Herbicide Effects on Sugarcane Growth, Pythium Root Rot, and Pythium arrhenomanes

Abstract

Six herbicides were evaluated for their effects on Pythium root rot and growth of sugarcane in greenhouse experiments and on in vitro mycelial growth rate of Pythium arrhenomanes. Pendimethalin and atrazine were most inhibitory to mycelial growth, but neither reduced root rot severity. Asulam, atrazine, and metribuzin were not phytotoxic to sugarcane and did not affect root rot symptom severity in clay loam or silt loam field soils. Atrazine and metribuzin increased shoot number, and atrazine increased total shoot weight for treated plants in silt loam soil. Glyphosate, pendimethalin, and terbacil were phytotoxic to sugarcane. These herbicides increased root rot severity, but the extent to which growth reductions resulted from increased disease severity or from direct herbicide injury was not clear. Adverse effects on plant growth and root rot severity were greater in clay loam than in silt loam soil. The results suggest that sugarcane injury from some herbicides is compounded by increased severity of root rot.

Variation of Pythium-induced cocoyam root rot severity in response to soil type

“…From literature, high silt content favours plant diseases caused by Pythium spp. Sugarcane root rot caused by Pythium arrehenomanes was severe in silt loam soil (Dissanayake et al, 1998). Johnson et al (1978) reported abundant Pythium ultimum in cotton seedlings growing in silt loam soils.…”

Effect of five postemergence herbicides on red clover shoot and root growth in greenhouse studies

“…Besides affecting target weeds, herbicides may interact in several ways with plants and soil microorganisms that may influence the plant-pathogen relationship (Altman and Rovira 1989;Dissanayake et al 1998). It is known that herbicides produce changes in the physiology and development of crop plants, thus increasing disease susceptibility.…”

Unexpected Side Effects of Herbicides: Modulation of Plant-Pathogen Interactions

“…Furthermore, root rot symptom severity was not reduced. However, atrazine inhibited mycelial growth of P. arrenomanes in vitro when applied at the label rate (Dissanayake et al, 1998). The mechanism of root and shoot growth stimulation of triazine herbicides was shown to be an increase in the activity of nitrite reductase and transaminase (Ries et al, 1967) and seem also to refer to pea and sweet corn (Wu et al, 1972).…”

“…Thus, the herbicide seems to reduce the plant's ability to protect itself against pathogens. Glyphosate was also shown to be phytotoxic to sugarcane and herbicide treatment resulted in increased disease severity caused by Pythium arrenomanes (Dissanayake et al 1998). Furthermore, glyphosate application caused injury and death of Lolium multiflorum as a result of increased Pythium root rot (Kawate and Appleby, 1987).…”

“…Dissanayake et al (1998) and Canady et al (1986) reported that pendimethalin and trifluralin inhibited mycelial growth of Pythium arrhenomones and root colonization of Macrophomia phaseolina, respectively. However, both herbicides seem to be able to increase disease incidence of seedling damping-off caused by Rhizoctonia solani in cotton (Neubauer & Avizohar-Hershenson, 1973) and germination of sclerotia produced by Sclerotinia sclerotiorum (Radke & Grau, 1986).…”