a talk with a farmer, LB cure

[tjg911]

i was asking about LB and was told they spray stuff to cure LB. i said that there is no cure. now i know that commercial growers have use of things the public does not. is there a cure for LB that they use? everything i have read indicates there is not.

tom

[carolyn137]

Originally Posted by tjg911

i was asking about LB and was told they spray stuff to cure LB. i said that there is no cure. now i know that commercial growers have use of things the public does not. is there a cure for LB that they use? everything i have read indicates there is not.

tom

No Tom, there is no cure.

Commercial farmers with pesticide licenses to have access to products such as Bravo and Tatoo, which are still Daconil but at a higher concentration, and one more I can't remember right now that starts with methyl something or other, but they cannot and do not cure LB.

[amideutch]

LATE BLIGHT FAQ. Cornell University

Prepared by Margaret Tuttle McGrath, Department of Plant Pathology and Plant-Microbe Biology, Cornell University, Long Island Horticultural Research and Extension Center, Riverhead, NY
[Updated 7/29/2009]
Note: More answers will added as new questions are asked.
1. Are all tomatoes and potatoes in the northeastern US doomed to get late blight this season because of the wet weather?
No. In addition to requiring that there be favorable conditions (cloudy, rainy, and not too hot) and a susceptible plant (tomato, potato, and some related weeds), late blight cannot develop unless the pathogen that causes this disease is also present.
This disease normally occurs sporadically in the Northeast, and rarely in many parts, because the pathogen is usually not present. For late blight to develop in a particular garden or field the pathogen has to be there, which it accomplishes by being brought in on infested potato seed tuber pieces or infected tomato transplants or blown in as spores (which function like seeds for pathogens) from affected plants in another location.
Some plants may ‘escape’ late blight if the pathogen does not get on them. However, the chances of this happening this year are very low based on the fact occurrence of late blight is very widespread very early in the summer growing season.
2. If I grew my own tomato plants from seed do I need to worry about late blight?
Yes. While the pathogen does not have a means to get into seed and it cannot survive on seed, this year there will be a lot of wind-dispersed spores with so many occurrences of late blight widely distributed in the eastern U.S. this early in the season. These spores can be moved long distances.
3. Are tomatoes grown in greenhouses or high tunnels protected from late blight?
No. In fact at some farms the tomatoes in high tunnels have been more severely affected than those in the field! The pathogen that causes late blight needs only high humidity to infect. Thus it is similar to the pathogens that cause gray mold and leaf mold, which commonly occur in tomatoes grown in these protected environments where humidity typically is higher than outdoors. Leaves need to
be wet for other pathogens to infect. Additionally, several need splashing water for dispersal, thus Septoria leaf spot, early blight and bacterial speck/spot are uncommon in protected tomatoes. The sides of high tunnels are rolled up on hot days, thus these structures do not provide a barrier that prevents spores of the late blight pathogen from getting to the plants inside. Greenhouses provide better protection, but most have vents and thus are not completely sealed.
4. Can plants be saved in a garden once late blight starts to develop?
This depends on amount of symptoms seen, type of symptoms, how early in disease development symptoms were found, environmental conditions, proximity to other gardens or farms where late blight is developing, and management steps being taken.
It is more likely possible to save plants in a garden if when the first symptoms are found:
1. There are very few.
2. They are on the leaves and not stems.
3. The garden has been inspected very thoroughly on a frequent basis (preferably daily) and thus the symptoms are discovered shortly after they formed.
4. Conditions are expected to be hot with no rain or lengthy dew for a prolonged period.
5. There are no nearby places with late blight that could be a source for more spores.
6. Further development of late blight will be slowed by regularly removing affected tissue (daily cut off and bag, preferably during the day when plants are dry and there will be sunshine for several hours afterwards) and applying fungicides (minimum of weekly).
Additionally, success is more likely if fungicides were applied before symptoms were seen (thus there will be fewer initial symptoms) and spray coverage is maximized by using a pressurized pesticide sprayer to plants that are trellised. Removing extra branches will also help.
Realize that even with an ideal situation (all above conditions met) there is no guarantee that success will be achieved. Late blight is a very destructive and difficult to manage disease. Impact can be great considering that tomato fruit and potato tubers that become infected can quickly rot.
Plants can be killed quickly when late blight is not managed. A spot (lesion) can form within 4 days of when a spore lands on a plant (even faster, less than 3 days, with one strain of this pathogen) and a day later be producing spores that can be dispersed by the wind to healthy plant tissue resulting in more spots within a few days. Lesions that develop on stems are especially destructive.
Late blight needs to be aggressively managed not only to try to save plants in the garden but also to avoid having the affected plants serve as a source of inoculum (wind-dispersed spores) for other gardens and farms. Promptly remove affected plant tissue on a regular basis. Realize that when symptoms are first seen, all points of infection likely are not yet visible.
There is a ‘latent’ period of a few days between infection and when symptoms are visible. No fungicide can cure tissue that is already affected, and this tissue will produce more inoculum.
