A critical-point yield model to appraise the damage caused to soybean by white-mold / Modelo de ponto crítico para estimar os danos causados pelo mofo-branco ​​em soja

A model to estimate the damage caused by white mold to soybean yield from experimental field data gathered during the summer season of 2009-10 was generated. Six soybean cultivars were grown on six sites of the Savana (Cerrados) region, resulting in a total of nine separate experiments. The gradient of disease intensity (plant stem incidence) and yield was generated through the application of different fungicides and rates three times over the course of the season. The disease incidence in plant stems was evaluated at the R1, R5.2 and R5.5 growing stages. Manual harvest at the physiological ripening stage was followed by grain drying, threshing, and cleaning. Finally, grain yield was estimated in kg/ha, and regression analysis was performed. Nine linear equations representing the damage function were generated. The mean damage function was y = - 6.7 x + 1,000, where y represents grain yield normalized to 1,000 kg/haand x represents WM incidence in plants. To appraise the damage caused by various disease intensities, these models should first be validated. Damage coefficients may be used to determine the level of economic damage.

Desenvolveu-se um modelo para estimar os danos causados pelo mofo-branco (MB) (Sclerotinia sclerotiorum) na cultura da soja, com dados gerados em experimentos de campo conduzidos na safra de soja de 2009/10. Seis cultivares de soja foram cultivados em seis locais perfazendo um total de nove experimentos em distintas regiões edafoclimáticas na região do Cerrado. O gradiente da intensidade da doença, avaliada em função de incidência de sintomas/sinais em hastes, foi gerado pela aplicação de diferentes fungicidas em momentos e doses distintas. A intensidade da doença foi avaliada, nos estádios fenológicos de R1, R5.2 e R5.5. A colheita foi realizada na maturação fisiológica e o rendimento de grãos expresso em kg/ha. As análises de regressão entre o rendimento de grãos e a incidência da doença foram realizadas para todas as combinações obtidas e geraram nove equações lineares da função de dano. Função de dano média de nove experimentos foi R = 1.000 - 6,7 I (onde R = rendimento de grãos normalizado para 1.000 kg/ha e I incidênciaa do MB em plantas). Para estimar o dano causado por intensidades diferentes da doença, esses modelos devem ser previamente validado. Os coeficientes de dano podem ser usados para determinar o limiar de dano econômico

Survival of Pratylenchus brachyurus under dry soil conditions.

Pratylenchus brachyurus, a root-lesion nematode, depends on host plants for growth and survival. Weeds, volunteer plants, and crop root residues may act as reservoirs for the parasite in the field, but little is known about the ability of P. brachyurus to survive in the absence of a host. This study aimed to evaluate P. brachyurus survival and infectivity in artificially and naturally infested soil under dry conditions. Two experiments were conducted, the first using artificially infested soil and the second using naturally infested soil. Soil samples were inoculated with a nematode suspension or infected root fragments. At 0, 30, 60, and 90 days post-inoculation, pots were planted with nematode-susceptible maize and soybean. Fallow pots were also analyzed. Nematode survival, infectivity, and morphology were determined 30 days after planting. P. brachyurus showed enhanced survival in soil in the presence of root fragments. However, inoculation method had no effect on the ability of surviving nematodes to infect host roots. Parasites showed signs of anhydrobiosis (C-shaped or tightly coiled body) after 90 and 120 days under dry conditions.

Performance and Profitability of Fungicides for Managing Soybean White Mold: A 10-Year Summary of Cooperative Trials.

White mold, caused by Sclerotinia sclerotiorum, is a yield-limiting disease of soybean in Brazil. Uniform fungicide trials have been conducted annually since 2009. Data from 74 cooperative field trials conducted over a 10-year period were assembled. We selected five fungicides applied two times around flowering: dimoxystrobin plus boscalid (DIMO+BOSC), carbendazim plus procymidone (CARB+PROC), fluazinam (FLUZ), fluopyram (FLUO), and procymidone (PROC). For comparison, thiophanate-methyl (TMET) applied four times was also included as a low-cost treatment. Network models were fitted to the log of white mold incidence (percentages) and log of sclerotia mass data (grams/hectare) and to the nontransformed yield data (kilograms/hectare) for each treatment, including the untreated check. Back-transformation of the meta-analytic estimates indicated that the lowest and highest mean (95% confidence interval [CI]) percent reductions in incidence and sclerotia mass were 54.2 (49.3 to 58.7) and 51.6% (43.7 to 58.3) for TMET and 83.8 (79.1 to 87.5) and 87% (81.9 to 91.6) for CARB+PROC, respectively. The overall mean (95% CI) yield responses ranged from 323 kg/ha (247.4 to 400.3) for TMET to 626 kg/ha (521.7 to 731.7) for DIMO+BOSC, but the variance was significantly reduced by a binary variable (30% threshold) describing disease incidence in the untreated check. On average, an increment of 352 kg/ha was estimated for trials where the incidence was >30% compared with the low-disease scenario. Hence, the probability of breaking even on fungicide costs for the high-disease scenario was >65% for the more effective, but more expensive fungicide (FLUZ) than TMET. For the low-disease scenario, profitability was less likely and depended more on variations in fungicide cost and soybean price.

Meta-Analytic Modeling of the Decline in Performance of Fungicides for Managing Soybean Rust after a Decade of Use in Brazil.

An apparent decline of fungicide performance for the control of soybean rust in Brazil has been reported but the rate at which it has occurred has not been formally quantified. Control efficacy and yield response to three fungicides applied as single active ingredients (a.i.)-azoxystrobin (AZOX), cyproconazole (CYPR), and tebuconazole (TEBU)-and four applied as mixtures-AZOX+CYPR, picoxystrobin + CYPR, pyraclostrobin + epoxiconazole, and trifloxystrobin + prothioconazole (TRIF+PROT)-were summarized using network meta-analytic models fitted to mean severity and yield data from 250 trials (10-year period). The effect of year was tested on both variables in a meta-regression model. Overall control efficacy ranged from 56 to 84%; the three single-a.i. fungicides performed the poorest (56 to 62%). Yield increase for single-a.i. fungicides was as low as 30% but ranged from 47 to 65% for the premixes. Significant declines in both variables were detected for all fungicides except TRIF+PROT. For TEBU, control efficacy (yield response) declined the most: 78% (18%) to 54% (8%) from 2004-05 to 2013-14. The recent surge of resistant populations of Phakopsora pachyrhizi to both demethylation inhibitor and quinone outside inhibitor fungicides is likely the driving force behind a significant decline after 4 years of fungicide use.