Potato season review – whatever are we going to do with our weather?

From a cold and wet spring turning to baking hot weather, East Anglian potato crops were tried to their limit this year, reports Norfolk-based independent potato agronomist Andy Alexander.

Planting was four or five weeks late, so rather than earlies, second earlies and maincrop all going in sequence, they were all bunched up together, he reports.

In addition, many growers became nervous that planting would be too late, and went on the land when perhaps they should have waited. This is having repercussions now, as such soils are now suffering from compaction so they are unable to perform as well as they usually do, he says.

Soil management in these conditions is crucial and good drainage can make a huge difference to being able to get on the land sooner. “Drainage has been neglected over the past 30 years, he says. This is partly because it used to be eligible for grants of up to 50 per cent, but more recent schemes have not encouraged drainage. “You need to get soil dry enough to travel on. Even light soils can be unworkable if soil structure is not good enough for you to get on the land.”

Preventing run-off is also crucial. Fields on slopes need small barriers to hold the water and prevent run-off, particularly when they back on to a highway or private gardens.

Moreover, as predicted by Andy, the long cold spring resulted in rhizoctonia becoming an issue in some crops. The Norfolk-based agronomist, who sits on the NFU Potato Forum, points out that while some potato varieties have managed to shrug off this year’s challenges, others suffered patchy emergence and stress.

Once the weather cleared up, it became not only dry, but very hot, and Andy believes this damaged the crops more than the drought. “When you have temperatures of more than 30 deg.C, the crop shuts down and does not even use the water it has access to,” he notes. For example, some experiments when 25mm were applied, showed the crop used 1mm when it would normally be expected to use 5-6mm a day. This illustrated that it was not uptaking enough water to achieve any yield increase.

Many of the potato farms he works with have irrigation, but it is often limited by lack of water and/or infrastructure. “One of the challenges is that the price difference growers receive from irrigated crops may not normally be enough to entice them to invest in irrigation, but this year those which received irrigation can be clearly seen.”

In unirrigated crops this year he has found daughter tubers re-growing, which means that they think a year has passed rather than six months. The problem this creates is that there are changes in the sugar: starch relationship, thereby affecting cooking quality and fry colour.

“We need to think that if we put these affected potatoes into long-term storage until June/July 2019, we will be moving into the unknown as far as taste is concerned.” However, he adds, it could be that the market will be so short of potatoes that it will be willing to handle it.

Andy has found wide differences in how varieties have reacted to stress, which has highlighted nutrition deficiencies in a number of potato crops. Tissue testing indicated magnesium deficiency, which, in some varieties, was illustrated by intercostal yellowing on younger leaves. Others, despite being diagnosed as deficient, did not have pronounced symptoms, he reveals, adding that he believes this could be because of rooting system differences.

“Twenty-five years ago, we didn’t see all this coming, so we need to learn to manage our way through in a responsible, environmentally friendly and profitable way. We need more research and development into irrigation and nutrition. For example, there is a real lack of information on the role played by zinc and boron and other minerals in the crop,”

He draws attention to recent work undertaken on the effect of sulphur, noting that research has found no uptake in yield, although his own work has recorded fewer defects such as internal rust spot.

“We may need to look at varieties to help us respond to adverse weather conditions, perhaps developing early varieties which are able to better cope with more extreme conditions. But the ultimate challenge is getting the end-user to like them and buy them. This is all down to the weather and we need to learn to adapt our varieties and husbandry to our changing environment.”

West Midlands

West Midlands-based potato agronomist Denis Buckley of Highfield Lodge Agronomy, remarks that a wet spring meant that planting was late by around two and a half weeks. “That alone was always going to have an impact on yield, even without the effects of drought,” he says.

“The drought itself (which got going properly in the last week of June) quickly laid bare any inadequacies in irrigation equipment and licences. Looking back at ADAS Irriguide records, it is clear that 200 mm of irrigation was the minimum required to keep the crops growing and avoid secondary growth,” he says, noting that 200 mm is probably twice what would be required in an ‘average’ irrigation season in the West Midlands.

“But, in fact, 250 to 280 mm was required to stop SMDs (soil moisture deficits) from ramping-up to the point where crops were under any sort of drought stress on loamy sands, and few growers have the capacity or licences to apply that volume of water.

“On well-irrigated crops (which were not under drought stress), daily transpiration rates commonly exceeded 5mm per day during this period, and occasionally peaked at around 6mm per day. That’s a lot of water going AWOL!”

He goes on to report that the drought began to break in the second week of August, and this restarted growth in most unirrigated or partially irrigated crops, although unfortunately, that often came in the form of secondary growth. “It remains to be seen what the effects of this will be on quality when these crops are harvested,” he says.

With the full economic cost of irrigation being around £6/ha mm it is clear that the net effect on growers’ costs has been to increase them significantly.  Also, growers (and their staff) have been left exhausted by the battle against the drought, he remarks.

“The only upside of the drought has been dramatically reduced blight risk, although with cooler, wetter weather, that risk is now increasing again, and late outbreaks of foliage blight can and will very quickly translate into tuber blight.”

Unusual season in Scotland

Although in general, conditions for growing potatoes have been less than ideal in 2018, Scotland got off more lightly than England, reports Stephen Hole, sales and logistics manager at seed potato specialists Caithness Potatoes.

Despite very low rainfall, Scotland did not have the very high temperatures which growers further south had to contend with; as a result, problems such as secondary growth and splitting are not proving to be as a great a problem as they are in England. Moreover, incidence of black-leg and virus are at an all-time low.

On the other hand, he adds, the dry conditions led to higher levels of the unsightly blemishing disease common scab (Streptomyces scabiei), says Stephen. “This may yet lead to concerns over export because some of the countries which import seed and ware potatoes, such as the Canary Isles, Israel and Egypt, have very tight tolerances which will mean a reduced availability for these markets.

“As a rule, low levels of common scab are rarely a problem in seed potatoes because it has no adverse effect on the crop. However, in countries such as Israel which have an important peanut crop, common scab can be a cause for concern. This is because when peanuts are grown after potatoes in the rotation, it can affect the shell colour which becomes darker.

“However, as yields are expected to be down on last year, any reduction in export is likely to be taken up by the UK seed and ware market.”