MASTER GARDENER TIPS: Citrus and recognizing greening, canker disease

Published 12:24 am Saturday, March 12, 2022

Hopefully, our recent warmer weather didn’t lull any fellow gardeners into believing spring had arrived in Southeast Texas!

March weather patterns are unpredictable, quickly changing from warm day time temperatures to frigid nighttime temperatures within a short period.

Dramatic temperatures swings can make even the most seasoned gardeners cringe, while determining when to plant annuals, perennial flowers, and vegetables (as I too, almost planted tomato and pepper plants this past weekend).

Both heat-loving plants would suffer severe damage or worse, succumb to cold temperatures but I digress.

This week’s subject Asian Citrus Greening and Citrus Canker, is part one of a two-part series, recognizing two citrus diseases.

There are numerous plant diseases which can attack citrus trees, most notably two of them are Asian citrus greening and citrus canker.

The Texas Department of Agriculture and U.S. Department of Agriculture have put forth considerable resources and effort to control the spread of both these devastating diseases.

Texas counties where the diseases have appeared are quarantined and a few of the counties nearest our geographical area are Harris, Montgomery, Galveston, Brazoria and Fort Bend. Home-grown citrus located within quarantine areas must be consumed within the local area and home-grown citrus trees cannot be transported outside of the quarantined area.

Lop-sided fruit

Commercial citrus enterprises, web-based retailers, and “mom and pop” roadside vendors within the State of Texas must be able to prove they are following Federal and State quarantine guidelines.

Before buying citrus trees gardeners need to ask questions of the seller. Make certain the seller is following Federal and State guidelines before purchasing citrus trees and that the citrus is not from a quarantined zone.

Citrus Greening is a bacterial disease caused by a bacterium, known as Candidatus Liberibacter Asiaticus, which is vectored (carried) by the Asian citrus psyllid (ACP). It is also known as the yellow dragon disease, found worldwide, and confirmed in Louisiana 2008 and Texas 2014.

Unfortunately, there is no cure for this disease.

While the disease poses no threat to humans or animals, it has devastated millions of acres of citrus production around the world, including in the United States.

Citrus trees infected by citrus greening may have the Asian citrus psyllid. The adult insect is about the size of a toothpick tip (about 3mm or ⅛ inch) with a distinctive 45-degree angled posture when present on leaves.

The ACP nymphs are yellow orange in color, smaller, and feed on new growth, leaving behind a waxy fluid. Once a tree is infected with the bacteria, the tree can remain without detectable symptoms for months or years.

During this symptomless phase, the tree can serve as a source of bacteria to infect other trees. Leaves will become yellowed, blotchy, or mottled, and may have raised veins with a corky appearance. Fruit will have a bitter taste though it poses no health issue for humans.  Further, fruit might be stunted, or lopsided while remaining green or partially green. And will sometimes fall away from the tree prematurely.

Blotchy, mottled, and yellowing leaves

As there is no cure for Asian Citrus Greening, and prevention is the best approach to managing following these guidelines:

  • Do not purchase or transport plants, fruit, budwood, rootstock, seedlings, or budded trees from quarantined areas.
  • Purchase certified plants from Texas Department of Agriculture (TDA)-certified citrus growers and nurseries.
  • Sound sanitation practices are paramount to reduce potential disease spread. Practice general cleanliness by using alcohol-based sanitizers, bleach solution, or antibacterial soap solutions to decontaminate equipment and tools which will reduce the risks associated with human or mechanical transmission of the diseases.
  • Remove and destroy diseased plants to eliminate potential bacteria for future infections.
  • Closely monitor nearby citrus plants. If new infections appear, act swiftly. TDA regulations require disposal of infected tree and plant material by incineration or bagging and burying it at least 2 feet deep at a municipal landfill.

Plant protection chemicals which contain copper can help prevent infection.

These products reduce risks but do not stop the disease from occurring or cure affected trees. Application timing is critical to provide protection, since new, growing tissues are the most susceptible to infection. Multiple applications will be needed to ensure proper coverage on the plant.

Proper chemical use and rates are available on the product labels. Read application directions and follow instructions before applying any chemical control agent.

For more detailed information on Asia citrus greening, visit plantclinic.tamu.edu or the Texas Dept. of Agriculture at texasagriculture.gov.

For more information or to have all your gardening questions answered, contact the Orange County Master Gardeners: Website: https://txmg.org/orange Facebook: Orange County Texas Master Gardeners Association Helpline: (409) 882-7010 Email: extension@co.orange.tx.us.