Question What's happening to my sweet potato?

Discussion in 'Fruit & Vegetable Growing' started by Berkeloid, Dec 29, 2017.

  1. Berkeloid

    Berkeloid Active Member Premium Member

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    Hi all,

    I managed to successfully grow some small sweet potatoes last year using the scrap of sunlight I get on my balcony, but this season something has happened to severely stunt growth and deform the leaves.

    Does anyone know what this is? I'm not having a huge amount of success locating possible causes. I thought at first it could have been a soil deficiency but various types of fertilisers haven't made a difference (although some promoted more growth, but it was all still deformed). I tried planting other slips in different root pouches and they started off well but then the same thing happened to them, so it looks like it could be some sort of airborne disease that's affecting them.

    I've included some photos of the leaf damage. Has anyone seen this before?

    sweet_potato.2017-12-29.unknown_disease.large_leaf.jpg sweet_potato.2017-12-29.unknown_disease.small_leaf.jpg sweet_potato.2017-12-29.unknown_disease.leaf_underside.jpg
     
  2. ClissAT

    ClissAT Valued Member Premium Member GOLD

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    Strange looking sweet pot leaves for sure.
    Did you start all the slips off the one potato or the one group of potatoes purchased at the same time?
    The leaf damage looks a bit like virus damage which could have emanated from the parent spud.
    Critters that do that sort of damage are red spider mite & aphids which suck the sap leaving the leaf deformed or reduced in size.
    Too much nitrogen can do a slightly similar thing but usually the growth is weak & soft as well.
    You say you use root pouches. What sort of growing medium do you use in them?
    Are you reusing medium from a previous crop?
    Is it soil or hydroponic?
     
  3. Berkeloid

    Berkeloid Active Member Premium Member

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    Some of the slips (and tubers) are from last season's crop, and others are new. It has affected all equally except for two - one of which has been hit by red spider mites (you can see the leaves turn pale as many little tiny white dots appear as the mites eat the leaf) and the other looks like it has only just started experiencing this problem - perhaps if it's a virus it has only just spread.

    So although I have plenty of spider mites around (more than I care for) I don't think they are causing this specific issue. I also can't see any webs around the leaves like I can on other plants (including the sweet potato) that are affected by the spider mites. I have plenty of aphids as well (mostly attacking a mouse melon and the woody stems of my basil plants) but I haven't seen any aphids on the sweet potato.

    I am wondering whether it's the sweet potato "scab" fungus as this is the closest thing I have found to what I am seeing, but even that doesn't quite match what I have. Either way, this afternoon I mixed up bicarb, detergent and olive oil in a water mix as the Gardening Australia website suggested this as an organic fungicide, so I'll give that a go and see if it changes anything. The tricky bit is that most of the deficiencies and many diseases I've read up on seem to kill the growing tip of the vines, yet mine happily keep growing, they just produce sub-par leaves (tiny, crinkled, etc.) The vine continues to climb a trellis apparently without too much of an issue.

    I'm growing in root pouches with a mix of Bunnings "soil", and "soil activator" (mix of compost, blood & bone, manure, etc.) Some of the slips are growing in the same pouch as last year's successful crop (a word I use quite loosely as the lack of sunlight reaching my balcony causes everything to grow very slowly, so the tubers last season were almost comically small) however some slips are in new pouches. This particular issue has also not spread to any different plants nearby, it only seems to affect the sweet potato.

    Very perplexing!
     
  4. ClissAT

    ClissAT Valued Member Premium Member GOLD

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    Thankyou for that extended explanation Berkeloid. Things make more sense now.
    Having such a wide spread infestation of red spider mite & aphid & knowing how mobile those critters can be, makes me feel they will continue to transmit disease throughout your plants the longer you allow them to live there.
    Using the white oil hopefully will send them packing although it may also 'burn' the plants, so be wary of that.
    Also, reusing that potting mix style of growing medium is never a very good idea unless you do significant revamping of the mix for each new crop. And even then there will be disease that remains in the old medium so you need to employ the rotation method as described by many organic gardeners such as those on Gardening Australia.
    This means that if you are only able to grow certain plants due to lack of sun, you aren't able to do the complete cycle of 6 different plant types to maintain soil health.
    So you are going to run up against diseased soil & surrounds right from the second crop grown in any given batch of mix.
    On a few occasions I have had to resort to a total clear out of my verandah garden to remove persistent pest problems. That means removing all plants to be burnt, ditching all pots & medium never to be used in the food garden again, then high pressure hosing the wood of the verandah & the bird mesh surrounding it that forms my 'tomato room'.
    Starting again from scratch with fresh seed or seedlings, fresh pots & growing medium & completely clean surrounds allows for another couple years of pest free growing.
    Hard one to do I know, but the alternative is too energy sapping for me.

