'The largest epidemic in more than 30 years'

'Five to twelve… All hands on deck… All signals on red'. In recent months, a lot of attention has been paid to the threatening situation surrounding phytophthora. In order to control the disease this season - and beyond - the Phytophthora Taskforce was established last autumn, a partnership of seven parties from the potato chain.

One of these parties is BO Arable Farming. Bayer spoke with director André Hoogendijk, who serves as chairman of the Taskforce.

In recent months, much has been written and spoken about the alarming phytophthora situation. How would you describe the situation?
"I see it as the biggest epidemic in more than thirty years. Phytophthora strains have never been so aggressive, making infections riskier than ever before. In short, there is no reason to downplay the situation. The situation is real serious."

Are potato growers sufficiently aware of the seriousness?
"Yes, in general. Many experienced the infections themselves last summer or saw them happen to a colleague. So growers know that something has to be done to prevent the situation from getting out of hand. Anyway, they have to will continue to put this message into practice in the coming months. That is why we will continue to repeat our message: cover waste heaps, combat storage and fireplaces, use a BOS, apply combinations of resources and alternate resources."

Seven parties from the potato chain are represented in the Phytophthora Taskforce, namely LTO, VAVI, NAO, Agrodis, Bionext, Avebe and BO Akkerbouw. They have all contributed their knowledge and insights in recent months. What has that achieved in concrete terms?
"It is very important that we together put forward a clear, unambiguous message that we all support. This gives such a message extra strength. Furthermore, we were also able to put the necessary information on paper fairly quickly, which meant that during winter lectures last winter The problem has already received a lot of attention."

"We have made a kind of 'cut' for this season and beyond. For now we have mainly focused on a short, practical message. After this season we will evaluate our message and the focus will be more on phytophthora control for the longer term."

Tackling phytophthora must take place on many levels - from breeding resistant varieties to sophisticated disease control in the field. Can you indicate where the biggest improvements can - or should - be made?
"We can make the greatest progress on the hygiene side. I am mainly thinking of combating potato storage. In my opinion, the sector is still too lax with this and an extra step really needs to be taken. Especially on rented land where potatoes have been growing. you still often see storage of corn, for example, the following year. We really need to prevent that! The first responsibility rests with the potato grower, but the livestock farmer who has rented out his land must also be aware of the consequences of potato storage very simple: no source = no focus = no infection."

Choose robust/resistant varieties as much as possible, is the message from the task force. But that's easier said than done. Last season, almost all dominant resistance genes were broken through. The flush of resistant varieties is therefore very thin...
"This message is indeed a difficult one. In fact, there are currently only about ten varieties with one or two resistance genes. These varieties have a so-called improved resistance. This means that they can offer more resistance to phytophthora, but not that they cannot survive without it. preventive spraying is possible! In fact, we must monitor these varieties very actively and keep them free of phytophthora at all costs, because if the resistance is broken, you will really lose them."

"Growers who grow varieties with improved resistance have received additional information from their trading company on how they can best protect them. And if resistance is unexpectedly broken, there is only one measure left: kill the crop immediately."

"For the longer term, we will have to do everything we can to protect existing resistances. In addition, breeders must make maximum efforts to breed varieties with multiple resistances. The task for trading houses and processors is to include these varieties in their package and to actively promote these to their customers. In short, we still have a lot of work to do."

It is feared that seed potatoes from plots where phytophthora occurred last season could now cause early infections. Some say that seed potato growers should take more responsibility for this - for example by explicitly reporting this to the buyer. How do you view that?
"Phytophthora infections from seed potatoes are indeed a potential source. But that source is often difficult to determine in practice. The NAK takes this into account in the inspections, but in my view there is a role here mainly for the supplier of the seed potatoes. As a seed potato grower, I wouldn't want my buyer to get into trouble, even though I knew there was phytophthora in my seed potatoes last year."

A number of Wageningen researchers believe that enforcement of measures to combat potato storage and covering waste heaps is now far too weak and also starts far too late. They argue for much stricter controls with much higher fines. What do you think of that?
"As mentioned earlier, I think that we definitely need to step up our game when it comes to combating potato storage. On the other hand, the rules regarding covering waste heaps have been complied with reasonably well in recent years. Personally, I am not in favor of higher fines. I I have no illusion that this will improve the situation. I prefer to appeal to growers' sense of responsibility and honor: address potato storage and confront colleagues if they do not do so. It is a collective task to prevent infections."

Last season, the most aggressive phytophthora strain - the EU-43 - once again gained ground. A new clone for the Netherlands is also emerging: EU-46. Both have a great sporulating effect, which has enormously increased the speed of development. How should you respond to that as a grower?
"Firstly, prepare for the fact that you will have to intervene earlier than you have been used to in the past. Secondly, take into account shorter spraying intervals due to the greater development speed of the fungus. And thirdly, observe the FRAC guidelines to prevent resistance development. To make the FRAC rules simpler and clearer for growers, we recently created a color scheme that shows how resources should be alternated.

"As far as the specific choice of means is concerned, I would like to leave the answers to specialists in this field. In general, what I said before applies: use combinations of means and alternate."

The Taskforce advocates the use of a BOS system (Decision Support System) to make better decisions regarding the control of phytophthora. In practice, only a small proportion of growers work with this. What do you think is the added value?
"First of all: there are still too many potato growers who spray according to the calendar. These are often larger growers who can supposedly make ends meet with their field sprayer during the season. I know that some people consider this efficient, but in my opinion you should simply provide more spraying capacity. As for the BOSs: there are now many systems that can predict very well how the infection pressure will develop. The growers I talk to about it are almost always very satisfied with it the disease pressure, makes them more careful in their considerations of how and when to spray and it provides a better informed decision for such a spraying. So I mainly see advantages."

The vast majority of experts state that phytophthora can only be controlled with a combination of resistant varieties and chemicals. This would mean that there is no future for organic potatoes in the Netherlands.
"I don't see it that way. What matters is that everyone knows their responsibilities and takes measures to prevent infections. For organic growers, this means: working with early varieties and as much growth as possible before the phytophthora season starts. And if an infection occurs: immediately killing the crop. In the event of an early infection, this may be a hard blow for the grower, but that is inherent to organic potato cultivation."

Finally: what will the situation look like in, say, five years? Do we still have phytophthora under control?
"Despite the current significant threat, I am hopeful that we will get the disease under control. It is very important that we guide and maintain existing resistances as best as possible, because this will allow us to combat the current, aggressive Phytophthora strains. In a sustainable way, we hope to have triple - or even more - resistance available by around 2030, which will give us even more options to sustainably control the fungus. In the meantime, we must do everything we can to combat it phytophthora as widely and effectively as possible. Because let me be clear: without chemistry we will not win against the disease for the time being. Finally, I stick to the fact that virulent strains come, but they also go and targeted approach, we keep potato cultivation future-proof."

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