Late Blight Rears Its Ugly Head Again

Late blight, the disease that wrecked many gardeners’ dreams of a fresh tomato sandwich last year, has been found, wide-spread, in western Pennsylvania. Many horticulturists, me included, were optimistic that we would be spared in 2010 but that hope now appears to be dashed. At this time, late blight has only been confirmed in three western PA counties but all Pennsylvania tomato and potato growers need to be vigilant. For a good discussion of the disease including images, see this site; or this site
To recap…. Late blight is a devastating fungus-like disease of both tomato and potato. Symptoms include rapid blighting of foliage and fruit. Tomato stems exhibit chocolate brown lesions. Leaves have blotchy brown spots and may produce fuzzy, whitish masses on the underside of leaves, especially in the morning when dew is present. Note that this is very different from early blight which results in yellow-brown lesions on lower leaves, containing concentric rings of dead tissue.

What’s a gardener to do? First, be vigilant. Inspect tomatoes and potatoes daily for late blight symptoms. Penn State will be tracking the disease in an attempt to alert commercial growers about the threat of late blight in their vicinity. It’s one thing to miss out on a tomato sandwich…quite another thing to lose a big chunk of your income. Farmers have a lot at stake with a crop of tomatoes or potatoes. Contact your extension office if you think you see late blight. Feel free to bring samples to the office for confirmation of the disease.

How about protecting those plants? Conventional gardeners and farmers can use products containing chlorothalonil, for starters. New foliage needs to be protected as it grows. Organic gardeners have copper fungicides, which will not provide the same level of protection as chlorothalonil but are better than nothing. If you plan to let Mother Nature take its course, and do nothing, at least be prepared to destroy infected plants at the first sign of disease… your neighbors will thank you. Best bet in small gardens is to bag the plants in plastic and cook them in the sun.

Any chance we’ll escape late blight in eastern PA? I was an optimist in the winter because it is known that the organism does not survive without living tissue in the North and Old Man Winter took care of that (except for potato cull piles) . But now that the cat is out of the bag…. I think we’re in for another year of greasy, black fruit in the tomato patch.

Dang… I was feeling good; tying up plants in the rain yesterday. Now I wonder if those raindrops were accompanied by late blight spores. Current conditions are ideal for late blight infection.

Tomato Time

Ask most vegetable gardeners what single thing they would not live without in their garden and it is probably the tomato. Makes sense, tomatoes are easy to grow and reliably produce lots of fruit; they are tasty, good for you and bear from July till frost. There is a huge selection of varieties to choose from so tomato growers don’t get bored. And it is just plain satisfying to pick a big, fat, ripe tomato and fix yourself that first sandwich or salad.

Growing tomatoes is so easy I hesitate to offer advice but here goes. Even veteran tomato growers got a surprise last year with late blight and I’ll offer a few thought s on this disease. Here’s a link to Penn State’s tomato growing guide. See page 55.  It contains lots of good detail on tomato culture…and its relative, the eggplant.

Grow your own transplants or rely on the local greenhouse? That is a big question. Certainly growing your own plants gives you more control over what varieties you’ll enjoy. But many of us just don’t have the time, growing conditions or skill to produce a good transplant. I find that small, local greenhouses offer the best chance at getting an excellent quality plant as well as decent variety selection. Try your local farm market, too. Sometimes farmers start more transplants than they need and sell the rest.

Tomatoes are heat loving plants. They will not tolerate a frost so we wait until mid-May in Bucks County to plant them out, unless you have some device that will protect them or are willing to gamble that Mother Nature is looking out for you. By Mother’s Day, we are almost always past danger of a hard freeze, so that’s a good tomato planting guideline. Makes sense to look at that 10 day outlook and adjust as necessary. You can plant out earlier using low tunnels, wall-of-water, row covers and other heat retention devices if you are the kind of person who wants that first tomato on the block.

Varieties… the list is endless. Entire websites are devoted to tomato seeds and varieties. Here are a few suggestions based on Penn State evaluations, personal experience and high praise from knowledgeable tomato people.
Brandyboy… an improved Brandywine type will give you excellent size and flavor without the downsides of straight Brandywine that heirloom folks praise. Fabulous…is just that, a fabulous, tasty slicer that will not disappoint you. Celebrity is an early fruiting, smaller but reliably good slicer. Mortgage Lifter is a good choice if you are in the heirloom market; and how can we overlook a variety called Bucks County from Burpee.

