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BANGKOK 17 August 2019 17:29
SOUTHERNSTAR

Thai Grapefruit disease

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We have a few grapefruit trees, during the last week they have developed a white coloring on their leafs. It is not powdery and doesnt rub off. The worst effected tree looks wilted. I have applied fugicide two days ago with no result. I tried dish washing soap as well with no result. Its raining everyday which makes sprays less effective. Attached are some photos. We try to minimize chemicals thus some leafs are rugged. Any advice ?20190814_140750.jpeg20190814_140741.jpeg20190814_140732.jpeg

 

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The tree you have is probably "pomelo" Citrus maxima or Citrus grandis.  The leaf damage appears to be "citrus leaf miner". It's a moth that lays it eggs, then the larvae hatch and tunnel as they feed, creating the galleries and leaf distortions..  

 

Prevention of new infestations is the best strategy, spraying an organic botanical repellent regularly (once a week) like a neem 'azadirachtin' product. 

 

It's not possible to control the existing larval population without using a systemic insecticide like imidacloprid. But then the insecticide may end up in the pomelo fruit you eat.  

 

There may also be some secondary leaf fungal infection there, I can't really see from the photos.   Insecticidal soap may help with moth control, but some soap products will damage the plant. Use a commercially formulated insecticidal soap, or search "homemade insecticidal soap" and follow the precautions and make your own.  

 

Spraying a repellent or insecticide is tricky timing because you don't want to repel pollinators - honey bees. 

 

The damage is ugly, but as the following paper suggests, control may not be necessary. 

 

http://ipm.ucanr.edu/PMG/PESTNOTES/pn74137.html

 

Don

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The tree you have is probably "pomelo" Citrus maxima or Citrus grandis.  The leaf damage appears to be "citrus leaf miner". It's a moth that lays it eggs, then the larvae hatch and tunnel as they feed, creating the galleries and leaf distortions..  

 

Prevention of new infestations is the best strategy, spraying an organic botanical repellent regularly (once a week) like a neem 'azadirachtin' product. 

 

It's not possible to control the existing larval population without using a systemic insecticide like imidacloprid. But then the insecticide may end up in the pomelo fruit you eat.  

 

There may also be some secondary leaf fungal infection there, I can't really see from the photos.   Insecticidal soap may help with moth control, but some soap products will damage the plant. Use a commercially formulated insecticidal soap, or search "homemade insecticidal soap" and follow the precautions and make your own.  

 

Spraying a repellent or insecticide is tricky timing because you don't want to repel pollinators - honey bees. 

 

The damage is ugly, but as the following paper suggests, control may not be necessary. 

 

http://ipm.ucanr.edu/PMG/PESTNOTES/pn74137.html

 

Don

Thank you for the detailed answer. We use a soap formula to spray and have used it with great effect against mealy bugs before. We use Neem oil as a preferred pesticide. The trees are still young only 18 months and we should be able to use a systemic product. One of the disadvantages of having forested areas next to your orchards is that it makes pest population growth faster but also helps with predators. Kind of a balacing act.

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Sorry I forgot to ask about tobacco extract. The bought some leafs and wonder if we could use it as a insect repellent.

The tree you have is probably "pomelo" Citrus maxima or Citrus grandis.  The leaf damage appears to be "citrus leaf miner". It's a moth that lays it eggs, then the larvae hatch and tunnel as they feed, creating the galleries and leaf distortions..  

 

Prevention of new infestations is the best strategy, spraying an organic botanical repellent regularly (once a week) like a neem 'azadirachtin' product. 

 

It's not possible to control the existing larval population without using a systemic insecticide like imidacloprid. But then the insecticide may end up in the pomelo fruit you eat.  

 

There may also be some secondary leaf fungal infection there, I can't really see from the photos.   Insecticidal soap may help with moth control, but some soap products will damage the plant. Use a commercially formulated insecticidal soap, or search "homemade insecticidal soap" and follow the precautions and make your own.  

 

Spraying a repellent or insecticide is tricky timing because you don't want to repel pollinators - honey bees. 

 

The damage is ugly, but as the following paper suggests, control may not be necessary. 

 

http://ipm.ucanr.edu/PMG/PESTNOTES/pn74137.html

 

Don



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5 hours ago, SOUTHERNSTAR said:

Sorry I forgot to ask about tobacco extract. The bought some leafs and wonder if we could use it as a insect repellent.

 


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I don't know about the concentration and effectiveness of the product you are considering. But I wouldn't count on a leaf decoction for much potency or residual effectiveness, unless you have directions for your product or experience that indicates otherwise.  

 

Nicotine, like pyrethins/pyrethrum, is a powerful botanical insecticide, but for a contact kill, not necessarily for residual repellent action. It biodegrades rapidly, and that's why it's organic program compatible. 

 

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Some organic growers use ta-kite (lemongrass) in a decoction with wood vinegar solution, as an easy and cheap contact spray and a few days residual repellent. 

 

From the photos, your trees appear young and they may not be fruiting yet.  But consider that if they are flowering, by spraying with any concentrated solution, you run the risk of damaging flowers and disrupting pollination.  I know it's disturbing to see leaf distortions from pest activity, but you should determine how much damage is really there, what percentage of the foliage is affected. If not extensive, and the pest is not a killer, and does not affect flowers and fruit, then maybe don't panic for cosmetic reasons. A tree with a minimal percentage of distorted leaves can still photosynthesize and produce flowers and fruit.  Spraying, even with botanicals, can negatively affect pollinators, beneficial pest predators and parasitoids.  So weigh all the factors. 

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Thank you.

Some organic growers use ta-kite (lemongrass) in a decoction with wood vinegar solution, as an easy and cheap contact spray and a few days residual repellent. 
 
From the photos, your trees appear young and they may not be fruiting yet.  But consider that if they are flowering, by spraying with any concentrated solution, you run the risk of damaging flowers and disrupting pollination.  I know it's disturbing to see leaf distortions from pest activity, but you should determine how much damage is really there, what percentage of the foliage is affected. If not extensive, and the pest is not a killer, and does not affect flowers and fruit, then maybe don't panic for cosmetic reasons. A tree with a minimal percentage of distorted leaves can still photosynthesize and produce flowers and fruit.  Spraying, even with botanicals, can negatively affect pollinators, beneficial pest predators and parasitoids.  So weigh all the factors. 


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12 hours ago, SOUTHERNSTAR said:

Thank you.
 

 

Also, consider your fertilization program. High NPK chemical fertilizers, especially high Nitrogen are a magnet for insect pests. Don't overdo it thinking green vigorous growth is good. Slow release, high nutrient density fertility is better.  It took me years to believe and trust this fact, but now that I do, my own garden and that of my customers simply don't have the pest and disease problems that I used to have to deal with.  

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