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Phytophthora in potatoes has become more aggressive

Phytophthora clone EU-13 was already known for being aggressive and difficult to combat. In recent years, two new clones have been on the rise in the northwest of Europe: Eu-36 and EU-37. These clones are supplanting EU-13. The characteristics that caused these two clones to expand has now been researched by Wageningen University & Research. This information allows the combat strategy of phytophthora to be improved.

The following characteristics that are important for the development of phytophthora in potato leaves have been researched:

The infection efficiency of the spores;
Phytophthora’s growth speed in leaves;
The latent period;
The size of the spots on the leaves;
The amount of spores created.

For most of the characteristics important for the development of Phytophthora in leaves, it has been discovered EU-36 and EU-37 developed more quickly and to a larger extent compared to EU-13. The combination of these characteristics translates into more aggression that could explain why EU-13 has been driven back in the northwest of Europe.

Sensitivity to fungicides
Earlier research showed EU-37 is less sensitive to fluazinam. The sensitivity of EU-36 and EU-37 to a number of other fungicides has now been researched. No proof has been found that these clones are resistant to other fungicides. However, a consistent pattern has been found that EU-36 and EU-37 could expand a bit more with very low doses in laboratory experiments compared to EU-13.

Looking for a suitable combat strategy
Even more alertness when combating the clones has turned out to be important. When disease pressure is high, the new clones will find the weak spots in the combat strategy more easily to cause a contamination more quickly. The middle choice, dosing and timing of spraying, should be even more accurate in the presence of the two clones compared to the situation about two years ago. In 2019, research will have to show whether the combat strategy for these two clones should be adjusted.

Source: Wageningen University & Research

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