Dear Neil: How can I eliminate Mexican petunias? They are so invasive. A: A broadleafed weedkiller (containing 2,4-D) will kill a certain portion of them, but at some point, you may just decide to rototill deeply and rake out as much of the root system as you can. Another option would be to lay a weed-blocking fabric over the bed for a year or two.
Put bark mulch over it to conceal it. They will gradually give up. Dear Neil: I have a 6-year-old pear tree that has fire blight.
I have two other pear trees and three apples. How can I keep the one tree alive, and what can I do to prevent spread of the disease? A: The past few years have been really rough for fire blight. The fact that only one of your five trees came down with it is encouraging.
Prune out the dead branches on the pear. Make each cut back into healthy tissue, disinfecting your pruning tools between each cut by washing them with a solution of 90 percent water and 10 percent chlorine bleach. Spray all the trees with agricultural streptomycin while they’re in full bloom.
It’s available at many full-service nurseries and farm supply stores. You might want to locate it over the winter and have it on hand. Dear Neil: I have about 30 hibiscus plants, and they are covered with whiteflies.
One nurseryman suggested Malathion, but another warned me that it would burn my hibiscus plants. I’ve also used a systemic, but I still have them. What works? A: Whiteflies are in love with tropical hibiscus plants.
Added to the fact that they’re among the most difficult of all insects to eliminate, that makes the problem especially difficult. The nursery person was correct — Malathion does often burn hibiscus foliage. The systemic insecticides present your best option, but it’s going to take several months to work through the entire population, as new whiteflies will be hatching from the egg masses on the leaves.
You might also use yellow sticky traps available from many organic gardening sources. The whiteflies are attracted to their color, and they get stuck to the surfaces. You could also use a pail of warm water and dishwashing soap and two soft sponges pulled across the tops and bottoms of the leaves to get rid of many of them.
I hope you can eliminate them before you bring the plants indoors or into a greenhouse for the winter. In those settings the pests are freed from all natural predators. Dear Neil: We are building on a heavily wooded lot, and we need privacy across the back.
We’ve had both redtip photinias and ligustrums around our house in years past, and both required constant pruning. They also had other problems. Would either of these be good if left unpruned? What would our best choice be? A: Don’t feel like you have to have a long, straight row of the same plant.
You might be able to use several types in more natural clusters and groupings. That said, redtip photinias should be the very last choices due to their great susceptibility to the fatal and incurable Entomosporium fungal leaf spot. Waxleaf ligustrums would be good, but they have been killed by cold in recent winters in many parts of the state.
Nellie R. Stevens hollies, Oakland hollies and shrub-form regular yaupon hollies would be top-notch. Hollies are great in sun or shade.
Let a local independent nurseryman show you your options and discuss planting plans. Dear Neil: I’ve used pre-emergent weedkillers, and I still have roadside asters. How can I keep from having them? A: The wiry little daisy-like roadside asters show up in lawn areas that really need a bit more water, fertilizer and frequent low mowing.
We usually see them in hot, dry parts of our yards. However, if they still persist, you can use a broadleafed weedkiller (2,4-D) to eliminate them during the growing season. Even though no one would ever say that they have broad leaves, that’s a horticultural distinction that’s used to separate weeds that are not grasses from true grasses.
Spray when they’re young and growing actively. The pre-emergent Gallery applied in mid-March and repeated in mid-June would prevent them, but the same amount of money spent on fertilizer and a bit more water would probably do just as well. Dear Neil: I planted a short row of seven dwarf Burford hollies this past spring.
Three of them have turned completely brown. I’ve looked really closely and I see no signs of any insects or diseases. What could have caused that, and what can I do to bring them back? A: I can guarantee you that the plants got too dry one or more times.
New plants have almost all their roots in their original soil balls that came within the containers. Those root balls dry out much more quickly between waterings than the adjacent “native” soil does. That’s why it’s so critical that we water new plantings by hand using a hose and a water breaker or bubbler every other day when temperatures are as warm as they have been.
Hollies don’t wilt when they’re dry, so they can pass the point of no return before we ever know it. Unfortunately, there is nothing we can do to bring them back. I have to deliver that bad news many times each summer here in Texas.
Have a question you’d like Neil to consider? E-mail him at [email protected] . Neil regrets that he cannot reply to questions individually.
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