Questions on: Impatiens
Ron Smith, Horticulturist, NDSU Extension Service
Q: I have planted impatiens in the same flowerbed for a number of years. The last couple of years, I have had problems with parts of some plants suddenly wilting and dying. They appear to have been cut at the stem. Sometimes the whole plant dies. Is this a fungus or insect problem? I have some planted in a window box that never has had this problem. (e-mail reference)
A: This sounds like cutworm activity. By now, the larvae probably have morphed into the adult moth and laid eggs for next year's feeding. You can place a granular insecticide, such as Sevin, into the soil at planting time to take care of this pest. It is a good idea to alternate your plant species each year to prevent insect and disease problems from developing. Window box plantings almost always use pasteurized, fresh soil each year, which eliminates this problem.
Q: I have several potted impatiens. They were growing great in large pots and cascading over the sides. Lately, they have been getting leggy. The branches are growing straight up, with flowers at the top only. I also have a problem with a pink double impatien. The base of the stems appears to be rotting. The plants are kept in moderate shade, good dirt and not overwatered. What am I doing wrong? (e-mail reference)
A: Impatiens can be cut back to force them to bush out. The plant that is rotting at the base most likely has a soil-borne pathogen. It isn't anything you are necessarily doing wrong. It just happens sometimes. Consider using a soil drench fungicide, such as Funginex, in the future before replanting.
Q: I recently planted accent deep pink impatiens in my back yard. After planting, we had seven days of very heavy rain. The leaves are now turning yellow and have black spots. Do you know why this happened? (e-mail reference)
A: Probably because of the saturated soil and cool temperatures. They will very likely die, at least the ones with the black spots and yellow leaves unless it is just a reaction to the weather and not a disease. You might try spraying with a common fungicide like Daconil 2787 to see if you can control any further disease development.
Q: I was wondering if 30-degree temperatures would hurt petunias, marigolds and impatiens that were planted outside now. (E-mail reference)
A: It depends. If they are close to the house, no; if they were hardened off, no; if the 30-degree temp comes for only an hour or so before sunrise, no; if a frost accompanies the temperature, most likely. The impatiens would be the first to go, followed by the marigolds, followed by the petunias. I suggest throwing a cover over them for the night.
Q: I have several questions that came up this growing season:
1. Our new house came with three overgrown and neglected crabapple trees, the pruning of which triggered what appears to be fireblight. I optimistically and lovingly planted and pampered an expensive new rosebush, not realizing until later that roses are related to apples. It turned brown and died within several weeks. Is there any way to grow healthy roses in our yard?
2. We collect rainwater from the roof and use it for houseplants as well as the garden. Could the blight bacteria be in the rainwater? My kitchen herbs are blackening, and the impatiens outdoors are also showing brown leaves.
3. We replaced all the house's old leaky windows with new ones having what they called "low-E" glass. They're wonderful for keeping the winter warm and the summer cool, but I wonder if they block too much of what our houseplants need of sunlight. They seem to get pale and leggy even in the sunniest windows. (Palermo, N.D.)
A: You ask some very good questions!
1. The fireblight bacterium is airborne and therefore present in rainwater. Being a bacterium, it can enter microscopic openings, which plants are full of. Concerning your rose passion, try it again only this time plant in another location, avoid water splashing on the foliage, if possible, and keep it sprayed with a multipurpose fungicide spray or a fungicide containing triforine. Lime-sulfur and Daconil 2787 are two other examples of the many fungicides available for roses.
2. Has your roof been re-shingled in recent years? Could be some chemical toxins coming off that. The fireblight bacterium doesn't infect all plant material, of course. You could also be getting Pythicum fungus started on your plants.
3. You bet! I don't know the range of light that is being blocked, but it has to be within the range that helps produce chlorophyll. There are "spot plant lights" which you can use to overcome this.
Q. Enclosed in the box are two specimens. What is the hard black lump off my Canadian red chokeberry tree? Any prevention?
The sick impatiens are here and there in a group. Plants around them look healthy. Is there any information on this and is there a prevention? You have been a great help in the past and I thank you. (Oakes, N.D.)
A. Your chokecherry has a fungus disease known as black knot. Normally, not a severe problem on cultivated stone fruits like your cherry. This disease has been showing up more frequently these past couple of years.
The best control methods are to prune out the visible knots, at least 3 to 4 inches below the swelling. Also check around your property and adjacent lots to see if there are other cherries with the same disease. Spray with lime sulfur next spring before leaf-out, and apply a protective fungicide like
Bordeaux mixture once the leaves have opened.
Your impatiens sample looked amazingly healthy with the exception of a few leaf spots, which might be a touch of botuytis due to the wet conditions the plants are normally kept in. Just try to avoid splashing water when irrigating.
Thank you for the nice compliment. Glad I have been helpful.
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