Pathogen isolates (individuals) were obtained from single powdery mildew colonies (lesions) on field-grown leaves collected near the end of the growing season from research plantings in California, Florida, Maryland, Mississippi, Ohio, and Texas in 2022 and/or 2023.
The leaf disk bioassay procedure was used.
Resistance to Endura (FRAC 7) was detected in FL (both years), CA (only 2023), MD (only 2022), and OH (2023).
Resistance to Torino (FRAC U6) was detected in FL (only 2022), MD (only 2022), and OH (2023).
Resistance to Quintec (FRAC 13) was only detected in FL, and only in 2022.
All three isolates from FL that were resistant to Torino were also resistant to Quintec. These isolates were not tested for resistance to Endura. Isolates with resistance to these three fungicides plus QoI (FRAC 11) and MBC (FRAC 1) fungicides have been detected in NY.
Isolates Collected in 2022
| Percent resistant isolates | ||||
| State | # Isolates tested | Endura | Torino | Quintec |
| CA | 9 | 0 | 0 | 0 |
| MS | 2 | 0 | 0 | 0 |
| FL | 4-5 * | 50 | 60 | 60 |
| TX | 4 * | 0 | 0 | 0 |
| MD | 4-5 * | 25 | 20 | 0 |
* 9 isolates total; not all tested
Isolates Collected in 2023
| Percent resistant isolates | ||||
| State | # Isolates tested | Endura | Torino | Quintec |
| OH | 11 | 64 | 27 | 0 |
| CA | 12 | 33 | 0 | 0 |
| FL | 13 | 31 | 0 | 0 |
| MD | 12 | 0 | 0 | 0 |