View Full Version : Problem with Colocasia esculenta 'Black Magic'
Dentate
05-27-2011, 01:14 PM
Hi all,
My young black magic Colocasia is having a problem. The periphery of the leaves have very recently started browning (pictures below). Using a 10x loupe magnifier, I cannot see any obvious pests, although small white spots are present on the upper surface of some leaves; the undersides look okay. Otherwise, it seems to be growing well adding a new leaf every 1-1.5 weeks. A Colocasia giganticia is under the same conditions described below and is not having problems.
Soil: MG with 50% sand/pebbles. pH is a bit high at 7.5, so I recently added sulfur (before the browning started).
Watering: About weekly (when surface is dry). I check the soil moisture periodically and it's never dry, always moderate to wet.
Humdity: It is dryish here (60% humidity, or so). I mist at least once per day (never before going under the lamps) and have ordered a humidifier.
Fert: 24/8/16 about every other week.
Light: Was under two 96w CFs, now under 432w T5 HO at night (started browning before the switch). It gets minimal indirect light during the day.
Pests: Adjacent plants had aphids, although they seemed to dislike the Colocasias.
Thanks for the help!
Robin
http://www.hostpic.biz/?di=XC2W
http://www.hostpic.biz/?di=7HGY
http://www.hostpic.biz/?di=G38B
http://www.hostpic.biz/?di=EMIY
john_ny
05-27-2011, 03:05 PM
pH was high, so you added lime?
Dentate
05-27-2011, 05:43 PM
pH was high, so you added lime?
Typo. Added sulfur. Thank you for pointing that out.
Carlo
05-27-2011, 05:47 PM
can't see the pictures
Dentate
05-27-2011, 05:59 PM
can't see the pictures
It seems that the site I'm using to host the pics has periodic problems. They're back up.
SilkKnoll
05-28-2011, 03:49 AM
They're not finicky about ph and are fine in strong sun to shade.
You have spider mites. You can try acephate systemically, but your best bet is Floramite. In commercial quantities, it's expensive, but you can buy a few ounces on eBay and use only 8 drops per quart in spray.
You can also interrupt their breeding cycle by misting top and bottom of every leaf 2-3 times daily ... forever.
They tend to come in dry periods or late summer, but they've been coming early the last couple of years.
If you have them indoors, you can't benefit from natural predators that can help keep them at bay.
Don't ignore them. They spread fast.
That regards the spots -- it's not uncommon to be unable to see them. They're all but invisible until the infestation is advanced.
I don't know about the burning on the edges. If the soil is constantly moist, at least make sure that it's not stagnating. Fresh, oxygenated water needs to be passing through regularly if it's always moist. Otherwise bacteria builds up, and you get root rot.
I don't know the various lighting specifications you listed. I use sunlight. Generally, they like a good amount of it, but I've grown them up to 7' tall in a location with 2 hours of sun a day.
I didn't see a mention of temperature. They have fewer problems when kept above 80F.
Nitrogen also seems high to me -- significantly more than I've ever used -- which could cause burning, especially if there isn't regular flow-through.
HTH
Dentate
05-28-2011, 11:33 AM
Thank you for the useful information, Robert; I appreciate your detailed response.
If the soil is constantly moist, at least make sure that it's not stagnating.
Your thought prompted me to inspect the roots: I can actually see healthy roots at the drainage holes, but not yet exiting. Thus, I think root rot is unlikely, but it seems that a pot upgrade may be approaching.
I don't know the various lighting specifications you listed. I use sunlight. Generally, they like a good amount of it, but I've grown them up to 7' tall in a location with 2 hours of sun a day.
I didn't see a mention of temperature. They have fewer problems when kept above 80F.
Although I'd prefer the house the plants outside, frequent high winds in my area would likely decimate the leaves. The new fixture provides 2000+ lumens to the upper leaves and 500+ to the lower leaves, which should be more than enough. The temperature is generally in the low 70s, and that is what I will have to work with until the weather warms.
You have spider mites.
I'm actually not convinced the spots are spider mites, especially considering they are on the upper surfaces of leaves and I cannot see any other evidence of mite infestation (although I have never had spider mites, so my experience is limited). That said, you could certainly be right. Regardless, I'm treating with an organic miticide and plan to humidify.
Nitrogen also seems high to me -- significantly more than I've ever used -- which could cause burning, especially if there isn't regular flow-through.
