Ya, with the heavy marbling of that brownish stuff, it certainly looks like something is growing, rather than just staining from the
nutrients.
Damping off
"Damping off is a term used to describe the death of small seedlings resulting from attacks by certain fungi, primary "Pythium Ultimum" and "Rhizoctonia Solani," although other fungi such as "Phytophthora ssp." may also be involved. Pythium and Phytophthora produce spores that are moved about in water. Damping off can occur at various stages and subsequent seedling stages."
"The environmental conditions prevailing during the germination period will affect the the growth of both the attacking fungi and the seedling. The optimum temperature for the growth of Pythium and Rhizoctonia is between 20 and 30 C (68 and 86 F) with a decrease in activity at both higher and lower temperatures. The moisture content of the germination medium is of great importance in determining the incidence of damping off. Conditions usually associated with damping off include over-watering, pour drainage, lack of ventilation, high density plantings (or sowing to deep), or damage to the roots or stem during transplanting." (End Quotes) Quotes taken from my new book "fresh Culinary Herb Production."
Though environmental conditions such as over-watering and/or temperature affect damping off, as well as how fast it takes over. Environmental conditions don't cause damping off, It's caused by pathogenic fungi that have gotten into the
growing medium and/or water. The growing conditions just determine how fast the pathogenic fungi grow and spread.
Control of damping off
"The control of damping off involves two separate procedures - the complete elimination of the pathogens during propagation by use of sterile media and the control of plant growth and environmental conditions witch will minimize the effects of of damping off or give temporary control until the seedlings have passed their initial vulnerable stages of growth. Use of
beneficial microbes such as Trichoderma in the seed raising media can give excellent control as the beneficial fungi out compete and suppress any pathogenic fungi present." (End quote) Again, quote taken from the book "fresh Culinary Herb Production."
The pathogenic fungi can be from any source, including in the air, or even in water supply, as well as from anything you touch or that touches your system. Filtering spores from the water supply, and or sterilization from UV light can eliminate it in the reservoir. But since the growing medium dosen't pass under the UV light, it can still grow there unimpeded. Household dust usually contains mostly things like dead skin cells, insect decay and faeces, fine dirt particles etc. etc., but also contain thousands of spores. So unless you use a air filtration system, and in an enclosed room, eliminating spores from the air is imposable. Therefor adding the Trichoderma fungi to your
nutrient solution may be your best bet to keep it from continually recurring in your system. If you decide to introduce the beneficial fungi into your system. I would turn off the UV light for a day or two to allow the beneficial fungi to become fully established in the system (including the growing medium), because the UV light will kill beneficial microbes just as easy as it does pathogenic ones. Once the beneficial fungi is established in the growing medium it can effectively suppress the pathogenic fungi in it.
But your probably better off starting new seedlings and using the beneficial fungi from the very start as suggested in the Quotes. Diseased plants tend to not produce well, even if the disease was later eliminated. One suggestion in buying the Trichoderma fungi, don't buy a product made by advanced nutrients, they have pour customer service, and questionable products from all I have herd about them. This link is included in the post about beneficial microbes (as the online extra)
what to look for in a High Quality Trichoderma Product and Low Quality Trichoderma Products (scroll to the bottom of the pdf. to see the list)
I posted this link earlier as well (in the beneficial microbe post)
http://ag.arizona.edu/ceac/pls-217-i...ponics-and-cea
I quote from page 10 of chapter 4:
"Pythium species:
*Usually non-host-specific, though some have host specificity.
*Infection is most often at the roots or crowns but can also be on the fruit.
*Optimum conditions: Most species prefer warmth (20-40C or 68-104F)
*General symptoms include brown roots, stunting or plant wilt/collapse; plants using the same water source will die simultaneously due to rapid spread by zoospores. Attack on seedlings (“damping off”) causes death.
*The disease is spread by motile zoospores that swim through the nutrient solution. This is especially dangerous in recirculating systems.
*CONTROL: Sanitation is very important, including disinfectant mats, cleaning of tools, hands and gloves, and removal of prunings. Surfactants in the nutrient solution have given 100% control over spread of disease." (End Quote)
It stated that "surfactants in the nutrient solution have given 100% control over
spread of disease." I need to do some research as to what exactly is meant by "
surfactants." I also assume by the term "spread" it's talking about spreading to other plants in the system, rather than eliminating the fungus that has already started. But I might e-mail Pat from the University of Arizona's department of Controlled Environment Agriculture Center (CEA) in the next few days for some clarification about it (she wrote the 15 chapter course). But I would be interested if anyone else has information about Surfactants as well, especially experience with using it.
P.S.
You may note that the optimum temperature range for the pathogenic fungi goes higher in the quote from Arizona's Controlled Environment department, than in Dr. Lynette Morgans book. Though I cant say for sure, I assume that's because it's likly including more overall species of pathetic fungi, and thus includes more species that prefer higher temperatures than Dr. Lynette Morgans book was referring to.