Plant breeders have been taking the best qualities of heirloom types and combining them with traits that improve yield uniformity and disease resistance. I’m not talking about those hard, red cardboard tasting things you find in the mega-mart. Plant a Brandywine and a Brandyboy side by side and judge for yourself. Space is limited so I’ll leave it to you to explore the plum, cherry, grape Roma and other small types but I will drop a name…Mountain Magic is reported to be a superb new “salad” size tomato that will be available in limited quality this year. In addition to yield and flavor it is resistant to late blight.

Ah late blight… the tomato/potato disease that took a lot of the fun out of last year’s garden. You may recall tomatoes turning a greasy, black color and croaking about mid July. For a more detailed discussion of the disease, check out previous blog entries.

Bottom line… no reason to expect late blight to be the scourge it was in 2009 but keep your eyes open and let us know if you see it. Gardening-wise, there are no special gardening practices that you can employ to prevent late blight. No need to sterilize soil, tools tec. Rotating planting location is always a good practice but will have no effect on late blight.

More likely, our old nemesis, early blight and Septoria leaf blight, will be infecting plants. Neither are the devastating fruit rotter and plant killer that late blight is but they overwinter her very well. Stake or cage plants to encourage quick drying and you’ll see less of these diseases. Inspect plants when you purchase and bypass those with spotted or yellowing leaves.

A final thought… consider planting through black plastic mulch. It is amazing what it does for soil heat and water retention, weed control and overall soil physical prosperities.

Late Blight of Tomato Continues to Spread

You’ve been warned. Late blight is here and continues to affect commercial and home plantings of tomato and potato. A farmer friend called me minutes ago to report a farm right across the river where tomato was confirmed with late blight.

Now it seems a matter of time before we see wholesale injury to this popular crop. Although relatively dry weather has prevailed recently, morning dew in enough to support late blight infection.

I could say more but my co-horts in Lehigh Co have done a great job. See this link.

The best pictures I've seen are from Cornell.

Late blight of tomato and potato arrives early this year

I had hoped that I would not write about late blight this year. Usually it is August or September before late blight rears its head in our area. So writing about it in early July is a bad sign for gardeners and farmers. But it is here. A perverse combination of the widespread sale of infected tomato plants and abnormally cool, wet, weather in June was the perfect storm. The disease has been confirmed in almost all Northeastern and mid-Atlantic states, including in Lancaster and Lehigh counties in southeastern Pennsylvania.

This devastating fungal disease is a threat to all tomato and potato growers. It is the same fungus that was involved in the Irish potato famine of the 1840’s. While no one will starve in 2009 due to late blight, it appears that we are in for an unusually early and wide spread epidemic. Plant pathologists are reporting that this is the earliest the organism has been found in such a wide spread area of the Northeast U.S. The problem is, this fungus can travel many miles in the air, settling out on host plants and spreading infections. Apparently, widespread sale of infected transplants has inoculated the northeast. Many of these locations will be home gardens where it will go unnoticed until it is too late. Nearby commercial plantings are at risk.

The fungal pathogen involved in late blight disease is Phytophthora infestans. It thrives under cool (60-70 degree) moist (dew rain, humidity) conditions. Host plants include tomato, potato, other tomato family plants and, believe it or not, petunia. Foliage, stems and fruit blackens. Unlike the slow progression of early blight described in the previous blog, late blight moves like lightning. That’s why plant pathologists watch like hawks for its emergence and alert commercial growers to its presence.

Fungicides can protect plants and limit the spread of the disease. Famers have good options but must be vigilant and proactive. Gardeners have the fungicides chlorothalonil and copper. Copper is a poor second choice but some forms are organically approved. More details, instructions and pictures from Cornell University can be found here. And at this Penn State site. Plant pathologists recommend treating now, rather than waiting for signs of infection. This fungus is amongus.

Spots and Rots and Blights...Oh My! Plant Diseases 101

You might find lions and tigers and bears frightening but farmers and gardeners would disagree. Groundhogs and rabbits and deer can be more destructive. And then there are the fungi. Early blight, late blight and anthracnose. Black spot and mildew and scab. Rusts and rots and wilts. It’s a jungle out there!

