Everyone’s on the hunt for a cure or treatment for citrus greening that will stop the disease in its tracks. There are many new products and therapies that have the potential for making an impact against the disease. Citrus grove owners play an important role in evaluating the effectiveness of treatments like bactericides, heat treatments, insecticide sprays, Psyllid traps and how changes in irrigation, fertilizer and other management affect citrus trees. They can best evaluate the usefulness of a treatment through Disease Indexing (DI), as explained in a Citrus Industry article.

Challenges in the Grove

The nature of an orange grove presents many challenges for evaluating the effectiveness of a treatment. Just like two people will have a different set of symptoms for the same illness, different citrus trees will present a variety of symptoms, even within the same grove. Additionally, the health of a citrus tree will also change over the course of the year. Changes in the seasonal climate and a citrus tree’s natural cycles all affect how healthy a tree is.

Rigorous field testing is the best way to test the effectiveness of a new treatment or a change in grove management, but it is not feasible for most growers. University of Florida’s Jim Syvertsen and Brandon Page, the field trial administrator for the Citrus Research and Development Foundation (CRDF), developed Disease Indexing parameters to evaluate CRDF field trials. Taking the framework from the methods of T. R. Gottwald, B. Aubert and Z. Xue-Yuan, Disease Indexing can be used by any grower to track individual citrus trees and assess the health of the grove over time.

Disease Indexing Steps

After you have chosen select citrus trees to track, the first step in Disease Indexing is to visually break the tree up into quadrants. This, according to the article, is because the symptoms of citrus greening are not uniformly distributed in an infected citrus tree.

Then, assign each quadrant a score from 0 to 5, with 0 being no visible symptoms and 5 being severe symptoms of HLB. Keeping track of each quadrant, the same process of quartering a tree visually and scoring each quadrant is repeated on the opposite side of the tree. The two sets of four scores are added together with 40 being the highest score possible.

It is recommended to use at least 20 treated trees and 20 untreated trees for Disease Indexing. Similarly, the trees should all have about the same degree of disease severity to properly gauge whether a treatment is having an impact or not.

Griffin Fertilizer is committed to helping both growers and ranchers make sound agronomic and economic decisions in order to maximize the health of their grove and pasture. As a full-service custom dry & liquid fertilizer blender and crop protection product distributor, we will continue our mission to further advance Florida agriculture. For questions or concerns about your farm or pasture, contact us and one of our team will be in touch.