Effects of Different Herbicides on Maize Growth and Weed Control in Maize Fields

Effects of four herbicides(paraquat, acetochlor, nicosulfuron and atrazine) on the growth of maize and control effect of plant quantity and fresh weight of weeds were studied. The results showed that 15 days after spraying the herbicides on weeds,the prevention and control effect of paraquat on weeds was the optimum, and its effects on the plant quantity and fresh weight of weeds were above 81.57%; the prevention and control effect of acetochlor on weeds was the second best; the prevention and control effect of atrazine on weeds was the worst, and its effects on the plant quantity and fresh weight of weeds were only 51.04% and 37.86%. After 30 or 45 days, the prevention and control effect of atrazine and nicosulfuron on weeds in the maize fields was better than the other herbicides, and their effects on the plant quantity and fresh weight of weeds were higher than 70.00% and 85.00%. Acetochlor and paraquat had certain phytotoxicity to the growth of maize after about 15 days, and its leaves became yellow and grew slowly. On the whole, nicosulfuron had good prevention and control effect on weeds and had no phytotoxicity to the growth of maize.

Global COVID-19 Pandemic Waves: Limited Lessons Learned Worldwide over the Past Year

The occurrence of coronavirus disease 2019(COVID-19)was followed by a small burst of cases around the world;afterward,due to a series of emergency non-pharmaceutical interventions(NPIs),the increas-ing number of confirmed cases slowed down in many countries.However,the lifting of control measures by the government and the public’s loosening of precautionary behaviors led to a sudden increase in cases,arousing deep concern across the globe.arousing deep concern across the globe.This study evaluates the situation of the COVID-19 pandemic in countries and territories worldwide from January 2020 to February 2021.According to the time-varying reproduction number(R(t))of each country or territory,the results show that almost half of the countries and territories in the world have never controlled the epidemic.Among the countries and territories that had once contained the occurrence,nearly half failed to maintain their prevention and control,causing the COVID-19 pandemic to rebound across the world—resulting in even higher waves in half of the rebounding countries or territories.This work also proposes and uses a time-varying country-level transmission risk score(CTRS),which takes into account both R(t)and daily new cases,to demonstrate country-level or territory-level transmission potential and trends.Time-varying hierarchical clustering of time-varying CTRS values was used to successfully reveal the countries and territories that contributed to the recent aggravation of the global pandemic in the last quarter of 2020 and the beginning of 2021,and to identify countries and territories with an increasing risk of COVID-19 transmission in the near future.Furthermore,a regression analysis indicated that the introduction and relaxation of NPIs,including workplace closure policies and stay-at-home requirements,appear to be associated with recent global transmission changes.In conclu-sion,a systematic evaluation of the global COVID-19 pandemic over the past year indicates that the world is now in an unexpected situation,with limited lessons learned.Summarizing the lessons learned could help in designing effective public responses for constraining future waves of COVID-19 worldwide.