Posts Tagged: lemon
The Orange County Master Gardeners have lived up to their name with their website information on citrus. It's a truly impressive information site for not only homeowners, but also growers:
The “Citrus Problem Diagnosis Chart” is especially work perusing:
Lime-induced Iron Chlorosis: a nutritional challenge in the culture of several subtropical perennial crops in California
Elizabeth Fichtner, UCCE Tulare County and Rachel Elkins, UCCE Lake and Mendocino Counties
Spring, and new leaves are coming out, but this could, but yellow could be a sign of iron chlorosis, as well.
Although iron (Fe) is the 4th most abundant element in the lithosphere, Fe deficiency is among the most common plant micronutrient deficiencies. Fe deficiency in plants is common in calcareous soils, waterlogged soils, sandy soils low in total Fe, and in peat and muck soils where organic matter chelates Fe, rendering the element unavailable for plant uptake. In California, lime-induced Fe deficiency is often observed in soils and irrigation water containing free lime, and is exacerbated by conditions that impede soil drainage (ie. compaction, high clay content), resulting in reductive conditions. Given that over 30% of the world's soils are calcareous, lime-induced Fe deficiency is a challenge in numerous perennial cropping systems including: grapes, pears, apple, citrus, avocado, pecans, and stone fruit (prune, almond, apricot, peach, nectarine, cherry).
In most soils, Fe oxides are the common source of Fe for plant nutrition. Solubility of Fe oxides is pH dependant; as pH increases, the free ionic forms of the micronutrient are changed to the hydroxy ions, and finally to the insoluble hydroxides or oxides. In calcareous soils, the bicarbonate ion inhibits mobilization of accumulated Fe from roots to foliage and directly affects availability of Fe in soil by buffering soil pH. When irrigation water is also high in bicarbonate, probability of Fe deficiency is enhanced because bicarbonate is continuously supplied to the soil, and more importantly, the roots may become crusted with lime as water evaporates, thus inhibiting root growth and function. Inside the plant, bicarbonate inhibits nutrient translocation from roots to aboveground plant parts. The adverse effects of high bicarbonate levels are exacerbated in very saturated, very dry, or compact soils, where bicarbonate levels increase concurrent with diminished root growth and nutrient uptake.
Symptoms of Fe deficiency in plants
Fe is immobile in plants; therefore, symptoms appear in young leaves. Interveinal chlorosis (Figure 1) is the main symptom associated with Fe deficiency, followed by reduced shoot and root growth, complete foliar chlorosis, defoliation, shoot dieback, and under severe conditions may result in tree mortality. Overall productivity (yield) is reduced, mainly from a reduced number of fruiting points.
Plant species and cultivars vary in their sensitivity to Fe deficiency, and are categorized as either "Fe-efficient" or "Fe-inefficient". Fe-efficient plants have Fe uptake systems that are switched on under conditions of Fe deficiency. Fe-inefficient plants are unable to respond to Fe deficient conditions. All Fe-efficient plants, except grasses, utilize a Fe-uptake mechanism known as Strategy 1. Strategy 1 plants decrease rhizosphere pH by release of protons, thus increasing Fe solubility. Some plants may excrete organic compounds in the rhizosphere that reduce ferric iron (Fe3+) to the more soluble ferrous (Fe2+) forms or form soluble complexes that maintain Fe in solution. Additionally, roots of Strategy 1 plants have specialized mechanisms for reduction, uptake, and transfer of Fe within the plant. Strategy 2 plants (grasses) produce low molecular weight compounds called phytosiderophores which chelate Fe and take up the chelated Fe with a specific transport system.
Amelioration of Fe chlorosis
Planting sites in calcareous soils should be well drained to provide optimal conditions for root growth and nutrient uptake. Waterlogged and compact soils contain
more carbon dioxide, which reacts with lime to form even more bicarbonate. These conditions, as well as very dry soils, also inhibit microbial activity which aids in
solubilization and chelation of Fe. Prior to planting, soils and water should be tested to determine the pH, lime equivalent, and bicarbonate concentration. Bicarbonate concentrations greater than 3 meq/L in irrigation water increase the hazard of lime accumulation on and around roots. If high bicarbonate water must be used, the pH must be adjusted to 6.0-6.5 to dissolve the bicarbonate and prevent it from negating the effects of soil-based treatments. In microsprinker and drip systems, acidification of irrigation water will also reduce the risk of emitter clogging, a common problem at bicarbonate levels over 2 meq/L. The cost of reducing the pH of irrigation water will more than compensate for the savings incurred from avoiding wasted investment in failed soil- and plant-based remedies. Systems can be set up to continuously and safely inject water with acids such as sulfuric, urea-sulfuric, or phosphoric during irrigations. Specific choice and rate will depend on crop, soil type, other nutrient needs, availability, and cost. Downstream pH meters are available to continuously adjust rate of acid use. Acetic and citric acid can be utilized by organic growers.
