What is this disease?

[natural]

Hi all,

I posted this under Photos and then realized it belongs here.

This is my first bad outbreak of disease. Any idea which disease I am dealing with?

I am growing in new bags with sterile potting mix. None of my neighbors have gardens.

Thanks.

[Patihum]

I'm fairly certain that what you have is septoria leaf spot. I've never dealt with it so don't know what to tell you to do about it.

[natural]

I was thinking Septoria also. But I checked the Cornell site and it also looks similar to Grey Leaf Spot. I have never heard of that. I never saw any yellowing of the leaves.

[Paradajz]

hi,

could you tell how long it took it to come to this?

if substances like boscalid or any of the Strobilurins ( azoxystrobin, pyraclostrobin, trifloxystrobin, etc. ) are available to you, or even better- if any of the products which contains both substances is available or you can make a mix of those substances... anyway, spray the plants immediately with it at 15-20% higher doses than recommended, and than after 24-48h spray mancozeb+copper tank mixture at regular doses, and finally repeat boscalid/strobilurin 7 days after that.

if you can't get those systemics, spray mancozeb+copper with copper at 25-50% higher dose than recommended, repeat after 7-10 days depending on weather.

br,
ivan

[natural]

thanks ivan.
Many of the plants looked beautiful about 5 days ago. They were lush and green. I was showing them off to a friend. That day, I added a small amount 2 Tablespoons of TomatoTone fertilizer to each 5 gal bag. The next day, many of the plants looked terrible, with spots everywhere. I don't think that we had rain that day, but we may have. It was a very hot day, but I have dripstakes in every bag and water twice a day. I quickly sprayed with Actinovate and EXEL ( that is all I have), but to no avail. Came back in town 2 days later and the entire crop of plants look devastated.
I cannot get the materials that you recommend locally. I think that it is too late for these plants. Probably too late for copper etc. I have 200 plants in 5 gal bags with organic potting mix. Probably have $1000 invested in everything, including the drip system, timers etc. Did this same thing last year and had very little disease, and that was very late in the season. I am just going to toss everything. I don't have time to perform triage on this level. I am mostly interested in determining the exact disease to know how to prepare for next time.

Thanks,
Bill

[TightenUp]

you can always try the bleach method i've been reading about here.

[natural]

I thought about it, but the disease has spread rapidly to a majority of the foliage on each plant. Whatever this is is spreading much quicker than EB. I should pick a small set of the "least" damaged" plants and trial that method.
thanks.

[Paradajz]

it's Corynespora cassiicola ( Target Spot ), but i'd also say that a few spots showing Stephylium solani ( Grey Leaf Spot ) could be mixed there.

the way to distinct Septoria/Stephylium/Corynespora is spot's center:
with Septoria it's smaller, grayish to light brown, and it's like a ''bump''- when you check it thoroughly it appears as a small hill on the leaf surface.
with Stephylium it's wider, pretty much the same color but mostly flatter or even slightly sunken into the leaf.
with Corynespora it's similar to Stephylium, but the color is distinctively dark.

overwatered ( weak ) plants+suitable weather conditions+high disease presence can unfortunatelly do it.
a simple copper prevention ( 10-14 days intervals, in combination with mancozeb it ''closes'' most of the bacterial issues too ) is highly effective with all spots, but once the Corynespora disease appears a systemic combination of boscalid and strobilurins would give the utmost effect, while the other spots stay in sufficient control with copper and mancozeb.

br

[Paradajz]

p.s.

still, if you happen to have some copper and mancozeb around you should try it, one never knows how far his plants are prepared to go

[natural]

thanks ivan. That is great information. I think that I recall in another thread that azoxystrobin is not available in the U.S.. However, I will begin my search.
It is possible that I was overwatering. I didn't think it was possible to overwater plants in black plastic bags containing nothing but organic potting mix (perlite and peat moss). The mix drains really well. I checked the bags everyday and the mix feels damp but not saturated. I was watering twice a day to attempt to "cool down" the root zone. However, I do suspect that you are correct. I think that it is a combination of sudden heat and humidity, coinciding with a dose of fertilizer, plus perhaps too much water somehow caused this sudden outbreak.

I tried to follow the same (very successful) regimen as last year, including watering using the exact same system and timer settings last year, but certainly the weather is one variable that we cannot control.

Thanks again for the advice,
Bill

[RayR]

Azoxystrobin is available in the US, it's just really really expensive since it isn't marketed in quantities for small gardeners.

I agree with Ivan, it looks like Target Spot
Not something I would be likely to deal with since it is found in southern climates.

Do you inoculate your "sterile" potting soil with mycorrhizae, trichoderma and beneficial bacteria?

[Paradajz]

Thanks, Ray, it's an excellent reading there, i love it
got any more like those?

br,
ivan

[natural]

Ray,

Thanks for the link. At transplant time I did add Mycogrow soluble, Actinovate, PlantSuccess . I think that was all. I need to verify. The mix that I use is Sunshine #1 Organic. Supposedly the TomatoTone has beneficaials as well. I need to compile the listing of all materials.

Any idea if Target Spot and Grey Leaf Spot can be seed borne? If so would a bleach/oxiclean seed treatment reduce those pathogens?

[RayR]

Originally Posted by Paradajz

Thanks, Ray, it's an excellent reading there, i love it
got any more like those?

br,
ivan

That's enough exciting plant pathology reading for you today.
I'll let you know if I find more like that.

Originally Posted by natural

Ray,

Thanks for the link. At transplant time I did add Mycogrow soluble, Actinovate, PlantSuccess . I think that was all. I need to verify. The mix that I use is Sunshine #1 Organic. Supposedly the TomatoTone has beneficaials as well. I need to compile the listing of all materials.

Any idea if Target Spot and Grey Leaf Spot can be seed borne? If so would a bleach/oxiclean seed treatment reduce those pathogens?

OK. I just wanted make sure you weren't a germaphobe gardener. Looks like you've got your bases covered in soil beneficials. I know how important they are at increasing disease resistance in the plant even at the foliar level with Early Blight and Septoria. I just don't know much about Target Spot since I've never encountered it. Actinovate as a foliar treatment is good against Early Blight and Septoria, but from what I've read it is not a good biological antagonist against Target Spot, but it might be worth a try. I don't know if there are any better proven biological controls.
I would say at this point that a copper fungicide might be the best route at control if you don't want to deal with toxic chemicals.

Foliar fungal pathogens are not usually seed borne, their spores are typically air borne or are present on top of the soil on infected plant debris. Seed treatments would be futile in this case.