#1. Monitor for signs of alternaria through June, looking on exposed leaves for large, brown spots which then turn black, watching the most susceptible varieties (Carmel, Sonora, Monterey, Winters and Butte).
You can also use the Disease Severity Value model to time fungicide applications, based on temperature and leaf wetness.
#2. Watch for scab lesions on green, 1-year-old twigs. Once twig lesions have sporulated, protective fungicide applications should occur prior to the next significant rain.
Additional treatment may be warranted if frequent rains continue into spring. Leaf lesions will initially appear as small yellow specks in late spring that develop into grey diffuse lesions, sometimes followed by defoliation in early summer when the disease is severe. Some shot hole sprays will also control scab.
Be aware that in some orchards, scab resistance to FRAC Group 7 and/or 11 fungicides has been documented. Treat following UC IPM guidelines.
#3. Anthracnose may be a problem if rainy weather persists though April and temperatures are warm, especially in orchards with a history of the disease. Anthracnose infects nuts and causes marginal leaf necrosis and branch dieback to the point where an infected nut is attached.
#4. Monitor shot hole leaf lesions for spore development (a small dark speck in the middle of the leaf lesions). UC guidelines suggest applying treatment prior to additional rain as soon as spores are evident since that’s when the disease can become epidemic.
Additional treatment may be necessary if rainy, wet conditions persist through spring.
#5. Watch for shoot strikes caused by PTB or OFM starting in mid-April, primarily in first-leaf orchards where you’re encouraging shoot elongation to establish tree structure.
There’s no consensus threshold of how much damage warrants treatment in young trees. But keep in mind that damage at the tip of a primary scaffold will stop that branch from growing longer and shift growth into side branching. That impacts the tree’s structure and makes primary scaffold selection more difficult in the first dormant pruning.
#6. Monitor for NOW. Traps (egg, pheromone, bait-bag) should have gone out by the first week of April, if not sooner. Check egg traps twice weekly to determine biofix. Many experienced practitioners in the Sacramento Valley use the first NOW eggs found in traps as the biofix. This differs from common practices in the San Joaquin Valley because our population pressure is often lower.
Pheromone and bait-bag traps can be used to track male and female flights and relative abundance.
#7. Manage gophers before their reproductive pulse – usually between March and May. While flooding may have increased winter mortality, increased rain-fed vegetation could increase reproduction this spring.
#8. About a third of crop nitrogen use will occur by early April this year (that’s adjusting for our late start). With all the rain, this is a tricky year for keeping nitrogen in the root zone where trees can use it.
#9. Re-evaluate your “Right Source” of nitrogen if rain persists. Nitrate and urea leach easily with excessive rainfall or irrigation, whereas ammonium-based fertilizers will not (though unused ammonium can be transformed to nitrate by soil bacteria after a few weeks in the soil).
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If you are worried your orchard may be nitrogen deficient, consider taking early season leaf samples by 45 (±6) days after full bloom. Careful following of leaf sampling protocol will provide a good estimate of how summer leaf levels will look.
#10. Before you start irrigating, consult plant and soil moisture sensors, and compare stored soil moisture and rainfall with this season’s evapotranspiration (ET) so far.
#11. Begin monitoring for large bugs (leaffooted bugs in April, stink bugs in May).