Dreaming of the perfect apple – a story of war and love

Vagn Nielsen's apple plantation would make a baroque king envious.

His apple trees stand straight as a die in long rows bursting with white spring blossom. Nothing out of line and no crooked branches here. The trees are well pruned so that each blossom – and soon every single young apple – receives the same amount of sunlight, wind and rain.

The apple grower from Snaptun near Horsens is trying to stay ahead of the field when it comes to conventional apple growing and optimising production.

So he is used to having consultants and researchers looking over his shoulder.

And one of these researchers is accompanying him as he inspects the trees on this sunny late-May day.

The researcher, Marianne Bertelsen, has just grabbed one of the branches and is now scrutinising a white flower.    

"Are you looking for frost damage?" asks the apple grower.

"No, actually I’m looking for attacks from weevils. Have there been many this year?” answers the researcher.  

We are witnessing a classic example of applied research and a – hopefully – fruitful meeting between science and practical reality.

Poisonous newspaper headlines

Apple grower Vagn Nielsen and Senior Researcher Marianne Bertelsen from the Department of Food Science in Årslev, Funen are on a joint mission; to reduce the percentage of pesticides in the fully developed apples to an absolute minimum.

In fact, the goal is what is known as zero residues, which means that there is no trace of pesticides when the consumer bites into the fruit.

"You’re not going to get Vagn to think that pesticides are dangerous," says Marianne Bertelsen before continuing:

"I don’t really think they are either, as we’re already dealing with very small concentrations. Plus pesticides have been tested so much so that any which could really be harmful have already been banned."

But why the mission then? Marianne explains:

“Because the population still think this is a problem. We know that each year we’ll see a newspaper headline about poison in apples, which worries consumers. We have to take this seriously,” adding that politicians have been applying pressure to reduce pesticide residues for a long time.  

The non-poisonous plan

At the same time, consumers have high cosmetic requirements for apples and reject the idea of brown blemishes from mildew or holes from insect larva.

“But it’s impossible to operate a fruit plantation without using pesticides,” she says.  

On the other hand, the researcher from Årslev has found a solution to this dilemma which can both realise the dream of pesticide-free apples and, at the same time, meet the consumers’ cosmetic requirements.  

By optimising pesticide spraying in March, April and up until petal fall at the end of May, it is possible to completely avoid the use of pesticides during the following period, which is where the tree has developed fruit and the apples grow until being harvested in August. In this way, it is possible to avoid pesticides in the fruit.    

At least this is what the results of Marianne Bertelsen's recently completed research project show. This project was carried out in the Department of Food Science’s test plantation in Årslev. The method has been christened the zero residue strategy.     

Five-year head start

But one thing is a closed test site with a limited area. A fruit producer’s practical daily work combined with very different geographical and weather conditions is something else again.

Marianne Bertelsen therefore approached three conventional fruit producers and offered them the chance to participate in giving the Årslev experiment a reality check. 

One of them is Vagn Nielsen and this is the second year in a row in which he has tested Marianne Bertelsen’s new cultivation methods in a section of his plantation in Snaptun. Vagn is happy to participate for the sake of science – and for the sake of his own business.

"I call it on-going development of production. In the old days we just drove out and sprayed, and then when we were finished, we picked the apples. But we keep learning more," he says.

If you are prepared to think outside the box, then perhaps you can anticipate developments and consumer wishes, says Vagn. 

"Maybe I can get head start on everyone else by taking part in this project, perhaps even four or five years. I learn much more by seeing things in practice, rather than sitting in a big meeting in the winter and listening to theoretical presentations from Marianne or one of her colleagues," he says. 

So as Vagn emphasises, he is more than willing to reduce the consumption of chemicals – which, it should be noted, are expensive to buy – as long as he can still maintain a high yield.

"It’s no good for us if we have to grow them using the new method and then end up saying ‘oops, the apple wasp took all our Discovery this year’. That sometimes happens to the organic producers. But that would be far too expensive," he says. 

