INDUSTRY NEWS
What do I plant ? A Californian researcher shares his thoughts
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ROGER Duncan has been an orchard crops farm advisor with the University of California Cooperative Extension for more than 30 years , working primarily in almonds and peaches . He works closely with growers , consultants and commercial tree nurseries in Stanislaus County , an area with more than 90,000ha of commercial almond orchards . Mr Duncan ’ s research and extension program has included testing new rootstocks and varieties , minimal pruning systems and orchard design for efficient almond production . While Australian almond growers grapple with what varieties they should be planting , Mr Duncan said that isn ’ t the only consideration that needs to be made . “ I tell our growers in California that choosing the correct rootstock is often more important than choosing the variety ,” he said . “ Rootstocks influence a lot of things including nematode and soil borne disease resistance , tolerance to soil and water chemistry problems , plus vigour , date of maturity , bloom time , nutrition , anchorage , and drought tolerance . “ Rootstocks can mean the difference between a high producing orchard with few remedial inputs vs . an orchard that requires constant intervention and still doesn ’ t produce well .” At the Australian Almond Conference , he explained that almond rootstocks largely come from three different genetic pools : peach , almond and plum .
• Peach has been the most common and includes varieties like Nemaguard and Guardian . Generally peach rootstocks have moderate vigour , goodfair anchorage and are highly compatible with almond . On the downside these rootstocks are salt sensitive so aren ’ t the best choice in orchards with high sodium , chloride or boron .
• Almond rootstock has evolved to be more drought tolerant , vigorous , and more resistant to calcareous soils , sodium , chloride and boron . Hybrid rootstocks of almond with peach or plum usually carry those characteristics .
In A Nutshell - Summer 2024 Vol 25 Issue 4
Orchard crops farm advisor Roger Duncan spoke at the Australian Almond Conference about his trials in California .
• Plum rootstocks are generally more tolerant of wet soils and soil-borne diseases . They have much lower vigour , especially in sandy soil or when drought stressed . There are often some compatibility issues with plum rootstocks and almonds . Krymsk 86 and Rootpac R are half plum and peach and half plum and almond , respectively , and have shown incompatibility issues with some almond varieties . While Garnem is a popular rootstock in Australia , Mr Duncan said he ’ s not aware of it being used commercially in California . Other peach x almond hybrid rootstocks , such as Hansen , Brights Hybrid # 5 , Cornerstone and others have gained in popularity . Rootknot nematode is a concern in some locations but almost all of the rootstocks that are used today are very resistant , with the exception of Krymsk 86 and Lovell . Ring nematode can be a real problem in sandier soils , especially in second generation orchards . Ring nematode can slow the growth of the tree , but more importantly it predisposes these trees to bacterial canker disease , where the top parts of the tree often die but the roots stay alive and they just get a bunch of suckers . “ If you want to protect yourself from ring nematode your best bests are Viking and Guardian , and in my opinion , I would choose Viking because it has many other positive attributes that Nemaguard and Guardian don ’ t have ,” Mr Duncan said . “ Viking can be a drop-in replacement for Nemaguard and Guardian , if you like that moderate vigour , but it protects against other things that they do not , including decent salinity tolerance , and it has much better anchorage ." Mr Duncan also acknowledged that most rootstocks are either susceptible or highly susceptible to phytophthora . “ There ’ s a lot more species of Phytophthora now than there was 25 years ago , as more and more species are being discovered ,” he said . “ Some species of Phytophthora can attack some rootstocks better than others , but in general if you want protection against Phytophthora , and this would also go along with having heavy soils and poor drainage , the plum rootstocks are hard to beat for that .” If having straight almond trees is a Continued next page