Soil based pre-plant treatments to reduce pH include elemental sulfur (S) and acids as mentioned above. It is only necessary to treat a limited area near the root zone to ameliorate symptoms because the tree only needs to take up a small amount of Fe. Material can be shanked in or banded and incorporated in the prospective tree row. One ton of elemental sulfur per treated acre is needed to mitigate three tons of lime, and may need to be re-applied every 3 to 5 years after planting. The addition of organic matter such as well-composted manures will benefit poorly drained or compact soils by increasing aeration for better root growth, fostering chelation of nutrient cations, and reducing pH (depending on source material).
If possible, choose a Fe efficient species or cultivar. In perennial systems, lime-tolerant rootstocks may be the first line of defense in combating Fe deficiency. Some rootstocksmentioned are peach-almond and Krymsk-86 for stone fruit, Gisela 5 for cherry, and Pyrus communis for pear. Ongoing research studies in Europe focus on screening rootstocks of grape and olive for lime tolerance.
Once soil and water quality improvements are made, post-plant management strategies may also be implemented to ameliorate lime-induced Fe chlorosis in the short term. Soil can be acidified as described above. Individual trees can be treated by digging four to six 12-24 inch
holes around the drip line and burying a mixture of sulfur and Fe fertilizer. Historically, two principal methods have been utilized: 1) foliar application of inorganic Fe salts (ie. ferrous sulfate), and 2) soil or foliar application of synthetic chelates. Application of Fe salts to foliage may have mixed results due to limited penetration of Fe into leaves and inadequate mobilization within the plant. Use of Fe chelates may be of benefit; however, they are expensive and pose an environmental concern due to their mobility within the soil profile. Because soil lime interferes with Fe mobility with the plant, repeat application of inorganic Fe salts or Fe chelates may be necessary throughout the growing season.
Choice of nitrogen (N) fertilizer may also influence solubility of rhizosphere Fe. When N is applied in the ammonium form (NH4+), the root releases a proton (H+) to maintain a charge balance, thus reducing rhizosphere pH. Alternately, fertilization with nitrate (NO3-) results in root release of hydroxyl ions (OH-), resulting in an increase in rhizosphere pH. Solubility of Fe3+ increases 1000 fold with each one unit decrease in pH; therefore, fertility-induced rhizosphere pH changes may significantly influence Fe availability.
New methods for amelioration of Fe chlorosis are under investigation. For example, container studies have demonstrated that inter-planting sheep's fescue, a Strategy 2 plant, with a Fe-inefficient grape rootstock may ameliorate Fe chlorosis in grape. In this system, the grass produces a phytosiderophore that enhances Fe availability to the grape. Additionally, soil amendment with Fe3(PO4)2• 8H2O), a synthetic iron(II)-phosphate analogous to the mineral vivianite, has been effective at preventing Fe chlorosis in lemon, pear, olive, kiwi, and peach. Vivianite has a high Fe content (~30%) and serves as a slow release source of Fe in calcareous soils.
Figures below: Shoot dieback in citrus and iron chlorosis in avocado
There's been a lot of avocado and citrus planting going on and this is a good time for a reminder about how to dig a hole. This is by our colleague Jim Downer in Ventura County, Horticulture Advisor and also past president of the International Society of Arboriculture, Western Chapter. In the text, where you see Fraxinus or some other tree name you don't recognize, just slip in avocado or citrus and keep reading. Also, check out the references.
Green side up! Oh, and do not sink the rootball below grade!
I have always been amazed at how the simplest of procedures or practices can go so wrong. For the green industry, the best example of this is planting. The act of putting green in the ground is our business. We do this. The problem is, we often do it wrong, carelessly, or without regard for the outcome—dead trees! A consultant friend often expressed how deep planting and covering the root ball with native fill are the most common mistakes he sees. I have to agree--landscape plants die at the hand of man more than from all the diseases and insects combined. There are various incorrect ways to plant a tree, such as adding too much organic matter to the backfill, installing a dry root ball and then not irrigating after planting, or adding too much fertilizer to the backfill. The practice I want to cover in this article is planting too deeply. The problem continues despite research about planting that recommends correct planting depths.
Planting depth is often ignored when plants are installed in landscapes.
Deep planting can result in death of woody and non-woody or herbaceous plants either because they rot (in moisture-saturated soils) or because they dry out. In either case, the symptoms are similar: wilting, sunscald or burnt leaves (necrotic tissues in the middle of the leaf), lack of growth, leaf drop, and eventually, necrosis of leaves, shoots and branches (all above ground parts). Irrigation usually does not improve symptoms because by the time they are noticed the plant has already been harmed beyond repair.