Testing the soil nutes would probably be reasonable; thanks for the thought. I've used this concoction for years on various plants and have never had a problem. Are Colocasias more sensitive to nitrogen levels?
Thank for pointing out the recurrent pic issues. They are now hosted on an alternate site, which will hopefully provide more reliable viewing.
Thanks again!
SilkKnoll
05-28-2011, 06:29 PM
I can see the pictures now. Robin, What do you have?!
Black Magic has matte leaves, with no black edging. Your first picture looks like C. fontanesii (a.k.a. Black Stem) to me. Fonanesii has a glossy, dark green surface. Its petioles/stems have a black-lacquered look, but, in low light, they might have burgundy tones. The confirming identification mark for C. fontanesii is a black line bordering the leaves on the underside.
The leaf in the bottom left corner looks very different, but I'd want a better view before venturing a guess.
Picture 2 could be Black Magic. The surface looks smooth and matte with the characteristic hues of green darkening to black which would be solid black in higher light.
I can see the spider mite damage clearly. At first, they live on the underside of the leaf, but the damage is first manifested in these spots on the upper surface. When the infestation is severe, they can cover the entire leaf. When they move to the upper surface, they will first be concentrated in the center of the leaf and along the veins, which is visible in Picture 4.
Picture 3 presents another enigma. What is that texturing? That is either severe deformity in a diseased leaf or different plant. It is neither black nor green; neither matte nor glossy. It is definitely not smooth-surfaced.
Putting aside identification questions, it is certainly good that you can see plump white roots in the drainage holes. I would tend to agree that it indicates that root rot is not a problem.
If it were not for your saying that you are getting a new leaf every week, I would think that, at 70 degrees, your plants are trying to go dormant, which begins with the older leaves yellowing and dying.
I think your plants are very confused. They are getting plenty of light and being fertilized very aggressively, which makes them put up new leaves, but their root systems are limited by pot size and cannot support many leaves, so you must be losing leaves as quickly as you are growing new ones.
At 70 degrees, they want to start going dormant, but your urging them to grow counters that.
To address this issue separately, I would encourage you to:
- cut back on fertilizing severely. You can continue to fertilize moderately since you are using a growing mixture that is mostly inert. You can resume aggressive fertilizing when they are actively growing when temperatures are at least 10 degrees higher. For now, consider this to be "maintenance mode" -- they can't aggressively produce foliage, but you do not want them to go dormant;
- allow the soil to dry between waterings slightly more than you are doing now -- about one inch deep;
- when you water, refresh the moisture in the pots thoroughly by flushing them with fresh water;
- consider reversing your fertilizer ratios: Minimize Nitrogen (near dormancy, they should not be forced to produce foliage). Increase Phosphorus/Phosphates as you would for bulbs that will grow and establish a larger root system in cool weather in order to be ready to support active foliage growth and flowering when temperatures increase. I use bonemeal as a natural source of Phosphorus, but I grow in-ground where microbes break down the bonemeal at a steady rate for availability to the roots. At cooler temperatures, bonemeal may feed bacterial growth. If you have a more highly accessible, liquid source, use that. A moderate amount of Potasium is fine (maybe half your current level). A simple, balanced, fertilizer at 5s or 8s would be fine if you alternate waterings or dilute by half at every watering.
I would only pot them up now if they are very rootbound and climbing out of their pots. Otherwise, I would wait until they naturally increase their growth with higher temperatures. Philosophically, I take my cues from what the plants do, rather than try to force them to do something they are not ready to do.
If you pot up now, gently pot them up, and only by 2":
- gently: Since I suspect they are in a transitional stage, I would avoid disturbing their roots as much as possible. Do not tease out the roots as one would normally do when potting up. Put enough soil/potting medium in the new pot to bring the base of the petioles to soil level or barely below it. Ease the whole rootball out of it's current pot. Do not disturb the roots, however rootbound it may be. Sit it in the new pot and fill around it, only tamping lightly.
- only increase the pot size by 2-3" to avoid having medium that is uninhabited by roots for very long. A margin of 1-2" on the bottom and sides will, at first, be wicked of moisture by the rootball as needed. Then the roots, if they are actively growing, will quickly invade the new soil, which will also remove moisture from that soil before it becomes septic with bacterial growth.
- larger amounts of uninhabited growing medium could hold water longer than needed and could be too much for the roots to quickly inhabit. Stagnant wet medium is like stagnant water: it becomes an anaerobic bacteria pool.
I think that should address the brown edges.
