Page last updated on: August 12, 2015

Root Diseases - Little Leaf Disease

Little Leaf Disease- (Phytophthora cinnamomi)

1. This particular disease is a misnomer because the disease has little to do with leaves (needles) except that symptoms of infection result in shortening or little leaves. Actually, the disease is a complex that involves soil, moisture, nutrition and tree species and is very site-specific. In this photo, the disease appears as a thinning of the crown with respect to a "normal" healthy-appearing crown. The tree on the far left looks healthy, while the tree on the right looks a little thinner.

2. One characteristic of the disease is that it is usually associated with soils that are highly eroded due to previous agricultural practices. These sites tend to have soils that are high in clay content, little or no "A" horizon and tend to not drain very well. Here is group of individuals standing on the edge of a gully that has been left over from the cotton farmers. It is a high hazard site with respect to Little Leaf Disease.

3. Of the pine species in the southern United States shortleaf pine is the most susceptible, followed by loblolly pine, slash, and Virginia pines. Longleaf pine does not appear to be a host of this disease. If a stand is considered high risk (based on soil characteristics), then you can expect to get no more than 25 years from shortleaf, perhaps 35 from loblolly pine. The tree on the left is exhibiting symptoms of Little Leaf Disease, while the tree on the right is not.

4. One way to control Little leaf Disease is through site amelioration which can be by increasing the drainage (ripping the soil) to minimize the rotation (pulpwood instead of saw timber) or planting a less susceptible tree species. The tree on the left is exhibiting symptoms of Little Leaf Disease, while the tree on the right is not.

5. Another method to minimize losses is through the addition of nitrogen to the stand. This increases the fertility of the soil and allows the fine feeder roots to obtain enough nutrients and essentially out-compete the fungus in the infection process. Applications of nitrogen (5-10-5) 400 lbs per acre every 4 years. This will not eliminate the pathogen from the soil, but will augment the mortality of the fine feeder roots. The tree in the center of this photo is exhibiting symptoms of Little Leaf Disease.

6. In many instances the decline and death of trees within the stand are sporadic within a year and scattered within the stand. Too often the disease is misdiagnosed as being killed by southern pine beetle which are attracted to the declining, stressed trees. The tree on the far left is exhibiting symptoms of Little Leaf Disease, while the two trees on the right are not (although the far right tree is beginning to show some crown thinning than may be due to Little Leaf Disease).

7. Serious infections of Little Leaf Disease on some sites can cause a chlorosis (yellowing) to appear on the infected trees. Here are branch samples of a healthy short-leaf pine (left) and an infected short-leaf pine (right) showing the differences in needle color. This symptom along with the shortening branch internodes along with the growth ring reduction, is a good indication that Phytophthora cinnamomi is present in the soil.

8. Another example of chlorosis of needles, shortening of branch internodes, and tufted appearance of needles (fox-tails) on a short leaf pine in Alabama.

9. The fungus responsible for the disease is a Oomycete which are a group of fungi with the characteristic of living in close association with water. In this photo, the fungus has produced a sporangium which is about to release its zoospores. These zoospores have whip-like hairs (flagellum) that propel the spore through the soil using the film of water found in poorly-drained soils. The spores infect the small, feeder roots on pine trees that are used to up-take nutrients and water. Continued infection and mortality of the fine feeder roots over time is what causes the leaves to become smaller and smaller, for the growth rings to become closer together, for the shoots to elongate less, for the chlorosis to appear in the leaves.

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