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Based on yield variability in orchards, it is evident that many trees receive too much or too little water and fertilizer under uniform management. Optimizing water and nutrient management based on the demand of individual trees could result in improved yield and environmental quality. A microsprinkler sensor and control system was developed to provide spatially variable delivery of water and fertilizer, and a prototype was installed in a nectarine orchard. Fifty individually addressable microsprinkler nodes, one located at every tree, each contained control circuitry and a valve. A drip line controller stored the irrigation schedule and issued commands to each node. Pressure sensors connected to some of the nodes provided lateral line pressure feedback. The system was programmed to irrigate individual trees for specific durations or to apply a specific volume of water at each tree. Time scheduled irrigation demonstrated the ability to provide microsprinkler control at individual trees, but also showed variation in discharge because of pressure differences between laterals. Volume scheduled irrigation used water pressure feedback to control the volume applied by individual microsprinklers more precisely, and the average error in application volume was 3.7%. Fault detection was used to check for damaged drip lines and clogged or damaged emitters. A pressure monitoring routine automatically logged errors and turned off the microsprinklers when drip line breaks and perforations caused pressure loss. Emitter diagnosis routines correctly identified clogged and damaged microsprinkler emitters in 359 of 366 observations. Irrigation control at the individual tree level has many useful features and should be explored further to characterize fully the benefits or disadvantages for orchard management.

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As much as one-third of California's almond and stone fruit acreage is infested with potentially debilitating plant parasitic nematodes, and even more of the land is impacted by Prunus replant disease (PRD), a poorly understood soilborne disease complex that suppresses early growth and cumulative yield in replanted almond and peach orchards. Preplant soil fumigation has controlled these key replant problems, but the traditional fumigant of choice, methyl bromide, has been phased out, and other soil fumigants are increasingly regulated and expensive. We tested fumigant and nonfumigant alternatives to methyl bromide in multiple-year replant trials. Costs and benefits were evaluated for alternative fumigants applied by shanks in conventional strip and full-coverage treatments and applied by shanks or drip in novel spot treatments that targeted tree planting sites. Short-term sudangrass rotation and prudent rootstock selection were examined as nonfumigant approaches to managing PRD. Trial results indicated that integrations of the treatments may acceptably control PRD with relatively little soil fumigant.A pproximately 1 million acres of California's best agricultural land are devoted to production of almonds and stone fruits (USDA 2011), and sustained high production from this land requires that the orchards be replanted every 15 to 25 years, depending on the production system. Research has documented myriad problems that can suppress growth and productivity in such replanted orchards (Bent et al. 2009;Browne et al. 2006;Larsen 1995;McKenry 1996McKenry , 1999Westerdahl and McKenry 2002). Abiotic soil factors related to previous crop production, such as compaction, salinity, suboptimal pH, nutritional imbalances and herbicide residues, can compromise the performance of replanted orchards, but many of these problems can be avoided or remedied without great difficulty or expense.Biotic replant problems, including plant parasitic nematodes and Prunus replant disease (PRD), can pose more of a challenge. Plant parasitic nematodes infest as much as one-third of California's almond and stone fruit acreage (McKenry and Kretsch 1987) and have the potential to compromise all phases of an orchard's productive life by inflicting root damage. Several rootstocks for almonds and stone fruit have shown genetic resistance to root knot nematodes, but little resistance has been demonstrated against the other two major nematode pests affecting these crops, the ring nematode and the root lesion nematode (McKenry 2007). PRD, which is much more widespread than nematode damage on almonds and stone fruits, is a poorly understood soilborne disease complex that suppresses early growth and cumulative yield in replanted almond and peach orchards (Bent et al. 2009;Browne et al. 2006). It afflicts successive generations of almonds and stone fruit planted at the same location and is associated with poor health of the trees' fine roots and incidence of several plantparasitic fungi and oomycetes. The severity of the disease varies greatly among orch...

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