What Causes Citrus Slow Decline – How To Treat Citrus Slow Decline


By: Teo Spengler

Citrus slow decline is both the name and description of a citrus tree problem. What causes citrus slow decline? Pests called citrus nematodes infest the tree roots. Read on to learn more about this problem and how to treat citrus slow decline.

What Causes Citrus Slow Decline?

Slow decline of citrus is a major concern to growers, and it should be to you as well if you have a home orchard. Trees with this condition lose vigor and show yellow foliage and small fruit.

The citrus nematode (Tylenchulus semipenetrans) is responsible for this decline. Nematodes are microscopic roundworms that live in soil and plant tissues and feed on plant roots. The citrus nematode was first noted in 1913. Today, it is found in almost every citrus-growing region in the world. It is present in at least half of the orchards in the nation.

Symptoms of Slow Decline of Citrus

How can you tell if your orange or lime tree or other susceptible plant (plants that can be attacked by this pest include citrus, grapes, persimmon, lilacs and olive trees) suffers from slow decline of citrus? Here are a few of the symptoms to look for:

The initial above-ground symptoms of slow decline of citrus include less vigorous trees and slowing growth. You may also see the tree leaves turning yellow and the fruit remaining small and unattractive. In addition, the tree canopies tend to thin out. When you see bare branches exposed on the crown of the tree, you have to start thinking about managing citrus slow decline.

But these are only the above-ground symptoms of a nematode infestation. The attack can happen without any of these symptoms. The underground signs of a citrus nematode infestation are the most important, like poor growth of feeder roots.

Managing Citrus Slow Decline

Managing slow decline used to be accomplished with chemical nematicide treatments. However, these chemicals are not permitted to be used as freely now as a few years ago. If you are wondering how to treat citrus slow decline today, prevention is considered the front-line defense. It’s recommended to do everything you can to prevent these problems.

When you buy a tree, pick one with a nematode resistant rootstock. Buy only plants that are certified to be free of nematode parasites. Another way to start managing citrus slow decline is to use excellent sanitation practices. Be sure that all soil and other products are certified nematode-free.

Also, it helps to rotate with annual crops for a few years before replanting citrus.

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Citrus greening showing up in North Florida

Often, we think of citrus greening as being a South Florida or commercial citrus problem. However citrus greening has gained a foothold and is well established in Northeast Florida. At the UF-IFAS/Duval County Extension Office, homeowners are sending images of their declining citrus greening daily. For many homeowners the diagnosis comes out of the blue. It is evident that many homeowners with citrus trees in their yard are unaware of this devastating citrus disease.

Citrus greening or Huanglongbing (HLB), was discovered in South Florida in 2005. Since then, citrus greening has spread throughout Florida in both commercial and residential sites. There are no citrus varieties resistant to greening. Since HLB was first found, the number of acres devoted to commercial citrus production has declined by 26 percent and the amount of citrus harvested has dropped by 65 percent. The typical lifespan of a citrus tree has gone from 50 years to just 15. Citrus growers reported in a recent survey that at least 90 percent of their acreage devoted commercial citrus is infected with citrus greening and 78 percent of the trees are infected.

Citrus greening is caused by the bacteria Candidatus Liberibacter asiaticus. The bacteria are transferred from tree to tree by an insect called an Asian citrus psyllid. The psyllid feeds on sap from an infected tree and transfers the bacteria when it feeds on another tree. Once in a tree, the bacteria inhibit the tree’s ability to take up and distribute nutrients, resulting in the gradual decline of the tree with discolored leaves, smaller fruit and lower fruit quality.

Citrus greening is also called Huanglongbing, which translates to “yellow dragon.” This name was given to the disease because an early sign of citrus greening is a branch or shoot turning yellow. The most identifiable symptom found on the foliage is called blotchy mottle. It can be described as yellow and green blotchiness on the leaf. The blotchiness is not symmetrical, meaning one side of the leaf is not a mirror image of the other.

The next noticeable symptom is where the term “citrus greening” comes from. The fruit can turn orange near the stem but stay green on the other end. Other fruit symptoms include lopsided or small fruits that taste sour or bitter.

