Early hull split, when the hull begins to open at the suture, is a don’t-want-to-miss timing in almond production. The crack in the hull does two things: releases nut volatiles so the navel orangeworm (NOW) female can find the nut (and lay eggs), and gives wound pathogens like Rhizopus and Aspergillus an opening to infect the hull. Spraying at the right time (b2 stage, see photo below) when hull split first begins (in the upper, southwest side of the tree) is critical to effective hull rot and NOW management throughout the orchard. Because it takes time to get across orchards, consider starting spraying just before nuts get to this stage.
Spraying the suture is the key. That’s where the NOW females prefer to lay eggs and that’s where the hull rot spores can infect. Delivering a good cover spray to tree crops is a lot like painting a large house. For good weather protection of house siding, even paint coverage (no gaps), is needed. In almonds at hull split, the whole canopy, leaves and all, must be evenly sprayed to protect the nuts —to leave no gaps you have to “paint the whole house”. There are 4-8 acres of leaf surface area in an acre of mature, vigorous almond trees. Multiple studies in almonds from Colusa to Fresno have shown that 150-200 gallons per acre (GPA) spray volume delivers better NOW control than 100 GPA.
Additional steps help deliver the best coverage possible. Slow tractor speed — 2 MPH – gives the sprayer fan time to move the spray material throughout the canopy. Spraying in dry, warm air (relative humidity below 40% and temperatures above 80oF) can reduce spray coverage 50% in the tree tops as spray evaporates.
For the best possible spray coverage and NOW and hull rot control in mature almonds at hull split, use 150-200 GPA, drive 2 MPH, and spray when relative humidity is above 50% and temps below 80oF. [If this approach sounds too expensive and time consuming, try it out where you have the most NOW and hull rot pressure.]
Hull split is a critical timing for pest control in almonds. NOW and hull rot pressure have increased the last few years. Proper spray timing and delivery will help make reject sheet reading less painful and almond growing more profitable.