Question from Dave:
Here’s a photo of the Reed avocado. It was my strongest tree last summer. Full of dark green foliage. As the rains progressed through the winter it became progressively more yellow. The adjacent patio drains into its planter and then runs off to the driveway The feeding through the winter months was 2/3 cup per month of 6-4-6 commercial citrus avocado fertilizer. In March, I gave it 2 quarts of alfalfa and worm casting solids (left over from making alfalfa and worm casting tea for the roses) and also sprayed twice with ironite and gave it 1/4 cup blood meal and 1/4 cup bone meal The photo shows the yellowing leafs as well as new growth at the end of the branch. Because the leaf cover is declining, I’m white washing the exposed branches to protect them from direct sunlight. Thank you.
Answer from Pat:
Thank you for sending the photo of your Reed avocado. The leaves show the signs of salt damage, bacterial leaf spot and overwatering. The plant may also have stem rot. Salt damage can come from too much fertilizer building salts in the ground. Salt damage usually shows up in burned tips and burned (brown) leaf edges as are seen on some of the leaves in this photo. Over-fertilization can also lead to crinkled and burned (brown) leaves as shown on the lower left. Usually when a plant has been over-fertilized the leaves will become distorted and bent out of shape, sometimes in stunted form as can be seen with some of these leaves. But the main problem here comes from wet soil. Yellowing of leaves comes from over-watering (or too much rain) and from waterlogged soil. The brown blotches on the leaves come from bacterial leaf spot which results from overly moist conditions.
An old rule of thumb says “Do not feed a sick plant.” It sounds as if you might have been over-feeding this plant in winter when the soil was cold and the plant had already lost some roots due to root rot. When plants are growing in wet soils with poor drainage, fungi present in soil can rot roots. Feeding a plant just increases the problem. Weakened and rotting roots cannot take in sufficient nutrients for healthy growth. Hence leaves go yellow. In this case the brown may be caused by salts but also general necrosis from inability to take in nutrients. Bacterial leaf spot is also present from overly moist conditions. (The round lighter brown blotches are typical of bacterial leaf spot and may also appear sunken.)
In circumstances like that it is better to allow the plant to recover before feeding it. Soluble gypsum applied to the ground and watered in can improve drainage of clay soils and wash away salts. If I were you I would take off all yellow and brown leaves and any rotting, damaged or sunken twigs that might have stem rot, and hope for the best. You could try spraying the cuts with Serenade, but I doubt it will do any good. I also hope your avocado plant will recover but I am not sure it will do so because of the loss of so many roots and the difficulty of preventing the spread of the disease once it has invaded the plant tissues. If the plant doesn’t show signs of improvement in a month or two as the weather warms up, it’s best to yank it out, give it a decent burial and start over. If this happens, you can cheer yourself up with the thought that every horticulturist has had a few failures. A good idea would be to build a raised bed in that spot for any future planting. A raised bed does not need to be very high to correct drainage. It only needs to be 4 inches high to allow a new plant to avoid root rot. Fill the raised bed with top soil while creating a marriage of soils by mixing the lower with the upper soil and then dig straight through into the soil below to make the planting hole.
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