Citrus Greening Disease (HLB)

Spread by an insect called the Asian citrus psyllid, the citrus greening disease, first found in Southern California in 2012, destroys production leading to bitter, inedible, misshapen fruit.

While research is on-going, there is increasing evidence that balanced nutrition can mitigate against HLB. For example, there is increasing evidence that citrus trees prefer the nitrate form of nitrogen and can experience toxicity to ammonium forms of N.

These increasing ammonium concentrations in the soil can also reduce uptake of potassium, calcium and magnesium and trees can test positive for, and exhibit, citrus greening disease symptoms.

In contrast, while trees with adequate levels of potassium, calcium and magnesium, don't exhibit the symptoms of HLB even if they test positive for the disease.

Your Yara agronomist or fertilizer supplier will be able to provide more information on this effect as the fast-track research continues.

Latest on Citrus Greening

California Citrus Farmers: Prepare Your Groves for Citrus Greening

Yara has been actively involved in the citrus greening issue in Florida, working with researchers to help find a way to mitigate or reduce the severity of the disease. We are sharing this knowledge to help California citrus farmers learn from this experience and hopefully avoid the devastating impact Florida farmers endured. 

Not long ago, HLB infection of a Florida citrus tree was considered a death sentence for the tree. The entire industry was threatened. Sadly, many groves were lost. But, today, many innovative farmers with 100% HLB infected groves have productive trees with many reporting quality fruit production near pre-HLB levels. Many are planting new groves as quickly as possible. What is happening in Florida? How have some farmers been able to prosper?

Farmers say that balanced nutrition and psyllid control are the reasons for their success until a new resistant variety, developed through plant breeding, produces a permanent cure. Have farmers changed their plant nutrition program? You bet they have.  

The Problem

HLB bacteria do not manufacture toxins or attack cell walls like many pathogens. They enter the plant’s phloem (conducting tissue) as the psyllid feeds. There they alter the metabolism of the citrus trees.

Nutrients that pose a potential harm to psyllids via initiation of a plant protection response are sequestered in leaves with high quantities of starch. Calcium, magnesium and boron were the first to be identified as deficient in HLB trees. Over time, the citrus tree canopy and roots are damaged by HLB. Tree stress exacerbates the problem. Hence, we must apply a balanced nutritional program that removes stress and supplies adequate additional nutrition for productive and healthy trees.  

Impact of Ca on shoot and root

Hydroponic trial: after 2.5 months the symptoms of Ca deficiency are visible in the trees without Ca supply

REF: Hydroponic trial conducted by Research Centre Hanninghof, Yara International, 15-DE-CT-18

Finally, calcium and potassium play a vital role in the plant’s immune system for mitigation of many diseases. Yara is currently conducting a detailed scientific  investigation to determine the benefits of a combination of a balanced tree nutrition program coupled with an aggressive psyllid control program to document tree health, fruit production and HLB disease mitigation.

Calcium and Nitrate Nitrogen are Key Components to Citrus Tree Health

Previous research has established that calcium nitrate is the best nitrogen source for citrus production. Today, it performs extremely well in 100% HLB infected groves in Florida. 

Secondly, HLB infected roots develop high root resistance that limits uptake of water and nutrients. Therefore, we must continually grow new roots. Root growth is severely limited without calcium.

HLB Infected Citrus Trees Respond Favorably to Balanced Plant Nutrition

By making YaraLiva Calcium nitrate the only source of N we were able to improve the canopy density and overall tree health thus allowing the citrus trees to recover and start producing higher yields.

2010

Yara dry application Calcium Nitrate, YaraLiva, an excellent source of plant available soluble calcium and nitrate nitrogen, became only source of Nitogen in ground program.

2012

Weak areas “filled” in with denser canopies.