Late tomato blight is here again

The most frequent question at the Master Gardener green line on Tuesday mornings is "What's wrong with my plant?" The simple answer is the weather.

We are experiencing the right weather conditions this year for severe infections of rusts, mildews and blights.

The most worrying disease at the moment is the late blight of tomatoes and potatoes. As of early last month, the disease had already been confirmed in 15 counties across Pennsylvania.

Late blight epidemics often start in home gardens where fungicides are less apt to be used.

When the disease develops unchecked, large quantities of late blight spores are produced and released into the air.

During moist weather, the spores can survive and be transported up to 50 miles on air currents to infect other plantings of tomatoes and potatoes. During favorable weather conditions, unprotected foliage can be infected in three to six hours; symptoms can appear within a week.

Those symptoms can expand rapidly during cool, wet weather and cause entire plantings to die within two weeks of infection. The disease is held in check by hot, dry weather.

When late blight appears, the entire plant is infected including the fruit, and should be pulled out and destroyed. The blight can overwinter in compost heaps, in plant debris, in cull piles of tomato and potato.

Therefore, every part of the plant must be removed and bagged for trash. It is important to search the ground around the plants for dead plant debris that could give the blight a winter home.

Remove all the roots in a clump, and don't shake loose the soil in the root ball. You may inadvertently shake loose plant material with the dirt.

The good news is that the blight doesn't survive in the soil if the entire infected plant is removed root to leaf. However, it is good practice to plant your tomatoes in a new location in following years in case any blighted tissue was left behind.

As a home gardener, it's important to deal with late blight by protecting your tomato plants. Fungicide sprays are the only sure way to avoid the devastating disease.

If you use chemical sprays in your garden, look for a fungicide labeled to prevent late blight in home vegetable gardens and use it according to the instructions. If you are an organic gardener, use a spray or dust containing copper.

You can get the blight from airborne spores, but there are other preventive measures you can take.

Blight can be brought into your garden by infected seed potatoes or infected plants from a nursery or box store.

If you have potato blight, bag up and throw away your potatoes. Don't save any for seed potatoes. Buy certified seed potatoes from a reputable source. Ask your nursery if the tomato plants you are buying are blight resistant.

Plant diseases can seldom be prevented, but they can be controlled and contained. Whether it is late blight, or the more familiar rusts and mildews, the most important thing is to prevent spores from forming and going into the air. You must learn to be a scout with an eagle eye for first symptoms.

Every home gardener has the potential to be a source of disease for friends and neighbors by neglecting infection in the garden.

When the first symptom of plant disease is detected, the next thing to do is scout around your landscape to see if any other plant is showing the same symptom.

Check weeds as well as domestic plants. An infected weed may be the source of the disease.

If you can't identify the disease, take a sample to the Penn State extension office in Jim Thorpe, and the Master Gardeners will send your sample to Penn State for analysis.

Don't spray all your plants with a one size fits all fungicide. It's expensive, and it can cause the disease organism to become resistant to the chemical in the spray.

Once the disease is identified, the next step is to determine whether it is something the plant can cope with on its own, or if it will kill the plant.

In the case of powdery mildew, the disease will eventually destroy bee balm and summer blooming phlox.

If you want to grow these plants, select disease resistant varieties, practice good sanitation and remove and destroy any leaves showing symptoms.

Peonies and sedum can also get a bit of powdery mildew and cope with it on their own. Since each strain of powdery mildew is host specific, the disease on your sedum won't infect your other garden plants.

For more information contact the Carbon County Penn State Extension Office at 570-325-2788 or by email at CarbonExt@psu.edu.