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Old 09-15-2010, 12:07 AM   #1
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Default Late tomato blight, potato blight, Phytophthora infestans, new strains

This thread, You Say Tomato, I Say Agricultural Disaster, totally irked the crap out of me since I definitely have neighbors buying their tomato plants in little pots from big box stores and garden centers and I spent a decent amount of money ordering potatoes for me to grow next year so I did some checking around to get a take on what I’d do if I got hit with early or late blight. So I started a search and wouldn’t ya know it. Tom Volk’s got this Phytophthora infestans as fungus of the month for March ’01, Phytophthora infestans, cause of late blight of potato and the Irish potato Famine, Tom Volk's Fungus of the Month for March 2001, alternate page. So what caught my eye? This caught my eye,The potato did well for the Irish, for the population of Ireland exploded from 4.5 million in 1800 to about 8 million in 1845. This is particularly amazing because most of the population was dependent on the potato for their nutrition for 10 months of the year. But then came the late blight of potato….Between 1845 and 1860 over a million Irish people died as a consequence of the blight; another 1.5 million emigrated, mostly to the east coast of the United States, where many became New York or Boston policemen (some shown to the right in the 2000 St. Patrick's Day parade in NYC) or workers on the transcontinental railroad (remember that the Irish laid track from the east and the Chinese from the west.) Nearly 150 years later, the Irish population has still not recovered from the disaster caused by the late blight of potato.”
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Americans are dependent on the potato and to a lesser degree the tomato too!!! Phytophthora infestans is "somehow" getting spread around the country and it's looking a lot like BigAg distributors like Bonnie Farms down south are doing our home gardens in at the same time they're threatening our food supply!
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Old 09-15-2010, 12:11 AM   #2
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So I went to the vegetable MD online, Late Blight of Potatoes and Tomatoes Fact sheet. Yaa, it’s sorta dated but I picked up on something, Late blight of potatoes and tomatoes, the disease that was responsible for the Irish potato famine in the mid-nineteenth century, is caused by the fungus-like oomycete pathogen Phytophthora infestans. It can infect and destroy the leaves, stems, fruits, and tubers of potato and tomato plants. Before the disease appeared in Ireland it caused a devastating epidemic in the early 1840s in the northeastern United States. P. infestans was probably introduced to the United States from central Mexico, which is its center of origin. After appearing in North America and Europe during the 1840s, the disease spread throughout most of the rest of the world during subsequent decades and had a worldwide distribution by the beginning of the twentieth century.
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Guess what…. looks like it was a gift from Mexico. Didn’t know that did you??? The author goes on to write this,
Reproduction occurs via sporangia that are produced from infected plant tissues (Fig. 1) and is most rapid during conditions of high moisture and moderate temperatures (60°-80°F). Sporangia disperse to healthy tissues via rain splash or on wind currents. Reproduction is asexual; each sporangium is an exact copy of the one that initiated the parent lesion, and each can initiate a new lesion.”
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That’s followed with this, During the early 1990s several exotic strains of P. infestans were introduced from Mexico. These strains have increased the severity of late blight on potato and tomato because they are more aggressive than earlier ones in the United States and Canada. They initiate infections more quickly and reproduce more profusely, causing epidemics to occur rapidly. To combat these strains it is necessary to use more resistant potato and tomato cultivars or to use fungicides more intensively.” Anyone else almost overlook this, “Hilling of potatoes increases the amount of soil between tubers and the soil surface and thus helps protect tubers from sporangia that land on the soil surface”
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With all those comments about needing to use protectant fungicides then needing to use more protectant fungicides then needing to use systemic fungicides on tomato and potato plants>>>? I do have to give him oodles of credit for this advice, Control tactics are constantly modified as new information and technology become available, so consult the latest Cooperative Extension publications for the best recent specific recommendations.”
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I followed his advice sorta….
