Signs your citrus tree may need help

Aloha, Garden Guy! I am enjoying your blog very much! I recently moved to Kula at 2,700-foot elevation.

Thanks to you, I discovered the leafminer on our valencia and tangelo tree and anthracnose on our mango tree.

I am noticing now some problems with our tangerine and pommelo tree.

There are tangerine blossoms in spring but no fruit appearing and a lot of dead branches and twigs. Pommelo had beginning stages of fruit and then stunted and dying.

The citrus leaves are curling and yellow. It has also spread to our night blooming jasmine. Our handyman mentioned that it might be “rust fungus” transferred from our fig trees.

I am new to citrus care and a bit overwhelmed. It’s very confusing to know how much to water, as there is just one little drip on each citrus tree and the pommelo has none. We have not fertilized either … I also noticed that the drip is hitting the trunks, they are wet and read from your blog that is not good.

Any help or suggestions you have to offer would be greatly appreciated. Many Mahalos from Upcountry K.K.L.S.

1. Blossoms but no fruit: This has been discussed before, but to summarize: citrus will drop its bloom and newly formed fruit due to some type of environmental stress.

This can include vog, nitrogen deficiency or excess, sudden high temperatures, a lack of water, too much water, a heavy insect/mite infestation, hot dry winds, and lastly, constant rain during the bloom period. Any one of these factors that occurs around the time of bloom can cause the flowers and young fruit to drop. In your area, if ample rain does not occur in the spring, the blossoms/young fruit will surely drop. The situation would be worsened by poor tree health.

2. Curled leaves: This is caused by aphids feeding on the new flush of growth. Once the curl is observed, the damage is done and the insect may have even disappeared. For older trees the damage is strictly cosmetic, I would not recommend treatment. For young trees, aphids will cause some stunting of the tree; apply a soap/oil solution. Spray only if the aphids can be seen. The yellowing may simple be lack of nitrogen along with general poor health.

Aphids feed on many different types of plants and can cause leaf distortion. The curling is not caused by the rust fungus from the fig tree and will not infest citrus.

3. Learning the proper amounts of water to give trees in a dry climate can be difficult. One drip emitter on a mature tree is certainly not enough; six would be more accurate or possibly one or two mini-sprinklers. Instead of a drip irrigation system, you may want to use high volume sprinklers or some type of modified furrow system. This way, you can apply large amounts of water, saturate the soil and water less frequently than with a drip system. For now, I think the trees can use a good soaking. Let the garden hose trickle for hours and allow the water to penetrate one to two feet down. Mulching the trees will also help to conserve water. Do not stack the mulch against the tree trunk. Likewise, do not place drip emitters next to the trunk.

4. The trees most likely need fertilization. They will definitely need nitrogen; as for a phosphate or potassium fertilizer, I would recommend taking a soil sample to your local UH CTAHR office for analysis. Giving the trees some water and fertilizer will go a long way to their good growth and fruit production.

5. There are many things that will cause twig dieback and dead limbs in a tree; neglect, of course, is one. It would help the trees to go through and prune out as much dead wood as possible. Note: I would consider removing any trees that have cracked bark on the trunk and do not respond to pruning, water and nutrients.

Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at askthegardenguy@earthlink.net.