Pistachio

While the tree is leafless, train young trees to a modified open vase with three or four scaffolds spaced about 8 inches apart vertically, the lowest around 4 feet up. On bearing trees, cut back into older wood every three to four years to force new shoots. Finish any tipping cuts on Golden Hills and Lost Hills early in the dormant window, well before buds swell. Pistachio flowers on one-year-old wood, so a tree that stops making new shoots stops making nuts. Opening the canopy also dries the interior, which is how you starve Alternaria late blight of the humidity it needs.

Apply ammonium sulfate broadcast in two equal doses: the first half before the first irrigation as growth begins, the second half in June. On bearing trees figure roughly one-tenth to one-twentieth pound of actual nitrogen (about a half to one pound of ammonium sulfate) per inch of trunk diameter per year. Apply no nitrogen at all after June. Pistachio fills its kernels on nitrogen taken up early, and splitting the dose keeps it available without pushing it past the root zone. Nitrogen applied after June keeps the tree growing soft wood into fall, which delays dormancy and leaves it open to winter injury.

Beginning at bloom, apply azoxystrobin or pyraclostrobin, timing each application ahead of a forecast rain and repeating at two to three week intervals for two or three sprays total. Botryosphaeria dothidea and Neofusicoccum mediterraneum splash from old rachises and cankers in rain and sprinkler water and infect buds, leaves and young fruit silently. The infections sit latent and only blight out once summer temperatures pass 86F, so spraying after you see symptoms is already too late.

From the start of nut maturation through harvest, adjust irrigation so water is not standing and the canopy is not being wetted, and knock down tall dense weeds and cover crops under the trees. Alternaria late blight builds through the last weeks before harvest, and it runs on humidity and leaf wetness rather than on rain. Sprinkler and flood water plus a dense weedy floor hold that moisture against the leaves and stain the hulls black.

When the earliest nuts begin to split, pull a sample and count how many nuts per 100 have split early, and check those nuts for navel orangeworm eggs. Consider treating at early split only if BOTH are true: more than 2 early split nuts per 100 total nuts, and navel orangeworm eggs are consistently found. Count early split nuts, not damaged nuts - early splits measure how much of the crop is already exposed, which is what decides whether an extra spray is justified ahead of the main hull split treatment. The shell splits before harvest and that opening is the doorway navel orangeworm larvae use to reach the kernel. Nuts that split early are open early, so they take the pressure of a whole extra generation. Counting them tells you whether this year's exposure justifies an extra spray, instead of guessing - and pairing the count with an egg check keeps you from spraying when the moths are not actually there.

At hull split, roughly a month before harvest, spray methoxyfenozide or chlorantraniliprole. This is the one spray most orchards cannot skip. Hull split coincides with the third navel orangeworm flight, and it is the moment the whole new crop becomes vulnerable at once - the split hull and shell let larvae walk straight into the kernel.

Harvest once the hull separates easily from the shell when rubbed. You have roughly a 7 to 10 day window. On Golden Hills and Lost Hills, go on hull slip alone - do not wait for the hulls to tatter the way Kerman's do, because waiting will not improve their split percentage. Tannins in the hull stain the shell once the hull starts breaking down, and every extra day on the tree is another day of navel orangeworm and Alternaria working on a nut that is already open.

After harvest, knock down and destroy every unharvested nut left in the tree and on the ground, and prune out blighted shoots, panicles and cankered wood, cutting 2 inches beyond the blighted margin. Get it done before the first rains. Mummy nuts are where navel orangeworm overwinters, and dead rachises and cankers keep producing Botryosphaeria spores for up to six years. Nuts pulled to the ground early rot away once soil moisture rises, but a mummy left in the canopy is next year's infestation.