Integrated Effects of Genetic Resistance and Prothioconazole + Tebuconazole Application Timing on Fusarium Head Blight in Wheat.

Integrated Fusarium head blight (FHB) management programs consisting of different combinations of cultivar resistance class and an application of the fungicide prothioconazole + tebuconazole at or after 50% early anthesis were evaluated for efficacy against FHB incidence (INC; percentage of diseased spikes), index (IND; percentage of diseased spikelets per spike), Fusarium damaged kernel (FDK), deoxynivalenol (DON) toxin contamination, grain yield, and test weight (TW) in inoculated field trials conducted in 11 U.S. states in 2014 and 2015. Mean log response ratios and corresponding percent control values for INC, IND, FDK, and DON, and mean differences in yield and TW relative to a nontreated, inoculated susceptible check (S_CK), were estimated through network meta-analyses as measures of efficacy. Results from the analyses were then used to estimate the economic benefit of each management program for a range of grain prices and fungicide applications costs. Management programs consisting of a moderately resistant (MR) cultivar treated with the fungicide were the most efficacious, reducing INC by 60 to 69%, IND by 71 to 76%, FDK by 66 to 72%, and DON by 60 to 64% relative to S_CK, compared with 56 to 62% for INC, 68 to 72% for IND, 66 to 68% for FDK, and 58 to 61% for DON for programs with a moderately susceptible (MS) cultivar. The least efficacious programs were those with a fungicide application to a susceptible (S) cultivar, with less than a 45% reduction of INC, IND, FDK, or DON. All programs were more efficacious under conditions favorable for FHB compared with less favorable conditions, with applications made at 50% early anthesis being of comparable efficacy to those made 2 to 7 days later. Programs with an MS cultivar resulted in the highest mean yield increases relative to S_CK (541 to 753 kg/ha), followed by programs with an S cultivar (386 to 498 kg/ha) and programs with an MR cultivar (250 to 337 kg/ha). Integrated management programs with an MS or MR cultivar treated with the fungicide at or after 50% early anthesis were the most likely to result in a 50 or 75% control of IND, FDK, or DON in a future trial. At a fixed fungicide application cost, these programs were $4 to $319/MT more economically beneficial than corresponding fungicide-only programs, depending on the cultivar and grain price. These findings demonstrate the benefits of combining genetic resistance with a prothioconazole + tebuconazole treatment to manage FHB, even if that treatment is applied a few days after 50% early anthesis.

Revisiting Fungicide-Based Management Guidelines for Leaf Blotch Diseases in Soft Red Winter Wheat.

Standard foliar fungicide applications in wheat are usually made between flag leaf emergence (Feekes [FK] 8) and heading (FK10.5) to minimize damage to the flag leaf. However, over the last few years, new fungicide programs such as applications prior to FK8 and split half-rate applications have been implemented, although there are few data pertaining to the efficacy of these programs. Eight experiments were conducted in Illinois, Indiana, Ohio, and Wisconsin from 2010 to 2012 to compare new programs to standard FK8 and FK10 programs in terms of disease control and yield response. The programs evaluated consisted of single full-rate applications of 19% tebuconazole + 19% prothioconazole (Prosaro) or 23.6% pyraclostrobin (Headline) at FK5 (pseudostem strongly erected), FK8, or FK10, or split half rates at FK5 and 8 (FK5+8), plus an untreated check (CK). Leaf blotch (LB) severity and yield data were collected and random effects meta-analytical models fitted to estimate the overall log odds ratio of disease reaching the flag leaf ( L¯OR ) and mean yield increase ( D¯ ) for each fungicide program relative to CK. For all programs, L¯OR was significantly different from zero (P < 0.05). Based on estimated odds ratios (OR = exp[ L¯OR ]), the two FK8 programs reduced the risk of LB reaching the flag leaf by 55 and 75%, compared with 62 and 69% and 67 and 70% for the two FK10 and FK5+8 programs, respectively, and only 32 and 37% for the two FK5 programs. D¯ was significantly different from zero (P ≤ 0.003) for all FK8, FK10, and FK5+8 programs, with values of 233 and 245, 175 and 220, and 175 and 187 kg ha-1 for the FK10, FK5+8, and FK8 programs, respectively. Differences in mean yield response between Headline and Prosaro were not statistically significant (P > 0.05). The probability of profitability was estimated for each program for a range of grain prices and fungicide application costs. All FK8, FK10, and FK5+8 programs had more than an 80% chance of resulting in a positive yield response, compared with 63 and 67% for the two FK5 programs. The chance of obtaining a yield increase of 200 kg ha-1, required to offset an application cost of $36 ha-1 at a grain price of $0.18 kg-1, ranged from 44 to 60% for FK8, FK10 and FK5+8 programs compared with 22 and 25% for the two FK5 programs. These findings could be used to help inform fungicide application decisions for LB diseases in soft red winter wheat.