Back to the spider mites: I have yet to encounter an effective organic treatment for spider mites other than water. This is why spider mites are among the only pests that force me to depart from an otherwise organic regime.
If you are sufficiently committed to thoroughly mist all sides of the leaves two or three times a day, for at least three or four days, it will break their reproductive cycle. Their reproductive cycle is three days, and they have to be dry to reproduce. Higher humidity may help, but direct, thorough misting is necessary for spider mites. I know some dedicated gardeners who submerge the plants entirely in water once or twice a day for spider mites. I wonder if this is as effective as misting because most Colocasia leaves repel water and could hold air bubbles where spider mites would survive, while misting moistens the leaves thoroughly.
Colocasia leaves' repelling water makes them more susceptible to spider mites. You can counter that effect by using a "Spreader-Sticker." It softens the water, making it less likely to bead off of the leaves. Dish liquid does the same thing. However, there has been a tendency among dish liquid manufacturers to make stronger concentrations ("Ultra") and to add "degreaser" chemicals which are too harsh and can kill foliage. Therefore, if you opt for using dish liquid, use a non-"Ultra" type that doesn't advertise that it contains "degreasers." I use original formula Palmolive. (I add it to any mixture I'm spraying to help it cover the leaves.) Only use a small amount -- not enough to make your mix frothy. Add the dish liquid after filling the container, then turn it upside down and right side up several times to mix it. Don't shake it violently, which would produce froth, which would be counterproductive for this use.
Also, remember that you are trying to let the growing medium go through natural moisture cycles. So, don't let misting the foliage turn into watering the soil several times daily with soapy water.
I still recommend Floramite. I can't mist that often. Floramite is also very targeted and only affects specific species of mites, with no effect on beneficial insects. When the number of insects increases here with the warm weather, I have fewer problems with spider mites, until late summer when the heat and dryness decreases the number of beneficial insects.
Spider mites rarely attack my gardens. They only attack plants in the house and on the porch, where there are fewer insects helping out.
I hope this is helpful.
Dentate
05-30-2011, 12:54 PM
Thanks again, Robert, for the very helpful response.
Below are a few additional pictures to assist with identification. Some of the leaves certainly do have a dark green tone (which is more pronounced on these pics than firsthand). There is a small vein running parallel to the underside border, but otherwise no black border is present. The stems are light green with the petioles getting progressively darker purple/burgundy as they approach the leaves. The leaf mentioned previously in picture 3 had the odd appearance since emerging; it was after a Dawn dish soap debacle (nearly killed two bananas, Colocasias fared much better), so that is the likely etiology.
I plan to hold off on potting up and alter the fertilizer ratios, per your suggestion. The plant has only lost one very small old leaf in the last month; of course, the browning may be loss in process.
Regarding the spider mites, I have been doing doing some aggressive spraying for the past few days (without saturating the soil). Otherwise, I'm really not too excited about spraying with strong insecticides, but will resort to Floramite if the organics fail.
Thanks again.
http://www.hostpic.biz/?di=FN38
http://www.hostpic.biz/?di=WGHX
http://www.hostpic.biz/?di=4JQV
http://www.hostpic.biz/?di=MPZM
http://www.hostpic.biz/?di=DXZX
http://www.hostpic.biz/?di=IFKQ
http://www.hostpic.biz/?di=SX42
http://www.hostpic.biz/?di=KF5P
http://www.hostpic.biz/?di=X3QB
http://www.hostpic.biz/?di=TP80
http://www.hostpic.biz/?di=7V7Q
SilkKnoll
05-30-2011, 02:08 PM
Your poor plant, Robin!
It helps a lot to see the full plant. I envisioned a greenhouse crowded with different plants slipping into the background, and perhaps close up pictures of leaves of multiple plants that you'd received as Black Magic, when some might be other species. The spade shape (compared to Black Magic's usual rounded heart shape) and the glossiness confused me. Maybe the light reflecting off the moisture in the surface cells of a new leaf made the picture come out that way.
DAWN explains everything you hadn't already covered. I intended to mention it by name as a definite leaf killer -- and, of course, this comes from having done the same thing myself.
I like the quotation from Niels Bohr: "An expert is a person who has made all the mistakes that can be made in a very narrow field." That sums up my learning process.
Your plant is essentially fine. The fertilizer, Dawn, spider mites and the temperature explain its predicament.
I've used all kinds of organic concoctions and only resorted to chemicals when nothing else worked for me, given the number of plants that could be affected and the number of man hours I can give them.
