Tuber phytophthora wreaks havoc on potato plots

The phytophthora pressure has been high for weeks. The leaf wet periods were often long due to the persistent precipitation and dew-wet nights, while the temperature increased only to a limited extent during the day. This created a high risk of infection, causing the fungus to strike many potato plots. Even during the relatively warmer, dry days, the potato blight remained lurking around.

Many phytophthora infestations were found nationally, with growers in the center of the country having to deal with the greatest pressure. The pressure was also high in the north and relatively lowest in the south, not surprising given the lower rainfall in the region. Tuber phytophthora has now also been observed in the ridges on several plots. "There are plots that have severe damage, in the worst cases more than half of the tubers on a plot. It is problematic," says a crop advisor from Flevoland. The idea is that the spores were washed hard into the potato ridges at the end of July during heavy rain, when the potato blight was in the leaves. "At that time, no tuber protection agent had often been administered."

Plots with few affected leaves affected
But remarkably, tuberous phytophthora is also found in plots that had little damage to the leaves. "Even in plots where little leaf damage was visible, we sometimes find tuber phytophthora. This is a cause for concern because not every grower has checked his plots yet." The Innovator chip variety has so far stood out with damage to the tuber compared to other chip varieties, insiders indicate. Phytophthora is also frequently found in the tubers in starch potato cultivation

The differences in disease pressure between potato varieties and plots are large. In adjacent plots, one plot sometimes has leaf and stem phytophthora and the other does not. Spraying a day earlier or a combination of agents could possibly make a difference in the risk of infection or not in the high disease pressure. It is often advised to shorten the usual spraying interval. Products that normally require 7 days had to be reduced to 5 days. For the well-known preventive drug Zorvec, an interval of 7 days was recommended instead of 10. But for growers with a large acreage, it is sometimes a challenge to be everywhere on time. The fact remains that with sky-high disease pressure, smaller areas are also affected. Let alone when spraying does not work due to sudden rainfall or when you cannot go into the field with the sprayer at all because the soil is too wet.

Resources package in jeopardy
Due to the high phytophthora pressure, the availability of resources has also shrunk considerably. This mainly concerns curative remedies that are sometimes difficult or impossible to obtain. For example, an insider reports that curative remedies that have only just been made are supplied directly to the intermediary. Preventive measures are generally still available. Although we appear to have passed the peak of phytophthora infestations, growers remain vigilant. Once the mold is in a block of potatoes, it continues to lurk around. Last week it also became apparent that at the slightest moment of infection pressure, phytophthora reared its ugly head again. While there was hardly any significant rainfall. And that will be the case in the coming days, given the weather forecast.

In addition, the infestations of tuberous phytophthora are only just coming to light. As mentioned earlier, there are also plots where infection in the leaves or stem hardly occurred, but the tubers were infected. Also, with the current phytophthora pressure, quite a bit of water can wash in in the near future.