Also rogue out any volunteer tomato plants growing from seed of previous year’s tomatoes and susceptible weeds like bittersweet nightshade. Given the amount of effort to try to save a garden once late blight starts to develop, especially when it is early in the season, and the chance the crop will be destroyed despite the effort, especially if fungicides are not applied frequently, the best option when late blight occurs might be to replace the plants with something like spinach or lettuce that grows quickly.
5. Can plants be saved in a farm planting once late blight starts to develop?
Yes. Potato growers usually are able to effectively control late blight. It is easier to manage late blight on a farm than in a garden because of the fungicides that can be used. Farmers can use fungicides able to move within the leaf that the spray lands on. Some fungicides can move into stems and new growth.
Farmers also have sprayers that can achieve better coverage of plant tissue than hand sprayers. As with a garden, success is affected by whether or not fungicides were applied before symptoms were seen and how severely the crop is initially affected if fungicides were not applied.
Typically farmers begin applying a broad-spectrum, contact* fungicide when conditions are favorable for late blight, inspect their crops regularly, and when symptoms are found start applying fungicides with specific activity for late blight. They also manage the usual initial source of the pathogen: affected tubers from the previous year or used as seed. See also answer to previous question.
6. Do I really need to apply fungicides preventively to control late blight?
If fungicides are not applied preventively, there is a risk that when this disease begins to develop, there will be too many symptoms to achieve control.
Fungicides cannot ‘cure’ a spot that has already developed (disease control in plants is very different from humans). This tissue will soon die, but before it does
the pathogen will produce hundreds of spores. The more spores, the greater the odds some will be dispersed to plant tissue that has not received fungicide.
It is difficult to achieve complete coverage of plant tissue with fungicide, especially when a contact* fungicide is used, even with the best farm sprayer. The underside of leaves is an especially difficult area to reach (the pathogen can infect through either surface), which is why farmers who can use fungicides able to move through leaves are better able to control late blight.
Only contact* fungicides are available to gardeners. Note that there are precautions that need to be taken when applying fungicides. Read the label to determine what protective equipment is required (e.g. water-proof or chemical-proof gloves, shoes plus socks, long pants, long-sleeved shirt, goggles, respirator).
7. Do I really need to apply fungicides frequently to control late blight?
Yes. Fungicides applied on a plant, even those that get inside of the plant, disappear over time due to being broken down biologically or by sunlight and/or being washed off by rain or irrigation. After about 7 days the concentration (dose) of many fungicides can be too low to be adequately effective.
8. Do I need to be concerned about bees when I spray fungicides?
Chlorothalonil and copper fungicides have been rated ‘relatively nontoxic’ to bees. Insecticides are a much greater concern generally than fungicides.
Additionally tomato and potato are pollinated mostly by wind and not commonly visited by bees compared to some other crops. To avoid exposing bees to pesticides, apply them during late afternoon or early evening when bees are less active. Applying when there is no wind minimizes the chance of drift to other plants that bees visit more commonly.
9. What other diseases could be confused for late blight?
There are several diseases that can cause dark spots on leaves and stems of tomato and potato plants. Most of these are smaller than those due to late blight. Botrytis gray mold is the most similar.
10. Could the late blight pathogen survive on tomato cages and stakes between seasons?
No. Therefore it is not necessary to discard or even disinfect the stakes to manage this disease. Stakes should be disinfected however, especially if bacterial diseases also developed in the planting.
11. Could the late blight pathogen survive in soil between seasons?
Unlikely except in affected potato tubers. This is an obligate pathogen that is thought to only be able to survive in living plant tissue in the northeastern US. It can produce a specialized structure that would enable it to survive without living plant tissue, but this requires that the pathogen reproduce sexually which it is not thought to be able to do in the northeastern U.S.
When late blight has previously developed in this region and the pathogen population has been examined, only one “mating type” has been found. This is the term used for the pathogen’s equivalent of male/female. Thus the pathogen has only been able to reproduce asexually. The characteristic white growth that develops on late blight affected tissue contains many asexually-produced spores. Both mating types have been found in Florida.
12. Could the late blight pathogen survive between seasons on perennial weeds that it is able to infect (e.g. bittersweet nightshade and hairy nightshade)?
No. This is an obligate pathogen that needs living plant tissue to survive. It only infects foliar tissue of weeds. Since the pathogen cannot infect roots, it cannot survive on weeds in areas where foliage is killed by cold temperatures. In the Northeast, potato tuber is the only plant tissue it is able to survive in.
13. Are affected tomatoes safe to eat?
Yes. This pathogen cannot infect people and it does not produce a toxin that can make people sick, as a few plant pathogens can do. However, considering how quickly affected tomatoes will rot, it is unlikely that they will be marketed.
14. Are there resistant varieties?
Not yet, but there are some tomatoes in the final stages of development expected to be available perhaps as soon as 2010.
* Contact fungicides remain on the surface of the plant tissue where they are deposited whereas translaminar fungicides can move in and through a leaf. A very few fungicides are systemic and can move in the plant to stems and new growth. In contrast, most human drugs are put inside the body and are able to move to where they are needed and they have a curative effect. Plant medicine is very different from human medicine.

