Rock pear stenphylosis: time to remove and destroy leaves

Latest information from the Stenphyliosis Working Group released by INIAV. Controlling the maturation of the future spores of the fungus that causes the disease is crucial to stamping it out.

Monitoring the development of the spores of the fungus that causes stenphylliosis, also known as brown spot disease of the pear tree, indicates that the time has come to remove the leaves from under the tree canopy, recommends the Stenphylliosis Working Group.

The maturity index (MI) of the pseudothecae - structures where the endogenous spores (ascospores) form during the winter - increased by 0.9 in the Alcobaça orchard, 0.8 in the Maiorga orchard, 0.5 in the Picanceira orchard and 0.4 in the Sobrena orchard, between January 25 and February 8, 2021. Compared to the same period last year, the IM in these orchards in Western Portugal is 0.4 lower in Sobrena, 0.2 lower in Picanceira and Alcobaça, and 0.1 higher in Maiorga.

The data can be found in 2nd Information from the Stenphilosis Working Group (Stenphilosis WG), coordinated by INIAV, in which it is considered important to “remove/destroy the leaves under the canopy before the pseudothecae mature and the ascospores are released (IM=7), so that the primary inoculum of stenphyliosis is minimal and, as a result, the incidence of the disease is reduced”.

Those responsible for the Stenphyliosis WG point out that, at this time, the ascospores won't necessarily infect the pear trees, “but they will infect the vegetation in the soil and, possibly, the organic matter on the surface of the soil” - where the inoculum will be produced during the spring.

On February 8, the orchard with the highest IM was Maiorga (IM=4.7, n=103), followed by Alcobaça (IM=4.2, n=90), Picanceira (IM=4.1,0 n=94) and Sobrena (IM=3.9, n=102). The IM of the Maiorga orchard, very close to stage 5, means that there are ascospores in formation and mature ones.

A stenphylosis, caused by the fungus Stemphylium versicarium, is a disease that affects the production and quality of the rock pear, and for which there are still no phytopharmaceuticals capable of effectively neutralizing it.

Feature image: Nicky/ Pixabay