Weed Communities In Direct Seeding Paddy Fields And Herbicide Development For Resistant Ammannia Arenaria Management

Weeds problem in direct seeding paddy fields was serious and difficult to manage in recent years,the indoor and field experiments were conducted to investigate the weed communities and distribution of eared redstem Ammannia arenaria H.B.K.in main direct seeding paddy fields in Zhejiang Province of China.The cross-resistance of different A.arenaria biotypes to representative ALS inhibitors were determined and the herbicides for controlling weeds such as A.arenaria were screened,which provided the basic hnowledge for integrated weed management in paddy fields.1.The results of weed investigations in Huzhou?Jiaxing,?Hangzhou?Shaoxing and Ningbo within Zhejiang province showed that there were 74 weed species and 5 varieties belonging to 51 generas of 28 families in direct seeding paddy fields.Among them,Leptochloa chinensis(L.)Nees.,Echinochloa crus-galli(L.)Beauv.,Ammannia arenaria H.B.K.,Ludwigia prostrata Roxb.,Cyperus difformis L.,Ammannia multiflora Roxb.,Monochoria vaginalis(Burm.f.)Presl ex Kunth,Fimbristylis miliacea(L.)Vah1,Alternanthera philoxeroides(Mart.)Groseb were the most harmful weeds.There were 20 types of weed communities including A.arenaria + L.chinensis + A.multiflora+ E.crus-galli+ C.difformis+L.prostrate.The structure of weed communities has changed greatly in the past decade.Some weeds such as A.arenaria,A.multiflora,L.prostrata,M.vaginalis,Polygonum hydropiper,Lindernia antipoda(L.)Alston and Aeschynonmene indica L.have been becoming dominant weeds,while other weeds such as Sagittaria pygmaea,Potamogeton distinctus,Marsilea quadrifolia,Eleocharis panula have becoming less important weeds.The eared redstem was found in 28.2%of the fields surveyed and its average density was 22.0 plants/m2,and its relative majority index was 3.5,and the harmful level of the weed was more than level 2 in 23.6%of the fields surveyed,and 6.2%of them were belong to serious or very serious level,the general harmful index of the weed was 15.2.2.The results of bioassay with agar method indicated that the concentration causing fifty percent inhibition of root length(IC50)of the bensulfuron-methyl,penoxsulam.bispyribac-sodium and imazethapyr to susceptive eared redstem biotype HZ001 were 4.0×10-3.1.3×10-3,3.7×10-3 and 0.019 mg/L,respectively.The resistance index(RI)of the biotype HZ 138 to bensulfuron-methyl penoxsulam?bispyribac-sodium and imazethapyr were 19.9,17.4,4.9 and 4.8,respectively;and the RI of the biotype JX089 to the four herbicides were 42.0,38.4,16.2 and 10.0,respectively.These results indicated that the bensulfuron-methyl resistant eared redstem was cross resistant to the other three ALS inhibitors.3.The results of field experiments showed that the oxadiazon(360 gai/ha),ZJU1(780.1 gai/ha)and ZJU2(378.8 gai/ha)were effective for the resistant eared redstem management by preemergence treatment at 3 days prior to seeding.The herbicides such as bentazone(1440 gai/ha),and bentazone+MCPA(1035 gai/ha),and ZJU5(1042.5 gai/ha)were effective for the eared redstem and other weeds control at 30 days after seeding,.The herbicides mentioned above were relatively safe to rice.