Fungi are certainly the most common organisms associated with plant disease. I say “associated” because the pathogen, by itself, does not equal disease. A susceptible host plant and the proper environment are also necessary.

Here’s a timely example. By now, tomato growers are probably noticing brown spots and perhaps yellowing of the lower leaves. On closer inspection, you may see that the “spot” is actually a lesion that has concentric rings of dead tissue. There may be tiny black dots in the dead tissue. As the season progresses more and more foliage is killed. Fruit infections cause soft spots and rots. All of these symptoms describe the common tomato disease called early blight. The disease also affects potato and eggplant. Some of you will be happy to learn that two weeds, horse nettle and black nightshade, are vulnerable, too. Since all of these plants are related, it is not surprising that they are susceptible hosts for the same pathogen. Note also that the early blight pathogen has no effect on asparagus, beans, cucumbers or you. (Sometimes folks ask if it is OK to eat diseased vegetables. It is.). The pathogen has a scientific name Alternaria solani.

OK we have a susceptible plant and a pathogen. The final ingredient needed for disease is the proper environment. This pathogen thrives and reproduces well under warm, moist conditions. The weather in the month of June, 2009 in Southeastern, PA was about perfect for early blight. Especially for tomatoes that were left to sprawl on the ground rather than trained to a support system which favored air movement and leaf drying.

Bingo! Early Blight of Tomato!

Maybe that was more than you wanted to know about early blight but it is useful. You can manage this disease (and all others) by thinking about three key disease ingredients: pathogen, host and environment. Sometimes it is possible and effective to eliminate the pathogen. But it can be equally effective to grow non-susceptible host plants or modify the environment. Disease resistant varieties have been developed for many of your favorite plants. Look for them when buying seed. Learn about the conditions that favor disease. Do what you can to change it. For most fungal diseases that means increasing air movement and reducing leaf wetness.

For a descriptions and gory pictures of common vegetable diseases, type “vegetable disease” into the search box at www.agsci.psu.edu.

For a complete guide to growing tomatoes and info on more tomato diseases go to http://pubs.cas.psu.edu/FreePubs/pdfs/uj230.pdf

Thanks to University of Minnesota Extension for the nice image of early blight shown above.

Lettuce bolting... tomatoes smoking

Lettuce is a wonderful garden crop. Easy to grow. Makes a crop in as little as 28 days. And if you find a good seed catalog you'll find dozens of lettuce types... stuff you don't even see in the stores. Almost nothing bothers lettuce except the occasional slug... and hot weather. The recent heat wave and lengthening daylight periods has caused my lettuce to "bolt". Bolting is the natural inclination of lettuce to form seed stalks under long days and high temperature. So there was a mass harvest in my garden and everyone I know is getting a bag full. Fortunately, I have seeded lettuce several times and the less mature plants are still coming on. Plant breeders have improved heat tolerance in lettuce varieties and this helps. For tips on growing lettuce check out Penn State's nifty fact sheet called growing leafy vegetables.



Some like it hot. Tomatoes, eggplant, peppers and melons thrive under the conditions we're having right now. You can just about see tomatoes plants grow before your eyes! Even the most tender vegetable crops should be in the garden now. Many gardeners used row covers and other devices to get a jump on the growing season, especially with these cold sensitive crops.



Tomatoes are almost as fool proof as lettuce, but we had a call in the Bucks County Extension office today describing a complete disaster. Twenty-five tomato plants went in... twenty-five are wilting. Same thing happened the previous year. While you will read and hear about Verticillium wilt and Fusarium wilt, these tomato diseases are now a rare occurrence because plant breeders have done a fantastic job breeding for resistance to these problems. So what was up? A quick look at our references came up with a possible cause. Question? Was there a walnut tree growing next to the tomato patch? Answer. Yes. Mystery solved! Walnuts produce a toxin in their roots (as well as leaves and other plant parts) that is deadly to tomato. Doesn't happen often but there it was. A CSI moment. Our web-based tomato fact sheet appear to be under revision but we'll mail you an old fashioned paper copy if you call 215-345-3283 and request it.