Backyard Aquaponics
A place to discuss aquaponics

Hello,

I am new to this forum. Not to aquaponics. I come from the Netherlands so excuse me if there are a lot of misspellings. I don't use English that often.

Can someone please tell me what the white spots on the leaves of my licorice plants are?

I have read some topics on powdery mildew but i don't think that this is the case. Where powdery mildew can easily be wiped of the plant leaves, these spots can't be wiped off. Is it possible that this is a deficiency? I had a major magnesium shortage 2 weeks ago. I have put in magnesium sulfate in my fishtanks and now two weeks later most of the tip burn and interveinal chlorosis is gone but got this in return. I also have peppermint and the larger shoots are all white due to these white spots while the shorter shoots are green and no spots are to be found. I also have Maroccan mint and they don't have any spots on them at all. They all grow in the same media bed. I know powdery mildew is contagious. I also have a wickerbed sytem and the photo's are from mint in this wickerbed. The leaves in my wickerbed are a littlebit lighter then the mint in my aquaponics system. I also have micro cucumber and honeytomatos in the same wickerbed and they doesn't have these spots on them.

I have a very high humidity in my greenhouse. 80%-100% all day round. For me it is hard to ventilate because the outside temperature is below 14 degrees celsius by day and 6-7 degrees celsius by night. Because my heating sytem isn't ready yet i temporarily heat my greenhouse with an electrical heater. if i ventilate, the temperature won't maintain and i have trouble to raise it again to 20 degrees celsius. during the day the temperature is between 20-30 degrees celsius and by night it is 17-20 degrees celsius.

If i don't find an answer to this soon, i have to stop growing during winter and have to wait till next year april. Licorice mint can't be sold with these white spots on them.

Does anyone have a suggestion?

Thanks in advance

Ferry

I'm not certain but check for spider mites on the top and underside of the leaves. They are extremely small so shaking or brushing a leaf over some white paper or using a magnifying glass might help.

It's also possible it's related to the deficiency - this wouldn't surprise me since the pattern of white is from the tips inward. If you don't find the spider mites I would treat for a potassium deficiency since this looks to be worse on the lower leaves. Magnesium competes with potassium and other nutrients - If you applied too much magnesium you may see deficiencies in these other nutrients and that may be what happened.

Scotty435,

Thank you very much for this fast answer. Tomorrow i will look for those spider mites. Allthough i don't think that that is the problem. In the past (before i started with aquaponics) for years i have grown marihuana. I have had major issues with them. Because i haven't seen any webs, i don't think that this is the problem. Becuase i can't measure my values in soil i don't know what the problem was.

I have put some mint from this wickerbed in my growbeds and because my growbeds have around 20mg/liter of potassium that must be the reason because all the new growth is green and without these spots.

I forgot to tell you that i have only put magnesium in my growbeds. I haven't put this in my wickerbed. I have read that the best way to prevent a shortage of magnesium, potassium or calcium it is best to put in a cocktail of all three of them in. Do you agree with that?

Can you also tell me how much grams i must put in say, 10 liters of water to not over feed them with potassium? Or should i just sprinkle the potassium powder directly on the soil?

Thanks anyway.

Ferry

I can't tell you how much to add, there isn't enough information. If your nitrates are fairly low and you have blood and bone there, then you could sprinkle some of this on your grow beds to provide the other elements (maintenance with low fish numbers would be about 25 to 50 gms per 1000L of grow bed). It would probably be good to initially spray on some of the potassium (in the form of Seasol or Maxicrop) since this avoids the competition for binding sites at the root zone.



A lot of times this is a good way to handle the problem but not always.

Scotty435,

Seasol and maxicrop can't be bought in the Netherlands. I have searched for months but that just isn't available here. Rock phosphate ditto. I use phosphates in liquid form that is usually used in aquariums and magnesium sulfate, potassium sulfate and calcium phosphate in powder form. Calcium is around 170gr/liter and i don't see any shortage. If i put in calsium phosphate i probably get problems with my magnesium or iron intake.

I have read that bone meal is dangerous for my aquaponics because of the mad cow desease. Whereas it eventually dissolves in gardens it stays recirculating in my aquaponics growbeds.

That's the problem here in the Netherlands. While it is a mega industrie in Japan, Australië and America, it still is in it's infancy here in Europe and in particular the Netherlands. Every single item i used in my aquaponics set up had to be re-invented. We don't have a dollar store here and almost all fertilizers are for agriculture and horticulture and only sells in bag bags. Afcourse i can buy some in small amounts but those fertilizers are usually for gardens. Even my vertical setup is one of a kind. Almost every aqaponics grower in the Netherlands uses horizontal setups.

Thanks for your advice. Maybe i just have to quit my wickerbed system. I have more problems with my wickerbed as i have with aquaponics.

Ferry

Where did you read this?

It seems highly unlikely just based on the number of cases involved. While I doubt it can be ruled out since proving bone meal doesn't contain any prions that cause BSE would be difficult, I wonder if they are basing this on any real facts? For what it's worth there are alternatives - see below for one.

Since you have a hard time sourcing some of these items a viable alternative for some is human urine. For AP, aging it a week or two first is a good idea, since it can result in high ammonia levels (you may want to test it before adding). The NPK is 11 - 1 - 2.5 according to this source - http://www.goveganic.net/article217.html.

Scotty435,

That was a very interesting article. I always like to try new things to increase my knowledge. This is certainly something i'll try this upcoming week. Just a little peace of my garden to find out if this works for me and what the difference will be comparing to my other plants.

About the bone meal. I have read an article some time ago that stated, 'allthough the chances are very small, there is still a chance that this can be dangerous. To avoid any problems in the future the advise was to try something else". If i would try this i can also use bat guano. They sell it here in the Netherlands in growshops.

Thank you very much for this new fertilizer.

I'll let you know in a couple of weeks how it works out.

Ferry

Might take a bit longer for you to see any results but let us know.

The bone meal itself is not the potassium source, in this case it's coming from the Blood portion so just getting this is perhaps an option (provided your comfortable with it's safety).

There are some additional sources of potassium out there.