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4-week-old seedling shows curious rust spots - its mates are all mostly unaffected

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    COCO COIR 4-week-old seedling shows curious rust spots - its mates are all mostly unaffected

    Greetings, growers! I’m a retired, small, home grower with minimal experience, this being only my third growing year.

    I searched for similar posts but failed to find any that looked precisely related, so I hope my photos will help lead to a proper dx.

    This year, I decided to do all feminized auto-flowers, growing in coco (Botanicare ReadyGrow Aeration). I have 6 plants, 4 strains - 1x Mohan Ram and 3x Northern Lights (all about 4 weeks old), 1x Cropical Fruit and 1x Girl Scout Cookies (both 8 days old). One of the three Northern Lights is struggling with rust spots that began somewhat subtly on the first pair of true leaves, larger and more prominent on newer leaves. One of the other northern has slightly mottled leaves, the third one (but first to germinate) is smaller than the other two. But only the 1 of 6 has the rust spots. Other than slightly different germination techniques (seeking best practice after experiencing some sad failures), all four plants have received the same care - light/water/nutrients/temp/medium. I’ve never seen this type of problem, so I can’t tell if it’s a disease or a pest, though I’m leaning toward some nutrient or uptake problem. I see no obvious signs of pests on top or bottom of leaves. I didn’t keep records well enough to be sure, but I think the ailing plant may have been the only one germinated in a MiracleGrow seed starting soil. And due to my inexperience I may have started it out with a slightly more acidic pH (in the 5.8 - 6.0 range); so those differences may be responsible for its suffering - is that likely? Has anyone seen rust patches like these before? It seems like the very newest leaves are looking a little healthier, so perhaps more time with new, stable conditions will resolve the trouble?

    I was about to trash the ailing plant, but I decided to join this forum first, to see if some community advice might help me rescue her.

    Nutrients I’m using at this stage:
    Botanicare Cal-Mag Plus (5ml/gal)
    General Hydroponics Flora-Grow/Bloom/Micro (5 ml/gal each)

    I’m adjusting the pH after adding nutrients, now aiming for 6.0 - 6.2

    They are all in 3-gal equivalent air pots. I move them outside whenever the sun and temp are favorable, and they spend the rest of their time in my garage under 900W LED with an oscillating fan providing a gentle breeze.

    One photo shows the ailing plant with obvious rust patches, another shows its Northern Lights mate with slightly mottled leaves, otherwise healthy. The third plant photo shows all 6 together as of today. I added photos of the coco bag to illustrate its contents and pH/feeding recommendations.

    Thanks in advance for any insight!

    #2
    5.8-6.0 in coco is a good starting feed pH but it really all depends on what your runoff pH is. What is the run off pH for the affected plants.
    Failure is an opportunity for improvement!!

    Current Grows:
    https://forum.growweedeasy.com/forum...s-jedi-og-grow

    https://forum.growweedeasy.com/forum...e-gorilla-grow

    Completed Grows:
    https://forum.growweedeasy.com/forum...ang-jack-herer

    https://forum.growweedeasy.com/forum...-northern-soul

    Comment


    • Obi-Wan
      Obi-Wan commented
      Editing a comment
      Test strips are fine to use. Measuring the runoff gives you an idea of the root zone pH. You want to measure the pH of the nutrient solution going in and coming out so you can determine if you need to adjust the pH of nutrient solution the next time. Nutrient salt accumulation in the coco could cause the root zone pH to drop out of the ideal pH range. Ideally your runoff pH will be fairly close to the nutrient solution pH going in but if it starts to go one way or the other you can prevent problems before they show in the plants.

    • bereid
      bereid commented
      Editing a comment
      Update: After replying to your explanation, Obi-Wan, I conducted a brief web search seeking additional details about how to implement the runoff testing you advised.

      My search yielded this website (https://www.cocoforcannabis.com/adjustph/) with an interesting and detailed discussion of the topic ‘How to Measure and Adjust pH’, particularly as it pertains to coco (my chosen medium this season). Some advice stated twice (but with slightly different phrasing) within the article, seems to contradict your recommendation. Here is an excerpt:

      "Although it is critical to adjust the pH of the inflow, you should not be concerned with the pH of the run-off water. Your only concern with pH is always providing nutrient solution (inflow) that is in the appropriate range."

      I’m not trying to be argumentative, but I would like to hear your thoughts after reading the article because it’s difficult for a relatively inexperienced grower like myself to digest such contradictory information, and make the best decision about which path to follow.

      TIA,
      Bruce

    • Obi-Wan
      Obi-Wan commented
      Editing a comment
      I definitely agree that the inflow pH is more important than the runoff and I wouldn’t over concern myself with the run off pH as long as it’s close to the desired range. For example a runoff pH of 5 wouldn’t concern me, sure it’s out of range but a normal inflow of 5.8-6.0 would correct it. Now if my run off pH was 4 I’d be a bit more concerned and I would probably run twice the volume of normal inflow at pH 5.8-6.0 through the medium to help correct the issue. In coco I would never give an inflow pH that is higher than the desired range, just more of it to flush the medium of the undesirable pH, so I guess in this regard I disagree with the advice that you read elsewhere. Coco has the wonderful benefit of not holding excess water so it’s nearly impossible to overwater plants in coco so long as they are in properly sized containers. I haven’t grown in coco in quite some time, but when I did I always gave inflow at pH 5.8-6.0

    #3
    Thanks for explaining that so well, Obi-Wan. It all makes perfect sense. Knowing what to aim for now will enable me!

    Comment

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