Root balls placed below grade cause several problems during establishment. Since native soil surrounds the root ball, there is an immediate problem with an interface between the two soil textures. Most container media are “light” to promote drainage characteristics necessary for container culture. When these soil-free media are planted in soil which is of a much finer texture, the resulting interface does not allow water to enter the root ball. Water must completely saturate the surrounding soil before it will cross the interface (Harris et al., 1999). As the plant draws down its container media moisture, the root ball desiccates beyond the permanent wilting point and the plant dies. This process is extreme in plants that are grown in peat-based media because the peat moss can become quite hydrophobic as it dries and then the interface issues are exacerbated. Special care should be taken with citrus and avocados to plant them at or above grade so the media itself is exposed to irrigations.
Acid plants are however, no exception to the above suggestion. Installing the plant at or above grade (if only ½-1 inch) will prevent excessive drying of the root ball due to interface smothering. It is however, very important that the root ball itself is irrigated in the first month of establishment not just the surrounding soil. Newly planted nursery stock does not absorb water from landscape soil, only from its own rootball. Until roots grow into the native soil, the plant must be irrigated to keep its rootball moist. The surface of the rootball can be protected with a coarse wood chip mulch.
Not all installers get planting depths wrong at the start. When the plants are first installed, everything looks good. The problem is sometimes related to the amount of digging used to make the planting hole. If the hole is dug too deep, and soil added back to bring the final grade to level, the plant can slump as water settles it. Digging destroys soil structure, so backfill under the rootball always settles - the plant sinks.Soil will wash in from the sides covering the root ball and sealing it from future irrigations.
Deeply planted woody plants are subject to diseases. The area where the roots of a plant join its main stem is the root collar. This area is very metabolically active and requires oxygen. In some cases, the stem above the root collar is green and photosynthesizes. Acer japonicum the Japanese maple has a clearly demarcated root collar region. Soil goes on the brown part and the green part should remain above ground. When the main stem is buried, the plant is predisposed to attack from canker forming fungi or other plant pathogens that can girdle the stem, killing it and all that grows above it.
It is quite clear from the literature that there is a strong species effect to the tolerance (or lack of tolerance) to deep planting. In a study of red maple and Yoshino cherry, only 50% of cherries survived deep planting, while there were no significant losses of maple to deep planting practices (Wells, et al., 2006). Arnold and others, 2007, found that green ash (Fraxinus pennsylvanica) was more tolerant to below-grade installation than golden rain tree (Koelreuteria bipinnata). In the same paper by Arnold et al., they showed that mulching can make deep planting worse. When trees planted below grade were mulched, mortality levels increased.
If plants survive deep planting, there can be other consequences. Wells and others 2006, showed that red maple (Acer rubrum) had increased numbers of girdling roots the deeper they were planted. When planted 6 inches below grade trees had 48% of their trunk encircled by girdling roots, when planted 12 inches below grade 71% of the trunk was affected.
Not all researchers found that soil over the root ball is detrimental. Gilman and Grabosky, 2004, found that if irrigation is plentiful (over an inch of applied water), trees survived and were less stressed three months later. Although planting depth did not impact growth of Southern live oaks, the study was relatively short term (7 months). I have also found in my own study of landscape shrubs that deep planting of five different genera of shrubs were not affected by planting depths of up to 4 inches below grade. The limitation of these studies is that they are short term. Over longer periods, disease and greater periods of hypoxia during high rainfall seasons may have cumulative detrimental effects not seen in the establishment phase of growth. When studied for three years, Arnold and others (2007), found that planting slightly above grade (3 in) improved growth of oleander and sycamore, while planting slightly below grade (3in) was harmful to all tested plants.
Broschatt, T. 1995. Planting depth affects survival, root growth, nutrient content of transplanted pygmy date palms. HortScience 30:1031-1032.
Arnold, M.A., G.V. McDonald, and D. Bryan. 2005. Planting depth and mulch thickness affect establishment of green ash (Fraxinus pennsylvanica and Bougainvillea goldenraintree (Koelreuteria bipinnata). J. Arboric. and Urban Forestry 31:163-170.
Arnold, M.A. G.V. McDonald, D.L. Bryan, G.C. Denny, W.T. Watson and L. Lombardini. 2007. Below-grade planting adversely affects survival and growth of tree species from five different families. J. Arboric. and Urban Forestry 33:64-69
Gillman, E. and J. Grabosky. 2004. Mulch and planting depth affect live oak (Quercus virginiana Mill.) establishment. J. Arboric. and Urban Forestry 30:311-317
Harris, R.W., J.R. Clark, and N.P. Matheny. 1999. Arboriculture: Integrated Management of Landscape Trees, Shrubs, and Vines. 3rd ed. Prentice Hall, Upper Saddle River, NJ.
