Studies On Co-fungitoxicity Against Phytophthora Infestans And Preparation Of Mixed Formulation Of Flupicolide And Pyraclostrobin

Potato late blight is a worldwide disease and can cause serious damage to potatoproduction. The disease is hard to control and common means cannot achieve good controlefficacy since it quickly breaks out and infects. Chemical control is the main method tocontrol the disease in production. Protective fungicides can prevent and delay the incidenceof the disease, reduce the damage of the disease, but they become nearly useless when theyare used after the disease breaks out. Though systemic fungicide can control the spread ofthe disease, resistance of the pathogen to systemic fungicides cannot be neglected. P.infestans developed different levels of resistance to metalaxyl all over the world now. It isreported that the control efficacy of cymoxanil (100μg/ml) against potato late blight whichwas caused by intermediate strains had decreased and there are high resistance risks to thesystemic fungicides which have single action site such as azoxystrobin. Developing newpreparations of fungicide mixtures by using fungicides which have good control efficacyagainst late blight and applying them in the field are shortcuts to control potato late blightbetter and reduce the cost of developing new fungicides and prolong the use life of theexisting fungicides. Fluopicolide and pyraclostrobin have excellent control efficacy topotato late blight and have different modes of action between them. The ready-mixturefungicide Infinito is mixtures of fluopicolide and propamocarb hydrochloride, can be usedto control potato late blight, and the active ingredient of Cabrio is pyraclostrobin anotherfungicide good for control of potato late blight. It is reported that phytophthora capsici hadmoderately high resistance risk to fluopicolide in the field. Pyraclostrobin might have highresistance risk due to the single site of action. Therefore, in this study, fluopicolide andpyraclostrobin were mixed together. The optimum ratio of them was screened throughbioassay method, then the formulations of the mixture of the two active ingredients weredeveloped and the field control efficacy trials were carried out. The main results are asfollows:1. Fungitoxicity of the mixtures of fluopicolide and pyraclostrobin in different ratioswas tested by mycelial growth assay and leaf disc assay. It was found that additiveinteractions and even synergistic interactions existed between fluopicolide and pyraclostrobin when they were used in mixtures at the different ratios. EC50of the mixturesat different ratios against mycelial growth of the tested isolates ranged from0.2999-0.6854μg/ml and the EC50against sporulation ranged from0.2477-0.7297μg/ml.Synergistic ratios of the mixtures of fluopicolide and pyraclostrobin at the ratios of1:4and10:1(F:P) against different development stages of the pathogen were ranged from1.56to5.27. EC50against the isolates with different sensitivity to metalaxyl ranged from0.1956-0.5610μg/ml. Synergistic interactions of the mixtures at the ratios of1:4and10:1were more obvious against metalaxyl-resistant isolates than against metalaxyl-sensitiveisolates. The mixtures weret more effective against zoospore release, cystosporegermination and sporangial germination than to the other developmental stages of P.infestans. EC50of the mixtures at the ratio of1:4against zoospore release was0.0044μg/ml,while the synergistic interactions of the mixture at ratio of10:1were most obvious and thesynergistic ratio was5.27. The tank-mixture of the two fungicides at the ratios of1:4and10:1(F:P) had excellent protective activity and curative activity and long duration ofefficacy. The control efficacy was more than95%14days after spray at the concentrationof200μg/ml.2. Dispersants of polymer polycarboxylate salts and naphthalene sulfonic acid saltswere suitable for processing water dispersible granule (WG) and aqueous suspensionconcentrate (SC) of the mixtures of fluopicolide with pyraclostrobin. It was easy to prillwhen25%fluopicolide·pyraclostrobin WG was processed according to the screenedformulation and the granules were plump and uniformity. The sample of25%fluopicolide·pyraclostrobin WG was disintegrated quickly (the disintegration time wasabout20s), had high suspension rate (about90%) and good storage stability. The sample of40%fluopicolide·pyraclostrobin SC had small particale size (about5μm), excellentdispersibility, high suspension rate (about90%) and good storage stability.3. Method of pseudo-ternary phase diagram had directive function to the formulationscreening of emulsion in water (EW) and can be used for selecting the types and dosagesof the emulsifiers in EW systematic and conveniently and efficiently. The results showedthat emulsifiers could not be selected only according to the emulsion area inpseudo-ternary phase diagram because the stability of EW was affected by many factors.But stable EW samples could be processed more easily with the emulsifiers which couldform bigger emulsion area in pseudo-ternary phase diagram. The content of emulsifierphase in EW were related with the content of oil phase in practical formula and usually theratios of SAA phase and oil phase ranged from1:9-2:8were more likely to obtain stableformulation of EW. Organic bentonite and Xanthan gum could enhance the stability of25%fluopicolide·pyraclostrobin EW.4. The control efficacy of the three preparations of fluopicolide mixed with pyraclostrobin (288-480g a.i./hm~2) to potato late blight in the field was about90%and wasequal or superior to the other common fungicides which were usually used to control thedisease. The formulations of fluopicolide mixed with pyraclostrobin could wipe out thepathogen effectively once the disease broke out, and protect the new leaves from beinginfected and prevent the disease from spreading.