Necrotrophic parasites of above-ground plant parts survive saprophytically, between growing seasons in host crop residues. In an experiment conducted under field conditions, the time required in months for corn and soybean residues to be completely decomposed was quantified. Residues were laid on the soil surface to simulate notill farming. Crop debris of the two plant species collected on the harvesting day cut into pieces of 5.0cm-long and a 200g mass was added to nylon mesh bags. At monthly intervals, bags were taken to Reis, E. M.; Baruffi, D.; Remor, L; Zanatta, M. Decomposition of corn and soybean residues under field conditions and their role as inoculum source. Summa Phytopathologica, v.37, n.1, p.65-67, 2011.Keywords: parasitas necrotróficos, restos de cultura, tempo de decomposição.Palavras-chave adicionais: necrotrophic parasites, crop residues, time of decomposition. RESUMOPa rasi tas nec rotrófi cos de órgã os aéreos s obrevivem saprofiticamente, na esntre-safra, nos restos culturais dos hospedeiros. Em experimento conduzido no campo quantificou-se o tempo, em meses, para a decomposição dos restos culturais do milho e da soja, posicionados na superfície do solo simulando o plantio direto. Os restos culturais das duas espécies foram coletados no dia da colheita mecânica, cortados em peças de 5,0cm de comprimento e uma massa de 200 g ac ond icionada em rec ipientes de malha de n áilon. Mensalmente foram removidos do campo e levados ao laboratório Reis, E. M.; Baruffi, D.; Remor, L; Zanatta, M. Decomposição dos restos culturais do milho e da soja sob condições de campo e sua função como fonte de inóculo primário. Summa Phytopathologica, v.37, n.1, p.65-67, 2011.the laboratory for weighing. Corn residues were decomposed within 37.0 months and those of soybean, within 34.5 months. Hw main necrotrophic fungi diagnosed in the corn residues were Colletotrichum gramicola, Diplodia spp. and Gibberella zeae, and those in soybeans residues were Cercospora kikuchii, Colletotrichum spp, Glomerella sp. and Phomopsis spp. Thus, those periods shoulb be observed in crop rotation aimed at to eliminating contaminated residues and, consequently, the inoculum from the cultivated area.aonde se procedeu a pesagem. Demonstrou-se que os restos culturais do milho foram mineralizados num tempo de 37 meses e os da soja em 34,5 meses. Os principais fungos necrotróficos parasitas diagnosticados em resíduos de milho foram Colletotrichum gramicola, Diplodia spp. e Gibberella zeae, e nos restos culturais da soja Cercospora kikuchii, Colletotrichum spp, Glomerella sp e Phomopsis spp. Pode-se inferir que estes são os tempos a serem observados na rotação de culturas visando à redução dos restos culturais e conseqüentemente do inóculo na área cultivada.

In in vivoexperiments the sensitivity of 18 isolates of Phakopsora pachyrhizifrom several regions of Brazil to IDM fungicides (cyproconazole, epoxiconazole and tebuconazole and an IQE (pyraclostrobin) were evaluated. The assessments were based on leaflet uredia density. Inhibitory concentration (IC50) and sensitivity reduction factor were determined for all fungicide x strain interactions. Tebuconazole sensitivity reduction was detected for most fungus isolates. In contrast, there was no fungicide shift in sensitivity of the fungus to pyraclostrobin. We conclude that the control failure of soybean rust found in some farms is due to the reduced sensitivity of the fungus to the IDM fungicide and that it remains sensitive to pyraclostrobin.

Published data containing fungicide concentrations that control 50% (IC50) of a given fungus were analyzed. In the analysis we considered: (i) the IC50 determined in vitroand in vivofor a given fungicide and for a specific fungus; (ii) the concentration (g/ha) of active ingredient for the fungicide indicated to control a specific disease in the field; (iii) water volume of 120/L used in the spray; (iv) the fungicide a.i. concentration (mg/L) in 120 L volume; (v) and the ratio of the concentration used in the field with that determined in the laboratory. The analysis were performed by using IC50 data for DMIs, QoIs, a carbamate and a benzimidazol against the following fungi Bipolaris sorokiniana, Drechslera tritici-repentis, D. siccans, Fusarium graminearum, Puccinia triticina, Exserohilum turcicum, Phakopsora pachyrhiziand Corynespora cassiicola. The fungicide concentrations sprayed in the field were 33.9 (D. siccansand trifloxystrobin) to 500,000.0 (E. turcicumand iprodione) times higher than that determined in the laboratory. It was concluded that the IC50 was not related to the concentration used in the field and therefore should be used to compare the power among fungicides and to monitor the fungal sensitivity shift towards fungicides

The objective of this work was to compare the leaflet severity of Asian soybean rust in farms sown in December and February in the state of Mato Grosso. In the survey, 28 fields were sampled in 14 counties in the North, West and South regions of the state. A total of 40 leaflets were collected per plot, in randomized treatments with four replication and three crop phenological stages. Leaflet severity was assessed according to a diagrammatic scale. The data were expressed as leaflet severity, submitted to linear regression analysis, calculated the area under the disease progress curve (AUDPC) considering the three phenological stages sampled, and the means compared by the Tukey’s test. Leaflet severity was significantly higher in the fields sown in December than in February, as well the number of fungicides sprayings. Our results indicate that the proposed change in seeding time from December to February can be implemented by significantly reducing risks and in compliance with the principles of IN 002/2015.

RESUMO O objetivo do controle de doenças de plantas com fungicidas é minimizar os danos causados à cultura, incluindo a redução de produção. No entanto, o uso de fungicidas impacta no custo de produção e aumenta o risco de seleção de linhagens de fungos resistentes. Esses dois fatores são dependentes do número de pulverizações. Atualmente, no uso de fungicidas na cultura da soja visando, principalmente, ao controle da ferrugem (Phakopsora pachyrhizi) não se adota qualquer critério científico, para definir quando efetuar a primeira aplicação. Nessa revisão é abordada a importância do monitoramento das lavouras de soja, da diagnose e da quantificação de danos causados pela ferrugem. Apresentam-se os principais indicadores empíricos para a primeira aplicação e o critério científico. A ocorrência da resistência cruzada e múltipla de P. pachyrhizi aos fungicidas sítio específicos carboxamidas, estrobilurinas e triazóis pode ter sido acelerada pelo uso desnecessário de aplicações desses fungicidas.