Almond and pistachio growers have intensified production practices in recent years in order to maximize yields. Unfortunately, higher planting density, more fertilization and increased irrigation provide ideal conditions for the development of diseases such as Alternaria leaf spot, anthracnose, shot role, rust and scab in almonds and Alternaria late blight in pistachios.
Alternaria has become much more important than it was 10-15 years ago, particularly as it becomes more prevalent in the northern half of the Central Valley. If not treated preventively with an effective fungicide, Alternaria can defoliate an almond tree prematurely at the expense of next year’s crop.
Protect Your Investment
I encourage almond PCAs and growers to apply a top-rated fungicide five weeks after petal fall as a first defense against Alternaria leaf spot. For instance, Quash Fungicide from Valent U.S.A. Corporation is very effective at controlling Alternaria at this timing, along with other tough diseases such as rust, anthracnose and scab. Quash stops fungal growth prior to symptom development. This ensures a normal leaf drop in the fall, allowing trees to preserve energy for next year’s crop rather than flushing early in response to a disease.
Quash is also active against both of the fungi that cause hull rot: Rhizopus stolonifer and Monilinia spp. Apply Quash at 2.5 to 3.5 oz/A at two to three weeks prior to hull split for Monilinia hull rot—this coincides with the last Alternaria timing in June—or at early hull split for Rhizopus hull rot suppression.
Pistachios Also at Risk
Similar to Alternaria leaf spot in almonds, Alternaria late blight is a disease that adversely affects pistachio crops. The combination of high humidity and leaf wetness stemming from frequent irrigation and morning dew provides an ideal environment for Alternaria late blight, which stains shells and can lead to mold on kernels and premature defoliation.
Alternaria late blight has shown resistance to QoI (strobilurin; Fungicide Resistance Action Committee – FRAC – Group 11) and SDHI (FRAC Group 7) fungicides in the Central Valley, there are no resistance issues with Quash. Also, unlike many of the commonly used premixes that may include, for example, a strobilurin, Quash offers a single mode of action and, therefore, a flexible fit in resistance management programs for both almonds and pistachios.
For optimum control of pistachio Alternaria late blight, apply Quash in June and July with a 2-3 week interval between sprays.
Remember: whether you’re growing almonds or pistachios, whether you’re located in the north or south half of the Central Valley, staying on top of your disease control program is of the utmost importance. If fungicides are applied after symptoms of a disease such as Alternaria become visible, your fungicide’s efficacy will be greatly compromised.
And even in seemingly dry conditions, preventive fungicide applications are a crucial component to maximizing yields—now and in the future.