Sweet Orange Scab (Update Oct. 11)

Sweet orange scab has now been confirmed on citrus (leaves and fruit) from 15 parishes across southern Louisiana and four counties in Texas including two in the Rio Grande Valley, the main citrus producing area of Texas. The widespread occurrence of the disease in both residential and commercial citrus suggests that it has been present for a number of years.
 
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About Don Ferrin

I am an associate professor and extension specialist in the Department of Plant Patholgy & Crop Physiology with the LSU AgCenter in Baton Rouge. I have statewide responsibility for issues and educational programs related to diseases of all horticultural crops in Louisiana.
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11 Responses to Sweet Orange Scab (Update Oct. 11)

  1. Vivian Adair Neely says:

    Please comment on the effect of this Sweet Orange Scab some years ago and was told it was nothing, would not hurt the quality of the fruit, just make it unsuitable for retail. Is that still the thought on it?

    • Don Ferrin says:

      Sweet orange scab, like the common citrus scab, is primarily a cosmetic problem as the scab pustules are very superficial on the rind and do not extend into the fruit itself. However, if fruit become heavily infected when they are young and have not expanded fully, they may not mature properly.

  2. H. Rider says:

    I live in Lake Charles, I have SOS on my citrus trees. How do I get rid of it, and how can I avoid it in the future?

  3. lynne schwartz says:

    I have a dwarf ruby red grapefruit tree in Savannah, GA. Two fruits have citrus scab. The others are scab free., Is it too late to apply a fungicide? I have a few fruits the size of tennis balls. What other brands can you suggest that are available in nursery centers? I do have a liquid copper fungicide by Southern AG. Is it to late to treat? Should I spray all my nearby citrus trees as a preventative? It is very hot (90’s) and humid everyday. What time of day should I spray? and how often? I have removed the infected fruit which was close to the ground on a low branch. The tree is in a bush form.
    Thank you.

    Lynne
    Lynne@amylyns.com

    • Don Ferrin says:

      Lynne, Yes at this point in the season it’s too late to spray to control sweet orange scab as the developing fruit should already be resistant to further infection. Since the disease is pretty much cosmetic and doesn’t really affect the fruit, you may not really need to spray if only two fo the fruit are infected. However, if you do choose to spray, the times to spray to control scab are (1) in late February to early March when the tree is putting on new growth and (2) late March (once the trees have stopped flowering) through May. The time of day is not critical, but avoid spraying when its hot (over 85-90 degrees). Bonide and other manufacturers make several copper fungicides that are available in many garden centers, and the product from Southern Ag should be fine. For more information, see my fact sheet at <a href="http://www.lsuagcenter.com/en/lawn_garden/commercial_horticulture/fruits_nuts/Louisiana-Plant-Pathology–Citrus-Scab-and-Sweet-Orange-Scab.htm&quot;

      • lynne schwartz says:

        Don,
        Thank you for the information re citrus scab.The leaf miners in my area(Savannah) have infected all new growth on my citrus trees despite spraying new leaves with Fertllome which is Spinosad 99%. I pick off the curled leaves, but can’t seem to treat this problem. I spray the new growth before it is attacked but the leaf miners still infect the new growth and even some of the older leaves on Eureka lemons. They have attacked the first and second flush of tender leaves.This is becoming a major problem. Any suggestions would be appreciated. Will the trees eventually die as all new growth is infected?

        Thanks.
        Lynne
        lynne@amylyns.com

      • Don Ferrin says:

        Lynne,

        Yes, leaf miners have been quite a nuisance in citrus all across the South this year. They are usually more noticeable on the summer flush of growth, but because of the mild winter, the spring flush of growth was really affected this year. Other than being unsightly, leaf miners really don’t do much harm to citrus trees, except maybe when they are really young. The curling of the leaves looks unsightly, but doesn’t affect production. In fact, we don’t recommend trying to control them in commercial orchards. If you are really concerned and want to control them, I suggest you use Bayer Fruit, Citrus and Vegetable Insect Control. It is a systemic insecticide that you apply to the soil prior to the summer growth flush. Spinosad is a contact material and once the leaf miners hatch inside the leaf they are protected. Since the Bayer product is systemic, it should do a better job of stopping the larvae, and you only have to apply it once.

        Regards,
        Don

        Donald M. Ferrin
        Associate Professor
        LSU AgCenter
        Department of Plant Pathology & Crop Physiology
        302 Life Sciences, Baton Rouge, LA 70803

        Office: 225-578-8537
        Cell: 225-573-6510
        E-mail: dferrin@agcenter.lsu.edu

      • lynne schwartz says:

        Don,

        Since we eat vegetables and the citrus fruit I am worried about the dangers of using a systemic.
        I think it might be OK for trees and shrubs but am concerned about using it on plants we eat.
        I do organic vegetable gardening and usually use neem oil to control problems. Would appreciate your input.I also have brown waxy scale on an Owari Satsuma.Is there any way to get rid of the scale .Most of the bottom leaves have the brown scale problem on the underside.I have been removing the infested leaves. Washing with a heavy stream of water does not work, and many of the leaves have yellow spots .The tree is 6 feet tall.

        Thanks.

        Lynne

      • Don Ferrin says:

        Lynne,

        Since you want to go organic, your best option for the brown waxy scale is going to be one of the horticultural oils, like Bonide All Seasons Horticultural Spray Oil. Just be sure to get the bottoms of the leaves as well and you should spray 3 times about 2-3 weeks apart.

        If you don’t want to use the systemic insecticide, you’ll have to keep spraying with spinosad or accept the unsightly damage from the leaf miners.

        Donald M. Ferrin
        Associate Professor
        LSU AgCenter
        Department of Plant Pathology & Crop Physiology
        302 Life Sciences, Baton Rouge, LA 70803

        Office: 225-578-8537
        Cell: 225-573-6510
        E-mail: dferrin@agcenter.lsu.edu

      • lynne schwartz says:

        I will try the Bonide Spray. It has been in the high 90’s in Savannah.Will the horticultural spray burn the leaves? When is the best time of year to spray horticultural oil on citrus and what is it supposed to do or prevent? Some of my citrus leaves are a bit yellow with green veins. I was told to put down ironide or a high nitrogen lawn fertilizer ie 23-0-0. Can you tell me when to put down fertilizer for citrus trees that are between 3-6feet? How much do you suggest?
        Would I be able to text you a picture of a citrus leaf that has brown spots with a yellow halo? I’m not sure what to do.It is a 7 foot Dancy tangerine and only a few leaves are affected.

        I hope it is not citrus canker or greening disease.

        Thanks.

        Lynne
        lynne@amylyns.com

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