Cold crop planting 'increases risk of infection'

Following what most growers regard as one of the most difficult seasons in recent experience, many potato crops won't have an easy start this season, says Agrovista Agronomist Andy Steven.

Looking after seed and ware potato crops in Northern Scotland, Steven warns of possible wet soils at planting, especially in areas further south where the weather has been wettest.

"Planting in to cold wet soils means slow plant emergence, which increases the risk of early infection by Rhizoctonia solani, the cause of stem canker and black scurf on tubers," he said.

Stem canker affects sprout development and results in uneven and patchy emergence and in severe cases emergence can be significantly reduced.

Black scurf is a blemish disease that seriously reduces pre-pack quality and is only tolerated at very low levels in potato seed.

"Freedom from tuber blemish diseases is particularly important for the markets we are growing for.

"Some of our seed is being exported to Egypt, Saudi Arabia and Thailand – these are markets particularly sensitive to black scurf."

Steven said growers to look at their soil type to help identify crops which will be at highest risk of Rhizoctonia infection and may need a seed treatment.

"In my area, the sandy loam soils in Morayshire will be some of the first to be planted, so crops will be growing early in colder soils so are more at risk of infection," he said.

"Washing seed samples and visually inspecting for black scurf and surface netting on tubers is a must before planting to further identify at risk crops and plan an appropriate seed treatment."

A further affect of stem canker infection is stolon pruning which can result in a variable size distribution of tubers within the daughter crop.

"Producing tubers of a uniform size is particularly important in crops produced for punnet prepacks, such as Maris Peer," comments Steven.

"In these crops minimizing stolon pruning is vital."

Treating seed tubers with a fungicide treatment such as flutolanil (RhiNo) reduces the risk of Rhizoctonia infection and its associated problems, says Andy.

But growers should remember that Rhizoctonia infection is also soil borne and while RhiNo may offer a degree of protection against soil borne infection, avoiding planting into cold wet soils, treatment of soil with azoxystrobin and extending rotations to 1:10 years rather than 1:6 years should be considered where soil borne infection is a significant risk factor.