Influence of Shade with Netting to Control Bird Injury on Fruit Production in Japanese Pear Trees, Pyrus serotina Rehder

Abstract

Recently, the fruits of Japanese pear trees were attacked by some kinds of bird just before ripening. Sometimes a few days of bird injury damaged more than 80% of harvestable fruits in the orchards of Tochigi prefecture. More than 60% of the pear orchards of Tochigi prefecture were covered with Russel nets (9mm mesh) or smaller meshes in order to protect them from hail, pest and bird damages.
The bird population increased with urbanization of the surrounding areas of pear orchards, because the birds, under consideration mainly gray starling, Sturnus cineraceus, can live together with man just like the Japanese sparrows.
1. Shade treatments were used with single white cheesecloth (#510) as 30% shade, and double sheets of white and black (#6100) cheesecloths as 70% shade of full sunlight. The use of cheesecloth or Russel net in commercial orchards shaded about 20 to 30% of sunlight.
2. Solar radiation was recorded in hourly calories per square centimeter using a Neo actinometer (Eiko Seiki Sangyo Co. Ltd). Hourly relative light intensities were calculated for each treatment block which recorded more than 20cal/cm²/hr, because less than 20cal. showed ambiguously for each block with diffused light and others.
3. All of the trees tested had three primary scaffold branches. Each of them was used for a plot. The shade treatment was carried out from 1978 to 1982 with three trees in each year, but the trees tested were not used continuously for two years.
4. The results showed that the decreasing rate of solar radiation in fruit bearing zone of a tree was positively correlated with higher shade treatment.
5. Effects of shading were clearly expressed in harvesting time, sugar contents in fruit juice and specific leaf weight (grams of leaf dry matter per decimeter square). The shade of 70% of full sunlight was statistically significant in these three parameters. Although 30% shade significantly decreased specific leaf weight, it did not clearly affect the above-mentioned components over a five-year period.
6. Shaded plots did not clearly affect fruit yield, mean fruit weight and mean leaf area.
7. These results safely suggest that a shade of 30% of full sunlight can be used for netting in order to control bird injury in commercial pear orchards.