magnolia disease

[slshaw]

Hello, I am new to the forum and to gardening, but am appreciating the advice given here. My family recently moved into a new home with a magnolia tree in the front lawn, but I don't know the tree's history. 2 months ago a few leaves got brown spots, but in the last month they have rapidly advanced and most leaves are covered (and many are rapidly dropping). It looks to be getting ready to bloom (tan colored fuzzy flower... pods(?) are forming all over the tree). Neighbors say it has the large white flowers, but I don't know the species. I live in Palo Alto, CA, and we had rainy season (rain most days) until a few months ago. Shortly thereafter is when the spots started. Now that we are in dry season I water with a soaker hose 5-8 hours every 3 weeks. There was some chlorosis about end of rainy season, and I used iron fertilizer and that worked well. Enclosed photos show the leaves. This tree used to be in the shade of a 40 yr old oak that succumbed to oak root fungus this winter and was removed. I've read this can affect some magnolias, but can't find other information.

Any help you can provide on what disease this is, and how to address it, would be much appreciated!

Stephanie

[Newt]

Hi Stephanie,

Congratulations on your new home! I suspect your magnolia has a fungal leaf spot disease due to weather conditions. You should find this helpful.
http://plant-disease.ippc.orst.edu/d...?RecordID=1345

Newt

[lilypotter]

Magnolia may be subject to leaf spots caused by the bacterium Pseudomonas syringae or a large number of fungi. They're distinguished by yellow, brown or black dead blotches on the foliage. Often spots come together to form larger patches of dead tissue. Heavily infected leaves fall prematurely. Leaf spots rarely require chemical controls. Rake up and dispose of infected leaves.
Recommendations include practices aimed at keeping the vigor level of the plant as high as possible. These include:
1) Water as needed. Plants need an inch of water/rain per week during the growing season; if droughty conditions develop, make sure the plant gets at least this amount of water. Use a rain gauge to determine how much water is actually being received by the plant.
2) Fertilize as needed. Use a balanced fertilizer; ideally a soil nutrient analysis should be performed to determine specifically what, if any fertilizers, are needed.
3) Avoid soil compaction around the plant (no swing sets, picnic tables, etc. near by!), and avoid mechanically wounding the plants (weed whacker damage, lawn mower damage, swings or dog runs bolted to the tree, etc.). Aerate the soil if compaction is a problem.
4) Make sure other obvious insect and disease problems are taken care of (defoliators, leaf spot fungi, etc.).
5) Conduct a general site assessment to make sure the plant is growing in the proper site (for example, yew plants do not tolerate wet soil conditions; azaleas and rhododendrons need acid soil conditions to thrive; plants that normally grow as understory shrubs do not thrive in open, unshaded areas); etc. If the site is not proper for the plant, consider replacing it with a plant better suited to the area. Also check the hardiness of more "exotic" plants to make sure they can survive local conditions.