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Check magnolia leaves for signs of trouble

Disease first shows up on magnolia's leaves

Q: I could use some help with two southern magnolias I had planted three years ago. They were about 6 to 7 feet tall and they are now about 7 to 8 feet tall; they blossom flowers and grow new leaves but it is only on the tips of the branches, leaving the rest bare. There are a lot of magnolias around my neighborhood. Most are full and beautiful but there are one or two that look like mine. So is there a disease I should be looking for or a nutrient that I need? Paul Wellman

A: There is one potential disease-causing organism (pathogen) called algal leaf spot that can attack southern magnolias, Magnolia grandiflora, that are unthrifty, not looking good to begin with. The symptoms begin with round, green, somewhat fuzzy or velvety colonies on the leaf surface. The green spot will turn a rusty brown with age; the leaf will yellow and prematurely drop. To control algal leaf spot, rake up and discard fallen leaves and also pluck diseased leaves from the tree. Adjust sprinklers so they don't douse the leaves, and spray the tree completely with copper compounds such as Southern Ag Liquid Copper Fungicide or Monterey Liqui-Cop, following label directions. Potential causes of the condition could be lack of water; magnolias like it wet so set up a temporary drip system to get your tree through dry times. It could have been planted too low. Dig down with your hand around the stem (trunk) probing for the first lateral root; it should be right on the surface. If it is 2, 3 or 4 inches down, redig the tree, cut any encircling roots and set on grade with the first lateral root at the soil surface. Fertilize with a quality 10-0-10 with 50 percent slow-release nitrogen in February, May and October along with Southern Ag Essential Minor Elements in July because magnolias are, by nature, slow-growing trees and need a little push.

Sickly gardenia may need a bigger pot or root pruning

Q: I have a gardenia planted in a large plastic pot. Over the past four years, it has always done well and produced many large flowers. Last year's crop was spectacular, developing many large blooms. I usually prune the plant back after the blooms are done and new growth shows in the spring, and did so last year. I maintained my usual watering and fertilizing schedule as in years past. I use a mild spray pesticide (pyrethrin) for aphids when necessary. There were none this year, only a few mealybugs, so I didn't spray.

Early in this growing season it began to develop yellowing leaves (which it always did in the past) but this year, the leaves kept falling off. I checked for aphids and mealybugs but found no infestation.

Initially, the bush also developed many small buds and I thought it would be another bumper crop. However, the buds steadily dropped off. I would guess over 200 buds have fallen.

Only two buds managed to bloom, though very small.

The plant has now begun to get new growth and what appears to be more buds.

My questions:

1. Could you tell me what may have caused the unusual amount of yellowing leaves and bud loss?

2. How I can avoid this happening next year?

3. Should I prune it back or wait? If wait, then when do I prune? Peter Ferrara, Belleair Bluffs

A: From your explanation, it sounds like your gardenia has become pot bound and needs a larger container or root pruning to keep it in the same pot. If transplanting into a larger pot, be sure to cut the encircling roots to redirect them to branch and form more new feeder roots. If root pruning, reduce the size of the root ball by about ⅓ by pruning back all roots, and then repot with added potting soil. There simply are not enough feeder roots to support a good bloom, hence all of the bud drop.

Resume all of the same cultural practices that supported the plant for the past four years, and next year, your bloom should return.

Need help? Dr. Hort (Greg Charles) answers questions about garden problems. Email him at drhort@tampabay.rr.com or mail questions to HomeLink, Features Department, Tampa Bay Times, P.O. Box 1121, St. Petersburg, FL 33731. Describe problem in full, and include your name, city of residence and contact information. If possible, include a good-quality photo. Fuzzy ones won't do. Photos cannot be returned.

Check magnolia leaves for signs of trouble 08/11/12 [Last modified: Thursday, August 16, 2012 3:25pm]
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