Letters to Maximum Yield
Dear Erik: I have a problem. I recently put together a system based upon your article on aero-hydroponics. I started with hydroponics and am now converting to rockwool as a medium. The system works just fine. I'm using a medium strength full-sprectrum hydroponics mix and watching the pH carefully with a well-calibrated quality meter. In spite of this, plants (very similar to hops) are dying. That is why your article on fungus gnats caught my eye.
Yes, I have seen those bugs hanging around the plants. I'm positive they are fungus gnats. I talked to my hydroponic store and they told me they took the product for this problem, Wilson's, off the shelf because people were complaining that it was ineffective for this problem. The store owner recommended another brand and I treated them with this. I also treated them with a fungicide. What else can I do?
From Erik: It sounds like you have identified the pest. Fungus gnat adults can easily be seen buzzing around. It's their larvel offspring in the rockwool that are the most detrimental. They feed on plant roots and transmit pathogens such as fungal infections and viruses. However, this might not be the cause of your plant's ill fate. The plants might me suffering from a nutritional disorder caused by an infection or other conditions such as high TDS levels in the root zone, as fertilizer build up can occur in the rockwool. Toxicicity from over application of pesticides at the roots is a consideration.
Start with fresh plants and media after thoroughly cleaning and fumigating the grow area and all of the equipment. Inline U.V. sterilizers for the irrigation sytem can be helpful but are not perfect.
Erik B.
Dear Erik: I'm having a problem with my growing. I use dirt sunshine mix in a 4X8 table about six to eight inches deep. I plant 50 to 60 plants. They are from clones that are taken from cups with well established root systems that fill the five inch deep cups before I transfer to tables and put them on a 12 hr cycle. I have two 1000 watt bulbs with star shades and I use General Hyrophonics Micro and Bloom with two parts Bloom to one part Micro. I use alternating waterings - one just water - one nutrient. I start off about 5ppm and with in four weeks I'm up to seven or eight. The problem arises at about the 5th week as the bud is established the leaves seem to turn yellow. But then they start to turn a nercosis type brown and I have no idea why. I'm not over feeding. I don't get near the same kind of yield I used to. This keeps happening table after table. I've used different strains and it is still happening. Any help would be appreciated. I enjoy your magazine and will continue reading. Thanks for your help.
From Erik: Thanks for the kind words. It could be any number of things, but the following is a likely scenario. In this type of system there is a dense plant canopy. There is also a lot of moist and fertile grow medium exposed directly beneath the leaves. As the plants begin to mature, they extract their reserves of sugars and nutrients such as nitrogen from the lower shaded leaves to feed the rapidly expanding upper portion. Think of those leaves: they are there but not alive (kind of like dead skin). This plant tissue is particularily susceptible to infections from fungal spores, etc that thrive in warm, moist, fertile conditions such as those found in the large planter tray.
Some solutions: Let the top inch of the planting medium dry out between waterings-this reduces spore populations. Increase the air circulation around the lower leaves-this stops moisture from condensing on the leaves which provides the gateway for spores. Cover the top of the growing medium with an inch of expanded clay "Gro Rocks" or black and white poly. If covering the media, waterings will be less frequent. Another possibility is a lack of potassium. If you have poor drainage it could still be salt build up. Try some of the above suggestions with a fresh batch of plants.
Keep at it, Erik B
Dear Erik: I use Oxy-Cal for soil based planting. I know it brakes down to lime, water and oxygen. Is there any way to use this in my hydro nutes (GH flora)?
Thanks for the great mag. I wait for each issue with great anticipation. Sounds like a commerical huh. It's true I really like the mag. You have good writers who put things in simple terms that helps us "non organic chemistry/biology experts" who post to usenet and other sites. It's wonderful info, but it's a pain wading through the tech talk to get the concept and then trying to apply that to the real world.
Thanks again,
Jim
From Erik: Thank-you for your inquiry. If you are growing in a recirculating water culture system there should be adequate levels of calcium and oxygen. If not, there are proven ways of meeting those requirements i.e increased aeration and additional calcium nitrate or products such as Cal-mag (beware of increased nirtogen). If you require calcium peroxygen for your soilless or rockwool medium it is best mixed into the planting mix.
When concentrated calcium comes into contact with phosphorous or sulfates it flocculates-turning into useless sludge. So if mixed into the reservoir, there is a good chance that this will occur. However, it might be worth a try, so proceed with caution. Let us know how it goes.
Regards, Erik B