Test plant tissue to understand dieback

Dear Neil: We have a grouping of Texas mountain laurels that is dying. Each of the three trees is 15 to 20 feet tall. Last year, one of the trees died suddenly, and this year, a second one did as well. Now, the leaves on the third tree are turning brown. We have another group nearby. What can we do to keep from losing them?

A: Your photos were really helpful. Thank you, for attaching them. Unfortunately, I don't have a good answer for you. I experienced the same kind of dieback and eventual loss on my own mountain laurel. It followed an extremely wet season and a severe cold spell several years ago, and I expected those to be the main contributors. One of your photos shows a black internal decay within one of the trunks, and I saw that, too. I didn't send a sample to the Plant Disease Diagnostic Lab at Texas A&M at that time. Now I wish I had. I just spent 30 minutes searching online websites, and I found no particular diseases of Texas mountain laurel (Sophora secundiflora). The only matches that popped up were for the northern mountain laurel (Kalmia) that is totally unrelated. I would suggest sending plant tissues from that decaying stump in one of your photos, along with a description and the same four photos. Please let us know what you learn.

Dear Neil: I have a splitleaf philodendron vine whose leaves don't split like they used to. What am I doing wrong? It's growing quickly, but the leaves are almost round.

A: That indicates that the plant has reached the top of its support post and is leaning over. Splitleaf philodendrons (P. pertussum) only develop the really split "adult" leaves when they're growing vertically. Put a taller pole into the pot and you'll probably see changes with successive leaves.

Dear Neil: Is there any way for an amateur to propagate yellow Lady Banksia roses? I've tried for years and I've yet to be successful.

A: Lady Banksia, like almost all of the other antique roses, has always been grown from cuttings. You'll see two kinds of growth on Lady Banksia plants — long, straight cane-like stalks, and more normal, small twigs that are not completely straight. The latter group provides the best cutting wood, and usually 4- to 5-inch cuttings of new growth in May and early June root best. Rooting hormone powder helps, as can "wounding" the base of each cutting to provide additional surface for root development. That involves removing a sliver of the outer green tissues gently with a very sharp knife before dusting it with the rooting hormone powder.

Dear Neil: We have a relatively low area in our lawn. I'd like to figure a way to get the water out of it, but it may stand for a day or two after heavy rains. What could we do?

A: Start by determining where the water is originating. If it's coming from another yard, consider some kind of channel or berm to keep it off your property. If it's coming off your roof, install guttering, or, if you already have it, consider adding more downspouts or directing their outflow farther away from your house and in a different direction. You might even be able to take them out onto the lawn where you could have an in-ground drain with a small cast iron or hard plastic lid. Let that drain carry the water via 4-inch piping to a lower ditch somewhere. In some cases you can also install a French drain, that is, a length of perforated 4-inch plastic pipe laid one foot deep in a bed of coarse gravel topped with finer pea gravel topped with sand and finished with topsoil. A landscape contractor can do this last installation for you.

Dear Neil: Enclosed are samples of leaves and stickers from a weed that has recently invaded our area. Broadleafed weedkillers and glyphosates didn't do anything to eliminate it. What can I use?

A: The samples were taped to paper, and they molded beneath the heavy tape, so I'm not able to identify them. However, they are definitely from a broadleafed plant, so any herbicide containing 2,4-d should eliminate them given one or two applications. Use a fine to medium-sized droplet pattern. Include one or two drops of liquid dishwashing detergent to help hold the weedkiller on the leaf surfaces. Spray when the plants are growing actively, and do not mow for 3 to 5 days before or after you apply the spray. Do not water for 48 hours. As one additional tip: you'll have much better results killing the plants if you spray them while they're young and growing most actively.



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