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Old 09-15-2010, 12:13 AM   #3
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First thing I started looking up was this “hilling”. I’m a native plant geek not a veggie head so this is uncharted territory for me. Here’s what I found, Late blight of potato and tomato,Hilling: Soil can be made deeper around the base of the plants after emergence of the young potato plants. Hilling helps in early weed control and minimizes tuber infections from sporangia that wash off the leaves of infected plants into the soil. Irrigation: It is important to minimize the time that leaves are wet to help prevent foliar infection (Figure 26). Irrigation should be timed so that length of the night dew period is not extended- i.e., no late afternoon, early evening, or morning irrigation in order to allow plants time for drying. Excessive irrigation can wash some of the "hilled" soil away from the base of the plants, exposing tubers to greater potential infection.
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Things that make you go hmmmmm since we’re dealing with . I really liked this webpage. Catch where they mention this,
Planting of pathogen-free tubers: Only certified seed tubers (Figure 25) should be planted. However, currently (2005), even certified seed tubers may be allowed to have up to 1% incidence of late blight. Fungicide treatments are available for protecting freshly cut seed tuber surfaces.
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That’s good sound advice and sure enough…. I checked my receipt from suunto’s ‘Potato Garden” source and that Ronnigers Potato Farm he recommended that I ordered from is certified disease free, Potato Garden: Certified Seed Potatoes. Thank you thank you thank you for turning me onto that source suunto!!! Everybody order potatoes from suunto’s place!!! Anywhooo, I also picked up this from that webpage,
Elimination of overwintering inoculum: In the absence of oospores, tubers infected during the previous season are the most important source of initial inoculum. Surviving tubers may be found in cull piles (Figure 20) and tubers left in the field at harvest. Culled potatoes should be left on the soil surface to freeze, trucked to a landfill, or buried at least 1 m (3 feet) deep. They also may be fed to livestock provided steps are taken to secure them during transport and dump them only on impervious surfaces. Volunteer plants in the spring should be destroyed to minimize initial inoculum.
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So why aren’t we requiring certification of tomatoes AND potatoes that are distributed and transported across the US? Rhetorical question. We’re really on our own and I’m thinking most everybody BUT ME here figured that out a looooong time ago.
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Old 09-15-2010, 12:15 AM   #4
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Uh oh spaghetti ohs!!! What’s this??? How come no mention of this anywhere easy to find online??? http://ppathw3.cals.cornell.edu/Fry/New_tomato_strain.pdf,The US22 strain of Phytophthora infestans caused epidemics throughout the Northeast in 2009. These slides illustrate some of its characteristics.” [/quote]And my my my…. what do we have here,US22*:
aggressive on potatoes and tomatoes
generally sensitive to mefenoxam
A2 mating type”.
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What strain are we up to in 2010…. I couldn’t find out but my guess is we’re already up to a…. US 24 or US 25??? So much for asexual reproduction once we got zapped with the introduction of more exotic strains of Phytophthora infestans in the 1990’s from Mexico.
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Old 09-15-2010, 12:21 AM   #5
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Totally discouraged by that US22 since it was starting to look like large scale producers of tomatoes and potatoes were on a fungicide treadmill climbing their way steadily to US100 and I have been buying tomatoes and potatoes from the grocery store since we don’t have decent farmers markets or organic produce available year round. I found this that at first glance looked like we were doomed with Bonnie Farms down south in toasty warm Alabama obviously “breeding” new strains of Phytophthora infestans then distributing to stores where everybody and their brother was buying their starts, http://diss-epsilon.slu.se:8080/arch...BA_2007_77.pdf,In some fields disease foci could be found in the same location from year to year indicating a soil borne inoculum source. The first more solid indication of oospores functioning as primary inoculum of P. infestans in Sweden came from a potato trial located at Ultuna, Uppsala during1996. Two years earlier, in 1994, a potato field trial was inoculated with P. infestans isolates of different origin. The resulting epidemic of late blight was very severe, and at the last blight assessment the untreated plots in the trial werecompletely killed by blight. In the areas treated with the highest amounts of fungicides about 0 – 0.1% of the leaf area was infected by blight, see figure 2.Tuber samples taken in different plots in the trials showed 40 – 50% infectedtubers in the plots with the most severe blight infection, and about 1 – 3% infectedtubers in the plots with low levels of blight on the haulm. The haulm and thetubers were left in the field and ploughed under. In 1996 a similar trial wasestablished in the same field, partly overlapping the trial from 1994. Just twoweeks after emergence heavy infections of late blight were observed with plants insome areas completely killed by blight (Figure 2). The infection foci in this trialcorresponded almost perfectly with the infections in the 1994 trial. This is a clearand strong indication of soil borne inoculum (Andersson et al., 1998 [Paper I])
