Ron Smith, Extension Horticulturist, NDSU Extension
Q: Every spring, when newer growth and buds begin, my rose plant gets a large infestation of aphids. What is the best treatment and is there a way to keep them from coming back? (e-mail reference)
A: Aphids love fresh growing roses! They always have and always will. About all you can do is spray the aphids with an insecticidal soap when they appear. If I knew a way to keep them from coming back, I would be “one rich Smith.”
Q: I transplanted established hybrid roses two years ago to a new fertilized bed, which gets full sun. About half of them budded and bloomed last year. This spring most of the stems budded and it looked as though they would flourish but the buds swelled, turned brown and died. The leaves have tiny holes but I haven't seen any bugs. Can you give me some advice? (Brookings, S.D.)
A: It’s probably thrips feeding on the flowers that have kept them from opening. The holes in the leaves are due to any character that is hungry for a quick bite out of a rose leaf. I suggest cutting the rose buds back to the first 5 leaflet leaf and spraying the plants with Orthene. Being a systemic, it will help control the thrips or any other feeders.
Q: We have a miniature rose plant that we brought in last fall. Every other week we have to spray the plant because white bugs get all over it. They make webs on the leaves and stems. There are also brown spots on the leaves. Whenever we spray, it sets the plant back. I used Schultz insect spray for houseplants and Eight insect control for house and garden plants. I also planted garlic in the soil and washed it many times. The bugs look like spider mites, and the directions on back of the ready-to-use spray said it was for spider mites. What do you suggest we do? (Fingal, N.D.)
A: Miniature roses are one of the biggest houseplant challenges a person can have. They don't respond well to the low light, dry, drafty conditions and cold water--all typical conditions during the winter. When I lived in Ohio, I was a big fan of miniature roses until I tried to get them through an entire year. I finally gave up!
If you wish to continue the battle, I would suggest the following strategy:
1.Get some insecticidal soap and dip the entire top of the plant in the solution. 2.Take the plant out of the pot and clean the container completely in hot, soapy water. Rinse, and then repot in fresh, high-quality potting soil. 3.Place the rose under fluorescent lamps (or other plant lights) about 1 foot from the top of the plant. 4.Always water with distilled, room-temperature water. 5.Keep the rose away from other houseplants so reinfestation cannot occur. 6.If this doesn't work, then give up!
Q. Can you tell me what is eating the enclosed leaf? It is from my Champlain shrub rose. (Linton, N.D.)
A. The damage resembles that of a slug or caterpillar. Use a systemic insecticide (Orthene) if there is no physical evidence of slugs. If there is evidence of slugs, use something like slug-getta, a molluscacide.
A: That is a weighty title you thrust upon me! I'm not sure I want it, as I am always learning something new as well. The only thing I can think of is the possibility of borers entering the cane cut ends last year after they were pruned back in the spring. They may have caused enough damage to keep them from flowering but not from producing vegetative growth. Ask her to inspect some of the canes on that rose plant, cutting back to see if the center was hollowed out by borer activity. If it was, she should cut back to where the canes are solid and light colored. I would then suggest sealing those cut surfaces with clear fingernail polish to help prevent the borers from entering again. If that isn't it, then I am at a loss.
Q: I have two potted roses the discount store was going to throw away. They are not hardy to my area. My area is zone 3. They are suitable for zones 5 - 9. My free babies produced large fragrant beautiful blooms all through late fall. I brought them in this winter to see if I could save them. Now I noticed very small green bugs on the leaves and the leaves are wilting. Aphids? I cut them back before I brought them in. They grew back nicely, but the leaves are very tender. Am I crazy for trying? Also, how do I plant a mango seed my parents brought back from California? (E-mail reference, Doran, Minn.)
A: Not crazy, just tender-hearted. The roses would have been better off being left in the soil in their outdoor environment, and allowed to harden off going into winter. You could have then covered them with soil and leaves to protect the crown and scion wood. I am afraid that from this point on, it will be nothing but a down-hill trip for the plants. If you have an unheated garage, I would suggest moving them in and allow them to go dormant. Water enough to keep the soil from drying out. If the temperature should drop to below zero, I suggest running a small space heater to keep it a little above that point around the plants. Then plant them in the spring and see what happens. Concerning your mango, since these are warm season tropicals, they should be germinated at about 80 degrees F. Since this is warmer than most homes are kept, I suggest bottom heat (from propagation pads or cables) and keeping the medium evenly moist. I have no idea how long it will take, but don't be surprised if it stretches into six weeks or more.
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