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Dr. Hort: What's likely killing Indian Hawthorn?

Indian Hawthorn

Photo by Jane Waltz

Indian Hawthorn

Water levels, new bug could be killing plants

Q: My back yard around the pool has many Indian Hawthorn plants. I lost about 50 of them around my sago palm, which I sprayed with the oil you suggested. Under this palm where I lost most of my Hawthorns, the rest of the Hawthorns are fine. I have them all over the back yard.

I replanted 40 a month and a half ago and they are now dying. I am at my wits' end trying to figure out what is going on in this area. I am attaching pictures before, then what they look like now. These plants are probably 30 years old but I still have surviving ones all over my yard.

Jane Waltz

A: After viewing your photos of the varying degrees of death and destruction of your Indian hawthorn, Raphiolepis indica, I've come up with three scenarios:

The first would be lack of water. Do the plants have irrigation? If the new transplants died from the top down, new, tender growth down to the oldest leaves, they could have dried out, especially if they were rootbound (roots winding around and around) when planted. It can take from two to six months for a 1-gallon plant to establish; a 3-gallon plant may take six to 12 months. (Establishment means that the roots have grown sufficiently out of the rootball into the existing soil to support the canopy with minimal irrigation). The same symptoms would also hold true for too much water, scenario No. 2. The plants could have been diseased when purchased and with irrigation a root rot set in.

In both scenarios, pull up a plant that is half dead and inspect the root system. If the roots are dry and brittle, No. 1 is the cause. If it's brown and mushy, No. 2 is at play. If the culprit is a root-rotting fungus, treat the other new plants with a systemic fungicide such as Cleary's 3336 or Fertilome Halt Systemic following label directions.

The third scenario revolves around a new kid in town, "chilli thrips," an insect that is wreaking havoc on many traditional landscape ornamentals. Since they have a rasping mouthpart, the leaves, from the new growth down, appear distorted and stunted, with small scratch marks, usually black in color. As their population grows, they can kill a plant.

Treat them with either 100 percent neem oil or products containing spinosad, such as Naturalyte Conserve, following label directions.

Weeds could be adapting to often-used herbicides

Q: I was asked a question by a colleague and I can't find an answer online, so I thought, why not see if you can help?

I've noticed that when we treat bulb oxalis/Bermuda buttercup with Atrazine and/or Basagran, which is our usual winter weed control mix, it seems to have little effect on the plant. It seems they get some brown edges, and then spring back with a vengeance.

What is it about this weed that our weed control doesn't make it submit? That type of control works so fantastically on all the other winter weeds. Does Atrazine/Simazine/Aatrex control it? If it doesn't, can you explain the biology behind why not?

Rebekah Wassung, Scotts Lawn Service, Tampa

A: The answer to why atrazine may not be working anymore on some tough to control broadleaf weeds is because it has been overused and not rotated with other classes of herbicides. Weeds, just like insects, can become resistant to products when they are in the same class and are used repeatedly.

I asked my good buddy and colleague Mark Govan at ABC Pest Control what he was using in rotation for oxalis/Bermuda buttercup and his response was Celsius plus a surfactant. Celsius WG contains the active ingredient (thiencarbazone-methyl) which is a newer class of herbicides that can be used to control a whole boatload of broadleaf and some grassy weeds in warm season grasses such as St. Augustine. It is used post-emergent and also carries about a 60-day pre-emergent period. You'll find a tiny bit goes a long way. Hope this helps.

Solution sought for killing Chinaberry

Q: Persistent Chinaberry! It's fairly close to our septic tank and I have read that this is very bad, as the roots search for water. We have cut this down to the ground, tried weed killer (probably the wrong kind). Someone suggested burning it, which I do not want to do. That seems dangerous and I would never choose that option … or is that truly the only option?

The fear of septic tank damage and those potential costs have me freaking out. How can we get rid of this Chinaberry?

Rebecca Segal, Port Richey

A: Persistent is the correct word when describing Chinaberry, Melia azederach, an unwanted tree in urban landscapes because of its fast growth rate resulting in brittle wood that breaks in high winds and its bountiful seed crop that sprouts everywhere. Its brother, Azadirachta indica or neem tree, is so useful, prized for its oil that deters and kills insects, provides insect birth control and acts as a fungicide for powdery mildew and other leaf diseases.

To kill the stump that continues to sprout you need to apply products that contain "triclopyr" such as Ortho Brush-B-Gon or Fertilome Brush and Stump closely following label directions and your problem will be solved. The root system will also decompose over time.

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. Please do not send plant samples.

Dr. Hort: What's likely killing Indian Hawthorn? 01/26/13 [Last modified: Friday, January 25, 2013 6:04pm]

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