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Eye on Potatoes: Treating late blight, pink rot with phosphorous acid

phosphorous acid effective protection from pink rot


March 7, 2008
By Eye On Potatoes

Topics

Two Maritime potato researchers
believe phosphorous acid may be the key to effective protection against
pink rot and late blight.

Written by Alison Finnamore

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Dr. Khalil Al-Mughrabi (left), a plant pathologist with the New Brunswick Department of Agriculture, and Dr. Rick Peters (right), a research scientist with Agriculture and Agri-Food Canada, are investigating  ways of fighting late blight and pink rot.  Photo by Allison Finnamore

Two Maritime potato researchers believe phosphorous acid may be the key to effective protection against pink rot and late blight.

Dr. Khalil Al-Mughrabi, a plant pathologist with the New Brunswick Department of Agriculture, and Dr. Rick Peters, a research scientist with Agriculture and Agri-Food Canada specializing in potato pathology, are investigating ways of fighting the two devastating potato diseases. The A2 strain of late blight, which is metalaxyl-m resistant, continues to be predominant in the region and there are indications thatpink rot is developing resistance to metalaxyl-m as well.

“Clearly, other options of the management of late blight and pink rot are needed by growers,” state the researchers.

From their research in 2005 and 2006, Dr. Al-Mughrabi and Dr. Peters discovered that applying foliar applications of products containing phosphorous acid provided excellent control of both late blight and pink rot in tubers. This control was equal to or better than control with metalaxyl-m. Higher rates of foliar application provided better tuber rot control than lower rates while applications made after infection were less effective than preventive applications.

The researchers also determined metalaxyl-m applied in-furrow at planting is a feasible control of pink rot, even with the metalaxyl-m-sensitive strain of the disease. Their results also found that foliar and drench applications of phosphorous acid provides good control of late blight and pink rot plus, when applied before infection of the tubers occurs, provides good post-harvest protection against pink rot.

The researchers believe late blight insensitivity to metalaxyl-m started in Canada in 1994 when the new A2 strain arrived in potato-producing areas of the country. Inspections in 2006 reveal the A2 metalaxyl-m resistant strain still exists.

With pink rot, most strains in Canada remain sensitive to metalaxyl-m, but
samples collected in New Brunswick in 2005 show some resistance.

With those results in mind, researchers set out to find a viable alternative to meta-laxyl-m. During field trials, the efficacy of in-furrow applications of mono and di-basic sodium, potassium and ammonium phosphites, and metalaxyl-m were tested against pink rot infection. Root drench foliar applications of mono and di-potassium salts of phosphorous acid at various rates and times were also evaluated. They were then compared to foliar application of mono and di-basic sodium, potassium and ammonium phosphites and in-furrow application of metalaxyl-m on pink rot and late blight trials in New Brunswick and Prince Edward Island in 2006.