First Report of Charcoal Rot Caused by Macrophomina phaseolina on Sunflower in Illinois.

In September 2009, sunflower (Helianthus annuus L.) plants (cv. Mycogen 8C451) from a University of Illinois field research trial in Fayette County, Illinois exhibited silvery gray girdling lesions on the lower stems and premature death. When lower stems and roots were split open, the pith tissue was compressed into layers. Black microsclerotia (90 to 180 µm) were present on the outside of the lower stem tissue and in the stem vascular tissue. Five pieces (approximately 1 cm long) of symptomatic stem tissue from five different affected plants (25 pieces total) were soaked in a 0.5% solution of NaOCl for 30 s, rinsed with sterile distilled water, and placed on potato dextrose agar (PDA; Becton, Dickinson, and Company, Franklin Lakes, NJ). Gray hyphae grew from all of the stem pieces, which subsequently turned black and formed black microsclerotia (75 to 175 µm). On the basis of plant symptoms and size and color of the microsclerotia, the disease was diagnosed as charcoal rot caused by Macrophomina phaseolina (Tassi) Goid (2). To confirm that the isolated fungus was M. phaseolina, DNA was extracted from the pure culture, and PCR amplification of a subunit rDNA and internal transcribed spacer (ITS) region with primers EF3RCNL and ITS4 was performed (3). The Keck Biotechnology Center at the University of Illinois, Urbana sequenced the PCR product. The resulting nucleotide sequence shared the highest homology (99%) with sequences of M. phaseolina when compared with the subunit rDNA and ITS sequences in the nucleotide database ( http://www.ncbi.nlm.nih.gov ). A greenhouse experiment was conducted to confirm pathogenicity; the greenhouse temperature was approximately 27°C and sunflower plants (cv. Cargill 270) were grown in pots and watered daily to maintain adequate soil moisture for growth. Sterile toothpicks were infested with M. phaseolina and placed through the stems (10 cm above the soil surface) of five 40-day-old sunflower plants that were approximately at growth stage R4 (1,4). Five sterile, noninfested toothpicks were similarly placed through sunflower plants to act as controls. Parafilm was used to hold the toothpick in the stem and seal the stem injury. Thirty-five days after inoculation, the mean lesion length on stems inoculated with M. phaseolina was 595 mm and no lesions developed on the control plants. M. phaseolina-inoculated plants also began to wilt and die. Cultures identical to the original M. phaseolina isolate were reisolated from stem lesions of the M. phaseolina-inoculated plants. This is the first report of charcoal rot on sunflower in Illinois to our knowledge. Sunflower is currently not a major crop grown in Illinois, but on-going research is focused on evaluating sunflower as a potential late-planted crop to follow winter wheat. If sunflower production increases in Illinois, growers may need to take precautions to manage charcoal rot. References: (1) L. K. Edmunds. Phytopathology 54:514, 1964. (2) T. Gulya et al. Page 263 in: Sunflower Technology and Production. American Society of Agronomy, Madison, WI, 1997. (3) N. S. Lord et al. FEMS Microbiol. Ecol. 42:327, 2002. (4) A. A. Schneiter and J. F. Miller. Crop Sci. 21:901, 1981.