Nonpareil Bloom Effects
February 6, 2012 Why is February a relevant time to discuss hull rot in almonds? The answer is because it is one of the most significant reasons for poor bloom density, particularly on Nonpareil hangers. I concur with University of California Cooperative Extension farm adviser Brent Holtz when he opines that hull rot in almond is responsible for more economic damage than most other more well-known diseases that affect production. Why then is it so widespread and commonly misunderstood? There are multiple reasons:
• Timing: Hull rot does not show up until right before harvest, and with the hustle and bustle of shaking and picking up, it is easy to overlook.
• Vigor: High-yielding orchards with heavy crop loads, high nutrient levels, good water status, and vigorous growth are the most affected.
• Identification: Because the visual impact of hull rot limb dieback is wilted looking hangers with dry leaves, it is easy to assume this is a normal response to harvest-time irrigation cutoffs.
• The “Silent Killer”: There are two main pathogens that cause hull rot, Rhizopus stolonifer (bread mold) and Monilinia fructicola (brown rot). I refer to Monilinia as the “silent killer” because the color of its sporulation on the hulls is identical to the color of the drying hulls at harvest and is difficult to see. With Rhizopus, you get the classic black fuzzy mold that is easy to identify. Fumaric acid, a byproduct created from the molding hulls enters the twigs and kills branches, hangers, and in some cases whole limbs. The extent of this branch death often goes undiagnosed until February when the trees start to bloom (or should start to bloom and don’t).
There are management strategies that will reduce the severity, but not eliminate the incidence, of hull rot. Cultural practices that can reduce hull rot include deficit-irrigating at hull split and not over-fertilizing. Conditions that are harder to manage include heavy crop sets and dense canopies and high-vigor orchards on hybrid rootstocks. Prompt shaking at the first signs of hull rot will lessen the limb death as detached hulls cease poisoning the twigs. Recent research has shown that certain strobilurin and DMI fungicides applied at hull split may reduce hull rot; however, greater impact can be realized from adjusting the cultural practices.
Subscribe Today For
