玉井檬果結果不良原因之調查

An Investigation on the Factors Causing the Yield Reduction of Irwin Mango (Mangifera indica L.) in Yu-chin Area of Tainan County

玉井檬果最近連續數年結果不良，經調查獲出主要原因有二：（一）植株生長衰弱；由于過去密植果園已呈擁擠，在未適時修剪，疏伐， 兼之多年不施肥料情形下，樹勢生長已極度衰弱，失卻結果能力，為減產立自然趨勢。（二）藥害影響：玉井果農為防治檬果病蟲害所噴藥液，大多超過安全濃度。每次所配噴液多達4種藥劑或更多，導致葉片，花結與著果等藥害現象極為顯著，葉片與著果大多早落，成為人為減產之重要原因。由于長期藥害造成之葉片衰弱，光化功能不彰，能產生之正常果實極為稀少。在肥料超過其需要情形下，氮肥愈多，產生之小果（nubbins）亦愈多。此種肥料超過其正常需要而產生小果之表現，是檬果特性，近年進口立新藥為賽文，亞素靈與萬靈等，經開花前，開花中與開花候之著果初期分別單獨試驗後，未曾發現藥害現象，果實產量與對照無差異，證明以上藥劑對檬果不是具疏果作用。

In recent years the reducing yields of the Irwin mango in Yu-Ching area has become worse. In this investigation, two factors were found to be mostly related to the yield reduction: (1) Poor growth of the plant due to over-crowded crown without prunning and thinning at proper time as well as no application of fertilizer to the soil for seveal consecutive years, so that most of the shoots of the plant became too weak to set fruits. (2) Damage of chemical agents: For controlling diseases and insect pests, fungicides and insecticides were usually mixed in solutions for spraying at the same time, and the concentrations of individual agent were usually much higher than the regulation permitted. Spraying of such mixed solution resulteP in the damaging of the foliage , flower and fruitsetting. Several days after spraying, it could be easily found that the leaves became discolored, thicker and hardier, and the growth of young leaves were inhibited. The damaged leaves always shed much earlier. In time of blooming, the flower usually became wilting and during the period of fruit-setting, the development of the fruit was inhibited. Afterwards, the fruits dropped seriously. Moreover, if too much N fertilizer was applied even under good management a large amount of small fruits (nubbins) would appear, but not increase in number of normal fruits. Solutions of Sevin (85 % W. P. diluted to 400 times with water), Azodrin (55 % E., diluted to 2000 times with water) and Lannate (90 % W. P. diluted to 2000 times with water) were tested to spray individually on the foliage, flower and setting-fruit of the Irwin mango throughout all periords of blooming, and no damages were found to occur on the foliage, flower and no fruit-thinning effect was detected either. It is suggested that the fruit dropping and the occurrence of small fruits (nubbins) of the plant under good management might be due to the damage caused by too heavy concentration of the chemical agents used.