Douglas J. Jardine

Aggressiveness to Mature Maize Plants of Fusarium Strains Differing in Ability to Produce Fumonisin

Four strains each of Fusarium moniliforme (syn. Fusarium verticillioides) and Fusarium thapsinum were tested for aggressiveness toward two maize inbred lines grown under greenhouse conditions. All strains induced significantly longer stalk lesions than those observed in the controls. Mean lesion length resulting from inoculation with strains of F. moniliforme was longer than the mean lesion length resulting from inoculation with strains of F. thapsinum. Within each species, however, there was a broad range of lesion lengths observed, and all tested strains of both species probably should be regarded as potential pathogens of maize. No isolate × inbred interaction was detected. Fumonisins may play a role in aggressiveness, but under our conditions, stalk rot and the ability to produce fumonisins in vitro were not correlated.

Soybean Cyst Nematode Reproduction in the North Central United States

An experiment was conducted in Heterodera glycines-infested fields in 40 north central U.S. environments (21 sites in 1994 and 19 sites in 1995) to assess reproduction of this nematode. Two resistant and two susceptible soybean cultivars from each of the maturity groups (MG) I through IV were grown at each site in 6.1 m by 4 row plots. Soil samples were collected from each plot at planting and harvest and processed at Iowa State University to determine H. glycines initial (Pi) and final (Pf) population densities as eggs per 100 cm3 of soil. Overall, reproduction (Pf/Pi) of H. glycines on susceptible cultivars in all MG was similar. Reproduction was higher on MG III and IV susceptible cultivars than on those in MG I and II. Resistant MG I and II cultivars reduced nematode population densities more consistently than those in MG III and IV. Reproduction of the nematode was similar among sites within the same maturity zone (MZ), defined as the areas of best adaptation of the corresponding MG. Nonetheless, careful monitoring of nematode population densities is necessary to assess changes that occur over time in individual fields.

Corn yield loss estimates due to diseases in the United States and Ontario, Canada from 2012 to 2015.

Annual decreases in corn yield caused by diseases were estimated by surveying members of the Corn Disease Working Group in 22 corn-producing states in the United States and in Ontario, Canada, from 2012 through 2015. Estimated loss from each disease varied greatly by state and year. In general, foliar diseases such as northern corn leaf blight, gray leaf spot, and Goss’s wilt commonly caused the largest estimated yield loss in the northern United States and Ontario during nondrought years. Fusarium stalk rot and plant-parasitic nematodes caused the most estimated loss in the southernmost United States. The estimated mean economic loss due to yield loss by corn diseases in the United States and Ontario from 2012 to 2015 was

A Coordinated Effort to Manage Soybean Rust in North America: A Success Story in Soybean Disease Monitoring

76.51 USD per acre. The cost of disease-mitigating strategies is another potential source of profit loss. Results from this survey will provide scientists, breeders, government, and educators with data to help inform and prioritize research, policy, and educational efforts in corn pathology and disease management. M U E L L E R E T A L . , P L A N T H E A L T H P R O G R E S S 1 7 (2 0 1 6 )

NITROGEN, PHOSPHORUS, AND POTASSIUM EFFECTS ON GRAIN SORGHUM PRODUCTION AND STALK ROT FOLLOWING ALFALFA AND BIRDSFOOT TREFOIL

Existing crop monitoring programs determine the incidence and distribution of plant diseases and pathogens and assess the damage caused within a crop production region. These programs have traditionally used observed or predicted disease and pathogen data and environmental information to prescribe management practices that minimize crop loss. Monitoring programs are especially important for crops with broad geographic distribution or for diseases that can cause rapid and great economic losses. Successful monitoring programs have been developed for several plant diseases, including downy mildew of cucurbits, Fusarium head blight of wheat, potato late blight, and rusts of cereal crops. A recent example of a successful disease-monitoring program for an economically important crop is the soybean rust (SBR) monitoring effort within North America. SBR, caused by the fungus Phakopsora pachyrhizi, was first identified in the continental United States in November 2004. SBR causes moderate to severe yield losses globally. The fungus produces foliar lesions on soybean (Glycine max) and other legume hosts. P. pachyrhizi diverts nutrients from the host to its own growth and reproduction. The lesions also reduce photosynthetic area. Uredinia rupture the host epidermis and diminish stomatal regulation of transpiration to cause tissue desiccation and premature defoliation. Severe soybean yield losses can occur if plants defoliate during the mid-reproductive growth stages. The rapid response to the threat of SBR in North America resulted in an unprecedented amount of information dissemination and the development of a real-time, publicly available monitoring and prediction system known as the Soybean Rust-Pest Information Platform for Extension and Education (SBR-PIPE). The objectives of this article are (i) to highlight the successful response effort to SBR in North America, and (ii) to introduce researchers to the quantity and type of data generated by SBR-PIPE. Data from this system may now be used to answer questions about the biology, ecology, and epidemiology of an important pathogen and disease of soybean.

