Nearly every person who spoke of their vegetable gardens last summer said the same thing, ''Late blight got my tomatoes.''
It was indeed a nasty summer for tomatoes and the perfect conditions for late blight to thrive and spread. So far, we haven't had the cool, wet nights that encouraged the disease last year, a disease that's been a problem throughout the country since the early 1900s. Although our weather is much improved, with warmer night temperatures and hot, dry days, the disease has reared its ugly head in Ohio in Harrison County earlier than usual according to Greenhouse Production and Management magazine.
Late blight, the common name of the pathogen Phytophthora infestans, is the same disease responsible for the Irish potato famine in the 1940s. We had it here as well, until a fungicide developed in the early 1970s was successful in nearly eradicating the disease.
In the early 1980s, a more resistant strain of late blight was found in Mexico, and it wasn't long before it traveled north through the U.S. and Canada.
The disease propagates by way of spores carried by the wind where they can land on their favorite host plants. Favorite host plants of Phytophthora infestans are members of the Solanaceae family of plants, which include tomatoes, potatoes, petunias, nightshades, tomatillos and eggplants.
Commercial, non-organic growers use fungicides to control the disease and if you choose to do the same, a diligent spraying system must be maintained. Be sure to purchase a product that is specifically labeled to control the disease.
Personally, I'm not a fan of using chemicals on my edible plants. If you feel the same, there are other techniques we can use to avoid problems.
If you aren't sure what the disease looks like, take a sample to the Ohio State University Extension office, 520 W. Main St., in Cortland for an accurate diagnosis. On tomatoes, symptoms begin with water spot-like lesions on leaves that begin at the tips or edges and are either circular or irregular.
The lesions grow rapidly and turn dark, almost purplish black in a very short time. When humidity is high and leaves are wet for long periods of time, a white mold can form around the edges. The disease thrives in moderate temperatures between 60 and 80 degrees and during long periods of wet weather. The disease can grow and reproduce, sending out sporangia - the part of the disease that produces spores - within a few days. Symptoms begin to appear within three to four days of infection.
The good news is the pathogen can't live without a host plant. It can't live in the soil, nor can it live on dead plant matter. It is spread from other infected plant by the wind or it can live on live plant matter, such as infected potatoes that were stored for seed over the winter.
Even though we're talking tomatoes, late blight can be spread from infected potatoes to tomatoes simply by handling one and then the other.
But here are a few tips to lessen the possibility late blight will get you again this year.
- Stake and prune your tomato plants. Keeping the suckers pruned out and the plants off the ground promotes good air circulation. Never stake or prune when the leaves are wet, however, as handling wet plants is a good way to spread the disease.
- The best way to water for more than one reason is drip irrigation. In home gardens, it is easy to do with soaker hoses. These are heavy hoses infiltrated with small holes that allow water to drip directly into the soil at the base of the plants. Overhead sprinklers not only water the leaves, which we are trying to keep as dry as possible, but also wastes water through evaporation.
- Feed with a lower nitrogen fertilizer. High levels of nitrogen mean more leaves and less fruit. Since leaves are the vehicle for the disease, we don't want to encourage bushy plants. Of course, leaves are necessary for photosynthesis and some leaf cover is needed for the fruit so it doesn't suffer sun scald, so be moderate with the pruning and the feeding.
- Be diligent. Keep watch for symptoms and if they are present, take off the offending leaves or stems and destroy them. Do not put them on the compost pile or leave them laying on the ground. Burning is good, but if you can't burn, bury them at least two feet deep.
- Weeds keep air from circulating through the plants, so it goes without saying that your garden should be weeded regularly.
Growers are working on disease-resistant plant varieties. There are plenty of diseases and insects out there ready to prey on our garden vegetables and plants. Late blight is just another we need to learn to control.