Where the lice pressure is normally observed with peaks, this year there is an upward trend over the entire season. Seed potato growers must be alert to prevent viral disease. The weather is partly the cause of this. The pressure is not only high in the Netherlands.
Inspection service NAK registers a lice pressure of 50 or more at various places in Eastern Flevoland, North Friesland and Groningen. In the Noordoostpolder this varies from 5 to 20. In collaboration with crop protection product producer Adama register supplier Profytodsd the virus pressure in Flevoland. The number of catches here varies from 5 to 45.
Especially peach aphid found
Olaf van Campen, Crop Manager at Adama, is involved in lice monitoring. “We empty the traps 2 to 3 times a week. We add up the catches,” he explains. “At the moment we mainly see a lot of peach aphid in the traps. They have a virus transmission factor of 1 and are therefore the most harmful. We also see other aphid species, such as the black bean aphid, which must be taken into account. These species still have a transfer factor of 0,1 to 0,3 and can also cause damage.”
No pressure drop
“Other years you see a peak in lice pressure at the beginning of June, followed by a peak in the first half of July. This year, the pressure will not level off, but it will continue to increase,” Van Campen outlines. “Normally rain helps to lower the pressure, but this year it is not showing. A warm June month ensured that the lice pressure started early. When the grain harvest starts, you see the pressure increase further, because the aphids come out of the grain.”
Select by time
Van Campen does not call the situation shocking. It often happens that the pressure is very high. “Virus disease has now also been found. That is very early in the season. With the current situation you have to be on top of it. That starts with selecting on time. In the past you often saw that growers started too late. If there are no virus plants in the crop, you prevent damage and the first profit has already been made. For now that is, of course, mustard after the meal.”
Don't skip oil spraying
Another important point, according to the seed potato specialist, is the use of oil. “Growers sometimes tend to skip spraying with oil. At high pressure it is important to use oil right up to the end. This makes the crop heavy, so it stays wet for longer. That in turn increases the chance of a phytophthora infestation. Not every grower therefore uses oil, especially on a large crop. You sometimes spray up to 7 liters per hectare. The maxim is 1 liter per day.”
Rejection by storage plants
The NAK has now completed three quarters of the second round of inspections reported it July 11. The reduction percentage is 5%. That was 2% and 6% in the past 3 years. The percentage of rejection is 0,6% compared to 1% in 2016 and 0,4% in 2015. More than 60% of the cases involved bacterial disease, followed by other items. The main remaining reason is varietal impurity, which is created by storage plants in the crop. In all cases, the infections are below last year's level.
Highest population in 10 years
High aphid populations are also observed in Scotland and other seed potato growing areas in the United Kingdom. At the end of June, 40 peach aphids were already found in Scotland. That is as much as is normally found throughout the season. At another Scottish location, it was 57 against a ten-year average of 3. According to AHDB Potato, a mild winter followed by a warm spring is the cause. Rain in early June made little difference. The first lice were found a month earlier than normal, around mid-May. A boarded up insecticide schedule is recommended. The only advantage is that the seed potatoes are relatively healthy. The reduction percentage of the 2016 harvest was the lowest since 2003. Virus was found in 6,7% of all Scottish seed potato crops last season.
Foliage killing started last week
On 11 July, the foliage of 1.600 hectares of seed potatoes had been destroyed. Growers started spraying and slapping last week. “I expect that by the end of next week most of the seed potato crops will be killed,” says Van Campen. Plots that I have assessed myself in Flevoland look good. A number of 11 tubers per plant is simply good. I also hear from colleagues about plots with 3 or 4 tubers per plant. That strongly depends on the region. In Flevoland there was still moisture available during tuber setting, or watering could be done. In the southwest, and the northern growing areas in Friesland and Groningen, it was later and it was much drier during tuber setting. That is clearly noticeable.