Nitrogen Management in No-Tillage and Ridge-Tillage Systems Affects Short-Season Corn Grown on Claypan Soil

Grain sorghum [Sorghum bicolor (L.)], grown on the often infertile claypan soils of the eastern Great Plains, requires attention to soil fertility. Experimental objectives were to determine the effects of phosphorus (P) and potassium (K) fertility levels, N application, and legume residual on grain sorghum production and stalk rot. Following alfalfa and birdsfoot trefoil, first-year sorghum yield was 7 Mg ha−1 and not affected by N fertilizer. In subsequent years, yield increases due to N were less than 20%. Sorghum yield increased at low P and K rates, especially with nitrogen (N) fertilization and was greater following birdsfoot trefoil than following alfalfa. In 1995 when fertilized with N, lodging and stalk rot severity were increased by P and reduced by K. In 1996, stalk rot severity was reduced by K fertilization. Grain sorghum, grown after legume crops, required minimal levels of P and K, especially when N fertilizer was added.

Re-emergence of Tobacco streak virus Infecting Soybean in the United States and Canada

Success of conservation tillage systems requires good fertilizer management, especially nitrogen applied to crops grown on claypan soils in the eastern Great Plains. Recently introduced, short-season corn (Zea mays L.) hybrids, that mature earlier and potentially avoid drought problems common on these soils in late summer, provide producers with another viable cropping option. However, information on N management in conservation tillage systems is lacking for short-season corn grown on claypan soils. The objective of this study was to examine the effect of fertilizer N at rates of 0, 30, 60, 90, and 120 lb/acre applied by surface broadcast, surface band (dribble), and subsurface band (knife) placement methods on short-season corn grown in no-tillage and ridge-tillage systems. Average corn yield in 1997 was about 25 bu/acre more with ridge tillage than with no tillage when fertilizer N was applied at any rate. However, this trend was not apparent in 1996 and 1998, when yields were lower because of less rainfall. In 1996 and 1998, yield was not increased at N rates greater than 60 lb/acre, but in 1997, maximum yield was obtained at the 120 lb/acre N rate. Nitrogen placement effects on yield were inconsistent. Yield improvements resulting from increased N rate can be attributed to improved yield components, especially the number of kernels per ear, which was doubled with N at 120 lb/acre compared to no fertilizer N. Increasing N rate resulted in small increases in crude protein concentration in the corn grain. Even though more samples were contaminated with aflatoxin and at higher levels in the drier years, tillage and N management had little effect on aflatoxin concentrations. Corn grown on a claypan soil can respond to increased N rate and conservation tillage systems, especially in higher rainfall years, but the effect due to N placement is inconsistent.

Assessing Heterodera glycines-resistant and susceptible cultivar yield response

Melissa D. Irizarry, Department of Plant Pathology, Iowa State University, Ames 50011; Carol L. Groves, Department of Plant Pathology, University of Wisconsin-Madison 53706; Manjula G. Elmore, Department of Plant Pathology, Iowa State University, Ames 50011; Carl A. Bradley, Department of Crop Sciences, University of Illinois, Urbana 61801 (current address: Department of Plant Pathology, University of Kentucky, Princeton 42445); Ranjit Dasgupta and Thomas L. German, Department of Entomology, University of WisconsinMadison 53706; Douglas J. Jardine, Department of Plant Pathology, Kansas State University, Manhattan 66506; Erika Saalau Rojas, Department of Plant Pathology, Iowa State University, Ames 50011 (current address: UMass Cranberry Station, University of MassachusettsAmherst, East Wareham 02538); Damon L. Smith, Department of Plant Pathology, University of Wisconsin-Madison 53706; Albert U. Tenuta, Ontario Ministry of Agriculture, Food, and Rural Affairs; University of Guelph, Ridgetown N0P 2C0, Canada; Steven A. Whitham and Daren S. Mueller, Department of Plant Pathology, Iowa State University, Ames 50011