Q. Dear Neil: My red oak tree leafs out beautifully each spring, but within a month or two, half of the leaves turn brown. Why would this happen?
A. Look closely at the trunk on that side of the tree. My guess would be that the bark has been damaged by sun scald several years ago when the tree was young. This is a very common occurrence. (In fact, I had another question asking about white mold and loose bark on a red oak. Sun scald was involved there as well.) Red oaks, red maples, and Chinese pistachios have very thin bark when they are young. They are grown side-by-side in nurseries and they shade one another. When we plant them in our landscapes they are suddenly exposed to full sun. It is very important that we protect their trunks with paper tree wrap for the first couple of years. My guess would be that the side with the brown leaves is the southwest or west side of the tree.
Q. Dear Neil: My Cora periwinkles are dying right before my eyes. I replaced them, and the replacement plants are dying quickly, too. They just shrivel up. I’m watering them carefully, so I’m sure they’re not drying out. What could be happening?
A. That is a water mold fungus called Phytoph-thora. If you examine the stems, they look like they’ve been pinched with hot tweezers. The Cora series was developed to have resistance to that disease, but over the years they have become susceptible, too. There is a “new and improved” type of Cora periwinkles that has improved resistance. Nonetheless, I would probably switch to some other hot-weather annual for a few years.
Q. Dear Neil: We’ve had six variegated privet hedges in our yard for more than 12 years. One died suddenly last summer and one died this spring. Another is now showing a few dead limbs. Have they just outlived their expected life span?
A. I can’t tell just from that information, but they are susceptible to the soil-borne cotton root rot fungus. It will kill them rather quickly, and it will move down a row one plant to the adjacent one. If you’re pruning them to stay at less than 7 or 8 feet tall you could also be wearing them out. Many people try to maintain them too short.
Q. Dear Neil: We have a bed of butterfly weed, but this weed is also there. It looks so much like butterfly weed that it’s hard for us to determine which needs to be pulled.
A. Butterfly weed (Asclepias tuberosa) is a perennial that comes back from one big, fleshy root system. I would think you could cut and fit a roll-type mulch around it and then conceal that with finely ground pine bark mulch.
Q. Dear Neil: How do I control grasshoppers that are eating holes in my tomatoes? (See photo.)
A. Judging from your photo, unless you’ve actually seen the grasshoppeds, it’s much more likely that you have birds dining on your tomatoes. Either way, cover the plants with frost cloth and you should be good to go. I know it’s not exactly frosty out there, but the gauze-like fabric should be fine for protecting the ripening fruit. Actually, you can also harvest the fruit just as it starts to turn pink and let it finish ripening indoors on a countertop. It will lose no flavor or nutritional value that way.
Q. Dear Neil: I planted two new peach trees (Ranger and Harvester) in April. I’ve taken perfect care of them, but neither tree has any fruit now. Can I expect them to have fruit next year?
A. I hope not. Peach trees need at least three years to get established before we allow them to start bearing. Fruit really taxes the new trees. It would be OK if you allowed one or two fruit to develop, but be patient.
Q. Dear Neil: My husband planted several Paulownia trees seven years ago. This year many of the lower branches have died. What would have caused that? I don’t find much information about them.
A. Empress trees (Paulownia tomentosa) are fast-growing, weak-wooded trees that are subject to this limb dieback fairly frequently. While they are beautiful while they’re blooming, their root systems can be trouble, and they are invasive in much of the U.S. That may be more information than you really wanted, but you can find even more by searching its scientific name and adding “Missouri Botanical Gardens.”
Q. Dear Neil: I have zoysia in both the front and back yards. My backyard looks great, but for some reason the front is spotty. Do you think this will fill in during this season?
A. I think so. It looks like there has been zoysia there that has died for some reason. If you see it declining at all this summer or fall, I would suggest sending samples of the affected grass to the Texas Plant Clinic at Texas A&M. Their website has all the details of payment and sampling instructions.
Q. Dear Neil: I have a 4-foot patch of clover in my St. Augustine. What can I use to kill the clover that will not harm my grass? It is directly beneath a large crape myrtle.
A. Apply 2,4-D according to directions on the label. There are a couple of products on the market that contain 2,4-D as their only active ingredient. The combination products have herbicides that will soak into the soil and could damage your crape myrtle. The 2,4-D will not. However, there are temperature restrictions on application of 2,4-D to St. Augustine. It’s very warm to be using it now. Buy a product in a trigger bottle so you can test it on a very small area. Give it a few days to see how you like the results. Spray it in a way that the beads of weedkiller don’t roll off the leaves of the clover. Be patient. It will take a week or two to do its job. All of that presumes you have white clover or some other true clover and perhaps not oxalis of one sort or another.