Controlling nutrient deficiencies, bagworms and scales
Q: I have two hibiscus plants that I have indoors in pots during the winter. They have been blooming, but also have black, flying bugs. I've been spraying them with a dish detergent and water mixture. It appears to help for a time, but then the bugs return. Is there a spray that I can purchase for this problem?
A: Any spray I recommend would have the same impact. You might try locating a systemic insecticide that can be soil-applied to control them if they are nibbling on your plant. I suspect they are fruit flies. I know the name doesn't fit, but they aren't very bright, either! Fruit flies have very short life cycles. They are more of an annoyance than a threat to the plant. Otherwise, just keep up with the insecticidal soap as they appear. You eventually will win the battle!
Q: I was given a spider plant as a gift a few months ago. Recently, the leaves have started to turn red. Do you know what could cause this? Is it being overwatered or too cold?
A: It could be caused by either one, but often it is a sign of some nutrient deficiencies. I would suggest repotting it in some pasteurized potting soil that is available on the market, such as Miracle-Gro. Use a free-draining container. When you water, only do it when the soil is dry and make sure water flows out the bottom. After 20 to 30 minutes, drain off any excess water remaining in the saucer. This should improve the plant without knowing what is causing the problem.
Q: We have what I believe to be a crab apple tree in our front yard. Recently, we had plumbing issues. The city came out and said our cleanout was below ground next to our tree. When we dug next to it, we had to cut three to four roots that were approximately 2 to 3 inches in diameter. Will this cause the tree to die?
A: It should not have a major impact on the tree if it was otherwise healthy. Removing three to four root sections the size you describe shouldn't be traumatic for the tree.
Q: We have an infestation of bagworms every year. To get rid of them, we have done everything from spraying the trees to picking the nasty little worms off. What are we doing wrong? We have eight very large white pines that were here when we bought the property. We planted 11 spruce and fir trees in the fall of 2007 and another six last November. What can we use and how should we use it?
A: Bagworms are difficult to control because often they are unnoticed until mature. Mature larvae often will pupate early if they detect pesticides on the plant foliage. Though there are a few known bagworm parasites and predators, they are not adequate in urban habitats to get rid of the worms. However, several options exist to control bagworms. Bacillus thuringiensis (Bt) is effective if used early enough in the season. Since you didn't tell me where you live, I can't be completely accurate with the date. In the upper Midwest, it is around the middle to the end of June. Doing it then will control the new hatchlings, which is the most effective. Using a chemical control gives you several options. Earlier applications are better than later. Some of the products available are Orthene, Sevin, Malathion and pyrethrum. How to use these materials is explained on the label. If you can, continue to pick off the bags you can reach during this dormant part of the season. Carefully cut the silk attachment to the branch because it has the potential to girdle the twig at that point in the future.
Q: I think one of my plants has scales. It's a plant I rescued without looking very closely at it. I scrubbed all the leaves and noticed it had many scale bug leavings. The leaves are mostly clean and I have applied a solution of water, alcohol, tea tree oil and dish soap to all visible parts of the plant. The recommendation from my local florist was to throw it out, but I can't do that just yet. Do you have any additional information about scale bugs? I don't know what the best resource online would be to learn more. Any help is much appreciated.
A: Scale insects are difficult to control once they get a foothold on a plant. However, with persistence, which you seem to have, it can be done. Washing the leaves was a good start. I encourage you to continue along those same lines. If the plant is manageable, place aluminum foil over the pot in a secure manner and swish the aerial part of the plant around in a tub of tepid water with a mild detergent added (about a tablespoon per gallon). If that doesn't work, look for products containing imidacloprid. It is a systemic insecticide that sometimes is found in potting soil or systemic insecticides on the market and sold by Bayer or Miracle-Gro. If you are loath to using any chemicals and the other nonchemical tactics don't seem to work, cut the plant back to a nub. Leave a stem about 2 inches long sticking out of the pot. Repot the plant in fresh, pasteurized soil and use a free-draining pot. Continue maintaining the plant normally with watering and light exposure. If it was otherwise healthy, there should be new growth coming up that would be free of any scale insects. If this plan doesn't work, then take your florist's advice!
To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or e-mail firstname.lastname@example.org.