Azoxystrobin is applied early in the sugar beet growing season in north-central United States for control of Rhizoctonia damping-off and Rhizoctonia crown and root rot caused by Rhizoctonia solani anastomoses groups (AGs) 4 and 2-2, respectively. Fungicide application timings based on crop growth stage and soil temperature thresholds were evaluated in inoculated small-scale trials and in commercial fields with a history of Rhizoctonia crown and root rot. Soil temperature thresholds of 10, 15, and 20°C were selected for fungicide application timings and used to test whether soil temperature could be used to better time applications of azoxystrobin. In both small- and large-plot trials, timing applications after attainment of specific soil temperature thresholds did not improve efficacy of azoxystrobin in controlling damping-off or Rhizoctonia crown and root rot compared with application timings based on either planting date, seedling development, or leaf stage in a susceptible (E-17) and a resistant (RH-5) cultivar. Application rate and split application timings of azoxystrobin had no significant effect on severity of crown and root rot. Other environmental factors such as soil moisture may interact with soil temperature to influence disease development. Cv. RH-5 had higher sugar yield attributes than the susceptible cultivar (E-17) in seasons conducive and nonconducive to crown and root rot development. All isolates recovered from both small- and large-plot trials in all years were AG 2-2. R. solani AG 4 was not identified in any samples from any year.

Rhizomania, caused by Beet necrotic yellow vein virus (BNYVV) and vectored by the soilborne fungus Polymyxa betae Keskin, is one of the most economically damaging diseases affecting sugar beet (Beta vulgaris L.). The virus likely originated in Europe and was first identified in California in 1983 (1). It has since spread among American sugar beet production regions in spite of vigorous sanitation efforts, quarantine, and disease monitoring (3). In the fall of 2002, mature sugar beet plants exhibiting typical rhizomania root symptoms, including proliferation of hairy roots, vascular discoloration, and some root constriction (2) were found in several fields scattered throughout central and eastern Michigan. Symptomatic beets were from numerous cultivars, all susceptible to rhizomania. Two to five sugar beet root samples were collected from each field and sent to the USDA-ARS in Salinas, CA for analysis. Hairy root tissue from symptomatic plants was used for mechanical inoculation of indicator plants. Mechanical inoculation produced necrotic lesions on Chenopodium quinoa and systemic infection of Beta vulgaris ssp. macrocarpa, both typical of BNYVV and identical to control inoculations with BNYVV. Symptomatic sugar beet roots were washed and tested using double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA) for the presence of BNYVV using standard procedures and antiserum specific for BNYVV (3). Sugar beet roots were tested individually, and samples were considered positive when absorbance values were at least three times those of greenhouse-grown healthy sugar beet controls. Samples were tested from 16 fields, with 10 confirmed positive for BNYVV. Positive samples had mean absorbance values ranging from 0.341 to 1.631 (A405nm) after 30 min. The mean healthy control value was 0.097. Fields were considered positive if one beet tested positive for BNYVV, but in most cases, all beets tested from a field were uniformly positive or uniformly negative. In addition, soil-baiting experiments were conducted on seven of the fields. Sugar beet seedlings were grown in soil mixed with equal parts of sand for 6 weeks and were subsequently tested using DAS-ELISA for BNYVV. Results matched those of the root sampling. Fields testing positive for BNYVV were widely dispersed within a 100 square mile (160 km2) area including portions of Gratiot, Saginaw, Tuscola, and Sanilac counties in the central and eastern portions of the Lower Peninsula of Michigan. The confirmation of rhizomania in sugar beet from the Great Lakes Region marks the last major American sugar beet production region to be diagnosed with rhizomania disease, nearly 20 years after its discovery in California (1). In 2002, there were approximately 185,000 acres (approximately 75,00 ha) of sugar beet grown in the Great Lakes Region, (Michigan, Ohio, and southern Ontario, Canada). The wide geographic distribution of infested fields within the Michigan growing area suggests the entire region should monitor for symptoms, increase rotation to nonhost crops, and consider planting rhizomania resistant sugar beet cultivars to infested fields. References:(1) J. E. Duffus et al. Plant Dis. 68:251, 1984. (2) J. E. Duffus. Rhizomania. Pages 29–30 in: Compendium of Beet Diseases and Insects, E. D. Whitney and J. E. Duffus eds. The American Phytopathological Society, St. Paul, MN, 1986. (3) G. C. Wisler et al. Plant Dis. 83:864, 1999.

No abstract

No abstract

of organic matter. The timing and method of nitrogen applications is as important as the nitrogen rate. Nitrogen fertilizer should be applied close the the planting date. Applying nitrogen after the six leaf stage will depress sugarbeet quality. Five nitrogen fertility trials were conducted from 2008 to 2010 comparing nitrogen rates, application timings and application methods. Information from three of the trials is not considered to be reliable due to field problems including sugarbeet cyst nematode infestations and soil crusting. Results from the two good quality trials are discussed in this paper. Research Objectives:The objectives of this research program are: 1) Evaluate nitrogen rates (50, 100 and 150 lbs nitrogen ai/A); 2) Evaluate application timings and methods including: a) Pre-plant incorporated (PPI); b) Starter (2x2) applied at planting (nitrogen applied two inches to the side of the row and two inches below the seed depth); and c) Side-dress nitrogen (SD) (applied at the 4 leaf stage with a fluted coulted applicator with stream jet nozzles following the coulters). Materials and Methods:These were small plot replicated trials. A Monosem six row planter modified for research was used to plant the trials. Sugarbeets were planted one inch deep. In 2008 the plots were planted thick and thinned to 180 beets per 100 foot of row at the four leaf stage. In 2010, beets were planted to stand at a four inch spacing and an average stand of 205 beets per 100 ft of row was achieved. The 2010 trial had a lot of corn residue left from the previous year. We were able to plant with row cleaners, however, ridges were formed between the rows at planting and the sugarbeet seeds were planted in a depression. The nitrogen treatments were applied as