Each set of two
<br />sensors was placed horizontally close the flag leaf. In addition, we collected the amount of
<br />dew water that deposited on rigid epoxy plates placed next to each sensors. Experimental
<br />results showed that LWD measurements revealed substantial heterogeneity among sensor
<br />positions. LWD is longer for sensors closer to the hedge mainly because of its shadowing
<br />effect. 3 to 4 hours of difference was observed between sensors located at 5 m and those
<br />located at 100 m, and besides, a significant quantitative difference (p < 0.0001) of dew
<br />deposit was observed between area beside hedge and those placed at 100 m. In summary, this
<br />study provides new information on how wetness is distributed on wheat leaves according to
<br />the distance from a hedge. This leads to local microclimate conditions that will contribute to
<br />the disease spatial heterogeneity.