In the context of the rainfall and unstable conditions this spring, we spoke with Héctor García, General Manager and Co-founder of Diagnofruit, who talked about the main diseases in cherry trees and how rain events and environmental humidity generate favorable conditions for their proliferation.
How do spring rains affect the development of diseases?
The rains, as a direct effect on pathogens, generate conditions for the development of fungi that had been very rare in previous seasons, which have been extremely dry; among these, Botrytis and Geotrichum stand out, and to a lesser extent Monilinia. These fungi are more “friendly” to conditions of high humidity and temperatures closer to 20 °C; unlike fungi such as Cladosporium or the dreaded Alternaria, which predominate more in dry environments with high temperatures, microorganisms that adapt to the conditions of climate change of drought, without the El Niño factor.
Beyond the optimal factors for the multiplication of the inoculum of certain fungi, the most critical condition that rainfall provides is the “susceptibility” of the fruit to fungal attacks through the generation of cracks. As you can imagine, a wound is the perfect entry point for fungi, especially for those that do not have a powerful enzymatic battery to break down the containment of a healthy fruit, such as Geotrichum, but at the same time generate a rapid infection, which ends in a fruit or a group of rotten cherries with no option of harvesting or developing it in storage.
How do rainfall, humidity and orchard conditions affect applications? Should phytosanitary programs be modified?
In general terms, the rains invite us to reinforce the programs, we analyze what we have applied in the orchards since flowering and we establish one or two more applications, depending also on the heterogeneity of the fruit development, something very characteristic of the current season, then beyond the modification I would talk about reinforcement, integrating the use of synthetic fungicides with others of biological origin, such as Bacillus and/or botanical extracts, such as tea tree oil, quillay or some high purity citrus extracts, which in addition to control raise the natural defenses of the plant against these stone guests.
What illnesses should I pay attention to in the next few weeks?
I think that Botrytis, gray rot, and Geotrichum, sour rot, and eventually, if we have rapid increases in temperature after rainfall, Alternaria, black rot, and other yeasts could increase their populations and with this an increase in the frequency of rot, along with cracks.
We have seen the development of Pseudomonas, orchards with the appearance of necrotic spots on leaves, which, although generally do not damage the fruit, cause early defoliation that could compromise the quality of the fruit and the vigor of the plant. Although it is not very common in cherry trees, in other Prunus or stone fruits, virus symptoms have been easy to detect, probably associated with environmental stress, especially in young plants; remember that this is the best sampling period to diagnose this type of pathogen.
What are the main recommendations?
We have already talked about reinforcing the programs, the strategy is to start with broad spectrum fungicides to advance to botryticides/alternaricides, and in any case at least one application of Tebuconazole as a measure to try a complex fungus like Geotrichum, of which we have evidence of its presence from the flower stage and several detections in citrus fruits during the season.
It is always better to apply before the precipitation event, because we need the product to interact with the fruit, as we would say more simply, “firm itself”, so that later, when the infection conditions occur, it defends the fruit against the development of the fungus. Based on the result, we evaluate the next application.
This season, I am not the one to mention the best way to do it, but we must prioritize the calcium load of the fruit, this factor is our first barrier against cracking and infection, together with a moderate to low nitrogen; we must avoid adding one more condition of susceptibility.
