Orchard Tips from Bob Beede

deflocculates (disperses) the soil particles, reduces the pore space between them, and further reduces downward water movement. Review of average soil temperatures at six inches at several CIMIS stations (cimis.water.ca.gov) shows the shallow soil depths ranging from 50-54°F. Concern for saturated soil is greatest as we approach bud break. Using isotopically labeled nitrogen, UC researchers Rosecrance, Weinbaum, and Brown (see Tree Physiology 16, pp 949-956) found that pistachios in their on-year took up twice as much N during the spring root flush between March 17 and May 24 than the off-year. Root studies on deciduous trees show initial growth at soil temperatures about 58°F; peak root growth is about 70°F...Based on this data, readers can see that by the week of March 19, orchards with saturated soil throughout their root profiles could be at risk for root damage from low oxygen. Again, all this depends upon daytime temperature, soil drainage and continued rainfall. It is years like this that support laser-leveling orchards with heavy soil texture prior to planting, even with drip irrigation, to allow rainwater to migrate to one end of the field where it might be pumped off. It is highly recommended that growers with standing water do what they can to mitigate it. Doing so reduces the amount that must infiltrate into an already saturated soil; it also increases the rate at which surface soil oxygen levels recover. Growers with excessively wet soil should monitor the emerging bloom and foliage for signs of yellowing, an indicator of low soil oxygen. This can result in bloom shattering off the tree from organic chemicals produced in the roots and translocated up the vascular system to emerging flowers and leaves. I’m not predicting gloom and doom, but merely trying to explain what might happen in some orchards if the storms continue into April. Even in well-drained soil, growers may not need to irrigate before mid-to-late May, depending upon spring temperatures. The pistachio water requirement in non-saline soil is less than 1.5 inches for the entire month of April! Thus, a 4-foot root zone at field capacity with almost 6 inches of available water provides plenty of water until mid-May. Those needing to apply nitrogen during April should keep the applied water to a minimum. Orchards with high-silt surface soil and an absence of vegetation in the middles may benefit from spring-toothing as soon as practical to break up the crust and assist in aeration

Monitor Bud Break and Bloom: Expect to see a sharper and shorter bloom period this spring in both Golden Hills and Kerman, providing we experience favorable weather from late-March to mid-April. This will reflect the fact that the rest (chilling) requirement of all pistachio cultivars was fully satisfied this winter in most regions. Visual signs of rest satisfaction are Peters developing ahead of Kerman, and the south side of east/west planted orchards developing faster than the north side. Research shows the male Peters have a higher chilling requirement than Kerman. Thus, when its rest requirement is fully satisfied, it can develop before the Kerman female tree. Complete rest satisfaction also results in the south side of east/west planted trees pushing before or simultaneously with the north because the south side receives less chill in warm winters due to the sun rising and falling 29°F south of east (griffithobservatory.org). With marginal chilling, the north side of the tree pushes sooner because it is not as affected by the warmer winter temperatures due to its orientation to sunlight. Cold and rainy weather will slow tree development due to lower heat units. Be sure to make some notes about the dates at which bud break, early, mid and late bloom occur. This tells you how strung-out fruit set is, and to what degree, if any, you were affected by inclement spring weather. This information also gives you some indication of how strung-out harvest maturity might be. If you installed the weather station I sent you for Christmas, make a file on your computer for temperature data occurring during bloom and early fruit set. This will aid you