Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Client's Request: I have a Crape Myrtle bush/tree that is about 15 years old. The last 4 to 5 years it starts out with new growth in the spring with nice green leaves. Then in about this time of year, the older leaves turn a yellow/orange color and start to drop off and continue to fall off till winter. I continue to get new sucker growth at the base of the tree, which I cut off. I do not see any indication of mold, fungus, or insects on or under the leaves. I do not spray the tree with any insecticide. I have several Petunias planted around the base of the tree, which get watered every other day for about 10 minutes during the warm summer months. I live on the Delta so the water table here is 2 to 3 ft below the surface. I don't know if I'm watering too much or not enough. I do not fertilize the tree, but I do plant the Petunias in potting soil which has slow release fertilizer in it. I also prune the tree every year in January. I have attached 4 pictures for you to look at.
My questions?
1. What is causing the leaves to turn yellow/orange and then fall off?…
2. Is the tree getting too much water or not enough?
3. Should I be fertilizing, if so, what should I use?
4. Are their insects or something else I'm not seeing that is causing the problem?
Will appreciate any advice you can give me.
UC MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk. Your pictures were very helpful. I also appreciate that our phone call in addition to your email as it allowed me to ask questions for additional information.
Your primary issue is… "What is causing your crape myrtle leaves to change color and fall prematurely/"
The questions posed in your email are as follows:
- What is causing the leaves to turn yellow/orange and then fall off?
- Is the tree getting too much water or not enough?
- Should I be fertilizing, if so, what should I use?
- Are their insects or something else I'm not seeing that is causing the problem?
First, we do note that the Town of Discovery Bay (a Delta community) lists Crape Myrtle on its Suggested Plant List for Discovery Bay Residents. We cannot confirm how that recommendation was made but perhaps contacting Town officials would provide their latest guidance and experience.
Following is a link to the University of California Integrated Pest Management website where it presents information of common problems associated with crape myrtle. http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/crapemyrtle.html……
One of those common problems is water management – either too much or too little. Recognize that too little water or too much water can cause nearly identical above ground symptoms to a plant. Following is a link to that discussion. http://ipm.ucanr.edu/PMG/GARDEN/ENVIRON/poorwater.html
I believe your situation is due to too little water. I base this on our discussion of your current watering protocols which essentially is shallow watering that takes place for the petunias near the trunk of the tree.
The following link will take you to a web site of the Vacaville Tree Foundation which will reinforce our discussion on tree watering. It will provide an illustration as well as information on how to water a tree – where in relation to the canopy, how deep and how often. As we discussed, as a tree grows its roots extend beyond the canopy and water applications need to also extend outward. This information is from Vacaville but I believe the environmental conditions are similar to your residence, Discovery Bay. Crape myrtle is a low water use plant and per this site should be watered monthly during the hot season to a depth of 18-24 inches per irrigation. http://www.phytosphere.com/vtf/treewater.htm
You mentioned that in your area you have a high water table. My concern with the above watering recommendations is I do not know exactly how high the water table is in your area – and I was unable to find that information. If it is so high that water is consistently available within the 18-24 inches then too little water is not your problem and conversely too much water may be your issue. You probably should check into exactly what your situation is. You can dig a hole out at the edge of the tree canopy and what you find should tell you the answer.
With regards to fertilizing – It does not appear that your situation is due to a nutrient deficiency. From your picture the leaves do not appear to be affected by a shortage of nitrogen or iron – the two most common shortages. UC does not recommend the regular fertilization of landscape trees. If you choose to fertilize I suggest that you wait until the watering situation – too much or too little - is resolved. If it turns out to be too little water then right after you irrigate, you can fertilize. Make your fertilizer application according to label instructions and if it is a soil application make it to the same area that is being irrigated – in and around the canopy. The Following is a UC IPM link to cultural tips, including fertilizing for trees and woody plants. http://ipm.ucanr.edu/PMG/GARDEN/culturalmenu.html
You also have questioned whether this situation may be the result of insects. Nothing that I see on your tree or heard from you would suggest insects as your problem – good news!
It was wonderful talking to you. If you have any additional questions, please feel free to contact us again.
Editor's Note: Pictures were intended to be attached, but software wouldn't let them be displayed appropriately before editor went nuts. Check back in a few days and maybe software will let me "fix" them.
Help Desk of the UC Master Gardener Program of Contra Costa County (EDC)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523, although we will be moving this spring. We will notify you if/when that occurs. We can also be reached via telephone: (925)646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (//ucanr.edu/blogs/CCMGBlog/)