Southern Magnolia Leaf Drop

Algal Leaf Spot

     Chicken Little is wrong again.  The sky is not falling; it is only magnolia leaves!  Every spring, people call expressing concern about leaf drop of their Southern magnolias.  Magnolias will begin dropping leaves in November and continue until early spring.  The degree of leaf drop depends upon genetic as well as physiological factors affecting the tree. Most of the leaves are old leaves and it is their turn to fall off.  The older leaves turn uniformly yellow suddenly throughout the entire plant before dropping.  New growth at the tips of the branches is often evident at this time. Once the yellow leaves drop off, no further yellowing or leaf drop occurs until next spring.

     Most Southern magnolia trees are grown from seed, and they exhibit a great deal of variability in leaf shedding since each tree is slightly different.  Some trees may become completely bare before new foliage comes out.  When trees are propagated by grafting or from cuttings, all trees will have about the same amount of leaf drop since they are clones.

Regardless of propagation method, the degree of leaf drop can also be associated with environmental conditions.  An extremely cold winter or a dry spring can result in accelerated or additional leaf drop.  Large trees with root systems restricted by to sidewalks or planting islands may drop more leaves since their restricted root system are not as able to supply the tree with water and nutrients during periods of stress.

This spring has been wetter and warmer than usual and this resulted in a increase in algal leaf spot.  This also causes increased defoliation.  Best control is to clean up and destroy diseased leaves.

You might want to apply 4 cups per 100 square feet of 13-13-13 or similar fertilizer to give them a little boost this year.

Pest Alert: Azalea Leaf Gall

Azalea leaf gall

   The warm, wet spring has been ideal conditions for leaf gall in azaleas. Leaf gall is a common fungal disease found on azaleas.  The  leaf gall of azaleas is caused by the fungus, Exobasidum yaccinii. Another fungus, Exobasidium camelliae, causes a similar problem in camellias. It occurs more commonly on the fall blooming ‘sasanqua’ varieties.

   This disease appears early in the spring. The new leaves and buds that are infected develop distorted growth. The leaves become thickened, curled, and pale green to white and in some cases pink. Leaves can be ten times thicker than normal leaves. The infected  leaves are covered with a white powdery substance in the latter stages of the disease. Galls eventually turn brown and harden as the season progresses.

   Fundal spores overwinter in the bark. When the buds open in the spring, the spores are blown by the wind to the plant. Rain can also wash spores from the bark to the plant tissue. Spores need moisture to germinate. Plants that are grown in areas of poor air movement, deep shade, and high humidity are more likely to be infected.   After the plant is infected, the fungus stimulates a growth promoting process which causes the thickening and distortion of the plant.

   There are some varietal differences among azaleas in susceptibility.  Reported resistant varieties include: Gloria, Sensation, Coral Bells, Mrs. G. G. Gerbing, Sunglow,  and Formosa.

   The disease usually does not do enough damage to require chemical control. If only a few plants are affected, prune the galls of the plant and throw them in the trash.  If the same plants get infected year after year then might be chemical control necessary.   Begin treat with captan, mancozeb, or triadimefon fungicide sprays starting wien the young leaves begin to unfurl then every 10 14 days after that until the young leaves mature. 

    Another procedure for controlling azalea leaf gall on badly diseased plants is to cut plants back severely. This is a good sanitation procedure and is a good way to reduce disease occurrence  the following season because galls will be removed along with the pruned branches. It is also advisable to replace mulch beneath such plants since this will insure that fallen galls beneath plants will be removed.