Comparison of Progress of Brown Rust and Orange Rust and Conditions Conducive for Severe Epidemic Development During the Sugarcane Crop Season in Florida

Abstract

Brown rust (caused by Puccinia melanocephala) and orange rust (caused by P. kuehnii) are two major diseases of sugarcane in Florida. To better understand the epidemiology of these two rusts, disease severity and weather variables were monitored for two seasons in cultivars CL90-4725 (susceptible to brown rust and resistant to orange rust) and CL85-1040 (susceptible to orange rust and resistant to brown rust). Brown rust was most severe during mid-May to mid-July, whereas orange rust severity peaked during two periods: mid-May to early August and then November to December. Overall, disease severity was higher for orange rust than for brown rust. Maximum disease severity was correlated with the number of hours at night with an average temperature of 20 to 22.2°C for brown rust one season and orange rust both seasons. Slightly higher correlation was obtained when relative humidity above 90% was included in the number of hours at night with an average temperature of 20 to 22.2°C for brown rust but not orange rust, suggesting that leaf wetness is not a limiting factor for either disease in Florida. Epidemics of brown rust began at lower night temperatures (16.7 to 22.2°C) in one season, but epidemics of orange rust lasted longer under higher temperatures. The correlation of rust severity on recently emerged leaves with conducive temperatures recorded in 10-, 20-, or 30-day windows starting 7 days before disease assessment suggested that earlier inoculum production is needed to create severe epidemics that result in yield loss.

Sugarcane Rust: Changing Disease Dynamics and Its Management

“…The uredospores of P. melanocephala germinated from 20 to 32°C and at 31°C, 40% of spores germinated and stopped germinating at 33°C. The germination of P. kuehnii uredospores dropped from 65% at 29°C to 18% at 30°C and was zero at 31°C (Sanjel et al 2019).…”

“…Whereas triazole (metconazole) and carboxamide (fluxapyroxad) fungicides were highly effective in reducing spore germination only at higher concentrations @ 10 μg/ml. Further it was observed that P. melanocephala is highly sensitive than P. kuehnii against the same concentration of fungicides metconazole and fluxapyroxad (Chaulagain et al 2019).…”

“…During 2014, the brown rust epidemic was reported in late March due to warmer environment favouring P. melanocephala (Sanjel et al 2019).…”

“…In Florida, spraying of fluxapyroxad + pyraclostrobin fungicide at three week-intervals on a popular variety CP 96-1252 during early, mid, and late season in the brown rust infected field resulted in 40-42% less rust severity than the untreated control. The fungicides also helped in 27-35% increase in mean stalk weight and minimum of two spraying are recommended for effective control of brown rust in Florida (Chaulagain et al 2019). The fungicide application at the initial time of orange rust appearance resulted in the lowest rust severity and development throughout the season and enhanced mean stalk weight.…”

Reaction of sugarcane genotypes to brown and to orange rust by leaf whorl inoculation

“…The average temperature between the inoculation and plant evaluation (30 days) was 21.5 ºC, with a minimum of 15.5 ºC and a maximum of 25.7 ºC, and according to SANJEL et al (2019) the ideal mean temperature for the development of both rusts is between 20 and 22.2 °C. Average relative humidity of air during 30 days was 80%, with accumulated precipitation of 177.6 mm.…”