Etude de l'hétérogénéité des traitements antigerminatifs au Chlorprophame des pommes de terre

Study of the heterogeneity of chlorprophame treatments used to prevent potatoes' germination

Context

The potatoes crop can have different outlets : the fresh, plant, processing market, … For the latter, the storage season of potatoes can reach more than eight months.
To meet the market’s requirements, the initial value of the product stored must be kept. In order to do so, the potato sprouting which depreciates the quality of tubers must be controlled.
The storage of tubers at low temperatures (lower than 6°C) decreases the storage effect but depreciates the organoleptic quality by causing “low sweetening”, the accumulation of soluble sugars. In order to avoid these problems, a sprout inhibitor treatment is applied on potatoes.
The only active matter allowed in Belgium for the treatment is Chlorprophame (or CIPC). The producer can choose between different application methods depending on its storage infrastructures and the variety of potatoes : dusting, fogging, or spraying. Studies carried out by the University of Ghent showed that more than one third of the Belgian potatoes production contained Chlorprophame residues. In 1999, a study carried out by that same university showed that almost 8 % of the samples taken in the storage rooms exceeded the MRL (maximum residue limit) in Belgium being fixed to 5 ppm of active matter on entire potatoes.

Objectives

Regarding this statement, a research programme was set up in 2001 in order to analyse especially the heterogeneity of the CIPC distribution within the pile of potatoes, main cause of the punctual overdosage of sprout inhibitor on tubers.
The different treatment techniques were then assessed as for : their quality of application (distribution), efficiency, easiness of utilization, …

Description of tasks

For this study, trials are carried out directly in farms so as to analyse the distribution of the product applied on the potatoes ‘ supply.
Trials only concern lots of bintje potatoes stored in bulk. This variety has been chosen because it represents more than 80 % of the Belgian production. The potato supplies are treated according to different application methods (dusting, fogging and spraying). Each storage hall is subjected to a thorough supervision all along the storage season.
In order to know the causes of the treatments’ heterogeneity, the characteristics of the storage halls are studied (methods of ventilation, capacity, temperatures, …) as well as the application techniques of the sprout inhibitor treatment. Some samples are taken off at different levels of the storage hall when piling up in order to assess the CIPC content into the whole pile. Furthermore, additional samples are taken once a month in the different storage rooms, in order to study the evolution of the active ingredient in the time and its effect on germination.
At the same time as these trials, some complementary researches were carried out, such as :
- technical analysis of the application equipment ;
- chemical analysis of the formulations ;
- study of the applicator’s safety ;
- analysis of the CIPC distribution of the tuber (peel – flesh) ;
- study of the efficiency of the different treatments ;
- ...

Results obtained

Some trials carried out in real conditions, that means in farms, put forward several interesting observations :

the dustable powder distribution is very heterogeneous, leading to high CIPC content on several tubers, sometimes higher than the MRL. Because of the powdery nature of the formulation and handling required by its application, this treatment technique also causes problems for the applicator’s safety. However, this treatment is very efficient ;

the sprout inhibitor treatment by emulsifiable concentrate formulation allows a more homogeneous distribution of the sprout inhibitor. During the tests, by applying the registered dose, no excess of MRL was observed when destocking. However, even though this type of treatment is very efficient, it seems to be less active than powdering.

fogging allows a quite homogeneous distribution of the CIPC within the pile. However, the quantity of active ingredient which remains on tubers after fogging is very poor, hardly 20 % of the dose applied, and it deteriorates quite quickly. The control of sprouting pressure by gas application is therefore less efficient than with the two other treatments. It is so necessary to treat regularly and preventively.