By: Carolina López, Market developer Colchagua – Constanza Lozano, Market developer VII north.
Before the start of each season, producers receive a phytosanitary program from their exporters and/or advisors, which broadly presents an application program for pest and disease management according to phenological state or monitoring, providing alternatives for phytosanitary products for each application time. This program is a guide for producers to prepare the management of plant health in their orchard during the season, considering subsequent specific recommendations from their agronomists and technicians, and is also the basis for the decision to purchase phytosanitary products.
When defining which products to apply, many factors are evaluated: efficacy, costs, availability of these in the distribution chain, advice, tolerances, etc. However, one aspect that is rarely considered is the management of the resistance of these products, which will be discussed in depth on this occasion, specifically in the case of fungicides.
From the point of view of cherry tree diseases, it is important to emphasize that, although Botrytis cinerea (gray rot) remains the main problem associated with rots, secondary fungi such as Alternaria alternata (black rot) are increasingly present in different geographical areas, attacking a greater number of varieties. These pathogens manage to establish themselves during the flowering period, as a consequence of cold springs and mornings with high environmental humidity. Although each season is different from the previous one, it is important to highlight that even in dry springs, diseases such as Alternaria They are capable of establishing themselves and causing visible damage to the crop.
Therefore, protecting the most susceptible periods is key to keeping orchards free of pathogens, thus preventing their establishment and rapid spread. To do this, having chemical control with the use of fungicides as an alternative becomes an irreplaceable necessity until now, where the rotation of active ingredients and, above all, the modes of action of these products is essential.
It is important to understand, first of all, what is resistance? According to the FRAC (Global Fungicide Resistance Action Committee), “Resistance is a heritable change in the susceptibility of a fungal population that results in the repeated failure of a fungicide product to achieve the adequate level of control when used according to label recommendations for that pathogen.”
How is this resistance generated?
When applying a fungicide, the most susceptible individuals are eliminated from the pathogen population present in the orchard, favoring the frequency of those less sensitive, thus generating a “selection.”
How does the emergence of resistance affect?
Detecting resistance of a pathogen to one or more of the fungicide action sites is unfortunately directly detrimental to the farmer. For this reason, it is important to be rigorous in order to delay the emergence of resistance as much as possible, since, once it is detected, it will not be possible to prevent it from continuing to advance throughout future seasons.
Some key actions to avoid generating resistance to fungicides are the following:
High control efficacy. This is the main anti-resistance mechanism, since by fully controlling the pathogen it does not generate survival, and is less likely to generate selection pressure on the surviving population. Use of full doses of fungicides: For both products with a single active ingredient and for mixtures, it is essential to respect the doses of the active ingredient(s) separately (never reduce the dose thinking that combining active ingredients will compensate). This helps to reduce the possible selection of strains that have intermediate sensitivity in the case of quantitative resistance (caused by changes in various genes that cause different ranges of sensitivity).
Alternate fungicide action mechanisms: It is crucial to alternate the use of fungicides with different action mechanisms and at the same time, alternate or combine between those active ingredients with a high and low risk of resistance (check FRAC).
Decrease the number of applications of the same mode of action during the season: The objective is to reduce the number of exposures to the same mode of action during the season. In the following table, you can see 2 cases, both with 4 active ingredients with different modes of action (A, B, C and D) as a basis for building a disease control program with 8 applications during the season. In the first of them (Case 1) it can be seen that when using these 4 products in a mixture (A+B and C+D) each active ingredient is exposed 4 times versus case 2, where each product is applied separately, achieving only 2 exposure times for each active ingredient.
If a mixture of two fungicides is used, it should ideally be preferred that one of them be multisite or at least, avoid both being at high risk of acquiring resistance (example: carboxamides with strobilurins). In addition, it is vital that both fungicides are effective against the target pathogen and provide similar control periods.
Respect label indications: This last point is very relevant, considering that product labels contain all the necessary information to use them safely and responsibly. For this reason, it is important to respect the indicated concentrations or doses (check if there are associated minimum doses), wetting volume, maximum number of applications of the active ingredient per season, etc., to achieve excellent coverage of the floral structures of the foliage.
As an exporting country, regardless of the reality of each field, it is the responsibility of all technicians and producers to take care of these tools to protect our production and ensure a good arrival at its destination from a phytosanitary point of view.
For more information, please visit www.corteva.cl
