Anthracnose is a condition of black or brown spots but zinc deficiency and rust is also a possibility. The cultivars most likely for these deficiencies are: Kiowa, Gloria Grande, Pawnee and Mohawk.
Pecan anthracnose is caused by the ascomycete Glomerella cingulata (Stoneman) Spauld. & H., it is a widespread disease throughout the industry. Pecan Anthracnose has been reported as far back in time as 1914 (Rand 1914), and as far away as Argentina (Mantz, Minhot et al. 2010). Glomerella cingulata has two anamorphs which cause disease on pecan trees, Colletotrichum gloeosporioides and Colletotrichum acutatum (Latham 1995). The occurrence of Colletotrichum on pecans has contributed to a significant decline in pecan production in various years.
An increase in Pecan Anthracnose incidence is highly correlated with heavy rainfall, especially in early spring. Severity increases as the season progresses, the disease will often cause leaf drop in the late fall; fall defoliation is linked to lower yield and nut quality (Brenneman 2010).
The financial loss due to Pecan Anthracnose in 2009 in Georgia was estimated at 3.4 million USD (Brock 2010). However, the actual loss due to the disease is difficult to quantify due to the nature of carbohydrate storage in perennials. The damage to pecan production is also likely to present itself in a lower yield in the year directly following a disease outbreak (Worley 1979).
Pecan Anthracnose is reported to have an unusually long latent period; it can take weeks to months from the time of initial inoculation to symptom development. Both ascospores and conidia can be found in the field and in culture, and both of these spore types can cause infection (Rand 1914). Pink conidial oozes can be observed emerging from acervuli with setae on leaves and shucks.
The Life Cycle of Anthracnose in layman’s terms
Anthracnose (Black Rust) spores are very common and can also be present in the soil where new trees are planted.
There is a high presence of Fungus in existing orchards.
Unicellular condia or ascospores are spread during the summer, during or after a rain storm when conditions are favourable for formation of fungi.
Fungi are A-sexual in the growing season and spread by forming stringy roots that breaks down during a rain storm. They called it condia spores and they are A- sexual or a clone.
Formation of fruiting bodies on leaves occurs during the growing season and fungi cause damage when the soft tissue on the growing points died backwards. This results that the following year’s crop will potentially be as nuts grow on first year wood that grow out of second year wood. Infection is spread when an comes in contact with an adjacent tree.
Some cultivars like Pawnee, Mohawk and Kiowa are more susceptible to the fungus than others. Trees that are more tolerant to the fungus like the Ukulinga, Wichita and Western are also infected when branches comes into contact with infected tree. During the winter infected leaves drop to the ground. The fungi that were A-sexual during the growing season, changed and become sexual.
When two mycelia meet, they swap chromosomes and formed an ascus with a Y shape and looks like a small toadstool. Theseascior fruiting bodies, protect the spores which were formed during the winter regardless the severity of the winter.
Once the growing season started, the fruiting bodies burst and the spores shoot high into the air and spread by hot upward air movement and wind. Some fungi can also survive in the wood of the tree without forming fruiting bodies. There they grow roots (condia spores), which break down when it rains.
The assumption that zinc deficiency are the only reason for the dying growth points, is not entirely correct. There are reported cases were observed under Wichita’s as well. During the next growing season, trees were badly infected and the growing tips died backwards.
To date, many farmers were under the impression that the symptoms of the dying growth points are due to a severe zinc deficiency.
Spraying of Copper as a fungicide is important.
Spraying low burette urea on trees suppress formation of fungus.
Spraying ordinary Urea on soil, suppresses the formation of asci