Propulse at the best approach Alternaria in potatoes

In potatoes we know of two types of Alternaria, namely A. solani and A. alternata. The A. solani is the most common, but in certain varieties we also regularly have to deal with A. alternata.

Characteristic for Alternaria are the numerous, small spots on the leaf. These are bordered by the veins of the leaf, giving the spots a slightly angular appearance. Also typical are the concentric rings in the spots. Tuber infestation does not or hardly occur in the Netherlands.

In a normally growing crop, Alternaria has little chance for the crop to ripen in our growing areas. However, at a certain point the 'physiological resistance' decreases, giving Alternaria the opportunity to develop very quickly. The influence on the yield can then be considerable. It is of course clear that optimal growing conditions reduce the chance of Alternaria due to optimal soil fertility, structure and moisture supply.

It remains difficult to estimate the moment when the 'resistance' of the crop decreases. In addition, the potato grower no longer has mancozeb at his disposal, this always provided a certain protection. Nevertheless, we can state that based on the research and practical experience, the first targeted spraying mid/end of flowering is a good time.

Trial results Alternaria

The above are the results of research in recent years. Two sprayings were carried out here, the first spraying at the end of flowering and repeated after fourteen days. Conclusion about these two different years:

• Good control of Alternaria
• This translates into a considerable return

How Sclerotinia works
Depending on the crop plan, Sclerotinia can also occur in a potato crop. Fluopyram is one of the active substances in Propel which is known for its good effect against this fungus. This is underlined in the 2020 study below with an artificial infection.

Botrytis
Later in the growing season, a potato crop is sometimes also affected by Botrytis. It is less clear to what extent a (very) late infestation affects the yield. We know from targeted research that Propulse has a good effect against Botrytis.

black speckle
Less well known is the occurrence of black speck on the stems in a potato crop. In tests last year, we established that where Propulse was used, there were clearly fewer stems with black speckles. This also translates into less damage from black speckle on the tuber, as shown by the research below.

More information?
Also view our crop page Time for potatoes for a complete overview of articles, recommendations, products and more.

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