What is in this article?:
- Managing powdery mildew in peach orchards
- Management of powdery mildew
- Powdery mildew of peach occurs worldwide, but is most damaging in semi-arid growing areas. This means that in some years in California the disease can be severe.
- The disease can be caused by several different species of powdery mildew fungi that commonly occur on Rosaceous plants.
Management of powdery mildew
Selection of less susceptible cultivars, cultural practices, and the use of protective fungicide treatments are the most important practices for managing the disease. Less susceptible cultivars should be planted in areas that commonly have a high incidence of disease. To reduce the relative humidity in the orchard, the frequency of irrigation periods should be minimized and low-angle sprinklers should be used to keep foliage dry. Fungicide applications are done from full bloom until the pit hardening stage of fruit development for peach. Adequate management of rusty spot was achieved with three to four fungicide applications including the full bloom treatment in the most favorable conditions for disease.
Several products are available for managing powdery mildew. Wettable sulfur has been known to be effective for many years but has the shortest residual residue. In orchards where mildew has been a problem, a pre-bloom treatment with wettable sulfur can be used to reduce the chasmothecia and subsequently the primary inoculum.
For bloom sprays the SBI fungicides (propiconazole/Tilt, Bumper, fenbuconazole/Indar, metconazole/Quash, myclobutanil/Rally, tebuconazole/Elite, Tebuzol, Orius in EC or WP formulations; the QoI fungicides (such as azoxystrobin/Abound) or trifloxystrobin/Gem; and wettable sulfur are effective materials. Other materials include premixtures such as pyraclostrobin & boscalid/Pristine and the newly registered propiconazole & azoxystrobin/Quilt Xcel. Several new premixtures will be registered this coming year and include azoxystrobin&difenoconazole/Quadris Top, trifloxystrobin & fluopyram/Luna Sensation and pyraclostrobin & fluxapyroxad/BAS703. In our testing this year we found that the new SDHI products, fluopyram and fluxapyroxad, are also highly effective against powdery mildew but will only be sold as premixtures. Thus the premixtures offer high activity, very consistent performance, and built-in resistance management with two different modes of action for powdery mildew management.
Lastly for petal fall (to pit hardening) treatments, the products mentioned above can be used, as well as two new materials that only have activity against powdery mildew. Quinoxyfen/Quintec, which was registered in 2010, has a unique mode of action and can be used to break-up overuse of SBI and QoI fungicides.
Another material with a different mode of action that is only active against powdery mildew is metrafenone. This material is not registered on tree crops but it is going through the specialty crop registration process. The outlook is very positive for new modes of action that are highly effective against powdery mildew. Just as using single-site mode of action fungicides, when using pre-mixtures or tank mixtures rotate between the FRAC Groups, never apply more than two consecutive applications of the same FRAC Group number, and, ideally, rotate between the FRAC Groups with every application.