How to use Captan for seed treatment

Santa Clarita, CA

I've been having a abnormal amount of problems with damping off my vegetable seedlings. It's not causing the stems to turn black or rot, but it's causing a web of pythium, looks like cotton growing on my soil, that's stunting the growth of the plants completely. I am aware of the precautions that need to be taken, and even with them am getting the same issue.

I think California's extremely harsh summer conditions have left it near impossible to reach the right conditions necessary to avoid damping-off. Although I know it's usually unneccessary for amateur home gardeners to need to use fungicides, it appears its my only hope. I really like the company and the seeds I'm getting and not ready to let go of my company and get pre-treated seeds. I decided to purchase Captan powder to do some seed treatment. Unfortunately, there is no information online about how the seed treatments should be done and there is some mixed information on the booklet, one of them says use a certain amount of water, the other doesn't even mention water. I am trying to find out if this is suppose to be a water combined slurry, or am I coating it directly in the powder. Do I need to add something to the seeds if i'm just using the powder to make it stick? And is it going to harm the soil somehow? Do I need to wait a certain amount of time for the seeds to try in the wet form? Am I spraying it on or dunking the seeds... There's no info on how to do this at all. If anyone has done it before and been successful it would be appreciated. I'm really hoping to find someone else who was unable to stop the damping-off and was also forced to get industrial fungicide, but any help or advice would be appreciated.

Just as some background info, I've used Peat pellets from Burpee, Peat pellets from Jiffy, and Coir pellets from Jiffy and Burpee, all ended up with Damping-off. I also tried Miracle Grow's seed starting mix, sterilized it properly, still got it. Purchased a humidity meter. a water meter, and temperature gauge, so I know for a fact i'm not overwatering, the airflow is proper and the temp is great. I do not have a heating mat because it's already 75-77 in my house. I use a cover, I tried without a cover, I tried water with hydrogen peroxide and /or Chamomile, and even Cinnamon dusting. I am bottom watering, but of course have tried above watering very lightly with a dropper. I'm not having any kind of condensation problem on the top. Seeds get to one inch before it hits, sometimes right before they pop it hits. Basically i've tried anything anyone has been able to think of, so this is really a last resort kinda thing. I am not bleaching the pans because I use new ones everytime, I don't want to take the chance, I dont have any reusable garden supplies that are causing it and i've used different rooms everytime its happened when I restart. I have even purchased neutral PH water at a local hydroponics store to avoid the bad Alkaline water Los Angeles has.

So please, do not judge on my use of fungicide, its a serious last resort.


Galesburg, IL

I certainly won't criticize, in fact when used properly, fungicides can be an important tool in seed starting. Before I say anything about use of Captan, Please read the entire label and adhere to all directions in regard to personal safety (that was a public service announcement : ) Captan does have some labeled uses for mixing as a spray, particularly for fruit. However, as a seed treatment, I also haven't seen any exact directions for mixing or applying as a seed treatment, but I will share what I do. When I use it in the garden, I typically mix the seed dry with a little Captan powder in a bag. You don't get complete coverage of the seed, but you don't necessarily need to. If you are using it with very small seeds, you might try rolling the seeds on a dampened paper towel and then putting them into a small baggie with the Captan. You definitely don't want to make a slurry with the Captan, only very small amounts are needed. You also don't want to have the seeds dripping with water when you treat them either as you will end up with a muddy mess.

To answer some of your questions: It will not harm your soil. The dry seeds don't absorb the Captan, so you can plant them immediately after coating.

Just one other comment: I usually germinate and grow my vegetable seedlings much cooler than your temperatures, usually not higher than 70 degrees. I typically don't have any problems with the seedlings so your warmer temperatures may be contributing to the problem to some degree. Remember, the disease triangle. For a disease to occur, you need three things to be present: First a susceptible host (all seedlings are susceptible), second, the presence of a pathogen, and third, conditions favorable to infection from the pathogen.

Matawan, NJ

i have a few suggestions:

1 before resorting to captan, you might want to try one of the commercial soiless mixes that have a biological fungicide bacillus subtilis mixed in, like Premier Pro-Mix BX
with BioFungicide [there are several brands now]

here is the product info for Pro-Mix BX:

Enriched with Subtilex®, a high-performance biofungicide that prevents root diseases caused by pathogens, such as Pythium, Fusarium and Rhizoctonia. Subtiliex prevents damping-off and controls root pathogens such as Fusarium, Pythium and Rhizoctonia. Patented bacterial strain of Bacillus subtilis*- MBI600 provides better performance and shelf-life over fungal inoculants.

