Mycosphaerella caryigena<\/em>, downy spot is often responsible for leaf loss early in the season. <\/p>\n\n\n\nSome cultivars are more susceptible to downy spot, such as Moneymaker, Pawnee, and Stuart. <\/p>\n\n\n\n
The first signs of downy spot appear in late spring when you will see spots on the lower surface of young leaves. As the disease progresses, the fungus produces spores, and the spots will turn white before going brown and also appearing on the upper side of the leaves.<\/p>\n\n\n\n
If heavily infected, leaf drop will happen earlier than for healthy leaves. Repeated premature defoliation from a heavy infection of downy spot will damage the vigor of the tree, and only a few nuts will be produced.<\/p>\n\n\n\n
As with other fungi, the fallen leaves will harbor the pathogen and start infecting other trees in spring before bud break. <\/p>\n\n\n\n
Prevention<\/h4>\n\n\n\n
Always ensure your trees are well cared for with a sufficient amount of water and nutrients. A fertilizing regimen suited to your climate and soil type will go a long way to help.<\/p>\n\n\n\n
Plant varieties of pecan that are resistant to downy spot, such as Success, Schley, Western, and Mahan, but be aware that Western and Schley suffer from pecan scab, and Western and Success often get problems with shuck dieback.<\/p>\n\n\n\n
Remove all fallen leaves, twigs, and branches regularly and burn them if possible. Some states have laws that prohibit this, so always check fire regulations first.<\/p>\n\n\n\n
Use a fungicidal spray program to help prevent infection. <\/p>\n\n\n\n
Treatment<\/h4>\n\n\n\n
Once infected, subsequent treatment is ineffective.<\/p>\n\n\n\n
Gnomonia Leaf Spot<\/h3>\n\n\n\n
Caused by the Gnomonia dispora<\/em> fungus, Gnomonia leaf spot is often confused with brown spot.<\/p>\n\n\n\nIt attacks trees that are deficient in zinc and causes spots to appear on the leaves. As the disease progresses, the spots expand but stay contained within the lateral veins.<\/p>\n\n\n\n
Symptoms first appear in early summer, shortly after the infection has taken place, and the lesions get larger and more elongated over time. <\/p>\n\n\n\n
Fallen leaves are again how the fungus survives through the winter and re-infects trees the following spring.<\/p>\n\n\n\n
Prevention\u00a0<\/h4>\n\n\n\n
Removing all leaf litter, twigs, and branches from around the trees is essential.<\/p>\n\n\n\n
Correct fertilization programs with a fertilizer that contains the right amount of zinc for pecan trees will be very beneficial in prevention.<\/p>\n\n\n\n
The application of fungicides, the same ones used for scab, will also help prevent an outbreak.<\/p>\n\n\n\n
Treatment<\/h4>\n\n\n\n
A cure is not possible, but control by removing infected areas may help the spread.<\/p>\n\n\n\n
Zonate Leaf Spot<\/h3>\n\n\n\n
Caused by a fungus called Cristulariella moricola<\/em> this disease is more transmissible during wet summers. <\/p>\n\n\n\nThe fungus causes extreme defoliation of the trees during mid-summer months, usually if there is frequent rainfall.<\/p>\n\n\n\n
Grayish-brown spots with concentric rings appear on the upper surface of the leaves. On the underside, the spots are pale brown in the center, darkening to a deeper brown towards the edge.<\/p>\n\n\n\n
The spores form a crystalline film over the spots. If there are many lesions, the leaves dry out and will curl up until they die and fall off the tree.<\/p>\n\n\n\n
The fungus can survive the winter by forming a sclerotium. This is a hard, compact mass of fungal mycelium. Inside the mass, there are food reserves that help the fungus survive harsh environmental conditions.<\/p>\n\n\n\n
For the fungus to develop, it requires moisture, and growth is most rapid on wet leaves.<\/p>\n\n\n\n
Prevention<\/h4>\n\n\n\n
No cultivar of pecans is resistant to this fungus, and it is a problem for areas with high humidity and soil moisture. <\/p>\n\n\n\n
Good pruning practices that keep the tree’s canopy open to allow good airflow can be beneficial.<\/p>\n\n\n\n
Treatment<\/h4>\n\n\n\n
At the first signs of this disease, using copper hydroxide or thiophanate-methyl can help to contain the outbreak. It is important to follow the directions for these products as laid out by the manufacturer. <\/p>\n\n\n\n
Liver Spot<\/h3>\n\n\n\n
Liver spot is caused by the fungus Gnomonia carvae.<\/em> In late spring and early summer, the appearance of dark brown, circular spots on the underside of the leaves along the midrib may be a sign of liver spot. The spots turn a paler cinnamon or liver brown by late summer.<\/p>\n\n\n\nExtensive defoliation is a significant problem with liver spot, and the disease flourishes during times of prolonged rain or high humidity.<\/p>\n\n\n\n
Prevention<\/h4>\n\n\n\n
Healthy trees are far better at resisting liver spot, so the best prevention is good pruning practices and ensuring trees receive the right amount of water and fertilizer.<\/p>\n\n\n\n
Treatment<\/h4>\n\n\n\n
