本研究以抑制種子胚根伸長達50%之劑量值，估算藥劑對薏苡及雜草之生物活性，及確認對田區內主要雜草的防除效果，作為薏苡田除草劑篩選的參考。將已登記之萌前除草劑處理薏苡、牛筋草及馬齒莧種子，調查藥劑對種子胚根伸長之抑制。結果顯示丁基拉草對三種植物之抑制效果相近。施得圃對薏苡的抑制程度約為測試雜草的2倍，復祿芬與樂滅草均能明顯抑制馬齒莧，但復祿芬對薏苡及牛筋草之活性較樂滅草為高。觀察四種萌前除草劑對薏苡、牛筋草及馬齒莧種子胚根伸長之抑制反應，發現丁基拉草對作物與雜草的活性相近，施得圃會明顯抑制薏苡的胚根伸長，復祿芬與樂滅草則對馬齒莧具較高活性。萌後除草劑伏寄普及快伏草對薏苡及牛筋草之活性較馬齒莧明顯為高。二、四－地對馬齒莧的抑制率雖高，但也抑制薏苡胚根生長。氟氯比僅對馬齒莧達70%之抑制率，在測試劑量範圍內對薏苡及牛筋草抑制率低於5%以下。由估算之抑制50%之劑量結果顯示，丁基拉草處理之薏苡其與牛筋草及馬齒莧之劑量比值分別為0.25及0.3，施得圃均為1.0，復祿芬分別為1.0及5.3，樂滅草為0.6及6.3。顯示復祿芬及樂滅草在較低劑量下，即能有效控制馬齒莧植株。測試之萌後除草劑伏寄普及快伏草對薏苡與馬齒莧之比值為6.0及4.0，優於其他除草劑。四種萌前藥劑在處理後兩星期內均會減少雜草的發生量，丁基拉草及施得圃之總草覆蓋率分別為40%及25%，低於對照區。丁基拉草對牛筋草之抑制較馬齒莧明顯為高，施得圃對兩者的影響則無明顯差異。萌後藥劑二、四－地及氟氯比之總草覆蓋率分別為41%及46%，較對照區之78%顯著為低，尤其明顯抑制馬齒莧的株數。伏寄普及快伏草雖可減少牛筋草的發生株數，但並未明顯降低小區之總草覆蓋率。百速隆及本達隆以測試劑量處理，對牛筋草幾無控制效果，對馬齒莧之發生株數則為對照區之45-62%。綜合測試結果，復祿芬及樂滅草對馬齒莧及薏苡與牛筋草之選擇性差異明顯，萌前施用對牛筋草幼株之發生有顯著抑制效果。二、四－地在適當用量下，對薏苡之生育影響不明顯，卻能有效抑制牛筋草及馬齒莧的發生。

Herbicides are heavily used for managing weeds in modern agriculture. The ideal management system of chemical control is safe to crops, users and environment. Before acceptance of herbicide registration, efficacy trials of herbicide in the field should be performed based on the reduction of weed population, the damage and yield loss of crops, and economic importance to the grower. Herbicides registered for specific crops generally have a wide range of crop tolerance to compensate for the possible misapplication and adverse environmental situations. The objective of this research was to screen some proper pre-emergence herbicides used in Coix lachryma-jobi fields. Ten herbicides have been registered in corn, soybeans, vegetables, or other major crops were evaluated in Coix lachryma-jobi fields. In a preemergence herbicide screening test, oxadiazon and oxyfluorfen were safe to tested crops at rates effective for weed control. In a screening test of postemergence herbicide, 2, 4-D gave acceptable weed control with crop safety. However, some herbicides, i.e., butachlor, pendimethalin, fluazifop-P-butyl, quizalofop-P-ethyl, pyrazosulfuron-ethyl, bentazon, and fluroxypyr, failed to provide an acceptable weed control effect without herbicidal damages to crops.