'If the basis is good, Alternaria will have less chance'

Extensive crop rotation, targeted fertilization and timely, preventive spraying. With those three basic conditions, Alternaria can be kept under control, say Hans van Ooijen and Dick van den Bogert.

It is the end of March and a watery sun is shining above the Bommelerwaard. Where the land allows, slurry is spread, fertilizer is spread and some summer grain is sown. The tractor units (and employees) are also fully operational at contracting company Struijk in Delwijnen (Gelderland). "I still look forward to this every year; that we can all go out on the land," says Hans van Ooijen, who, with 33 years of service, can be regarded as the figurehead of the contracting company. Van Ooijen has been spraying weeds for a few days now. But it hasn't gone smoothly so far. "We had some problems with the pump, which caused us to stop for a while," he says in the company canteen. "Fortunately, everything is running again now. And rather a delay now, than later in the middle of the season."

Despite the increasing crowds, he likes to take the time to talk about crop protection – and more specifically: combating Alternaria. Dick van den Bogert of ADAgro is also present to support. "Dick has been here for almost as long as I have," says Van Ooijen, "He knows the company through and through and has been my right-hand man when it comes to crop protection for many years."

'Potatoes grow well here'
Although contracting company Struijk mainly focuses on activities for livestock farming, it has also had its own arable branch of approximately 200 hectares for many years. Not only are maize, grain and beets represented, but also about 25 hectares of ware potatoes every year. In an area with predominantly heavy basin clay (and therefore a lot of grassland), this seems at first sight a striking choice. Still, according to Van Ooijen, there are sufficient opportunities for cultivation, especially on the higher ridges and in the floodplains. "I don't really want to give anyone ideas, but potatoes do just fine here. Both the yields and the quality are downright good," he says. Van den Bogert also sees sufficient space and future for cultivation, although the better (lighter) and less scab-sensitive soils must be selected for this. Moreover, there is always the risk of flooding on the floodplains, which is something Van Ooijen is only too good at talking about. Last summer, two blocks of 4 hectares were lost due to the extremely high water in the Maas…

In order to keep the available land suitable for potato cultivation, a wide rotation of 1-to-7 has been maintained for years. This has been successful so far, for example through land exchange with livestock farmers. Much attention is also paid to green manures, so that the soils remain fertile and workable. A point of attention here is increasing pressure from soil insects - in particular from snails and wireworms. "Green manures with a lot of mass above ground attract a lot of snails. That is why we consciously choose species with less mass above the ground and more underground mass, such as mixtures with Facelia and clover," says Van den Bogert.

Fungal diseases well under control
There have never been any problems with Phytophthora in recent years. "Maybe I should knock it off, but we have had the disease under control for years - also last season when the pressure was high," says Van Ooijen. According to him, it is of course beneficial that there are few potatoes in the area, but that does not mean that the Phytophthora control is being tackled a little more loosely. "On the contrary, we always have a fairly tight spraying schedule here, where I pull the work forward rather than push it back," he emphasizes. A great convenience here is that the self-propelled field sprayer has a considerable capacity. "Every year we spray about 45 hectares of potatoes – our own and for third parties. However, the plots are widely spread out, which means that there is quite a bit of driving time. But with this machine I manage to complete it within twelve hours," says Van ewes.

Alternaria has also never been a major issue at the company so far. According to both men, this is partly due to the extensive crop rotation and targeted fertilization, which gives the crops a 'large portion of resilience'. For example, (in addition to the main fertilization) easily absorbable phosphate granulate is added during planting and, in combination with disease control, an over-fertilization is carried out with nitrogen and potassium foliar fertilizers. Furthermore, from the second half of the flowering period, an agent against Alternaria is added to the Phytophthora spraying approximately every two weeks. Last season they were – alternately – Narita® and Propel† According to Van den Bogert, the new product Propulse has been given a basic place in the control of Alternaria almost everywhere. "We have seen both in trials and in practice that Propulse has an excellent effect against Alternaria. It is therefore only logical that almost all potato growers have adopted this agent."

^{Narita® is a registered trademark of Globachem}

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