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This issue:Does citrus nutrition influence citrus diseases?

Three key points about YaraLiva calcium nitrate products

In this newsletter, Dr. Bill Easterwood will address the ad-vantages of using YaraLiva calcium nitrate instead of am-monium sources of N to strengthen your trees against fungal pathogens. Before you read this article, I want to review a few key points regarding the use of calcium nitrate.

First, in Florida groves today, there are fertilizer blends being applied with over 1,000 pounds of YaraLiva calcium nitrate in each ton of fertilizer. A 9-1-14 2Mg blend contain-ing CN, TSP or MAP, SOP and KMag has performed very well. (Note: Do not add DAP, urea or ammonium sulfate. These sources are not compatible with CN and will cause blend deterioration.)

Second, spoon-feeding trees throughout the season with YaraLiva calcium nitrate dry and/or liquid blends is an excellent practice. In the last newsletter we saw the superior nitrogen use efficiency of CN compared to AN. Therefore, optimal tree growth and productivity can be obtained at 160-180 pounds of N/year compared to AN at rates of 220-250 lbs. N/year. Hence, fertilizer cost may be equal or slightly above AN blend cost.

Third, consistency is the key to success when using a YaraLiva-based specialty nutrition program. By ensuring that calcium nitrate is available to the trees throughout the growing season, the full horticultural and economic benefits can be realized without the negative effects of ammonia-cal N. Please keep these points in mind as you make your fertilizer blend choices in the coming weeks and months. Invest in YaraLiva calcium nitrate starting now to build up tree reserves for spring flush and you will be pleased at your return on investment at harvest.

And now is the best time to begin or enhance your fertiliza-tion program with YaraLiva calcium nitrate for another reason. Yara’s Fall Value Program, described on the back page, gives you even greater incentive.

All the best,

Eric WaldoRegional Manager - Premium Offerings Sales, Florida

Citrus EditionIssue 3 • 2015

Sharing crop nutrition knowledge from Yara North America, Inc.

Does citrus nutrition influence citrus diseases?

Benjamin Franklin once stated that “an investment in knowledge pays the best interest”. We increase our knowl-edge by building on the principles others before us have discovered. If we do not utilize this “investment in knowl-edge”, our profitability is lost. We in the Florida Citrus In-dustry must review all information from those before us to optimize citrus health and production if we are to survive.

The Link between Citrus Nutrition andCitrus DiseasesHealthy trees withstand pathogen attack much better than weak trees. The same principle applies to humans and animals. So, nutrition is key to citrus tree health. In the last newsletter, we saw from studies published in 1999 and 2014 that the nitrate form of nitrogen is far superior to ammoni-um nitrogen in citrus production. Ammonium toxicity limits tree and root growth, fruit yield and grower profitability. Calcium is important also since it plays a role in mitosis or cell division, cell wall strength and thickness, water use efficiency and as the messenger to initiate plant defense mechanisms. Now, let’s look at literature relating to citrus nutrition and fungal diseases.

PhytophthoraPhytophthora is a fungus that destroys weak citrus fibrous roots. Ammonium N application stimulates the fungus. When nitrate N with calcium is applied, the fungus is sup-pressed. This information is found in many journal articles and DOACS DPI Plant Pathology Circular No. 299 pub-lished in September, 1987. So if the rooting system of the tree is calcium deficient, there will be less root development and damage that will optimize Phytophthora infection.

Hence, nitrate N and soluble calcium can be applied with a single product, YaraLiva calcium nitrate, which suppresses

Phytophthora activity. The referenced study was published in 1958.

Citrus BlightNo specific pathogen has been identi-fied as the causal-agent of Citrus Blight although there are indications that Blight-like symptoms can be created by naphthazarium toxins re-leased by the Fusarium solani fungus even when no infection is observed. Fusarium solani is present in all soils where citrus is grown. But there is one thing that has been identified. Toxins

See Citrus Nutrition, continued on page 3. With Without calcium calcium

Root tips die in a short term when there is not enough calcium in soil solution.

Calcium nitrate helps prevent Fusarium toxins developingAmmonium-containing fertilizers, including ammonium nitrate, support Fusarium growth

Fibrous root rot symptoms caused by Fusarium solani in a citrus grove at Bartow, FL.

Fusarium naphthazarium toxins extracted from cultures grown with ammonium nitrate (Lanes A and B) and cultures grown with calcium nitrate (Land C), and developed on thin layer chromatography plates. Note the absence of toxin in the calcium nitrate-produced cultures.