MacDonald, J.D., L.R. Costello, J.M. Lichter, and D. Quickert. 2004. Fill soil effects on soil aeration and tree growth. J. Arboriculture 30:19-27.
Wells C., K. Townsend, J. Caldwell, D. Ham, E.T. Smiley and M. Sherwood. 2006. Effects of planting depth on landscape tree survival and girdling root formation. J. Arboriculture and Urban Forestry 32:305-311.
The proceedings of the 5th International Conference on Huanglongbing (IRCHLB V) is now published, available and citable online through the Journal of Citrus Pathology: http://escholarship.org/uc/iocv_journalcitruspathology
Joseph (Josy) M. Bové - Selected Photos
Joseph (Josy) M. Bové Dedication
Tribute to Prof. Dr. Joseph Bové
If you download the Bové Dedication pdf file, there is a link near the top of page 3 that will redirect you to the video interview of Prof. Bové. This is the video that we could not show during the meeting due to audiovisual technical difficulties. You must download the pdf for the link to be active. The link is not active when simply viewing the publication online.
The keynote speakers are working on their contributions. These will be available shortly and we will send another email announcement when they become available as well.
sIn the bottom left corner is the Search box for finding authors and topics of the abstracts.
providing some advantage to the farmer. Frequently, these are new fertilizer mixes presented as proprietary cocktails promoted and dispensed with promises of a multitude of profitable (yet improbable) benefits to the buyer. With the large number of new products available, and the number of salespeople promoting them, it is often difficult for growers to distinguish between products likely to provide real benefit, and those that may actually reduce the profitability of the farm.
In all situations when a company approaches the University or a commodity research board with a new product or technology for sale to California growers, these institutions act as grower advocates. They are charged with sorting through the available information; asking the right questions; getting the necessary research done if the available information warrants this pursuit; disseminating accurate information on these new technologies and products, and doing all that can help maximize grower profits now and in the future. When approached with a new product or technology it is obligatory to challenge claims with the following questions:
Is there some basic established and accepted scientific foundation on which the product claims are made?
Language that invokes some proprietary ingredients or mysterious formulations, particularly in fertilizers mixes registered in the State of California, raises red flags. A wide range of completely unrelated product benefit claims (such as water savings, pesticide savings, increased earlier yield) raises more red flags. Product claims that fall well outside of any accepted scientific convention generally mean the product is truly a miracle, or these claims are borderline false to entirely fraudulent.
Has the product undergone thorough scientific testing in orchards?
Frequently, products are promoted based on testimonials of other growers. While testimonials may be given in good faith, they are most often not backed up by any real scientific testing where a good control was used to compare orchard returns with and without the product.
A “test” where a whole block was treated with a product and which has no reliable untreated control does not meet accepted standards for conducting agricultural experiments. Also, a treated orchard cannot reliably be compared to a neighboring untreated orchard; and a treated orchard cannot be compared to the same orchard that was untreated the previous crop year. Even a test with half a block of treated trees and half untreated is not considered dependable by any known scientific standard of testing.
Only a well designed, statistically replicated, multi-year trial allows for direct comparison of untreated versus treated trees with statistical confidence. Verifiable data from tests that meet acceptable standards of scientific design, along with access to raw baseline (before treatment) yield data from the same trees (preferably for the two years prior) should be used to determine the validity of test results provided.
Are the test results from a reliable source?
If the testing were not done by a neutral party, such as university scientists, agency, or a reputable contract research company using standard scientific protocols, this raises red flags. If the persons overseeing the tests have a financial interest in seeing positive results from the product, it raises red flags.
Does the product have beneficial effects on several unrelated farm practices?
A product that increases production of trees, makes fruit bigger, reduces pests, reduces water use, and reduces fertilizer costs, is more than a little suspicious. In reality, if such a product really existed, it would not need any testing at all because its benefits would be so obviously realized by the grower community that it would spread rapidly by word of mouth and embraced by the entire grower community.
Are other standard and proven farm products put down in the new product sales delivery?
If a new product vendor claims that their product is taken up 15 times faster than the one growers are currently using, or is 30 times more efficient, it probably costs 15 to 30 times more per unit of active ingredient than the standard market price. Growers should always examine the chemical product label to see what active ingredient they are buying. There has to be a very good reason to pay more for an ingredient where previously there had been no problem supplying the same ingredient at a cheaper price to trees in the past.
There are impartial sources of such information available to farmers to help corroborate information provided by product vendors. Perhaps the most reliable and accessible impartial research and education resources for growers are their local Cooperative Extension Farm Advisors and commodity research boards.
When promising products emerge, local university Farm Advisors can advise growers on how to evaluate these products and may help design a small trial to test a particular product on a few trees under local orchard conditions. If in these pursuits a truly promising new product or technology emerges, research board funding may follow but only on the recommendation of that board's Research Committee.