Potato Review

12 POTATO REVIEW SEPTEMBER/OCTOBER 2020 DISEASES T oo many people in the potato industry have taken their eye o the ball, allowing the risks of black scurf and black dot to dominate their seed treatment strategies and overlooking the losses and cost impacts that can be caused by dry rot, gangrene and skin spot, it has been claimed. is has been exacerbated by the loss of chemical formulations to control the key “early base disease”. Independent potato consultants David Turner and Paul Overton believe new thought processes are needed to ensure the historic diseases don’t take their toll on both seed and ware crops. “It used to be standard practice to apply Storite Super ( iabendazole and Imazalil co form,withdrawn from the market) early on in all seed storage and grading, and it was required in most seed contracts,” said David. “But unfortunately, owing to timing and application issues, early application of Gavel & Storite Excel has dramatically reduced.” It is possible to apply Gavel (imazalil ) and Storite Excel ( iabendazole) as individual products but issues with tank mixing and labels make the application window very small, he said. e lack of clearance for animal feed of treated potatoes is also causing major Historic enemies are making a return Old diseases pose new challenges to the current seed and ware industry. problems for several products and solutions are being sought as it’s creating di culties for both growers and agronomists. is is creating “a perfect storm” for these diseases to get a foot hold back in the industry. e loss of Diquat to give growers a fast burn down and skin set allows seed diseases a chance to establish. Many of the most popular varieties are susceptible and have major weakness against dry rot, gangrene and skin spot. Early storage issues e current industry practice of harvesting straight into boxes may have cost and e ciency savings but has caused issues in the early stages of storage. “Fast harvesting and the ability to put the boxes straight on a drying wall is very attractive to growers and we need to work with this desire, but we need to recognise the problems,” said Paul. “Currently under-size and over-size tubers cannot be treated, ese are needed for other non-seed markets. e costs of treating possible waste tubers is high and bad practice. Harvesting straight into boxes also causes several application problems for growers while placing applicators in the process is problematic. Good sta training is therefore essential.” Water volume and the fear of “over wetting” of crop at treatment has always been a fear for both growers and advisors. e investment by growers on drying walls and cold storage has many bene ts, however will not control Dry Rot, Gangrene & Skin Spot on their own. A vast number of Varieties currently in the market place are susceptible to Dry Rot, Gangrene & Skin Spot. Paul said: “ ere is some very good research work being done by Innes Jessman and the SRUC team on the chemical retention on tubers plus the dose response of Gravel, Storite Excel and Maxim 100FS on early storage diseases. But I agree with a comment made by Eric Anderson of Scottish Agronomy that there is a real need for a new look at the latent tuber species of these diseases in the seed production system and any shift in their sensitivity to current chemistry, as the last work was done in the late 1970s.” Application and equipment Application equipment should be set up and calibrated correctly, David stressed. is should not be a problem at two litres per ton with a well-positioned applicator giving good coverage even at high throughputs. David said: “Applicators are bespoke to each farmer’s system. e basic elements of pump tank and nozzles are common to all set-ups but from there onwards grower can opt for direct injection and other bespoke elements to t their system. Grower uptake and investments in a new system in Scotland have been impressive. e use of a Team Sprayers Application methods are changing. Dry rot.