Citrograph May-June 2010 - Citrus Research Board

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and trees were obtained from a private nursery. Similar growth characteristics to those measured at LREC were monitored on Fukumoto and Washington navel trees on Carrizo rootstock, planted in large 20-gallon pots that contained either neutral (pH approximately 6.5 to 7) or alkaline soil (pH 8.0 or greater}. Pots were acidified with soil sulfur or made more alkaline with hydrated lime. Soil samples from the pots were analyzed by the Agriculture and Natural Resources laboratory at University of California Davis. Measurements associated with pH, such as available zinc, iron, copper, manganese, calcium, sulfates, carbonates, electrical conductivity, and other compounds were also tested in the soil and in leaves. Sum of suckers and water sprouts 40 30 20 10 Tree 8 Tree 21 Tree 26 Tree 39 Tree 55 Tree 66 Tree 73 Tree 90 Tree 108 Tree 119 Tree 128 Tree 141 Effect of irrigation and soil pH on Fukumoto decline The level of irrigation and soil pH achieved in these LREC and UCCE Kern experiments did not produce any severe decline symptoms or any measured growth characteristic in the Fukumoto trees. Drought stress, though, was clearly evident between irrigations in all varieties in the treatment receiving the lowest irrigation application rate in 2007, 2008 and 2009, and leaf yellowing and early leaf drop was evident in the alkaline pots. Poorly performing Fukumoto trees were present in both experiments, but they appeared randomly across all irrigation treatments and in pots with both neutral and basic soil pH. Fukumoto trees on citrange rootstocks (i.e. Carrizo and C-35) were more likely to be stunted as reflected in their smaller scion diameters and reduced ratio of scion diameter to rootstock diameter (Tables 2 and 3). Fukumoto Average number of suckers and water sprouts per tree 14 12 10 8 6 4 2 0 2005 2006 2007 2008 2009 22 Citrograph May/June 2010 Fukumoto/Carrizo Washington/Carrizo Fig. 3. Average number of suckers and water sprouts per Fukumoto or Washington navel tree per year on Carrizo rootstock in large pots at UCCE Kern. For Year 2009, the total is as of June 18. 0 2004 2005 2006 2007 2008 2009 Fig. 4. Annual total number of suckers and water sprouts for each Fukumoto tree on C-35 rootstock in the LREC trial (identified by position in the trial regardless of irrigation treatment). For Year 2009, the total number of sprouts is as of June 11. trees were also more likely to produce large numbers of suckers (sprouts produced below the graft union) and water sprouts (scion sprouts produced within four inches of the graft union) compared to Washington navel at LREC (Fig. 2) and UCCE Kern (Fig. 3). Production of large number of suckers and water sprouts in many tree crops has been considered a sign of incompatibility of the scion with the rootstock but may be caused by other factors as well. This excessive sprout production is characteristic of many trees in most Fukumoto orchards. Fukumoto on C-35 rootstock, generally, demonstrated more sprout production and a smaller scion/rootstock diameter ratio than did Carrizo (Table 2 and Fig. 2) Differential sucker and water sprout production between Fukumoto and Washington navel did not begin to occur at LREC until the third year of the trial (Figures 2 and 4). Citrus trees growing in the 20-gallon pots of the UCCE Kern experiment were usually under considerably more transient water and salt stress than those growing in the ground because of a poorer soil water storage reservoir and poorer drainage. In UCCE Kern, unlike the trial at the LREC, differential sucker and water sprout production between Fukumoto and Washington navel was observed during the first year of the trial (Fig. 3). The average values shown in the tables and figures tend to minimize the actual differences seen in the experimental plots or pots between the best and poorest performing Fukumoto navels for all measured growth characteristics. For example, the number of suckers produced by a given Fukumoto tree varied considerably (Fig. 4). Note, also, that trees that produced excessive sprouts at an early age continued producing high numbers of sprouts as they grew older even though the trunks were shaded by the leaf canopy. Variable performance of individual Fukumoto trees within a grower’s field is commonly observed in commercial orchards as well. Why some Fukumoto trees perform similarly to Washington
navel on the citrange rootstocks and others perform poorly remains unknown. Ants were present in the LREC test plot in 2006, and their presence was associated with tree trunk gumming. In some Fukumoto trees, the gum was frothy, with small branches breaking at their attachments to the larger scaffolds as occurs with foamy bark rot. Twenty-four percent of Fukumoto navel trees were exuding gum, compared to only 9 and 1% of Washington navel and Clemenules mandarin, respectively, suggesting Fukumoto navels produce more gum and so are more attractive to ants. Observationally, the gumming in Fukumoto not only occurred under the tree wrap as in the other two varieties, but commonly higher on the scaffolds and in the leaf canopy. At LREC, Fukumoto fruit yields in 2007 and 2008, the only years measured, were not significantly different among the four rootstocks (data not shown), although with time the stunted trees would probably fall behind the vigorously growing trees. No late-maturing or off-type fruit was observed in the trials. Differences were not found among cultivars and rootstock combinations for midday leaf water potential made in June and July of 2006 at LREC, or for differences in starch accumulation above the graft union among the best-performing or worst-performing Fukumoto trees made in December 2009. Accumulation of starch above the graft union may have been indicative of graft union incompatibility; however, profuse sprout production below the graft union may have been sufficient to mask lack of translocation through the graft union. Application of research results for Fukumoto navel growers The cause of Fukumoto tree decline remains unknown, and scion-rootstock incompatibility remains a possibility. Based on the results from this project, the following suggestions are made for growers planting or that currently are cultivating immature blocks of Fukumoto navels: • Extra effort in identifying and eradicating southern fire ant infestations is warranted. • Growers accustomed to growing other navel cultivars, such as Washington navel, may find for similarly aged trees under similar environmental conditions that Fukumoto navel may require less water than Washington navel as a result of a smaller canopy. • More frequent passes through the orchard to remove “Consulting for Production Agriculture” A complete line of: • Nutritional Sprays • Herbicides • Insecticides • Fertilizers • Organic products Locally owned Servicing the citrus belt for over 60 years 11 PCA’s with over 350 combined years of experience 3 Convenient Locations: Ivanhoe Lindsay Terra Bella 798-1153 562-4946 535-4461 May/June 2010 Citrograph 23
Page 1: Citrograph May/June 2010 Citrograph
Page 4 and 5: ON THE COVER Citrus Pest and Diseas
Page 6 and 7: EDITORIAL By JIM CRANNEY, President
Page 8 and 9: A Mexican technician employed by AP
Page 10 and 11: Eyes under the soil Carl T. Gwillia
Page 12 and 13: Citrus Roots Preserving Citrus Heri
Page 14 and 15: By: Rahno Mabel MacCurdy, V.A. Lock
Page 16 and 17: Dowlin L. Young, co-founder of Youn
Page 18 and 19: Governor Schwarzenegger at center w
Page 20 and 21: CRB Funded Research Reports 2009 Re
Page 24 and 25: suckers and watersprouts will be re
Page 26 and 27: Citrus Quarantine, Sanitary, and Ce
Page 28 and 29: California Citrus Clonal Protection
Page 30 and 31: that environmental conditions in th
Page 32 and 33: annual budwood distributions. Any t
Page 34 and 35: Table 1. Comparative summary of the
Page 36: C L E A N C I T R U S Clonal Contai

Citrograph May-June 2010 - Citrus Research Board

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