James F. Stewart

Effect of Headline (pyraclostrobin) as a yield enhancer for sugarbeets in Michigan.

Headline is an effective fungicide for controlling Cercospora leafspot. It has also been promoted as a yield enhancer beyond its effect as a fungicide. Some farmers use Headline for this yield improvement on other crops, and a benefit has been found to Headline on sugarbeets in some research in other areas. Michigan Sugar Company has tested this claim for four years and Sugarbeet Advancement tested two locations for one year.

Evaluation of XBEEJTM, an enhanced sugarbeet priming system

Sugarbeet emergence is a key factor in production management of a sugarbeet crop. Cold soils, soil crusting and other factors can impact speed of emergence. Faster seed germination and stand establishment can increase yield and quality of sugarbeet. Primed seed is used to ensure quicker seed germination and stand establishment. Field trials were established to evaluate XBEET™ seed priming system developed by Germains Technology Group (GTG). This enhanced priming system was enabled by various technological breakthroughs in seed lot calibration, machinery and process control. Studies were conducted in Minnesota at the Northwest Research and Outreach Center (NWROC) in Crookston as well as at multiple locations in Michigan. The objectives of the studies were to compare XBEET™ treated sugarbeet seed and GTG standard PAT priming treatment with non-primed seed. XBEET™ priming provided superior speed of emergence, final stand, yield and recoverable white sugar per hectare in all trials with PAT being intermediate compared to non-primed seed.

RHIZOCTONIA SOLANI; CONTROL MEASURES IN MICHIGAN

Rhizoctonia solani root and crown rot is a serious problem in the Michigan Sugar Company growing area. Company Agriculturists would recommend the use of a susceptible variety and no fungicide on only 1.1% of the acres. Only these few acres would be considered to have no Rhizoctonia. Their recommendation for the use of a tolerant variety increased from 50% of the acres for 2011 to 69% for 2013. Their recommendation for the use of a tolerant variety and two Quadris (Azoxystrobin) applications increased from 15% to 36% for the same two year period. There are two reasons for these changes; disease pressure is increasing and there is now one variety being sold that has good production and Rhizoctonia tolerance. We started testing Quadris for Rhizoctonia control in 1999. Trials have confirmed that Quadris is the most effective product to control Rhizoctonia in our growing area. We continue trials to find the most effective foliar application time and the best rate and band width for T-band application at planting. There is tolerance to Rhizoctonia in some varieties available but there is a large difference in tolerance levels. There are a few varieties with a good level of tolerance but most are poor.

INFLUENCE OF EARLY HARVEST IN MICHIGAN ON SUGARBEET YIELD, QUALITY AND GROWER INCOME

Introduction: Sugarbeet yields in Michigan increased by approximately ten tons per acre during the past decade. Michigan Sugar Company has improved factory efficiency and capacity but at a slower rate than sugarbeet yield increases. In order to process the increased sugarbeet yields our Cooperative needs to reduce acreage, increase processing capacity, start slice earlier or finish processing later in the spring. Running the factories into late March or early April is very risky as warming temperatures can cause sugarbeet piles to spoil. Michigan Sugar Company has increased the capacity of the factories, reduced acreage when necessary and we are processing later in the spring than in past years. However, to maximize income sugar processing needs to begin around September 1 or even earlier if the sugarbeet yield is above normal. Michigan Sugar has developed an early harvest incentive payment program to compensate growers for early harvest and to ensure an uninterrupted supply of sugarbeets after processing begins. Small plot replicated trials have been conducted in recent years to gain a better understanding of sugarbeet yield and quality levels in our growing region during mid to late August and September.

CERCOSPORA BETICOLA INSENSITIVITY IN MICHIGAN AND MICHIGAN SUGAR COMPANY’S RESISTANCE MANAGEMENT STRATEGIES

Introduction Cercospora leafspot, caused by the fungus Cercospora beticola, is the most serious foliar disease of sugarbeets in Michigan. Research trials conducted in Michigan show that poorly controlled Cercospora leafspot (25 to 50% canopy desiccation) resulted in losses of 2 to 4 tons per acre and from 0.25 to 1.0 point of sucrose. The disease is managed with an integrated program which includes proper rotations, varietal tolerance and fungicide sprays. Most of the varieties in Michigan have relatively good tolerance to Cercospora; however, our highest producing varieties are quite susceptible to the disease. Michigan growers benefit from the predictive model BEETcast, which monitors leaf wetness and temperatures at over 50 locations and predicts optimum fungicide application timings. Cercospora infection levels were high in 2005 and 2006 then trended lower until 2010, 2011 and late season of 2012, when disease levels increased significantly. For the most part, Cercospora leafspot is adequately controlled in Michigan. However, with the introduction of high producing varieties that have less disease tolerance some control problems have occurred. More aggressive Cercospora control programs have been implemented by the Cooperative which has been successful in protecting varieties with low levels of Cercospora resistance from yield and quality losses. The use of strobilurin and triazole fungicides along with the BEETcast spray model improved the level of Cercospora leafspot control in Michigan significantly. By 2008, Michigan Sugar Company growers were planting Roundup Ready and nematode tolerant varieties without adequate tolerance to Cercospora. In 2010, control of Cercospora became more difficult despite more aggressive BEETcast spray recommendations. The following year, QoI resistant isolates were identified to harbor the G143A mutation. This mutation was discovered in Michigan Sugar Company’s efficacy trial near Elkton, MI, and was confirmed by Michigan State University and USDA-ARS (Figure 1). To effectively manage Cercospora in Michigan, tank-mixed fungicides were recommended prior to the first sign of the leafspot. Application timing was also modified by Cercospora tolerance level of the variety being grown. Fungicide insensitivity in sugarbeets can be managed; however, growers needed to follow a resistance management program set by Michigan Sugar Company.

