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Don Kinzler, Published July 13 2012

Hortiscope: Rain, wind may be cause of fruitless tree

Q: Last year, my apricot tree had lots of fruit, but it was leaching a sticky liquid. I read that those parts of the tree that are leaching should be removed, so that is what I did. This year, the tree is doing very well and there is no leaching. However, it is not bearing fruit. Any ideas? (France)

A: There are many reasons why trees fail to bear fruit. The problem could be rain or cold weather at a time when the pollen is ripe or the stigma is receptive to the pollen, or windy conditions prevented the pollinating insects from being active. It could be too high a nutrient level (especially nitrogen) to set the reproductive organs. Widely fluctuating temperatures in late winter could have caused the flower buds to deharden to the point where a normal freeze killed them. Finally, last year’s heavy fruit production may have exhausted the energy resources of the tree to the point where no flower buds were set. Sex in any form requires energy. Next season, assuming none of the other factors are at play, you should get your apricots back.

Q: The top one-third of my birch didn’t produce leaves this year. The rest of the tree looks healthy. We didn’t have an intense winter, and there was no digging done in the area. Do you have any ideas about what may have happened? (Ottawa, Canada)

A: This sounds like it might be the work of bronze birch borers. Check the bark for d-shaped exit holes or rippling in the bark. If this much of the tree has been hit by this pest, you are better off having it removed. Go to http://tinyurl.

com/3qv258v for more information on bronze birch borers and photos of the damage these pests inflict on trees.

Q: I have a bergamot plant that has been in the ground for two seasons. It is waist-high but has sparse leaves and they look mottled. I was thinking maybe it’s not getting enough sun, so I bought another one and put it where it will get full sun. I can’t compare them yet because the new one has been in the ground for only two weeks. Any ideas? (email)

A: Bergamot is a very popular herb and good-looking perennial plant. Bergamot loves light, moist soil. A great spot to plant your bergamot is in a place that just gets morning sun. If you can do that, the flowers will bloom longer and the foliage will dry faster, which will reduce the possibility of powdery mildew showing up. You can add bergamot to your garden by using plant cuttings or sowing seeds. However, if you sow the seeds, the bergamot will grow more slowly compared with using cuttings. Bergamot is a creeping plant that tends to spread, so you will need to contain it. However, to my knowledge, it isn’t considered invasive. My guess is that your plant needs to be dug out and divided, which should be done in the early spring.

Q: I have a lady who has some kind of pest eating holes in her peppermint plants. These pests are doing a lot of damage. The pests also are damaging one of her tomato plants. She would like to use something all natural to get rid of the pests. Would Bt work for something like this? Also, she has cutworms in her corn. Is diatomaceous earth matter the best way to get rid of the cutworms? (email reference)

A: If she has cutworms working on her corn, I suspect she has another variety of the beast called the climbing cutworm working on her peppermint and tomato plants. Similar to typical cutworms, climbing cutworms do their dirty work at night. We had a peak in their activity recently, so now they are gone. Sevin or diatomaceous earth will take care of both species. Bt might be OK, but it takes too long to work on vegetable crops.

Q: I’ve noticed a lot of cottony stuff floating in the air. It looks like cotton from cottonwood trees. However, isn’t this too early for them to shed, or did the mild winter/early spring get them to produce this cotton much earlier than normal? (email)

A: As many folks have noted, the cotton from the female cottonwood trees seems to be coming earlier than in years past. It may or may not be true in some areas of the region. A fact I want to mention is that cotton seeds from female trees do not cause pollen allergies. It is the male tree that produces the pollen.

Wind forces do an excellent job of distributing the pollen. While the female tree produces the cotton that leads to an annoying mess, to date, no health problems have been associated with this “storming of cotton.” Nurseries typically sell male clones that are promoted in the retail trade business as “cottonless cottonwoods.” For those who want a fast-growing tree that is tolerant of just about any force of nature for the first 25 to 50 years of life on a roomy piece of property, this has the makings of a sure sale.

A question I often hear: I purchased a cottonless cottonwood eight to 10 years ago that didn’t produce cotton until this year, so what’s going on? The best explanation is that a mistake was made at the nursery while propagating the trees by using cuttings. The nursery mistakenly propagated a female that now has reached a level of maturity to produce the annoying cotton. Can anything be done to stop this? I would have to say no because a mature cottonwood’s production of cotton is a subtly timed event. I would say that people will have to learn to live with the cotton for a few weeks every year or have the tree removed.

Q: I have a small pasture that I mow. The area is very rough because of ridges and some depressions that can be up to a half-foot deep. Some websites recommend putting dirt down an inch or so thick at a time to smooth the lawn but not kill the grass. This could take a long time. Another recommends uprooting the turf and underfilling it with dirt. There is some mention that putting down enough soil to even the lawn will cause the dying grass underneath to release a gas and kill the new grass on top. What do you think? (email reference)

A: Dips that deep can be dangerous to mow over and should be eliminated as quickly as possible. Don’t piddle with the little stuff. Locate a source of good-quality topsoil to level the field. We’ve actually had to do this a couple of times in the past on our NDSU football practice fields. Don’t worry about what it looks like because it will look horrible while you are engaged in the operation. Overseed with the variety of grass you want and then water and fertilize. The seed will grow and the grass that was not covered also will revive. Our football practice fields cover about four acres, so it took a couple of days to get the job done. By fall, we had a field prized by the coaches and players, and they proceeded to tear it up during practice in less than two weeks.

Q: I have been raising pumpkins and selling them as my mission project to build churches in India since 2000. It has been great fun. Last year, I harvested 5,000 pumpkins from my little 1.5-acre patch. This year, I am having problems with the plants dying. I can’t figure out what’s going on. I planted 2,000 seeds (same variety as usual) in peat pellets around the first of May. I put the plants in the field on May 22. They were healthy and vigorous and doing well until last week. I thought they were dying because we had a very strong wind.

However, it appears the stems are drying up at the point they touch the soil. It has not been hot or dry and the plants have not been exposed to chemicals. The one row that I planted from seeds is doing fine, but about one-third of the seedlings in the other rows have died. It is not cutworms and I don’t see evidence of anthracnose. Do you have any ideas? (email reference)

A: Because no insects are present and the stems are not cut off at soil level (cutworms), I suspect one of the wilt diseases is at work, which could be phytophthora, fusarium or verticillium. Which one (or a bacterial wilt) can be determined only through a lab test. At the symptomatic stage with this crop, nothing can be done except remove the infected plants and spray an

all-purpose fungicide on the plants that are not infected.

While your mission is very humanitarian, you need to understand that planting the same crop on the same site every year eventually will lead to problems such this. Crop rotation is a must. I’ve copied your email and my response to Kasia Kinzer, our NDSU plant diagnostician, who will email you instructions on how to submit a sample for lab analysis and proper treatment options. Let’s hope that most of your crop can be saved and your mission can continue its successful course.


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.