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Published May 06, 2011, 12:00 AM

Hortiscope: Powdery mildew can reduce crop production

Q: I had a man stop today to ask a question about garden peas. Last summer, he raised peas in his small backyard garden. He said that when the plants reached mature height, he noticed what he called white mold on a few plants.

By: Don Kinzler, INFORUM

Q: I had a man stop today to ask a question about garden peas. Last summer, he raised peas in his small backyard garden. He said that when the plants reached mature height, he noticed what he called white mold on a few plants. Within a few days, all of the plants had the mold. However, the plants continued to produce pods and the peas maintained flavor as he continued to pick the mature pods. He wants to know if this is a type of white mold and what he can do to eliminate the problem. Thanks for your help. (email reference)

A: This probably is powdery mildew, a low-grade fungus that lowers the production of the crop it infects. High humidity and temperatures mostly cause the problem. There are sprays that can be used but aren’t recommended. I would advise him not to overwater, and to try to improve the air circulation around the plants as much as possible. He might want to try planting in a different garden location and carefully select hybrid peas that are more resistant to this fungus.


Q: I have read with interest a zillion sites giving advice on getting rid of ants organically. These ants are the tiny ones that nest by the millions in my potted plants, compost and under the bricks on my terrace. The ants also have made their way inside to investigate my pantry. I have a formidable list of things to try, ranging from boric acid to cinnamon and diatomaceous soil.

However, I need to know if any of these solutions will be bad for lizards because my garden is a haven for lizards. I enjoy watching them scuttle around and bask in the sun. The last thing I want to do is harm them or drive them away. Can you advise which program would be best to use with lizards in mind? (email reference)

A: Ants are nature’s marvelous engineers. As humans, we should be thankful they don’t get to be the size of our pet dogs. I’ll make a couple of suggestions that I’ve heard others swear by and leave it up to you if you want to employ these tactics. Boiling water poured on an ant nest will do the job of killing the colony. Then dig it up and try to locate the queen to kill or remove her.

Cornmeal will serve as a food source that will kill ants. Sprinkle it along their runs and around the nests that you can locate. Orange citrus peels may or may not work. Some swear by it, while others swear at it. All I can say is try it. The peels of two average oranges, soaked in boiling water overnight, may do the trick. I’ve never tried this, so you are on your own. I’ve never heard of diatomaceous earth being effective. It is good for slug control, but I think the nimble ants would just move it out of the way to get where they want to go. Ant hotels are found in most garden center outlets. The hotels contain boric acid, which is a toxin to ants. It will take quite a while to kill them off because it is slow-acting. The ants attracted to the hotel enter and exit with food to be carried back to the nest. This is done repeatedly until the colony is wiped out.


Q: I thought I’d ask a question about pomegranate trees. I live in zone 7A, which is about 30 miles south of Oklahoma City, Okla. I planted a pomegranate bush last fall. At this time, I see no leafing. We had a hard winter, with a few days below 15 degrees. I’m wondering if the plant is dead. Is it too early to give up on the bush? Can you recommend a hardy pomegranate for my zone? (email reference)

A: See if you can locate the Russian cultivar known as Favorite. It supposedly is hardy to 10 degrees. Another one touted as being cold hardy is Nejikan, but my references don’t say how low it can go with temperature tolerance.


Q: I have a poinsettia plant that has survived two Christmas seasons. However, now I am wondering about how to continue caring for it. Do I cut it down again and repot? Do I start 14 hours of darkness in October again? (email reference)

A: Yes to all of your questions. Summer it outdoors to stimulate good growth.

Take a cutting from the plant and root it in a separate pot. This will give you two plants to celebrate with next Christmas.


Q: I live on a sand ridge between Thief River Falls and Roseau, Minn. I have a birch tree that is about 15 inches in diameter and 20 feet tall. It is dying on the top but has shoots that are coming up next to the base. Can I cut the tree down? If so, what time of the year would be best? How high should I leave the stump? How many of the young saplings should I save? (email reference)

A: I don’t recommend that anyone except a qualified arborist cut down a tree that tall. Go to www.treesaregood.com/findtreeservices/FindTreeCareService.aspx to find a qualified arborist in your area. It sounds as if the tree is being attacked by borers, which should be addressed by the same individual who visits your home.

With proper pruning and treatment, you may be able to save the tree.


Q: What do I do about snow mold? (email reference)

A: The best approach is to wait until the frost is out of the soil and the soil is a little drier. Assuming you are a homeowner, get out the rake and give the affected areas a good raking. Sprinkle grass seed over the area and lightly mix it into the surface of the soil. Even if you do nothing, in most instances, the grass will turn green if it is a typical Kentucky bluegrass lawn. The above treatment should accelerate the process. If snow mold is a chronic problem every year, core aeration usually lessens the impact and extent of the problem.


Q: I have very lumpy turf that started about a year ago. It looks like night crawler mounds. What can I do to repair this situation and prevent the crawlers from coming back, or am I going to have to live with this situation? I have heard that keeping the lawn healthy and fertilized will keep night crawlers at bay. Will thatching and aeration help? Thank you for any comments. (Moorhead)

A: You sound like the kind of person who is willing to roll up your sleeves and get after this common problem in our area. There are a series of operations that will minimize the impact of these soil engineers and help aerate the soil naturally. Once the soil dries somewhat and the grass is greening and has had at least one mowing, rent a core aerator and plug aerate the lawn. Allow the cores to dry for an afternoon or a day and then rent a power rake to bust up the cores and knock down the night crawler mounds. Next, fertilize and overseed after picking up the duff that the power rake left behind. Then allow the grass to grow for a couple of weeks. As spring progress into mid-May, have your lawn treated for beetle grubs. This should kill about 30 percent of the night crawler population. Repeat this process for the next three years. If the pests start to pop up again, rent a ballast roller to roll the mounds flatter. You can ignore the problem, of course, but then I’ve heard that people have rolled their ankles quite painfully from these pilings getting out of hand.


