Wet soil conditions and very high disease levels pose the biggest risk to crops, with wet rots likely to cause most storage headaches this season.

Growers will have to be vigilant for tuber blight, blackleg and soft rots including pink rot, as soil and weather conditions continue to favour these diseases in the field.

Growers will need to be quite judgemental about which crops are going to be stored and which aren’t, says Adrian Cunnington of the Potato Council’s Sutton Bridge Crop Storage Research. “We need people to be looking at crops in the field and digging some samples so they can get an appreciation as to what they’re dealing with. The risk of putting it into store and then trying to sort out a major problem would be too high.”

Identify the risk

High levels of foliar late blight will pose a risk of tuber blight. “Growers will have appreciation as to what the level of blight has been in the field and that will give an indication of what the extent of tuber blight risk will be,” he says. Blight can still continue to spread late in the season, so maintaining blight control right up to burn off is important, he warns.

Tuber blight is characterised by rusty brown patches on the skin where blight spores have washed down the plant to the tuber. The infection gets under the skin which can’t always be seen which will break down later on in store. Growers need to be cutting tubers in the field to assess the damage, he says.

Similarly blackleg levels are reported to be high this season. Foliage symptoms in the growing crop will indicate current levels, but it can change quite dramatically when we start getting warm and moist weather, warns Mr Cunnington. Tubers are characterised by brown sunken water soaked areas on the surface. The infection comes from the stolon or through wounds caused during harvest and causes a rot inside the tuber.

Most crops will be able to be stored long term, but if there are very high levels of blight or blackleg the risks of storing these crops will probably be too high and in these cases, growers will need to sell off the field or consider some temporary storage if they have the capability to do so.

The main concern for Jim Aitken, senior field manager at Branston in Scotland, is the condition of the soil and the risk from soft rots from wet and waterlogged soils. “Because we are facing a high price season it will be a temptation for growers to keep lifting into wet areas thinking that someone will handle them because they have to be worth something. Wet, rotting potatoes can write off stocks.

“This is the season where you’ll be able to sell virtually any potato providing it’s not rotting.”

Blackleg and soft rots management checklist

• Avoid harvesting in wet conditions
• Ensure good skin set and minimise damage during harvest to prevent moisture loss and infection
• Do not store if more than 1% rot found, or provide temporary storage
• Segregate tramlines, headlands and known wet areas within store
• Where possible grade and discard infected tubers, but maintain hygiene on equipment
• Priority to dry as quickly as possible maintaining good airflow
• Pull down temperatures as soon as possible after drying on seed and table crops
• Avoid condensation at all costs
• Monitor stores at least weekly and higher risk segregated areas more often
• Maintain a dialogue with packers and processors on the management of stocks
• Contact the Potato Council storage advice line on 0800 02 82 11 for specific tips and information

Potatoes don’t have to be literally under water, on some heavy ground that has been lying wet for long periods the lack of oxygen causes them to break down. Potatoes can only stand a short time of that. We have already seen early signs of various strains of bacteria causing breakdown once we have washed and packed them, he says.

Segregate

Mr Aitken’s advice is to keep headlands, tramlines and wet areas separate from the rest of the field and segregate within store. “Keep poorer material to one side and aim to move those as quickly as possible because they are highest risk.”

This is important because the risk is not always that apparent. Growers can have fields that look as if they have drained very well, crops look fine, skins have properly set and lenticels in the growing season have receded and closed off and look sound in store. Yet the infection is already there and there is potential for breakdown in store, he warns. The past two wet summers have shown that careful management by reducing moisture coupled with low temperatures can reduce, but not eliminate the risk, he adds.

Growers can hot box to see what the relative risk of breakdown is. This allows them to prioritise between one crop and another and is a good way of ranking the crops in terms of risk, adds Mr Cunnington. Segregating the high risk won’t put the rest of the crop under threat, which will be especially important in bulk storage situations.

There is also a strong case for grading into store, if feasible. It is better to take wet rot out rather than put into store, but there is a risk of wet rot contamination so equipment needs to be washed down, he adds.

Ventilate

Main priority will to get the crops dry this season through use of the ventilation that is available and the most important thing is to make sure the air is circulating well within the store and is going through as much of the crop as possible and avoiding any short circuits, explains Mr Cunnington.

If there is rot potential then reducing the temperature is also important as rot will tend to develop more quickly at higher temperatures.

But drying is more important than the temperature. The cooling will follow as a secondary effect of the moisture evaporating, he adds.

Dry curing and pulling temperature down later will be dispensed with by Mr Aitken’s growers in Scotland, where potatoes are going into cold storage.

Harvest delays to allow for bulking or poor weather could leave growers lifting into late October and November with some crops then not getting out the ground at all, he warns.

“Growers should be accepting an 80% crop as a good crop this year. So growers need to lower expectations in terms of quantity, their expectations have already been greatly heightened in terms of the price and the returns.”

Harvesting in wet conditions not only increases the risk of bacterial soft rots developing in store but with increased amounts of soil going into store on the potatoes reduce drying efficiency and increase the development of silver scurf and black dot.

Skin blemishes are likely to be of secondary concern this year as those potatoes will still find an outlet. Losses in store could be less than last year because of supply and demand. The biggest loss has already been in the field with yields down 20%, says Mr Aitken.

Depending upon the end market, Mr Aitken suggests growers with risky crops who don’t have cold storage consider selling off potatoes early.

“Scotland has a lot of cold storage, which will not be full because there will not be enough potatoes out there. So if a grower only has ambient or bulk storage Branston as a company will be keen to buy those potatoes or encourage them to be taken to cold stores where space is available.

“I don’t want to see potatoes going off in ambient stores when there are cold stores only 80% full.”

Disease reports

Pink rot
A potential threat with reports of it in the West. It is exacerbated by wet, warm conditions in August especially in water saturated fields. The fungal rot is characterised by internal salmon pink coloration of cut tuber after 15-20 minutes exposure to air before turning black.

Pink rot breaks down very quickly into a wet rot and will spread in store. Management is the same for other soft rots.

Hollow heart
There are a few reports that some varieties, Marfona being the highest risk, have a higher risk of hollow heart this season which is caused by differential growth rates in dry and wet periods leaving a small cavity in the centre of the tuber.

Although they don’t store any differently it is not worth incurring the additional storage cost and will require extra vigilance to identify in the field.

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