After doing a bit more research on Pythium, I have found that it is an opportunistic pathogen. This means it is always there but only becomes an issue when conditions are right and a plant is unhealthy.
The best prevention is to keep reservoirs around 68 degrees, keep it well aerated and keep debris out. Also, even a small amount of the fungi in plant stems can make a plant difficult to clone so it is a good idea to keep a mother in some good soil in case your hydro system shows signs. My plants show only some slight browning of the roots and this is enough to make cloning a challenge. I did get lucky and get a few to take, thus saving my prized strain.
NOT
As I said before and will say again chlorine at low levels will not harm your plants or effect the taste of your buds. Chlorine addition to nutrient reservoirs is a good treatment and preventative measure for many bacteria, protozoa and fungi problems including Pythium.
Pythium is is not always there if you kill it and keep a residual level of chlorine present to maintain a zero level of pythium. It is nearly impossible with the many bad growng sytems in use to always keep Pythium at non injurous levels with the measures you suggest. With most systems being poorly designed (small tube aeros, NTF in small gutters and fense posts) so that roots are nearly always laying in very low DO water or even totally anoxic water and with DWC and Bubblepoincs systems full of dead and dieing roots and low DO levels reagrdless of all efforts to raise DO and reservoirs not being changed regularly (at least once a week) simply aerating the water and keeping the temp low will not keep phytium in check. Period.
Does anyone really think nearly every commercial green house grower uses chlorine constantly just to support the chlorine industries. No they use it to eradicate Pythium and to keep it from being able to return to cause harm.
Pythium and Recycled Irrigation Water
- By Ping Kong, Patricia A. Richardson and Chuan Hong
Chuan Hong is an assistant professor of Plant Pathology, Ping Kong is research scientist and Patricia A. Richardson is research specialist at Virginia Tech’s Hampton Roads Center, Virginia Beach, Va.
Research Results
Genetic codes of biological
agents are stored in chemicals called deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). For Pythium pathogens, these genetic codes are stored in double stranded DNA. In this project, we developed a DNA fingerprinting technique for rapid and accurate species identification. The underlying mechanism of this technique is to separate the two complementary DNA strands, then let individual strands form secondary structures (conformations). Under prescribed fingerprinting conditions, formation of secondary structures depends on the DNA sequence thus can be a reliable character for species identification. The fingerprinting technique is called single-stranded conformational polymorphism (SSCP) analysis. With a single DNA fingerprint, we were able to differentiate 36 Pythium species assessed so far.
With this DNA fingerprinting technique, we have identified more than 20 species of Pythium from irrigation water. The most abundant species include P. dissotocum, P. torulosum, P. sulcatum and P. porphyrae. All identified species are plant pathogenic but vary in degree of aggressiveness. These results indicate the diversity of Pythium species present in irrigation water and the need for water decontamination in greenhouse and nursery production, especially those recycling irrigation water.
A total of 15 isolates were tested with zoospores for chlorine sensitivity and were assigned a number/letter combination. These isolates included six from nonchlorinated irrigation water, five from chlorinated water and four from diseased plants. Chlorine assay of each isolate was repeated twice. Efficacy of chlorine treatment was measured by the average number of colonies per petri dish with the most colonies per dish for control (0 ppm). Numbers of colonies varied among the repeated tests of the same isolates. They also differed with isolates from the same sources (nonchlorinated water, chlorinated water or plants). Differences among the isolates within the three sources remain unclear. Figures 1 and 2, below, illustrate the data; detail assay data of the 13 other isolates were omitted for simplicity.
No colonies were recovered at 2 ppm or above for the majority of isolates. Four isolates produced a few colonies at 2 ppm or above in one or two of the three repeated tests. Isolate 17C2 produced two colonies at 2 ppm in one test. Isolate 23J3 produced 0.3 colonies at the same concentration in two tests. Isolates 4E1 and 5J5 produced a few colonies at 8 ppm in one test, but none at 2 ppm or above in the other two tests (see Figure 1, page 33). Isolates producing colonies at 2 ppm or above produced colonies only at 1 ppm or lower in additional tests. These results suggest that the previously recommended 2 ppm free chlorine at discharge points (risers or sprinklers) for control of Phytophthora species also will effectively control Pythium zoospores in irrigation water. It must be noted that substantial numbers of colonies were recovered at 1 ppm for a majority of the isolates, and there essentially were no differences in colony recovery between 0.25 and 1.0 ppm of chlorine for most isolates. This chlorine response is considerably different from that of Phytophthora species reported previously. The mechanism behind this is unknown. But these results suggest that any failure to maintain recommended 2 ppm chlorine may expose entire crops in the production facility to Pythium diseases.
Pythium diseases are a major limiting factor affecting floral crop production. This problem will continue to aggravate with growing global water scarcity and pollution. Identification along with pathogenenicity tests of Pythium species present in irrigation water suggested that decontamination of recycled water before use is required to produce quality plants. Growers should use this recommendation as a guide when building a new production facility (e.g., greenhouse) or modifying an existing facility to minimize Pythium disease risk.
If anything chlorine should be used at heavier doses than I recommended. However as few people have a colorimeter or even a dye test to test for residual levels of chlorine I usually just reccommend adding chlorine at lower levels near 1 ppm and suggest higher levels be added only when lower levels appear inadequate.
For anyone that buys a colorimeter to test for residual chlorine or even a dye test I recomend the 2 ppm level initially and lowered to 1 ppm after the first Pythium killing dose of 2 ppm residual held at that level for at least 30 minutes. Depending on the amount of Pythium present and the amount of dead roots it can take several small doses after the initial large dose so as to maintain the residual level at 2 ppm for at least 30 minutes.
