Evaluation of fungicides for the control of carrot cavity spot

Abstract

Cavity spot is one of the most common and serious diseases of carrot (Daucus carota L). The disease, caused by different species of Pythium, including P. violae Chesters & Hickman, P. sulcatum Pratt & Mitchell and P. sylvaticum Campbell & Hendrix, leads to frequent high rejection rates during grading worldwide. In the area of the city of Québec, the disease is caused mainly by P. sulcatum, P. sylvaticum and P. macrosporum Vaartaja & van der Plaats-Niterink. Cavity spot can be controlled with metalaxyl, but reports are emerging that this treatment show little or no efficacy in many regions. This situation reinforces the need for alternative fungicides. The objectives of the present study were: (1) to determine the sensitivity of 14 pathogenic isolates of P. sulcatum, P. sylvaticum and P. macrosporum collected from carrots produced in the area of the city of Québec to different broad-spectrum and oomycete-specific fungicides (chlorothalonil, etridiazole, fludioxonil, fosetyl-Al, metalaxyl, zoxamide), (2) to evaluate the efficacy of the fungicides in controlling cavity spot, and (3) to evaluate the risk of resistance development of isolates with the best-performing fungicide(s). The determination of EC50 for the fungicides tested showed that most isolates were highly sensitive to both metalaxyl and zoxamide but insensitive to fludioxonil, fosetyl-Al and chlorothalonil. In greenhouse assays, only zoxamide provided significant and consistent disease control as measured by the number of cavity spot lesions caused by P. sulcatum. Investigations into the risk of resistance development to zoxamide showed that, for specific isolates, repeated exposure to the fungicide resulted in a loss of sensitivity.

Differentiation of Pythium spp. from vegetable crops with molecular markers and sensitivity to azoxystrobin and mefenoxam

“…Even more important than the detection of single resistant isolate is investigating the resistance frequency in a given population requiring a minimum number of isolates to be included in the tests. Obviously, many Pythium isolates in our study were sensitive to mefenoxam, which is in accordance with sensitivity reports from other studies . The presence of 19% intermediate resistant isolates along with 36% resistant and 45% sensitive isolates may suggest the occurrence of sexual recombination in some Pythium spp.…”

Incidence and Severity of Cavity Spot of Carrot as Affected by Pigmentation, Temperature, and Rainfall

“…This also promoted healing of lesions and limited lesion expansion and the potential for alloinfection. In this study, it was observed that CS was initiated when mean air temperatures were between 10 and 15°C and that disease was low at temperatures ≥18°C, and is in agreement with other field studies (14,26,35,40,46). McDonald (28) reported that soil temperatures of 16 and 17.5°C during the 6 to 8 weeks after seeding was associated with high CS incidence, and Vivoda et al (46) reported more CS at 15 than at 20 or 25°C.…”

“…The disease is currently managed by using cultural practices such as avoiding fields with a history of CS, growing carrot cultivars on raised plant beds (19), and applying fungicides. Registered products include metalaxyl (Ridomil; Syngenta Crop Protection), an acylalanine (phenylamide) compound that is a systemic fungicide with activity against oomycetes (8,18,25,26,33); and cyazofamid (Ranman; ISK Biosciences Corporation), a phenylimidazole compound with activity against a broad spectrum of oomycetes at very low use rates (33). Management of agronomic aspects of production such as irrigation, soil cultivation, and the length of time crops are grown may all be used to reduce CS; in addition, selecting carrot cultivars with some field resistance may also be beneficial (7).…”

Antifungal activity of aluminium‐containing salts against the development of carrot cavity spot and potato dry rot

“…There are a few efficient chemical options for the control of carrot cavity spot ( P . sulcatum ) such as metalaxyl (Hiltunen & White, ; Martinez et al ., ). This chemical is effective at reducing the incidence of cavity spot; however, it loses its effectiveness because of an increase in its rate of breakdown.…”