Rootstock selection is an important component of commercial citrus production worldwide. Soil type, scion compatibility, mineral tolerance, disease tolerance, and growth traits are the primary concerns when choosing a rootstock type.
Hybrid species of trifoliate rootstocks are popular with growers in California's San Joaquin Valley. Carrizo and C-35 are two of the most common varieties for oranges and mandarins. Both share the same scientific name, Citroncirus hybrid sp.
Many of the research plots at Lindcove REC utilize the common commercial varieties of both scion and rootstock, for example Parent navel on C-35, or Nules clementine on Carrizo. This allows the results of experiments to more closely resemble actual fruit production that comprises a hefty share of the domestic and overseas markets.
This month the staff at Lindcove REC are transplanting rootstock seedlings grown in cone flats to larger pots. The seedlings will grow quickly during the fall and will be large and healthy for budding next March.
A new planting of 500 Tango mandarin trees is scheduled for this month and field preparations are well underway. Senior Agricultural Technician Jose Hernandez uses heavy equipment to dig a trench for the irrigation line.
The new orchard will provide trees for insecticide trials for Dr. Beth Grafton-Cardwell's citrus IPM program. She plans to study the uptake and impact of systemic insecticides on various pests and the growth and development of young trees. Beth is an IPM Specialist and Research Entomologist with the University of California, as well as the Director of Lindcove Research and Extension Center. For more than 20 years Beth has been carrying out pesticide trials to determine the efficacy and suitability of selected chemical formulations for use against citrus pests in California. To learn about key pests of citrus and pest management tools and information, log on or subscribe to Beth's Citrus Bug Blog.
The trees were propagated here at Lindcove REC. Center staff grew the Carrizo rootstocks from seed in the greenhouse, and budded the trees with budwood purchased from the Citrus Clonal Protection Program.
The emergence cycle of captured walnut twig beetles (WTB) is being documented at LREC. The tiny beetles, in addition to a suite of other log-dwelling insects (including their parasitoids), emerge nearly year-round from infested walnut logs that are housed in outdoor enclosures. The insects are collected weekly, and then sorted, sexed, and counted. In 2013, WTB emerged from March-September, with peak emergence in mid-late June. In 2014, peak WTB emergence peak occurred in May-June, and emergence counts are falling off rapidly now that it is midsummer. One notable week's collection was May 13-20, with 1940 emerged WTB from one of the six emergence chambers.
Dr. Elizabeth Fichtner (Farm Advisor, Tulare UCCE) has recently acquired Yelena Martinez, a participant in the College of Sequoias SURGE (Student Undergraduate Research Group Experience) program, to assist Katie Wilson (UCCE Tulare) and Therese Kapaun (LREC) with the staggering number of weekly counts during the peak season. This photo shows Yelena viewing insects under a dissecting microscope and separating the different species into containers. Katie and Therese will continue to monitor and count emergences for at least the next twelve months.
WTB has been recently found to be associated with Thousand Cankers Disease, a fungal pathogen of several walnut species in North America. The pathogen was also recently reported on black walnut in Italy. More information on the disease, as well as the beetle can be found at:
UCCE In a Nutshell Newsletter Tulare County (pages 5-7)
Dr. Carol Lovatt (UC Riverside, Dept. of Botany and Plant Science) and Elizabeth Fichtner (UC Cooperative Extension Tulare County) continue olive research at Lindcove REC. A foliar application of plant growth regulator treatments in combination with urea was applied to mature olive trees this week to determine the potential value of these products to reduce or eliminate the alternate bearing cycle in olives.
Toan Khuong is seen here applying the foliar spray. Toan is a Staff Research Associate in Dr. Lovatt's lab at UC Riverside.
In March we budded more than 2000 citrus trees with various scions for upcoming research projects. May is a great time of year to watch the phenomenal growth of vegetation in a greenhouse. Vigorous varieties such as lemons have been putting on up to five inches of new growth each week, while navel and mandarin varieties are growing well although not as fast.
This photo shows what newly pushing buds look like, with the upper rootstock tops cut off and bent over at an angle. After the new growth of the scion reaches six inches or more, the remaining rootstock above the scion is removed completely so that the scion becomes the dominant trunk for photosynthetic activity and nutrient movement.