Pecan Diseases:

Pecan trees are widely grown is South Carolina both for shade and nuts. Pecan trees have several disease problems, which reduce both the shade value and the nut crop but seldom kill the tree. These diseases are difficult to control with chemicals as spraying Pecan trees usually is not feasible for homeowners because of tree height.

1-SCAB

The causal organism:   Cladosporium caryigenum
Symptoms:

Is the most common and damaging pecan diseases. It is caused the fungus. The fungus forms small, circular, olive-green to black spots on leaves leaf petioles and nut shuck tissue. In severe cases, the scab fungus can also attack new twigs and even catkins (male flowers).

Scab lesions often run together, causing the terminals to die and catkins to drop. Pecan tissue is must susceptible when it is young and actively growing. When scab attacks young expanding leaves and nuts, it stunts and deforms them. By the time the leaf is mature, it is no longer susceptible to scab. The greatest scab damage occurs from nut infection. Early-season infection can significantly reduce yield and crop quality .Fruit, infected early in the season, often drop or crack where scab lesions run together and serve as a point of entry for other pathogenic fungi.

The scab fungus survives the winter on plant parts infected the year before, most spores are released in mid-April, just after bud break. Spores are spread locally by dew and splashing rain and over longer distances by wind. Scab spores need free moisture to germinate, usually supplied in the form of dew. Spores also require moderate temperatures to germinate, between 65 and 85'F.Very little infection occurs during dry, hot weather, which is the major reason scab, is lees important in the more arid western states.

Control:

1-Plant scab-resistant varieties such as cap fear, Elliot, Gloria Grand and Owens.

2- Complete removal and destruction of leaves and shucks during the winter can reduce carry-over of scab.

3- It is critical to begin fungicide applications at bud break to prevent early scab infection. Two to three fungicides sprays should be applied at 10-to 14- day's intervals during this critical period.

4- Fungicide that homeowners can use for control is thiophanate-methy1. Follow the direction on the label.

2-Downy Spot:

The causal organism:   Mycospaerella caryigena

Symptoms:

Can cause early leaf loss on susceptible cultivars like Stuart, Pawnee and moneymaker. Repeated defoliation from severe downy spot infection can cause losses in nut production and tree vigor. Downy spot first appears on the lower surface of young foliage in late spring as small yellow spots. These spots may turn whit as spores are produced. Later in the season, the lesions turn brown and begin to appear on the upper surface of the leaf. Heavily infected leaves drop earlier than healthy ones in the fall. Downy spot survives the winter in fallen leaves. Spores are released prior to bud break. Downy spot begins in the lower parts of the tree and spreads upward.

Control:

1- Plant resistant or tolerant varieties such as Schley, Success, and Mahan.

2- Remove and destroy fallen leaves. Apply a preventative fungicide spray program (see scab control)

3-Brown spot:

The causal organism:   Cercospora fusca

Symptoms:

Only affects mature leaves and does not appear until Jun or July. Brown spots is found primarily in neglected orchards is areas that have abundant rainfall or high humidity. Primary lesions develop on the lower leaf surfaces as small dots, which enlarge and become reddish-brown with a gray cast. Brown spot may defoliate the tree by October if steps are not taken to control it.

Control:

1-Brown spots is best controlled by keeping the trees healthy. Eliminate any stress by watering and fertilizing the trees when needed.

2-Leaves on trees that are fertilized properly seldom are infected with the brown spot fungus. Fungicides that control scab also effectively control brown spot.

4-Gnomonia leaf spot:

The causal organism:   Gunomonia disora

Symptoms:

This fungus only infects poorly nourished trees that are deficient in zinc. The first symptoms appear in June a few days after infection. The spots resemble those caused by the brown spot fungus, but as they expand, they are restricted by the lateral veins. They develop large, elongated, dead areas within the lateral veins. The fungus over winters in fallen leaves.

Control:

1-Sanitation (the removal of dead and diseased plant material).

2-Proper fertilization will control this fungus. Fungicides applied for scab also effectively against Gnomonic leaf spot

5- Liver spot:

The causal organism:   Gonmonia carvae.

Symptoms:

                   The first sign of the diseases spears in May and June. Circular, dark brown spots appear along the midrib on the lower surface of the leaves. In late summer the spots turn a cinnamon brown or liver color. Liver spot can cause severe defoliation, particularly during prolonged periods of wet weather. Weak trees are more susceptible to liver spot than are healthy trees.

Control:

The best control for liver spot is keeping trees healthy by watering and fertilizing them when needed. This disease can also be controlled by fungicide sprays used for scab.

6-Powdery mildew:

The causal organism:   Microshaera alni

Symptoms:

                   Forms a characteristic superficial powdery-like growth on both the leaves and the nuts. Infected leaves are seldom seriously damaged by the fungus. Nuts are affected more adversely than leaflets. The amount of damage causes to nuts depends on their stage of development at the time of infection. Nuts infected early may abort or be undersized with poorly developed kernels. Nuts infected when they are mature sustain little or no injury from the disease.

Control:

Some pecan cultivars are more susceptible to powdery mildew than others. Stuart and Schley are extremely susceptible. Fungicides applied in the course of the regular scab spray program will control powdery mildew.