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I’d highly recommend anyone growing their own potatoes or tomatoes read this thesis in its entirety but if you’re not into that kinda thing, I’m pulling the other tasty tidbit from it to save you some time, Epidemiological studies The control of late blight demands frequent, repeated fungicides applications, and as a direct consequence of this the use of pesticides is high in potato compared toother agricultural crops. Despite the introduction of more effective fungicides andimprovements in the application technique the problems of controlling late blightare growing. This is reflected in an increase of the number of fungicide applications used against late blight. In south Sweden this number has more thandoubled during the last 20 – 30 years. Nonetheless, late blight is considered to be more aggressive; the epidemics startearlier, the disease develop faster in the potato fields and the resistance to lateblight in the cultivars is not as effective as it used to be. P. infestans has also been able to infect alternative hosts.
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Not giving you warm fuzzies since we know sporangia disperse by riding wind currents? Me either but…. it got me motivated looking around for research in the US to see what I could do if my tomato and potato plants got hit up from neighbors’ plants dispersing sporangia… which is bound to happen sooner or later.
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Old 09-15-2010, 05:04 AM   #6
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Well, that's an education! No problems here that I can see, so the take-away from this for me is: buy clean seed potatoes, and start all tomatoes from seed.

As for burying infected potatoes 3 feet down, that's not exactly home gardener advice, although I do love digging!
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Old 09-15-2010, 09:05 PM   #7
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Sorry Benj1…. I fell asleep half way through the roll I was on before I finished getting all my notes into the thread last night. Oopsie. BTW, you can toss infected potatoes in your burn pile with brush or bake em in your oven at >250F instead of burying them to 4'. Then you could toss them in a composter. Anywhoooo.... lotsa hope for northern home gardeners and I knew it the minute I read this, Potatoes New Brunswick - The Voice of New Brunswick Potato Producers – Conference & Tradeshow – Canada, “Factors affecting potato blight epidemic risk potential in North Central Region

Climatic conditions in Michigan have been becoming steadily more conducive for the initiation and development of potato late blight epidemics since 1950. Epidemics of potato late blight are initiated from mycelium of Phytophthora infestans, which survives over winter in infected potatoes left behind in the field after harvest (volunteer) and waste (cull) potatoes. With the recent trend for warmer winters, more volunteer and cull pile potatoes are surviving the winter and acting as sources of inoculum in the spring. Studies at MSU have shown that mycelia of newer genotypes of P. infestans (e.g. US-8 and US-14) are becoming more tolerant to colder temperatures and are tolerant to -3 to -5oC for up to three days continuous exposure. Tubers of most varieties appear to breakdown after exposure to -3oC for about one day, although a lethal range of temperature and exposure periods has not been established experimentally. A synopsis of winter soil temperatures from some growing regions of MI indicates a greater risk for volunteer and cull potato survival. The epidemic risk potential could be aggravated by 1) production issues that increase in culls; 2) warmer winter soils; 3) increased pathogen tolerance to temperatures near freezing.
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Wow and double wow!!! A glimmer of major league big time hope!!! I don’t make it a practice of calling folk to bounce thoughts off them when something’s scaring the bejeevies out of me but…. I did just order potato starts and tomato seed and was getting a little panicky so I called him. Yup, I called him since it’s a no brainer to me that none of the BigAg Bonnie Farms out there growing in the toasty warm south would be shutting down their fields for 4-5 years and since it’s almost laughable thinking we’d enforce any certification of P. infestans-free tomato plants before letting these types of growers ship anything to sell to home gardeners. BigAg will just spray and spray and spray claiming they’ve got it under control while they’re trucking their tomato plants from sea to shining sea making $$$ and saying oopsie…. sorry about your tomato and potato plants…. we sprayed…. we didn’t know we “accidently” shipped a “new” US 35 around….
