The right time to start spraying is crucial against late blight. Resistance management when using fungicides is also moving more and more into focus. Many funds will expire after 2021.
The drought in spring and summer kept late blight infections at a low level in 2020. Significant occurrences were only found at individual locations. This made it possible to save some fungicides in the past year . This year it is important to be careful and to eliminate risk factors for late blight in advance.
Late blight: this is how you can prevent infections
Phytophtora infestans is the potato disease most relevant to yield . The fungus overwinters in infected potato tubers. Aphids and the wind also play a role in the spread. It is therefore important to consistently combat volunteer potatoes and avoid piles of waste with potato residues. Further row spacing prevents moisture from collecting within the stands. Choosing the right variety and quality of the seedlings also help prevent infections.
The spray season in the potatoes usually begins about three weeks after emergence – depending on the infection situation and at the latest when the row closes. The late blight pathogen tends to develop resistance. You should therefore consistently change the active ingredient classes (FRAC) in the spray sequence.
This is how you find the optimal spray start for potato diseases
The right spray start lays the foundation for successful and economical Phytophthora control in potato growing . The right time can be determined, for example, with online forecast models. Current forecasts for the beginning of infestation can be found on the website of the Information System Integrated Plant Production (Isip) under www.isip.de retrieve. There you will find decision-making aids for starting the spray (Simblight1 / Simphyt1). There is a separate forecasting tool for organic potato cultivation, Öko-Simphyt.
The models predict the probable start of the infestation on the basis of current weather data. The first treatment should always take place shortly before. However, the tools are not meaningful for potatoes under foil or fleece. The plant protection services of the federal states also give regional advice on starting the spraying process.
Local infestation factors, such as heavy rainfall or waterlogging in the soil, do not always capture the prognoses. It is therefore important to check your own areas regularly in order to detect sources of infection and early infestation in good time.
These late blight ingredients will expire in 2021/22
With Mancozeb , a proven crop protection product will be eliminated in 2022. The use-by period for agents containing mancozeb ends at the latest on January 4, 2022. The approval situation for other preparations is also uncertain in the coming years. Around half of the previous late blight products will currently only be available in 2021. In the course of 2022 , more approvals of agents against late blight and also against Alternaria will end .
Only the systemic agent Zorvec Endavia from the manufacturer Corteva was added in 2021. It replaces the remedy Zorvec Enicade. Resistance management in potato growing will become more difficult in the future due to the lower number of available funds. Strategies beyond chemical plant protection will have to come to the fore.
In the future, potato cultivation will depend even more on averting resistance by changing the classes of active ingredients as well as the correct combinations of fungicides and the timing of spraying.
The leaf mass increases rapidly during the main growing season of the potato up to about flowering. At this time, partially systemic or translaminar fungicides are often used against Phytophthora . They offer limited protection for the new growth.
In order to avoid resistance , however, you should pay attention to a change in the active ingredient. This is pointed out by the Rhineland-Palatinate Service Center for Rural Areas (DLR) in Oppenheim.
A tabular overview of all available fungicides as well as an overview of the dates of use of the fungicides for late blight can be found in our article in the digital edition.