The one symptom that is first usually noticed by homeowners is the fruit dropping prematurely. Many residents affected with the disease have reported that their fruit started dropping in August. Since then there has been a steady loss of fruit from local trees.

The only way to get an accurate diagnosis of citrus greening is to send a sample to a lab and have them look for the DNA of the bacteria. This test is called a PCR test. The University of Florida charges a fee of $80 to perform the test. However, there is a field test using household iodine that can help you determine whether it is “likely” your tree has the disease. The iodine field test is easy and takes less than 5 minutes. The fact sheet that details the instructions can be found at crec.ifas.ufl.edu/extension/greening/PDF/HS37500.pdf.

At this time, there is no cure for citrus greening. Researchers from all over the world are studying options to combat the disease. They are looking at several strategies that include discovering a treatment for citrus greening, developing resistant citrus varieties, perfecting alternative citrus management options and trying come up with viable options to combat the psyllid.

If your tree has citrus greening, there is no way to rid your tree of the disease. There are things you can do to keep your tree productive a little longer with the use of quality fertilizers and micronutrient sprays. Citrus specialists recommend that when fertilizing infected citrus trees, a controlled or slow-release fertilizer be applied periodically throughout the growing season. The amount of fertilizer applied would depend on the percentage of nutrients in the bag and the age of the tree. For example, a 5-year-old tree would need 13 pounds of a 12-4-16 controlled release fertilizer applied in three equal amounts between March and September.

Controlled-release fertilizer is formulated so that it releases nutrients to the tree gradually over a longer period of time. This allows the tree to absorb the nutrients as it needs it. The fertilizer used on citrus does not have to say “citrus” on the bag. Homeowners can look on the fertilizer label to find a fertilizer with slow-release,or controlled-release fertilizer. It is also recommended that fertilizer used on citrus contain a higher amount of micronutrients such as zinc, manganese and iron. Another tool that helps prolong the productivity of the tree is the use of a micronutrient spray applied to the foliage. It is relatively easy to find in most retail nurseries. As always, read and follow the label when applying these products.

For those of us that do not want to give up on citrus, there is a mandarin hybrid that is not resistant but is more tolerant of citrus greening. This variety is called “Sugar Belle.” This tree is hard to find and may entail several phone calls to local citrus nurseries, but the effort should be worth it. For more information on the “Sugar Belle” go to nwdistrict.ifas.ufl.edu/phag/?s=sugar+belle.

Larry Figart is urban forestry extension agent from the University of Florida/IFAS.


Rot Rot

Phytophthora rot root is a soil-borne disease that causes the bark to peel at the soil level. The trunk may become girdled, with visible wound tissue. Over time, the tree may show symptoms of decline such as leaf chlorosis, leaf and fruit drop, branch dieback and ultimately, death. One of the primary signatures of root rot is (unsurprisingly) rotting rots, which may be visible if you dig the soil back. To help correct root rot, avoid mulching the tree and only irrigate in the morning. Keep the area under the tree clear of grass and weeds.


Restrictions

To help limit the spread of citrus greening disease, all or part of the states of Florida, California, Arizona, Georgia, Louisiana, South Carolina, Hawaii, Mississippi, Alabama and Texas have quarantines on citrus trees, including kaffir lime, or quarantines on the insects responsible for spreading the disease. Trade in plant material may be restricted in these areas.

Kristen Kelly started writing professionally in 2010. She previously wrote technical papers while working as a research assistant. She has a Bachelor of Applied Environmental Management from Lakeland College in Vermilion, Alberta.


Q. I have grown 9 citrus plants seeds from the fruit we have eaten. They are all planted in one 14-inch diameter pot. The plants ar

e 2 each Meyer Lemons, 5 ruby-red grapefruits, and 2 Eurika lemons. My question is: WHEN THE ROOTS FROM THESE 3 DIFFERENT CITRUS PLANTS BECOME ENTANGLED, IS THIS IN EFFECT THE SAME AS GRAFTING? If I graft a ruby-red grapefruit stem to a Meyer lemon stem will I get any results?

It will not be the same as grafting. They will fight for water and food, that is why they are entangled. There will be no odd results.


Watch the video: How to manage Citrus Decline or Die-back


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