[carolyn137]

Ami, thanks for that but I know I've already posted here the current Cornell update to LB, I don't know which thread at this point, which includes the FAQ's that you just posted.

From posts at DG and GW and even here at Tville I really haven't seen anyone who has been able to save plants that show symptoms of any kind.

Just take a look at Sequee's pictures at DG for one example.

I know that I for one would not even try to save a plant with known LB b'c of the possibility of spores spreading from one plant to another if in the rare case that not all plants in a specific area are affected all at roughly the same time, which appears to be the case.

The Cornell Coop Ext in my area has posted bulletins in my area describing the tremnendous loss of commercial tomato fields as well as home grower gardens and some are even speaking of a tomatoless summer.

My fingers remain crossed here at my place.

[Wi-sunflower]

At my farmers market yesterday (Wed) in Madison, a person from the Wi dept of Ag was handing out a flyer to all the grower with a Late Blight alert.

Aparently last week the first instance of LB was found in Wi. They want growers to report any suspected finds.

I talked with the guy a bit and mentioned that our fields have been hurting for rain. He agreed that LB is not likely under dry conditions. I also mentioned the Bonnie plant issue and while he was non-committal about that, he obviously knew the story.

We have a forecast for hot, humid and rain for Fri - Sun. While we need the rain, hopefully it won't be persistant enough to get disease going. All the tomatoes in my area are late this year due to not enough heat so we need a long season this year.