Last year, I combined all the natural insect deterrents my arsenal. I steeped A LOT of cayenne pepper, crushed garlic and basil, and, after filtering it, added vinegar and a little rubbing alcohol.
Sure, it made the mites unhappy, but it didn't get rid of them. The effect certainly wasn't worth the effort and ingredients.
Seriously, for spider mites, if you absolutely shun chemicals, H2O in fine, thorough and frequent mistings is the most effective treatment.
Once I accepted that organics wouldn't work for my situation, I first went to systemic treatments. Systemics will only impact creatures that are feeding on the plant, so predator insects and pollinators are safe. I relied on acephate for years, but either my stock had lost its potency or a different kind of mite had come to town.
It took me much research to settle on Floramite. I stumbled on it when my searches turned up a high-level discussion of the problem in a forum for (I'm going to assume legal, medical) marijuana growers. I really think that is a group that is dedicated, educated, informed and experienced at a level that leaves the rest of us in the dust. I'm not saying they're rocket surgeons -- just intelligent people who have an admirably focused commitment to their plants.
Floramite's standard dilution is much stronger than I mentioned, but these fellows had worked it out: seven drops per quart wasn't effective enough, and eight drops worked as well as nine.
My standard spray (mainly for brugmansias) used to be a mixture of pyrethrin for insects and neem for fungus, and it was effective. But pyrethrin, while it is organic and breaks down quickly, it is nonselective and will kill any insect it touches, including the dedicated crab spiders that, since I stopped using it, have taken up their posts in the crown of each cluster of leaves, reliably protecting the delicate new growth.
Since your plant is indoors, and you're not relying on beneficial insects, pyrethrin would kill the mites. But a new generation will hatch the next day and start repopulating.
If you use neem on Colocasias, note that the oil will magnify the heat of sunlight (and perhaps your artificial light, idk). So, to prevent burning, use it only in the late afternoon, after the sun (or strong lights) are off the leaves.
About repotting: It looks fine. As a rule of thumb, I pot my EEs up when the leaves are two times the diameter of the pot.
I was puzzled by your using so much sand and pebbles in your growing medium. (I don't know what MG is.) I wondered if it was a hydroponic approach. But, since you are inside at lower temperatures, the rapid drainage is a smart way to fend off bacterial growth and rot. I have been using an all organic medium because these are, after all, marginals, and will happily grow in wet mud -- but only during the warm season. When it cools off, they stop growing, and a moist medium allows bacterial growth to overtake them. Cool and moist almost always = mush where your rhizome should have been.
Good luck, and keep us posted!
saltydad
05-31-2011, 12:08 AM
MG= Miracle Grow
SilkKnoll
05-31-2011, 12:24 AM
Thanks.
Don't use that.
Actually, the composition is good, but it's pre-loaded with their slow-release fertilizer, which amplifies anything else you do.
It's good for single-season potted plants -- annuals, tomatoes, etc. But don't dump it in your garden or compost pile when you're done ... unless you have a compost bin exclusively for container growing.
Some of the chemical compounds that make up their fertilizer, especially phosphates, will recombine with minerals in your soil, creating stable compounds and making those minerals unavailable to plants. Long-term use of such chemical fertilizers in inground gardens commonly result in significant mineral deficiencies.
But, in containers, imo, it doesn't matter. You can always compensate for what the plant needs.
natej740
06-01-2011, 10:45 AM
I had the same problem with my black magic last year...it looked just like that. Spider mites killed it this past winter.....the mites came later on I never did know why it was brown on the edges I bought it that way from the nursery here...
Dentate
06-06-2011, 09:38 PM
Thanks, Robert, Howard, and Nate. The smaller black magic stem has started losing leaves quite quickly. It has also been unusually cold here, frequently falling into the mid 60s.
The spider mites seem to be under control for the time being (no white dots, at least). I've been spraying twice daily with water and a touch of soap, and using neem/Safer Soap weekly. Unfortunately, Floramite is not available in California, although I could still obtain it with a touch of difficulty, which I may end up doing should this method fail.
The MG is gone and I have been planning on replacing it with another brand.
In the end, trying to grow large, tropical plants indoors in Northern California without ideal lighting is probably a huge mistake, but at least I have been learning a tremendous amount and having fun while doing so!
Thanks again and I'll keep you updated!
vBulletin® v3.6.8, Copyright ©2000-2020, Jelsoft Enterprises Ltd.