Influence of Glyphosate on Rhizoctonia Crown and Root Rot (Rhizoctonia solani) in Glyphosate-Resistant Sugarbeet

Abstract

Previous greenhouse studies with a noncommercial glyphosate-resistant sugarbeet variety indicated that susceptibility to Rhizoctonia crown and root rot could increase after glyphosate was applied. Greenhouse and field experiments were conducted in 2008 and 2009 to determine if glyphosate influenced disease severity in potential commercially available varieties of glyphosate-resistant sugarbeet. In the first greenhouse experiment in 2008, Hilleshög 9027RR, the most tolerant variety to Rhizoctonia crown and root rot, exhibited an increase in disease severity when glyphosate was applied. There were no significant differences between herbicide treatments in Hilleshög 9028RR, and glyphosate decreased disease severity in Hilleshög 9032RR when compared with the no-herbicide treatment. Experiments conducted to determine if glyphosate influenced Rhizoctonia solani growth in vitro indicated that glyphosate did not increase the radial growth of R. solani, except at 10× (190 µg ae ml−1) the normal rate of glyphosate plus ammonium sulfate (AMS). Field and additional greenhouse experiments were conducted using four commercial varieties. Differences in disease severity were observed when comparing varieties, but glyphosate did not significantly influence the severity of Rhizoctonia crown and root rot when compared with the no-herbicide control. Choosing a glyphosate-resistant sugarbeet variety with the best demonstrated tolerance to Rhizoctonia crown and root rot is an important factor in reducing disease severity and maintaining sugarbeet yield.

How glyphosate affects plant disease development: it is more than enhanced susceptibility

“…Subsequent research found no effect of glyphosate resistance or glyphosate resistance on resistance to R. solani. 56,57 In addition, there was no effect of glyphosate on fungicide management of this disease. 56 However, it was noted that different glyphosate resistant sugarbeet varieties do differ in resistance to R. solani.…”

“…However, this effect was not observed in beets that were inoculated with a more virulent F. oxysporum isolate or with R. solani AG‐4. Subsequent research found no effect of glyphosate resistance or glyphosate resistance on resistance to R. solani . In addition, there was no effect of glyphosate on fungicide management of this disease .…”

Glyphosate and fungicide effects on Cercospora leaf spot in four glyphosate-resistant sugar beet (Beta vulgaris) varieties

“…c CLS-program ¼ three fungicide applications; pyraclostrobin followed by tetraconazole followed by trifloxystrobin (rates in text). sugar beet (Barnett et al, 2011(Barnett et al, , 2012. The CLS fungicide program in our experiments on CLS systematically improved yield and sugar quality parameters in both years and, considering the high level of disease pressure and the efficacy of the fungicides used, this was not unexpected.…”

“…Reductions in rust and powdery mildew on glyphosateresistant alfalfa have been reported with glyphosate applications in greenhouse experiments (Foster-Hartnett and Samac, 2008). For soil-borne diseases, some studies have shown no effect on disease severity (Lee et al, 2000;Nelson et al, 2002;Njiti et al, 2003;Barnett et al, 2011Barnett et al, , 2012 while other studies have reported potential for increased disease severity (Sanogo et al, 2000;Nelson et al, 2002;Larson et al, 2006).…”

Soil microbial communities in diverse agroecosystems exposed to glyphosate

“…For example, several studies have observed that GR beets and soybean have increased susceptibility to pathogens when glyphosate is applied at recommended rates [14–16]. One study found no effect of glyphosate on disease induction in GR beets until rates exceeded normal field application rates by one order of magnitude [17]. However, other studies with GR crops have found no influence of glyphosate on disease [18], as well as instances of fungicidal activity against plant pathogens, especially rusts (reviewed by Duke [19]).…”