Dutch spy snitches about fungal attack   

One of the biggest challenges to growing apples in our corner of the world is mildew attacks, which are spread by fungal spores from dead leaves in the soil.

The threat of mildew is greatest during the spring, and it is therefore important to Vagn to spray as precisely and efficiently as possible against the fungal spores until the tree starts to develop fruit.   

For this purpose and to generally limit the use of pesticides, the apple grower uses a Dutch developed state-of-the-art monitoring system.               

Standing in the middle of Vagn Nielsen's apple plantation is a weather measurement station. It might not look like much, but it collects important data on temperature, wind, air and leaf moisture, and sends all the information to a server in the Netherlands.  

From here, the Danish fruit producer can retrieve the information in Snaptun and download it in his monitoring software on the computer in the living room.

If an airborne attack is under way from the fungal spores, the software snitches to Vagn, so he can react at the perfect time and with the perfect precision weapon.

The Dutch spy has not, however, completely replaced Vagn ‘sown judgement.

"As a rule, my intuition about this kind of thing is very good already," he says with a laugh.

All’s fair in love and war

Eradication of insects can be a bit more challenging, explains Marianne Bertelsen. This is because the location of pests is very much dependent on localities.   

"We’ve seen some weevils here with Vagn, which we have not seen at the test plantation in Årslev in twenty years. This is why we need to test our experiments here at the growers, so we can find out whether and how we can manage the problems that arise," she says.

In addition to weevils, Vagn Nielsen's plantation was plagued by tortrix or leafroller moths last year. This is a small species of moth that uses silk threads to entwine the leaves of the host plants into small rolls (hence the name, leafroller).

Fortunately, leafroller moths are just as stupid as people, explains Marianne Bertelsen.

They let themselves be enticed by pheromones – also popularly know as sex hormones.

Studies show that pheromones play an important role in sexual attraction in humans as well as animals. Entrepreneurial companies have therefore developed perfumes for both men and women containing the substance, which reportedly lead to extra attention from the opposite sex.

The very same “attraction effect” is what Marianne Bertelsen and Vagn Nielsen are aiming for with the leafroller moths by hanging the pheromones up around the plantation.

However, they’re not intended to help the leafrollers with their love life. Quite the opposite in face; their purpose is to confuse the males, so they find it more difficult to find and fertilise the female moths, explains Marianne Bertelsen. 

The collaboration between researcher and grower in brief

Vagn Nielsen has earmarked a 1.2-hectare area of his plantation for Marianne Bertelsen's experiments with the zero residue strategy. This comprises about 3,000 apple trees. 

Half of this area is reserved for normal cultivation, which means that Vagn Nielsen continues to spray pesticides over the summer months after the apples have appeared on the trees.

He cultivates the other half in accordance with the zero residue strategy. Therefore he stopped using pesticides in this section of the area at the end of May this year.

The apple producer has the last word

Vagn Nielsen is paid for the working hours he spends on the trial, but he also bears any risk if he gets injured or has to reject some of the harvest.

Therefore he has a right of veto and can choose to go out and spray, if he assesses that the risk of attack becomes too great.  

This is the second year in which Vagn Nielsen has taken part in the experiment, which extends over a period of three years.

Danish fruit without pesticide residues

Known as DAFRUS, this is the name of the collaboration that Marianne Bertelsen and her colleagues from the Department of Food Science have entered into with three commercial plantations to test the zero residue strategy in practice. 

With a previous experiment in a test plantation, the researchers have shown that utilising an optimal spraying of the apples in the period before fruit setting makes it possible to avoid spraying during the period in which the fruit develops, without this leading to major losses and without pesticide residues on the fruit.

DAFRUS will help determine the implementation of the zero residue strategy in the industry in relation to its scope and which varieties of apple it can be used for.

The commercial plantations are located in Snaptun, Tåsinge and on the island of Fejø.

Translated by Peter Lambourne.