| Isatis indigotica is one of the key brands of Chinese herbal medicine“Heilongjiang focus on the development of nine kinds of Chinese herbs”in Heilongjiang Province and is one of the main cultivated Chinese herbs in Daqing region,accounting for nearly one-third of the national production;however,the high cost of manual weeding in production and the selection and unreasonable application of chemical herbicides cause Isatis indigotica to often suffer from drug damage and affect yield and quality.In order to screen out herbicides and their application doses that have little effect on the growth of woad and are environmentally friendly,this study investigated the effects of eight herbicides commonly used in the region on the growth and physiological and biochemical properties of woad seedlings using seed germination tests and indoor pot tests.The main findings were as follows:1.The four preemergence herbicides inhibited the germination rate,germination potential,germination index and the cotyledon length,cotyledon width,plant height and plant fresh weight of woad seedlings to different degrees.The overall inhibition effect was significant with higher herbicide application concentration.The symptoms of herbicide damage in woad seedlings gradually decreased as the growth time increased.Among them,dimethoate(750m L/hm~2)and ethofumesate emulsifier(450m L/hm~2)had the least effect on the germination rate and germination index of woad seed germination;spermacetam(375m L/hm~2)had the least effect on the germination potential of woad seed germination.Therefore,within the recommended dose range of herbicides,the low concentration doses of three preemergence herbicides,dimethoate,spermipropylmethyl and ethofumesate emulsifiable oil,had less effect on seed germination of woad and were safer.2.Postemergence herbicides inhibited the growth indexes of woad seedlings,such as height,root length and dry and fresh weight,to a certain extent.As the concentration of herbicide application increased,the inhibitory effect on the growth indexes of woad seedlings became more significant.In this experiment,the highest recommended concentrations of all four herbicides had a consistently significant inhibitory effect on root length growth of woad seedlings;the inhibitory effects of 20%aminopyralid-dichloropyralid-azadirachtin dispersible oil suspension and high performance flumioxazin emulsifiable oil on plant height decreased to no effect over time;high performance flumioxazin emulsifiable oil had good effects on dry and fresh weight growth of woad seedlings at all concentrations.The effects of these two herbicides on plant height were reduced to no effect over time.Therefore,lower doses of several postemergence herbicides are also recommended to reduce the damage to S.platyphylla seedlings.3.Post-emergence herbicide spraying promoted the root diameter expansion and thickening of woad seedlings;photosynthetic pigments a and b and carotenoid content were reduced to different degrees;and the stress effect was more obvious with higher herbicide application concentrations,but the recovery rate was faster with the growth time,and the normal growth was basically restored at 15～20d.Except for 17.5%quinquat-oxaprobin emulsifiable oil,which had a greater effect on root thickness and photosynthetic pigment content of woad seedlings,the persistent effects of the other herbicides were weak,so the use of17.5%quinquat-oxaprobin emulsifiable oil was not recommended for weed control in woad.4.The study on the effects of post-emergence herbicides on physiological indicators in the test seedlings showed that all four herbicides stimulated the protective enzyme system in the plants to different degrees,and the SOD,POD activities and MDA contents were increased,showing different degrees of drug damage symptoms.The effects of drug damage increased with the increase of reagent concentration,while gradually alleviated with the extension of growth time.The herbicides with higher overall safety performance were20%aminopyralid-dichlormide-enopyralid dispersible oil suspension and high efficiency flumioxazin emulsifiable oil.Therefore,20%aminopyralid-dichlormide-enopyralid dispersible oil suspension(750m L/hm~2,1500m L/hm~2)and high efficiency flumioxazin emulsifier(300m L/hm~2,450m L/hm~2)were recommended as post-emergence herbicides.In summary,spraying chemical herbicides can cause different degrees of stress to the growth and development of woad seedlings.From the perspective of crop safety,it is advisable to select herbicides with medium and low concentrations in the recommended range of use for weed control.Among the pre-emergence herbicides,dimethoate(750m L/hm~2),ethofumesate emulsion(450m L/hm~2)and spermacetam(375m L/hm~2)have less inhibitory effect on woad seedlings and recover faster.Post-emergence herbicides can be applied with high efficiency flumioxazin emulsifier and 20%aminopyralid-diclofenac-alkenone dispersible oil suspension(750m L/hm~2,1500m L/hm~2)were used as herbicides in the seedling stage of Panax notoginseng. |
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