Factors affecting the development and control of black dot on potato tubers

Abstract

Field trials were carried out over a 4 year period (2004)(2005)(2006)(2007) to determine the effect of agronomic factors, specifically cultivar resistance, irrigation, crop duration and chemical control (in-furrow application of azoxystrobin), on black dot development on potato tubers grown in fields where soilborne inoculum of Colletotrichum coccodes was present. In 2004In , 2005In and 2006, two field trials were performed each year and in 2007, 19 mini-field trials were carried out across Scotland and England. Cultivar resistance was clearly demonstrated to be an effective method of reducing black dot disease severity on tubers (described here as the percentage of unmarketable tubers, i.e. those with symptoms covering a surface area of >10%). In the four field trials carried out in 2004 and 2005, in irrigated and fungicide-untreated plots, 43Á8% of tubers of cv. Maris Piper were unmarketable, compared with 17Á0% of tubers of cv. Sante. Assessments of disease development on underground plant parts (stems, stolons and roots) revealed that cultivar resistance acted only at the tuber level, as disease symptoms on other parts were often high irrespective of published disease resistance ratings. Irrigation increased the severity of disease on tubers in two trials (England 2004 and 2006), but its effect was less significant when rainfall was high. Delaying harvest by 2 weeks increased disease severity in all six trials, whilst application of azoxystrobin consistently reduced black dot severity. There were significant interactions between factors. The results clearly show how black dot disease severity can be reduced through an integrated approach to disease management.

The effect of post‐harvest storage conditions on the development of black dot (Colletotrichum coccodes) on potato in crops grown for different durations

“…Brierley et al . () demonstrated that in four out of six field trials, extending crop duration by 2 weeks increased black dot severity. The present study establishes that extending crop duration by up to 6 weeks increases the severity of black dot on progeny tubers.…”

“…Brierley et al . () demonstrated that at a site in England, black dot developed on underground stems of Maris Piper at 90 days after planting (DAP) and on tubers at 104 DAP, well before defoliation, which occurred at 118 DAP. Data for crops grown in four consecutive years showed that the relationship between black dot and crop duration was almost entirely accounted for by the total length of time that the crop was in the ground, and in fact crop duration has a consistent and significant effect on disease severity.…”

“…Research to improve skin finish demonstrated the importance of minimizing crop duration in controlling black dot in cultivar Estima (Wiltshire et al ., ), and Brierley et al . () demonstrated that increasing crop duration by 2 weeks increased the severity of black dot at harvest in four out of six field trials. The fungicide azoxystrobin was effective at reducing black dot on progeny tubers when applied over four applications: in‐furrow at planting and foliar applications 60, 83 and 93 days after planting, each at a rate of 218.6 g a.i.…”

“…ha −1 (Nitzan et al ., ); and as a single in‐furrow application at planting at a rate of 750 g a.i. ha −1 (Brierley et al ., ). Although there is variation in cultivar susceptibility to black dot, which can provide a substantial level of disease control, cultivar choice is often based on market requirements rather than disease resistance.…”

Vegetative compatibility groups in Colletotrichum coccodes from Turkey and their aggressiveness to potato

“…The pathogen survives in soil for at least 8 years as sclerotia (Dillard & Cobb, ). Fungicide applications reduce the incidence and severity of black dot disease on both stems and progeny tubers, but these applications are not economical or provide inadequate control (Nitzan et al ., ; Cummings & Johnson, ; Brierley et al ., ). An integrated approach incorporating diagnostics, risk assessment and disease management tactics, to reduce initial inoculum and the rate of disease development, as well as appropriate potato storage conditions are more likely to provide more durable disease control (Lees & Hilton, ; Johnson et al ., ).…”