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Old 09-15-2010, 09:17 PM   #8
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I asked a point blank question, “What do we do if our plants get hit from neighbors growing plants infected with P. infestans…. roll over and buy fungicide laden tomatoes and potatoes from the grocery store?” Their best advice was “new soil, new location”. I asked what to do with the “old” soil when we’re growing in a garden setting so we didn’t infect someone else…. rent a backhoe and dig it up ourselves then move it to the curb and add it to a landfill so we can hope for the best planting a different veggie in the old location for the next 5 years to be on the safe side? They laughed. I’m not gonna recap the whole conversation but I’ve got a game plan for me that might work for somebody else out there since I balls out asked them if they had done any testing to find out what temps P. infestans was dead at when frozen. Drum roll…. their technicians tested it on culture plates and a week at -5C controlled it…. no guarantees at -5C but…. it DIED at -20C for a week I think they said. Not good news for anyone down south in a USDA Hardiness Zone of 6 or higher but FANTASTIC news for me. -5C = about +23F and -20C = -4F. This got me thinking that they probably had done some culture plate tests at higher temps so I balls out asked what temp it was dying at when cooked since most of us sterilize soil we want to reuse in ovens for a couple hours at +180F thinking that temp might do it in. Nope…. +100C does it in. +100C = 212F so no chance of this pathogen baking from regional warming down south and no chance of our compost piles getting hot enough to do it in but…. if we’re growing tomato plants in 5 gallon containers, we could always toss the medium on a bottom shelf of our ovens when we’re baking cakes so we wouldn’t have to pitch it. My game plan is going to be calling back sunnto’s potato supplier and doubling my potato order right now so I can grow the 4 varieties of potatoes I bought separately in each one of my 4 4x4 raised veggie beds. I’ll keep notes on what I grew where each year and be on the lookout for problems. I’ll grow my tomatoes from seed and I’ll plant them in a different location and I'll watch them like a hawk too. I’ll use that “hilling” planting method I learned about for potatoes and tomatoes. If I spot a problem, I’ll burn the plants then go through the soil with my hands looking for roots and tubers and burn them. No leaving behind any live plant material…. that’s the fastest way to re-infect next years’ plants if a new US#something or other manifested itself that was -20C cold hardy. That’s it…. no screwing around with this. My winter temps in Zone 5 are low enough for long enough that my raised veggie beds should freeze solid if I shovel snow off them that would provide insulation. It’s not uncommon for stretches where we get a week of -10F and sometimes night time temps of -20F so I should be home free growing tomatoes and potatoes the following year using my 4 4x4 raised veggie beds if I get hit…. who woulda thunk!!! I do grow some peppers in 5 gallon buckets. Peppers are in the nightshade family and P. infestens US20#whatever we’re up to now is infecting alternate hosts so if any of my peppers get hit…. I’ll burn them too then bleach my buckets and cook my soil with cookies in my oven so I can reuse it. That phone call to MSU was the MOST productive phone call I made this year since I bounced my ideas off them and they felt that I had a good game plan…. no promises though with “new” US#whatevers being discovered yearly. I’m totally psyched and really glad I took off a half a day to get myself set straight on what to do about late blight that’s here to stay with a strain in the making that'll be able to survive temps colder than -20C.
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Old 09-16-2010, 07:36 PM   #9
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Thank you for the superb detective work Equilibrium.
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Old 09-17-2010, 12:09 AM   #10
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Thank you thank you thank you. I did that more for myself. You know.... if anyone does ever get hit with a blight.... they could always grow sweet potatoes in the old soil for 5 years. I'm pretty sure sweet potatoes are more nutritionally complete anyway and they're a totally different family.
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