Carol

[amideutch]

Carolyn, sometimes it's better to throw it out there rather than give links that can get lost in the shuffle. I've been using the Triple A's this year with good success concerning all the rain we have been getting to include almost all of July. This week we have had a heat wave here in Germany so hopefully this will put the disease in check for awhile. The farmers have been running their combines like crazy this week harvesting their grain crops before the rain hits again.
What are my three A's.
1. Actinovate, as a soil drench and foliar.
2. Azoxystrobin as a foliar.
3. Agri-Fos (EXEL) as a foliar and it is a Systemic as well.

The other thing I've found is my plants which have a roof over their heads have had no problems. Under the balcony, in my open greenhouse with no sides with just a roof and even my enclosed greenhouse. Keeping the rain off of them allows your fungicide application to remain on the foliage protecting your plant from disease. Ami

[hasshoes]

I am editing /deleting my post because I don't want to be such a Negative Nelly. Good luck everyone. . . and spray, spray, spray!!!!!

[rnewste]

ami,

Could you give us your application procedure and frequency of your preventative "3 AAA" treatment process.

thanks,

Ray

[amideutch]

Ray, This year the application schedule has been willy-nilly as has the weather. Last year I used Actinovate and Azoxystrobin with good results. Actinovate is used in seedling plant out and brewed with my Microbe tea for foliar application. I do this twice a month. Azoxystrobin I apply as a foliar normally once a month.
This year I came across EXEL (Agri-Fos) and you took the product and ran with it with good results leading to my purchase of Agri-Fos. As a added benefit it is a SYSTEMIC fungicide. So this year I added it to my spray routine. Normally I keep my applications to once a week when the weather allows. Because each product has it's own unique way of fighting disease, this allows them to do their thing before applying the next product. I have had not a week go by without rain so it works out pretty well. To me relying on just one product decreases your chances for disease control versus three. Ami

[rnewste]

Thanks Ami,

Too many folks (me included) tend to wait until we see a "problem", then try to "cure" it. Your preventative routine instead tries to nip it BEFORE an infestation pops up. I am going to try to adhere to a preventative spraying schedule next season with multiple products, as you do.

Ray

[hasshoes]

For one set of plants I used:
MycoGrow (spray and drench), Serenade, Actinovate (spray and drench), molasses, neem, and Neptunes Harvest (but mainly Serenade and Actinovate.) Also copper recently.

I sprayed a ton--- even in the rain (there was no lightening) with Molasses to help make it stick. I sprayed "a lot". . . I think it may be against federal law to spray too often so I'll leave it at that. :0)

I know I covered my plants completely because I spent a ton of time on it. . . and due to perhaps the darkness--- my plants were very short---- but had tons of flowers and some many new maters.

Notice I'm talking about my plants in the past tense!

This set of plants didn't have any fungus or spots. . . but the morning after I saw them looking perfect I got a call. . . .

All gone!

I'm not complaining. . . I just think there may be some luck involved with the various miracle cures and home remedies people keep talking about. Now I'm not saying spray the Earth with funk if you don't want too. . . but if you're okay with it I would definitely listen to Dr. Carolyn.

[hasshoes]

I just tried to edit my post but it wouldn't let me?

Anyway. . . I want to add the PS

I'm not dissing Ami's advice but speaking in general terms---- I obviously didn't use the same sprays he did, and I always appreciate everyone's thoughtful advice. :-)

I just want people in the NE to be prepared for the potential letdown.

[korney19]

In past tests, Serenade had very little effect on Late Blight.

"Plots treated with Seranade (biological fungicide) had disease ratings not significantly different than the untreated check plots."

There are some "Big Guns" type fungicides out there that are listed as "curatives" or "eradicants" plus others that will feed on the spores or anti-sporulants. I extracted this from a pdf presentation on LB:




The next two screencaps were from a different report by Cornell/Dr. Zitter. They rated the fungicides' effectiveness, up to 4 stars I believe.

[amideutch]

Mark, excellent information. Ami

[hasshoes]

Cool info.

I'd really like to know what tests Serenade goes through to be able to list as "controls or suppresses" Late Blight.

I have an ongoing joke with a friend about this that I won't post here.