EFFECT OF PLANTING DATE AND POPULATION ON SUGARBEET YIELD AND QUALITY

In the effort to improve beet yield and quality in Michigan, planting date as well as the populations at those dates has become an important topic. The decision to risk planting early as well as the decision to replant a lower population field is a major concern through the first few weeks of the growing season. Three trials have been conducted testing multiple dates of planting, as well as various populations on those dates. The goal of these trials was to better understand the benefits or drawbacks from an early planting, as well as determining if certain populations at earlier dates can perform better than higher populations at later dates.

ASSESSMENT OF STROBILURIN RESISTANCE IN CERCOSPORA BETICOLA ON SUGAR BEET IN MICHIGAN AND NEBRASKA, USA

Cercospora leaf spot (CLS) caused by Cercospora beticola Sacc. is the most important foliar disease of sugar beet (Beta vulgaris) worldwide (Jacobsen & Franc, 2009). CLS is controlled mainly with fungicides, including strobilurins (FRAC group 11). Resistance to strobilurins in C. beticola was first confirmed in 2011 from several fields in Michigan and in one field in Nebraska, USA (Kirk et al. 2012) following anecdotal reports of reduced fungicide efficacy. In these fields, sugar beet treated with strobilurins had severe CLS and diminished control was also noted in small plot trials in Michigan. Individual leaf spot lesions were sampled from leaves and grown on sugar beet leaf extract agar (SBLEA). A conidial germination bioassay was done on SBLEA amended with pyraclostrobin, azoxystrobin or trifloxystrobin at 0, 0.001, 0.01, 0.1, 1, 10, or 100 μg/ml supplemented with salicylhydroxamic acid (SHAM) to block the alternate oxidation pathway (Olaya et al., 1998). After 24 h incubation at 22°C, under ambient light, the percentage of germinated conidia (n = 50) was calculated from three replicates per treatment. Germination was recorded as positive when the germ tube was at least half the length of the conidium. A representative wild type isolate was unable to germinate over the 0.01 μg/ml concentration. Effective concentration for 50% reduction in germination (EC50) values for each isolate were calculated by regression analysis of percentage spore germination vs. the log fungicide concentration using Sigmaplot Version 9.01 (Systat Software, Chicago). The EC50 for the sensitive isolate was <0.01 μg/ml. Isolates from several counties in Michigan had uninhibited germination and EC50 values exceeded the highest concentration tested. Isolates also grew on spiral gradient dilution plates (Forster et al., 2004) amended with the three strobilurins. Two isolates were obtained from Nebraska and each showed a similar response to strobilurin fungicides in amended plate assays. In 2012, widespread strobilurin resistance was recorded in isolates of C. beticola collected in Michigan although a few isolates submitted to the program were sensitive. Pure cultures of a subset of resistant isolates were grown in potato dextrose broth at 125 rpm, and DNA extracted. A fragment of the cytochrome b (CYTB) gene was amplified by PCR using the C. beticola primers of Malandrakis et al. (2011) to amplify the region of the CYTB gene likely to contain resistance mutations (Malandrakis et al., 2011). This fragment was sequenced at the Genomics Technology Support Facility (MSU, East Lansing, MI) and showed 99% identity with both the C. beticola cytochrome b mRNA, partial sequence (GenBank Accession No. EF176921.1) and the C. kikuchii mitochondrial gene for cytochrome b partial sequence (AB231863.1). Sequence results revealed that each resistant isolate contained a change in codon 143 that is predicted to lead to a substitution of G143A, which was demonstrated to confer QoI resistance in several other fungi (Ma & Michailides, 2005). All Michigan isolates with the G143A mutation germinated at 100 μg/ml pyraclostrobin (50% of conidia), while sensitive isolates that lacked the mutation failed to grow. Additional isolates that contained the G143A mutation included representatives from Michigan and Nebraska. A high proportion of isolates (~90%) from the commercial growing region that were screened in 2012 have been found to contain the G143A mutation by PCR-RFLP screening using digestion of the above PCR products. These findings reveal that reduced CLS control in some commercial sugar beet fields may be due to the development of resistance to strobilurins. In 2012, three consecutive applications of pyraclostrobin treatments failed to adequately control C. beticola at the Michigan State University (MSU) Saginaw Valley Research and Extension Center. In addition to the strobilurin sensitivity monitoring, the program at MSU also tests for development of insensitivity in the CLS population to Difenoconazole (Inspire); Tetraconazole (Eminent); Prothioconazole (Proline), Flutriafol (Topguard), Thiophanate-methyl (Topsin) and TPTH (Tin). Some triazole-insensitive isolates have been recovered in MI beet fields over the past 10 years but the proportion is low for all these fungicides, however in 2012, nearly 100% of isolates tested were insensitive to Thiophanate-methyl. The challenges for the sugarbeet industry with respect to CLS control include a lack of products from diverse FRAC groups; a general increase in inoculum due to the prevalence of CLS susceptible cultivars grown in the Michigan and Ontario sugar beet production regions; an increase in proportion of isolates insensitive to strobilurins (e.g. pyraclostrobin); the industry is inexperienced with tank mixes and has a perceived distrust of TPTH (label restrictions). In addition, to the lack of available chemistries from diverse FRAC groups there is confusion on what to start and end a program with in order to delay the onset of insensitivity to other fungicides. A strobilurin is the mainstay for Rhizoctonia control in MI therefore there is a need for new products with alternative modes of action so that a CLS disease management program starts with a product not used earlier in the season for other disease management. Acknowledgements The authors would like to thank Tom Goodwill for his excellent technical assistance.