Lane A

Lane B

Lane C

Calcium nitrate strengthens the root cells against fungal attacksOranges (cv 'Homosassa') - pot experiment, USA.Some fungi can cause fibrous rot

REF: Klotz et al. 1958 USA

from Fusarium kill fibrous roots leaving only scaffold roots (see photo below). Fusarium only produces the toxins when ammonium N is available and do not produce toxins when the tree is fertilized with nitrate N as calcium nitrate. We can see this from work by Dr. Stan Nemec (USDA, retired) whose work has also been confirmed by researchers in South Africa and Venezuela. Other potential Blight pathogens include viruses.

Post-Bloom Fruit DropPost-bloom fruit drop is a devastating disease since grower profitability is lost early. Added maintenance to keep trees healthy reduces profit-ability further. The fungus, Colletotrichum acutatum, is the pathogen responsible for the disease. Currently, the pathogen is controlled by crop protection chemi-cals. But, applying YaraLiva calcium nitrate has many benefits. Calcium influences pollen tube elongation (fruit set), mitosis (cell division) and abscission layer devel-opment (fruit drop). Hence, abundance of available calcium increases early fruit. Early fruit set removes the infection sites (flower petals) for Post-Bloom Fruit Drop.

Does nutrition directly influ-ence the PFD pathogen? No studies have been conducted to directly answer this question. However, there is a close comparison in strawberry. Nitrogen fertilizers do influence anthracnose crown rot in greenhouse-grown strawberries. The strawberry pathogen is Colletotrichum fragariae which has the same genus as the PFD fungus. The conclusion of the USDA-ARS Plant Pathologist is as follows: “Seven N sources were each evaluated at three levels. Among plants receiving 160 PPM N, those treated with calcium nitrate had least disease. When N fertilizer is applied to strawberry plants as calcium nitrate, anthracnose crown rot severity should be less severe than when N is applied in ammonium forms.” Hence, there is a potential trend of PFD reduction with calcium nitrate.

HLB infected trees pose a second potential mechanism to

cause fruit drop through phloem plugging. From the last newsletter, I provided information from our study in Brazil comparing ammonium nitrate and calcium nitrate fertiliza-tion of citrus. One of the variables I did not mention is the vascular tissue surface area of leaf and flower cross-sections. Below is the flower cross-section. Please note that the CN fertilized flower has a vascular tissue area of almost 2 times the size of AN fertilized flowers. Hence, it is easier to plug a smaller pipe than a larger one. So here, we have another benefit of using calcium nitrate rather than ammonium nitrate.

Finally, from grove observations, growers who use CN as their only N source indicate that they have had minimal PFD.

Fertilize for Tree Health, Growth andProductivityDoes citrus nutrition influence tree health, growth, produc-tivity and citrus diseases? You bet it does! However, you must use select nutrients/nutrient forms like calcium and nitrate nitrogen to obtain the effect. If you use ammonium N, you are stimulating the disease you are trying to miti-gate. So, use YaraLiva Calcium Nitrate, the optimal source for citrus fertilization.

Citrus Nutrition, continued from page 2.

See Citrus Nutrition, continued on page 4.

Flower - AN (80 kg ha-1) Flower - CN (80 kg ha-1)

E = Epidermis, M = Mesophyll, VT = Vascular Tissues

E = 25.2 µm +2.0 µm E = 27.2 µmM = 635.1 µm +80.3 µm M = 715.4 µmVT = 80.6 x 96.3 µm x 1.7 VT = 150.1 x 86.0 µm

If you have enjoyed reading this information and would like to be added to the mailing list for this newsletter, please email: eric.waldo@yara.com.

Yara North America, Inc. • 352-215-8480Customer Service: 1-800-234-9376www.yara.us

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We have addressed fungal pathogens in this newsletter. In the next, we will address bacterial diseases – canker and HLB.

ReferencesPhytopathology ( 1958) 48:616-622Canadian Journal of Microbiology. 1995. 41 (6): 515-524Plant Pathology (2001) 50 (2) 258-265Smith, B. J. 2009. Nitrogen fertilizer affects the severity of anthrac-nose crown rot disease of greenhouse grown strawberries. Online. Plant Health Progress doi:10.1094/PHP-2009-0609-01-RS.

Citrus Nutrition, continued from page 3.Contact your dealer for special citrus

Fall Value Program on YaraLiva® CN-9®

and Tropicote®

Valid in Florida through 12/18/15

Now and laterMaximize strong citrus root health with YaraLiva® calcium nitrate products

Scan to watch the video: research proves that CN is better than AN for citrus tree nutrition.