As the 2026 almond season moves through petal fall and into early leaf development, Red Leaf Blotch (RLB) continues to be an important disease consideration for California growers. Observations from UC Cooperative Extension and current field monitoring suggest that disease risk this spring remains present, even under drier conditions, reinforcing the need for timely, informed management decisions.
According to Florent Trouillas, UC Cooperative Extension plant pathologist, spore trapping data from multiple locations, including Stockton and Merced, show continued detection of Polystigma spores over the past two weeks – despite the absence of rainfall – in sprinkler and drip-irrigated orchards.
What We’re Seeing in the Field This Season
Based on current monitoring, spore release has occurred under a range of spring conditions. Sprinkler irrigation, especially systems that wet leaf litter, remains a concern for increasing disease risk. While relative humidity alone is generally insufficient to drive infection, the presence of free moisture on leaf surfaces, including dew, may provide the conditions needed for spore germination and infection.
Seasonal Timing Still Matters
This season, fungicide timing remains a central consideration. In 2026 field trials, applications were made during the first week of March, with follow-up sprays planned approximately three weeks later. These timings reflect current best judgment for managing disease pressure this year, based on both California observations and experience from other production regions.
Trouillas recently noted that petal fall and the following two to three weeks remain critical windows for protecting emerging leaves. While some growers may consider delaying applications during dry stretches as a cost-saving measure, this approach should be weighed carefully against orchard history, irrigation method, and overall disease pressure, which has been high statewide.
In previous seasons, even a single well-timed application in early March helped keep orchards relatively clean, with symptoms appearing later and limited mainly to new shoot growth that emerged after treatment. These observations continue to inform seasonal recommendations as more California-specific data are collected.
