bonsai tree care

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I was puzzled, this year, by the appearance of yellow foliage on some of my young pines. yellow foliage is common in weak trees and often results in bad ground under nursing or various kinds of infestation. All my pines are on the same floor, receive the same sunlight and fertilizer and show no signs of infestation. However, some trees are decidedly yellow.

Strong and weak growth

healthy dark green foliage and yellow foliage unhealthy

The only place that was not registered was the floor. I scraped off the top inch or so of soil. Almost no roots had grown since the tree was replanted in late winter.

Signs of infestation

There are no signs of new roots

After a closer look, I saw a suspicious white spot. I took a photo, I went to the house and enlarged or reduced as far as I could on the monitor. Aha – root aphids

Signs of infestation

The culprit – root aphids

had suspected root aphids as I had seen a few while transplant, but have not caused problems of this type in recent years – at least, not that I would have been aware of. I reviewed some of the young pines.

One-year-old pine trees below looked good at first glance.

Weak growth


One year old

Until compared them with a plant healthy seedlings is the same age. Something was wrong.

Strong and weak growth

seedlings weak flank of healthy seedlings

I checked these bare-rooting trees. The floor looked clean.


clean soil

As with the oldest tree, there were few signs of root growth. Healthy trees usually fill the container with roots mid summer. Magnified the photo below and saw more suspicious white spots.

Signs of infestation

No new roots; small white spots – It seems that aphids root

root aphids are difficult to handle because they are difficult to see and difficult to achieve. I thought about what to do with it for some time.

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In the following weeks I reflected on the loss of several young pine trees during the winter. Various professional opinions suggested different causes of death, but laboratory analysis found no evidence of disease or fungus. Symptoms were similar – yellow foliage and little or no root growth. I started thinking about the root aphid may have been the culprit.

During my recent visit to Bonsai Mirai, Ryan Neil and I talked about root aphids and different approaches to managing them. Standard treatment is applied systemic insecticide ahead of infestation. active infestations may require a faster response, and severe infestations can not always be avoided with systemic. The next best option is to use a soil drench.

With a soil drench, you can use contact insecticides for aphids on the floor. The only thing to consider is the phytotoxicity.

I decided to do some tests. I prepared a solution of soap and pesticide soaked some trees for 2 minutes each.

Dunking the tree

Soak a black pine

To ensure that the solution was contacted with all the roots, using a tool transplant to drill the center where the roots of the root ball and degraded soil made it difficult for moisture to penetrate.

Dunking the tree

pierce the rootball

After soaking the trees they were closely monitored. Also, stop feeding them. root aphids love trees encourage obtained from nitrogen, so I thought removing the extra food could highlight more insects.

As pines can be slow to show signs of stress, it is difficult to say how long it might take for signs of phytotoxicity. That said, it is difficult to measure the continuing adverse effects of infestation. After two weeks passed with no visible signs of stress, extended the experiment.

Over the next week I plunged 116 two and three years old, red pines and black in seven different treatments. (The application rates and dates are provided to help me keep track of what I’ve done.)

  • soap pesticide (47%) – 5 oz / gal
    • applied to 4 7/1 and 7/12 trees 16 trees
  • neem oil (70%) – 1 oz / gal
    • 24 applied to shafts 7 / 18
  • imidacloprid (1.47%) – 6 oz / gal
    • Applied to 20 trees 7/14
  • Bayer all in one (0.80% tebuconazole, imidacloprid 0.15%, fertilizer 9-14-9) – 1 oz / gal
    • Applied to 16 trees 7/14
  • Bifenthrin (25.1%) – 75 ml / gal
    • Applied to 16 trees 7/21
  • malathion (50%) – 1 tsp / gal
    • Applied to 4 trees 7/18
  • beneficial nematodes – 7000000 dissolved in 1-2 liters of water
    • Applied 7/14 16 trees by watering, not to wet
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it’s too early to say what will come of the experiment, although some of the weaker trees have budded a bit. Others are as yellow as always – they may be too late for treatment. I began to fertilize two weeks after treatment and gradually build up to higher levels of fertilizer.

As not know what trees were affected or how bad infestations were, I do not expect to make any broad conclusions about which treatments are most effective in stopping root aphids. What I hope to learn is whether or not the treatments are toxic to trees and whether or not see evidence of infestation when replant next year. If trees are healthy and do not see a lot of aphids, I’ll be ready to treat more mature trees as the need arises.

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