Contributes significantly to improved germination and survivability of transplants, while enhancing plant vigor and reducing the incidence of disease. Compatible with a wide range of chemical pesticides. Reduced management costs for disease control . *SUBTILEX is a registered trademark of/and the strain of Bacillus subtilis is a product of Becker Underwood, Inc.

Pro-Mix BX with Biofungicide is composed of Canadian Sphagnum Peat Moss (75-80 % / vol.); Dolomitic & Calcitic Limestone (pH adjuster); Bacilius subtilis-MB1600 (biofungicide); Macronutrients; Perlite (horticural grade); Micronutrients; Vermiculite; and a Wetting Agent

2 most treated seeds are coated with thiram powder, tinted hot pink to be obvious. stokes seeds is an excellent mail order company that sells mainly treated vegetable seeds. i would wear disposable gloves while handling them.

3 another possibility is to start your seeds in a different place [office, friends house] especially if that other place has no houseplants. usually damping off only affects young seedlings, so if you can get them with a few sets of true leaves, you can bring them back to your house.

4 i personally would actually buy my seedlings rather than have captan used in my house.

5 i did use captan in the 1970s on indoor seed trays. i mixed it up in a plant mister [the 1 qt misters they sell at home depot type stores] and misted the surface of the soil. i would wear disposable gloves for this too. and keep everything away from pets and children, especially the used gloves, ie work in a closed off area and take out the trash right away.

i really hope you dont have to resort to captan.

Everett, WA(Zone 8a)

>> looks like cotton growing on my soil,

I don't much about the RIGHT way to start seeds, but I think I'm familiar with many BAD ways. Thanks for mentioning one problem I have NOT yet had, or not yet had that badly!

With aggressive and omni-present fungus such as you descirbe, you may want to keep on improving the environment in every way you can, in addition to dusting with a fungicide. You seem open to trying many things, so here is my list of possible things to try, just in case there are any you skipped.

When I use peaty seed starting mixtures such as you mentioned, they always seem much wetter and less airy than is desirable.

If you can find or make a faster-draining mix, the seeds and sprouts may be happier. For example, more "chunky" components like pine bark nuggets around 1/6th-1/8th inch. Even a tiny amount of peat or fine pine bark fibers hold enough water to get seeds started. If you add too many fines, you defeat the "chunkiness" by filling the pores that would otherwise have allowed air in and encouraged water to drain.

I've seen suggestions for making the top few mm of the soil pure coarse vermiculite or sand.

I assume you never re-use soil and clean pots and tools with scouring powder and bleach and leave them in bright sun for days (UV).

You might also consider a fan for air movement. Lower humidity?

Repeatedly disinfecting the whole grow room?

Less fertilizer? Use inorganic fertilizer at first? "Cottton" sounds like really-well-fed fungus, as if it had a rich organic medium to feast on. Seeds don't need much fertilization at first. Consider trying "none".

If you now start them indoors, is there a sheltered spot outdoors? Maybe there is enough UV in your sunshine to deter fungus.

Please let us know how it goes for you! I always have some damping off and some "stalled" seedlings. Once zero seeds sprouted in 128 cells: maybe as mnay as 200 seeds. I blame soggy soil and stale air and insufficient light. For that tray, also too-cold and too-variable temperatures.


Calgary, AB(Zone 3a)

This is an excellent link for information regarding damping off

Central, TX(Zone 8b)


It would be a good idea to have your soil tested to determine just which pathogen has a foothold in your garden soil. Your state's land grant agricultural university will have a plant pathology and soils lab to perform the test. The lab and/or county horticultural agent can make recommendations for resolving the problem.

Certain disease pathogens infect vegetable families and can be active in your garden soil for years to come. Have you practiced "vegetable family" rotation? [Some crops won't grow well if planted immediately after pathogenic crops.] Focused on soil microbial health with the addition of composted organic matter and green manure cover? Used compost tea as a soil drench to build microbes?

Ms. Tommie

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