I’ve had a few calls this week from growers who are starting to feel like they’re seeing more downy mildew showing up recently despite spray programs that they feel should be keeping the disease in check. It is somewhat concerning that DM infections are already showing up this early in the season, although the weather has definitely become more DM-friendly over the last couple of weeks.
I have mentioned that we have found populations in the Finger Lakes that have the gene mutation that confers resistance to these fungicides, and my concern is that we will be finding more over time. THIS IS NOT TO SAY THAT GROWERS SHOULDN’T USE REVUS AND REVUS TOP ANY LONGER! It is a reminder, however, that good resistance management practices (i.e., no more than 2-3 uses per year and not back-to-back) are critical with this material. Katie Gold and I are still interested in collecting DM samples this year in vineyards where there is concern about Revus (FRAC 40) losing effectiveness against DM. If you are concerned that Revus/Revus Top/Zampro might not be working quite as well as they used to, reach out to me and we’ll make arrangements to come and collect a sample.
Katie offered some bullet points for me to include in this week’s newsletter about other materials that are still very viable DM materials if growers want to consider scaling back their use of FRAC 40 materials.
- There’s might still be time to apply RIDOMIL GOLD MZ (ridomil + mancozeb) for immediate post-bloom, which I STRONGLY recommend if you are concerned about downy this year. Only use this ONCE. Ridomil Gold/Copper (ridomil + copper) is another option with a shorter PHI.
- Growers can use GAVEL (zoxamide + mancozeb) to give mancozeb a bit of an extra oomph until it runs out. Gavel also has a 66-day PHI.
- Half of ZAMPRO is still safe and EFFECTIVE to use! Ametotoctradin (the material that is not in FRAC 40) is VERY effective against DM and can stand on its own without the dimethomorph (Revus cousin) to back it up. The risk is that ametotoctradin is also material with a HIGH resistance risk, and if you have Revus resistance then you will NOT have the Revus cousin to back it up. DO NOT USE TWICE IN A ROW. ALWAYS rotate with unrelated material between applications. Can use up to 3x total (less if you sprayed Revus this year). I recommend using no more than twice.
- [Ranman + Phosphyt/Rampart] combo can be used up to 3x per season. If you have bad DM and don’t want to use captan you can rotate this with Zampro in the late season. This combination is expensive but will keep it under wraps.
- Use CAPTAN in late season if you are already seeing DM right now. Cueva is another option if you don’t want captan.
