I see little microscopic brown dots under the leaves that smears off and turns my finger brown. Now I have noticed some webbing between the leaves and steams, but I have not seen any insects. The plants are turning brown at the bottom and leaves are dying as you move up.
Any ideas ?
Spider mites!!! EEK
Sounds like spider mites.
How are spider mites transmitted? Since these plants are grown in soil-less conditions I would figure bugs would either have to fly or be in the media already.
Spider mites can enter your grow room from you, can be brought in by a pet, and last can be introduced by air from your intake. Your best bet is to ditch the plant before the mites move onto other plants and infest your whole grow room!
This is no treatment for them?
Sure there is, but if their is already webbing, usually that means that you have a somewhat established adult breeding population...which then makes your position less tenable. The earlier you catch them, the easier they are to successfully treat. Bi-weekly spot inspections of your plants with a magnifying glass is a real good habit to get into for a whole host of reasons...Spider mites being just one of them.
You can use the 'ol 3-5% oil + 0.5% dish washing detergent remedy...works well but you have to be real careful to get as little of the concoction into your system and take measure to cover up your FT to protect from overspray. And even this low % of oil will burn pepper plants if you have any...won't damage them beyond repair or anything, just don't be freaked out by the necrotic lesions that will be left on their leaves. peppers seem especially sensitive to this type of treatment.
A better/easier/more fish safe bet might be a naturally occurring fungus called Beauvaria bassiana that will take care of a whole host of common garden pests...spider mites included (and then some). B. bassiana can be purchased under the trade names Botaniguard, Naturalis-L or Mycotrol-O the later two being ok'd by OMRI...and more importantly it is fish safe (unlike any kind of oils or most soaps).
Whatever you spray with make sure to repeat after 3 or 4 days...then again after 3 or 4 days...and then once more...since most of these sprays wont kill the eggs that they've laid...so make sure you get the bastards that have hatched...and spray the under-sides of the leaves...Good luck. Spider mites are a royal PITA.
In addtion to the recommendations Vlad gave, there is yet another option. If you have access to fresh worm castings, make a brewed worm casting tea and spray your plants on all surfaces. This will kill the spider mites. It is safe for the entire AP system, and will give your plants a nutrient boost too. Making a brewed worm casting tea is simple...let me know if you need instructions...
I wish you the best in getting rid of these pests!
I do not know the area of plants you need to cover, so I will give you the measurements to make one gallon of tea. To make more just multiply the measurements. When we brew this we do it in batches of 50 gallons...
Add 2/3 cup fresh worm castings (as not not stored in a sealed container) to one gallon of non-chlorinated water. It can be added loose or in some kind of 'tea bag'. Once the brewing process is complete the 'tea' will need to be strained if the worm castings are added loose, so the 'tea' can be applied with a sprayer. Add 2 TBSP of molasses or table sugar (do not use honey). Put an air stone attached to a fish tank pump and let aerate for 12 - 24 hours. After 24 hours the beneficial microbial population will have increased...Spray all the plants on all surfaces. Use any hand pump spray bottle. Keep it aerated to keep the beneficial microbial population alive....After removing from the source of aeration the micorbial population delcines. The nutrients still remain, making it a great nutrient boost.
Do not store in any container with a tight lid. It will build up pressure.
Hopefully this is helpful...Let me know if anything is not clear...or if you have any more questions.
Thanks Vlad and Converse for the info. You guys are really helpful and it is much appreciated.