Q: I read your information on how to keep deer away from evergreens. A friend used crime tape and the plastic barrier tape used by road crews. It whips in the wind and makes a noise that scares the deer. He says it works well. (email reference)

A: Wow, if something this easy works, it will revolutionize how to keep deer away from evergreens! I’m sure many will try it and report their results to me.


Q: Now that the snow is finally melting, evidence of voles doing their thing in the grass is apparent. It is no big deal, but they also chewed all the bark off one of my mature apple trees about 8 to10 inches off the ground and all the way around the tree. I think the tree is toast. Am I right? (email reference)

A:


Q: I stumbled across your website while looking for what may be wrong with my cherry tree. From what I’ve read, it sounds like I may have black knot. I live in the high desert area of Frazier Park, Calif., which is about 5,000 feet above sea level. We usually get a decent amount of snow. The cherry was planted around 1957 and stands about 30 feet tall. There are numerous types of cherry trees in our area. When we moved in five years ago, the tree was loaded with what appear to be Bing cherries. For the first few years, the harvest was amazing. We gave it Jobes fruit spikes as recommended. We have had late frosts for the last couple of years, so our cherry crop was wiped out. Now we are losing limbs and have noticed large oozing wounds. The buds are diminished and I fear we are going to lose the whole tree. This area suffers from a large amount of ants, and I’ve noticed them around the base of all my trees. (email reference)

A: This sounds like borer activity. The ants are seeking out the ooze due to the high carbohydrates it contains. It makes a great food source for these scavengers. You need to contact someone locally at the Extension Service. Go to http://ucanr.org/County_Offices/ to find the office nearest you.


Q: Last summer, my parents bought us a pin oak tree as a housewarming gift.

About a month or two later, we noticed it was being attacked by Japanese beetles. We purchased Sevin to get rid of the bugs and got a beetle trap, which seemed to get the bugs away from the tree. How can I tell if our tree is going to make it back or if it needs to be replaced? The bark looks good and the branches are bendable and don’t break, but it doesn’t look like there are any buds on it yet. When do pin oaks bud and how can I tell if this tree is going to come back? (Missouri)

A: The tree should have survived the onslaught of Japanese beetles and will come back this year. However, the tree may bud a little later and be a little weaker.

With the accelerated high temperatures you are experiencing, the tree should be breaking bud soon. Contact the Missouri Extension Service agent nearest you for a more accurate analysis of the situation. Go to http://extension.missouri.edu/directory/Places.aspx to find your county contact information.


Q: I just discovered your Hortiscope page and I’m wondering if you can dispense some advice about two of my dear plants. I have zebra and mona lavender plants that are not doing nearly as well as I would like. I moved from Colorado to northern Arizona with my houseplants about four months ago. I know moving can cause stress, but my other plants seem to be doing just fine. I purchased the mona lavender in a 6-inch plastic pot while it was in bloom and the foliage was very beautiful. The foliage is dense and dark green with deep purple undersides.

The blooms dropped off, but the leaves remained healthy. Shortly after moving, all of the leaves dropped off. The plant has been growing rapidly and is several inches taller than it was. The plant continues to grow new leaves that fall off while they are still tender and pale green. The stems and the new leaves seem healthy and there is no obvious disease or infestation, but the leaves won’t grow past about the size of a nickel before dropping. About three weeks ago, I transferred it to a slightly larger terra-cotta pot and pruned many of the taller branches. However, it still looks bare and spindly. I water it when the top of the soil is dry. I use an organic liquid fertilizer about every other time I water. I want to restore this plant to its original health and beauty but am at a complete loss on how to do it. I moved the zebra plant at the same time as the mona lavender. It seemed to be doing fine until a roommate left a door open in December, so it got cold in the room. As soon as I noticed, I moved the plant to a warmer location, but the plant lost all of its leaves. The trunk remained firm and healthy and began sprouting new leaves as soon as I moved it to a warmer location. For the past three months, it has been growing new leaves that look very healthy, but they turn brown and dry at the tips and then fall off. The old leaves are replaced by new leaves that do the same thing. Again, there are no obvious signs of disease or infestation. Except for the leaves dropping, it seems healthy and even bloomed this spring. As instructed, I do not allow the plant’s soil to dry completely between watering and mist the plant about every other time I give it water. I also fertilize the zebra plant on a regular basis. Although neither of these plants seems to be in grave danger, I would like to see the plants as healthy as they were when I purchased them. It’s discouraging to have such success with other plants but be unable to help these two. Any advice you can give me would be greatly appreciated. Thank you in advance. (email reference)

A: Most likely, you are fighting a cultural problem rather than any disease or insect challenge. Generally, leaf drop and edge browning are an indication that the plant is being kept too wet or dry, it is getting too much fluctuation in air temperature or the humidity is too low. Try putting the plants on a tray of pebbles that are set in water to increase the moisture in the air surrounding the plants. Also, check your water source. Is it high in soluble salts? If so, it may be a contributor to these problems. Try watering with distilled or bottled drinking water for a time to see if that improves the situation. This is the best advice I can come up with based on what you have told me. Hope it helps.


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 email ronald.smith@ndsu.edu.

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