If a tree has been newly infected, this can be controlled with the use of the same fungicides that are used to prevent scab. <\/p>\n\n\n\n
Powdery Mildew<\/h3>\n\n\n\n
Powdery mildew disease is caused by another fungus called Microsphaera alni<\/em>. You will notice a characteristic white powdery substance on both leaves and nuts. <\/p>\n\n\n\nAlthough the leaves are not generally seriously damaged, it can be more problematic for the nuts, and the extent of this damage will depend on what developmental stage the nuts are at. <\/p>\n\n\n\n
For nuts affected while still young, the chances are they won\u2019t develop kernels correctly and will be generally small.<\/p>\n\n\n\n
Almost no problems are encountered for nuts infected when they are mature.<\/p>\n\n\n\n
Prevention<\/h4>\n\n\n\n
Cultivars such as Schley and Stuart are highly susceptible to powdery mildew, and both prevention and cure can be dealt with by using fungicides that control scab. <\/p>\n\n\n\n
Treatment<\/h4>\n\n\n\n
Use fungicides suitable for scab.<\/p>\n\n\n\n
Anthracnose<\/h3>\n\n\n\n
Another fungal disease, this time caused by a fungus called Colletrotrichum<\/em>. <\/p>\n\n\n\nThe ailment can be diagnosed by the presence of black-brown lesions on the leaves and shucks. They have a sunken appearance.<\/p>\n\n\n\n
You may also find salmon or cream-colored spores that form concentric rings on the shucks. <\/p>\n\n\n\n
Heavy, frequent rain seems to be a causal factor in this fungus spreading and infecting trees.<\/p>\n\n\n\n
Spores are broadcast during the rains in spring and early summer. The more frequent the rain, the more trees contract the disease.<\/p>\n\n\n\n
Prevention<\/h4>\n\n\n\n
There are some varieties of pecan that have a natural resistance to Anthracnose.<\/p>\n\n\n\n
Treatments<\/h4>\n\n\n\n
Only commercial growers can access fungicides strong enough to have any effect on the disease. The only other thing to do is spot it early and cut off and burn any parts of the tree which are affected.<\/p>\n\n\n\n
Crown Gall<\/h3>\n\n\n\n
Rather than a fungus, Crown Gall is caused by the bacteria Agrobacterium tumefaciens. <\/em><\/p>\n\n\n\nThis bacteria can change healthy plant cells into tumerous ones. These growths are easily confused with callouses, but as they progress, they become rounded with a rough texture and dark color.<\/p>\n\n\n\n
The bacteria live in the soil and can do so for several years. They are introduced into the pecan tree through the roots or low down on the trunk by entering through any small wounds, such as those made by insects, at graft sites, or by any other means.<\/p>\n\n\n\n
The growths are known as galls, and they inhibit the flow of nutrients and water in the tree’s vascular tissues. <\/p>\n\n\n\n
Due to a lack of water, the exterior part of the galls fall off the tree, and this enables the bacteria to be reintroduced into the soil. <\/p>\n\n\n\n
Prevention<\/h4>\n\n\n\n
Great care must be taken when planting new trees to ensure that the roots and trunk are not damaged. Trees must be disease-free and healthy if they are to flourish. <\/p>\n\n\n\n
If you know there is a problem with crown gall in your area, you can take the extra precaution of dipping the tree\u2019s roots in a solution that contains an antagonistic bacterium called A. radiobacter<\/em> (strain K84) prior to planting. This is not harmful to the tree but helps to prevent the invasive bacterium from striking.<\/p>\n\n\n\nTreatment<\/h4>\n\n\n\n
There is no treatment for crown gall once the tree has become infected.<\/p>\n\n\n\n
Stem End Blight And Shuck Dieback<\/h3>\n\n\n\n
The first signs of Stem End Blight are brown or black spots that appear on the shuck of the nut near the base.<\/p>\n\n\n\n
This will gradually spread until the dark coloration envelopes the entire nut. Once this occurs, the nut will often fall from the stem. <\/p>\n\n\n\n
Shuck Dieback becomes noticeable when the shuck turns black. The tip of the nut will also die. <\/p>\n\n\n\n
The reasons for these two blights are not properly understood. The fungus Phomopsis<\/em> has a close association with the diseases.<\/p>\n\n\n\nThe shuck is killed, and the quality of the nut is reduced with both ailments. <\/p>\n\n\n\n
Some cultivars of pecans seem to be more susceptible than others, \u201cSuccess\u201d is one of these, but it is not the only one.<\/p>\n\n\n\n
Stress is the main cause for the tree to become infected by either disease, and this can come from almost any cause, water, drought, nutrition, etc.<\/p>\n\n\n\n
Prevention<\/h4>\n\n\n\n
The most effective way to prevent trees from contracting either of these diseases is through good tree management and preventing stress.<\/p>\n\n\n\n
Ensure they are correctly irrigated, thin the tree to allow good light and air circulation, and ensure the trees have the right soil pH and nutrient values. <\/p>\n\n\n\n
Treatment<\/h4>\n\n\n\n
Unfortunately, fungicides are ineffective for these problems. <\/p>\n\n\n\n
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