Evaluate nitrogen rates, application timings and application methods for sugarbeets in Michigan

Introduction: Nitrogen is generally the most yield limiting nutrient in sugarbeet production in Michigan. Adequate nitrogen supplies are needed early in the season to promote early growth and canopy development. Smaller amounts of nitrogen are needed during the middle of the season to maintain the canopy and promote root growth and sugar storage. Excess nitrogen late in the season will decrease sugar levels and increase impurities. Michigan State University recommends applying four pounds of actual nitrogen per acre for each expected ton of sugarbeet yield. This recommendation is modified by other factors including the previous crop. Sugarbeets following corn need an additional 30 pounds of nitrogen to reach maximum sugar per acre yields. When growing sugarbeets after alfalfa or clover less added nitrogen is needed. The MSU recommendations are very similar to the Michigan Sugar Company nitrogen recommendations. Michigan Sugar recommends 90 to 120 pounds of nitrogen following soybeans or dry beans and up to 150 pounds following wheat or corn. Sugarbeets following corn with heavy residue require more nitrogen than sugarbeets following wheat. Considerations are also made for alfalfa or clover as the previous crop, for recent manure applications and for soils with high levels 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.

Variety approval “points” system based upon yield, quality, emergence and resistance traits

Introduction Sugarbeet yields have improved significantly in Michigan over the past ten years, however, quality levels have remained relatively constant. Our variety improvement efforts have focused on developing varieties with Rhizomania, Rhizoctonia and other disease resistance traits in addition to developing glyphosate tolerant varieties. Michigan Sugar Company has established new goals of improving yield and quality levels significantly over the next five years. We have evaluated several varieties with high yield and quality potential but these varieties have not been able to not pass our variety approval system. A new approval system has been developed which considers more traits and provides substantial incentives for improved quality. The Cercospora leafspot approval level has been changed in the new system so that varieties with less Cercospora resistance can be approved. The new approval system considers sugarbeet yield, quality, emergence and tolerances to Cercospora, Rhizomania, Rhizoctonia and root aphid for approval. The previous system considered only sugarbeet yield, quality and Cercospora tolerance. Table 1 illustrates the differences between the new and old variety approval systems.

Rhizoctonia solani; the extent of the problem and control measures in Michigan

Introduction Rhizoctonia solani has been an extensive problem in Michigan for many years. We have been testing varieties with a level of tolerance to Rhizoctonia since 1990. We started testing Quadris for Rhizoctonia control in 1999. Rhizoctonia is most severe in areas where sugarbeets have been grown the longest but is found in all areas. In 1986 sugarbeet production expanded in Michigan and Rhizoctonia was found in fields where beets had never been grown before. Dry beans have been a common crop in the beet growing area of Michigan and are probably the reason for Rhizoctonia to be present in those fields. If a farmer did not have dry beans they probably grew soybeans and both are hosts for the strain AG 2-2 IV. Until recently corn was recommended as a good rotation crop to reduce Rhizoctonia. The strain AG 2-2 IIIB is becoming more common and is now found about 50% of the time. Corn is a host for the 2-2 IIIB strain. To evaluate the extent of the Rhizoctonia problem throughout our growing area we did a survey of what the agriculturists would recommend for variety tolerance use and Quadris fungicide application for Rhizoctonia control (Table 1). There are very few acres that can use a susceptible variety and no Quadris application and most of those acres are in Ontario, Canada. Only those 4.8% of the acres would be considered Rhizoctonia free. The agriculturist’s recommendation is split about even between using a susceptible and a tolerant variety and over 30% of the acres should have two applications of Quadris.