    Another thing to consider regarding those mixes sold by the likes of Bunnings is that they are exhausted of fertility quite quickly. After that they become imbalanced & very hard to rebalance so the plants begin to be unhealthy with less ability to fend off disease.
    They are mostly based on composted bark & pine fines so as the wood begins to break down it chews up the nitrogen & the micro-flora dies so the food in the medium becomes less available to the roots.

    You can get products that you 'brew' in a bucket using a small aquarium aerator that grows bacteria & fungi by the trillions overnight. You then water that sparingly onto the pots every so often on a time scale that you have to work out for yourself depending on you conditions. This replenishes the micro-flora in the potting mix which makes all the available food resources in the mix suitable for the roots to uptake.
    I use a product called BAM (Beneficial Activated Microbes) otherwise known as 'Micro Life Force' from Nutritech at Yandina, Qld
    https://www.nutritiongardening.com.au/collections/products
    which you can buy mail order if you don't live in SE Qld.
    https://www.nutritiongardening.com.au/collections/products/products/life-force-micro-force-home-pack
    There are probably other similar products but I doubt you will find anything of quality at Bunnings.
    I apply it all my container gardens of which I now have around 50. They start out as potting mix 50/50 with coir & fertilizer. For their second crop I add my own compost along with a top up of the 50/50 potting mix & fertilizer.

    So that is something to consider if you feel you need to start again from scratch.

    Something to note regarding the growing habits of sweet potato is that you really don't need all that vine to get potatoes. What you need are many roots in the ground.
    I start them by sitting a freshly purchased root over a cup of water & held in place with 3 tooth picks so the stem end faces upwards. Thin hair like white roots form from around the bottom half of the potato where it contacts the water. After a couple weeks shoots will appear from the top half & when they get to around 80cm long I snap them off right against the skin of the potato making sure to get a 'heel' that will grow roots quickly for the new plant.

    Those are then wound around my hand with just 25cm of the growing tip hanging free, then planted in their allotted place in a fruit tree mound. This gives the heel where it was snapped off from the mother root along with several leaf nodes planted in the ground so in theory a new root should develop from most of those points. This means all your new potatoes will be in the one small circle.

    Check out this video from Doug & Stacy off grid



    The plant doesn't need too much vine length. The vine should be broken off once it gets to anything between 50cm & a meter in length so more side shoots form to grow more leaves close to the ground. One long scrawny vine wont produce much in the way of energy for root development.
     
  5. Helen Auriga

    Helen Auriga Ecological Farming & Landcare Premium Member GOLD

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    I'm using lacewings to control aphids with excellent results. Red spider mites you need to get the humidity as high as you can, they like hot dry not hot moist. I've tried Californicus and Persimilis with varying success as the red spider mites over winter in the soil.
     
  6. Bea

    Bea Active Member Premium Member

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    FIRST: get rid of that soil.
    SECOND: grow the potatoes in a large rubbermaid tub constructed for self watering and use the trellis for something else using ClissAt's method. here in the mountains of Ecuador, once you get a vine growing you never need to start roots again. We take a length of vine, form into a circle, lay it on the ground (which tends to be quite poor), water and wait. I usually place a heavy stone along the vine at leaf nodes. the damn potatoes just bulge up from the ground are harvested and just waiting for the next set.
    THIRD: you just dont need a lot of 'excellent' soil. Just dirt of some kind deep enough for the tubers. Fertilizer should be from a top layer of compost, then just forget about the plants.
    FOURTH: I had a large balcony in Vancouver with an eastern exposure. so sunlight was at a premium, and lots of those large black rubber pots used by the nurseries for shrubs or roses. I made compost in a similar way to the japanese style, i think. I put down a oversize tray; then a black pot into which I threw a few inches of what ever finished soil I had, including the stuff your potatoes are growing in. Then I would add kitchen scraps and cuttings from the balcony garden and cover with more soil, then watered until it drained into the tray. I did this until the pot was almost full, placed another pot on top and started again. when a third pot was almost full i took the structure down and the compost material in the first pot had sunk down a bit, and that pot now went on top. Once that one was on the bottom again it was used on my potted plants. believe it or not i got great compost and everything on my balcony thrived. It would be useful to have a carbon layer each level - straw, shredded paper, dry leaves, etc. the top pot was also covered all the time with another tray. Living in a port city such as vancouver meant rats and I never saw any on my balcony. It obviously takes a while to get this going but once established you never again need to add purchased soil.
    FIFTH: find a way to collect the runnoff from the compost, dilute, and water the rest of your garden/
    You can grow sweet potatoes in an ordinary bucket but will get only about four of them but this is useful to know.
    also, clip off the vine ends and either stir fry or ditch the stems and throw in a salad. of course you can also clip the vines back and throw into your compost. who knows, you may be surprised to see new vines growing.
     
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