Backyard Orchard News
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UC Kearney Agricultural Research and Extension Center scientists have found that production costs can be cut dramatically by growing “dwarf” trees that minimize the need for ladder access. However, the limiting factor for peaches has been the lack of acceptable dwarfing rootstocks for the best peach varieties.
In 1987, UC and USDA scientists began a landmark rootstock evaluation project. More than 100 varieties that were either collected or bred by USDA plant breeder David Ramming were planted at Kearney. Five trees each of O'Henry peach and Santa Rosa plum were grafted on the rootstocks and extensively evaluated over the next seven years.
For peach, eight selections showed good potential as dwarfing or semi-dwarfing rootstocks and were propagated for further evaluation. In 2004, two of these were patented as the slightly dwarfing rootstock, “Controller 9,” and the very dwarfing rootstock, “Controller 5.”
At UC Davis, now retired researcher Fred Bliss bred rootstocks using Harrow Blood and Okinawa as parents. UC Davis pomologist Ted De Jong has taken over the program, which patented and released three new rootstocks: Controller 7, Controller 8 and Controller 9.5. A fourth, Controller 6, will be released soon.
The research blocks with Controller 6, 7, 8, and 9.5 at Kearney are continuing to be monitored for production performance and sustained productivity. So far, their performance looks positive but, because of funding cuts, the long-term outlook for maintaining the plots is questionable, De Jong said. UC Cooperative Extension farm advisor Kevin Day is conducting trials of “controller” rootstocks in conjunction with growers to help them determine which ones best fit their farming operations.
De Jong said there is significant interest in Controller 9 because it has been available the longest. Trees on Controller 9 are only slightly reduced in size but require significantly less pruning than trees on the standard rootstock, Nemaguard. There is also substantial interest in Controller 6 by growers who are more aggressive in their interest in smaller trees. Controller 6 causes a substantial reduction in tree size without reducing fruit size.
“I think that Controller 7 may be an optimal choice for many growers because it offers modest size-control and trees on it have had excellent production characteristics and is not such a large leap to a smaller tree,” De Jong said. “However there has been limited interest in it thus far.”
Controller 5 likely makes trees too small for commercial California peach production and trees on it tend to produce smaller fruit. However, it has good potential for home gardeners who have limited space, prefer not to prune much and aren’t very concerned about fruit size.
De Jong, Day, UC Davis pomology specialist Scott Johnson and numerous students have conducted extensive research concerning the dwarfing mechanism involved in these rootstocks and published more than 10 scientific articles on different aspects of the research. These articles and more information about the California Rootstock Breeding Program are available on the UC Fruit Report website.
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Soil solarization involves covering a field with clear plastic mulch to trap solar radiation in moist soil. During the hot summer months, the soil temperature can rise to levels that can kill soilborne diseases, nematodes and weed seeds. This system has proven especially useful to small-scale, limited-resource and organic growers who produce specialty crops in warm climates.
Last summer’s research, coordinated by Kearney-based integrated pest management plant pathologist Jim Stapleton, was part of a bi-national, multi-institution collaborative effort led by UC Davis biological and agricultural engineering professor Jean VanderGheynst. The research was funded with a grant from the Binational Agricultural Research and Development Fund, which supports agricultural research in Israel and the U.S. that is mutually beneficial.
Environmental science students at Fresno Pacific University, under the supervision of professor and project collaborator Ruth Dahlquist, were enlisted to carry out some of the research on micro plots at Kearney. They subjected black mustard seed to a solarization regimen that mimicked typical farming conditions to study the effects of the treatment on the seeds and the physical and biological properties of the soil.
Two of the Fresno Pacific students were honored by the California Weed Science Society at its annual meeting in January for posters they developed based on their research findings. DeeAnn Kroeker earned first place in the student poster contest for her analysis of the effects of volatiles produced during solarization of compost-amended soil on black mustard seed inactivation. Kate Hernandez was awarded third place for her poster about the field effects of solarization and compost treatment on inactivation of black mustard seed.
The research at Kearney continues during the summer of 2012.
The Israeli counterpart of the solarization research is focused on the impact of a different type of compost and solarization on fungal plant pathogens in the soil.