Haulm destruction

After his previous inspections of Mr. Geluk’s potato plot, the NAK-inspector has been back to give mr. Geluk the green light to commence haulm destruction. Timely haulm killing is important to minimise the spread of diseases, in particular of viruses carried by aphids. Although Mr. Geluk regularly checks his crop for any diseased plants, virus infections are unfortunately not always visible to the naked eye, especially if they occur late in the season. So to prevent the risk of a virus being transmitted to the tubers, it is essential that the haulm is destroyed at the right time, or at least before viruses can reach the tubers.

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Each season the NAK determines the best times for farmers to destroy the haulm. Their decision is largely motivated by aphid counts, but also depends on the varieties' susceptibility to the potato virus Y, the infection pressure in the field and the crops' maturity.

Catch that aphid!

To gain insight into current aphid numbers, the NAK monitors the aphid migrations during the growing season. To his purpose they place catch trays at 38 different sites throughout Holland. The aphids are attracted by the yellow colour of the tray and are caught by a small layer of fluid. The trays are drained daily from the beginning of June until mid-August. Before the trays are placed, the NAK shakes potato plants in different potato plots throughout the Netherlands on a weekly basis, directly after emergence in mid-May.

Apart from the trays, three suction traps are run continously on separate locations. These draw in air constantly at a hight of twelve meters. Samples are taken daily from May until September.

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Catch tray (left) and suction trap used by NAK.

Vector pressure

All samples that are taken from the traps are transferred to the laboratory, where the aphids are identified to species and counted. The identification to species is vital, as some species of aphids are more efficient vectors than others. With these data the NAK estimates the current vector pressure for aphid-transmitted potato viruses, such as potato virus Y and potato leaf roll virus (PLRV). This vector pressure is the main factor in determining the most favourable haulm destruction dates.

After the haulm has been destroyed, the NAK-inspector will be back to check if the haulm has been destroyed completely, as re-grown plants are highly susceptible to virus infections. However, destroying the haulm timely doesn't garantuee that the seed potatoes will comply with the virus standards. This is why, in addition to the field inspections, extra laboratory tests are carried out to search for the presence of viruses, known as post-harvest virus tests.

Preparing for harvest

After haulm cutting, Mr. Geluk’s potatoes will rest for about two weeks so their skin can set, which will facilitate the forthcoming harvest. In hotter climates such as that of Libya the potato haulms will generally die off earlier. As the temperature in bare, unprotected ridges can rise considerably, farmers tend to keep the soil of their ridges moist. This will not only lower the temperature inside the ridge, but also prevent cracks through which tuber moths can enter.

Photos of the Catch tray (left) and suction trap courtesy of NAK. Text in part written with the aid of information of the NAK, in particular the brochure ‘The Inspection of Dutch seed potatoes’, available for download via the website nak.nl.