|
The FRAC CAA Working Group was set up in 2005 to generate common resistance management recommendations for the Oomycete fungicides dimethomorph, flumorph, iprovalicarb, benthiavalicarb, mandipropamid and valifenalate.
All of the above-mentioned fungicides exhibit cross resistance and are grouped under the FRAC Code No. 40 in the FRAC Code List.
| CODE |
TARGET SITE
OF ACTION |
GROUP NAME |
CHEMICAL
GROUP |
COMMON NAME |
COMMENTS |
| 40 |
phospholipid biosynthesis and cell wall deposition (proposed) |
CAA -fungicides (Carboxylic acid amides) |
cinnamic acid amides |
dimethomorph
flumorph
|
Low to medium risk. Resistance management required. |
| valinamide carbamates |
benthiavalicarb iprovalicarb
valifenalate
|
| mandelic acid amides |
mandipropamid |
As shown in the table, the group name Carboxylic Acid Amides (CAA) has been chosen. This name best represents compounds from three different chemical groups.
The mode of action of CAA compounds has not yet been fully elucidated. There are proposals for inhibition of phospholipid biosynthesis and for interference with cell wall deposition.
Sensitivity monitoring studies over several years revealed that in populations of the late blight pathogen, Phytophthora infestans, all isolates were fully sensitive to CAA fungicides. However, in populations of the grape downy mildew pathogen, Plasmopara viticola, isolates can be found in certain regions, which are resistant to all CAA fungicides.
Inheritance studies (Gisi et al., Plant Pathology, 2007, 56, 199-208) showed that sexual crosses between sensitive and CAA resistant isolates of Plasmopara viticola lead to a co-segregation of resistance to dimethomorph, iprovalicarb, benthiavalicarb and mandipropamid, but not to the phenylamide, mefenoxam, which was tested in parallel as an independent marker.
Further, the inheritance studies showed that the gene(s) for resistance to CAA fungicides are inherited in a recessive manner. Therefore, the entire F1 generation of crosses between sensitive and CAA resistant isolates was sensitive, and only in the F2 progeny did CAA resistance reappear in some isolates. These results suggest that the resistance risk can be classified as moderate (as compared to high for phenylamide and QoI fungicides) and that it can be managed by appropriate product use strategies (see below).
| 
