Gardeners, growers urged to guard against Late Blight

July 20, 2004|by BOB KESSLER/Penn State Extension Office

Late Blight is not usually a disease that we concern homeowners with, but this year is an exception.

Late Blight has been found in several counties in Pennsylvania, the closest being York.

Conditions have been perfect for the development of Late Blight in Franklin County, and homeowners with potatoes and tomatoes should take some protective action.

Late Blight was the disease that caused the Irish Potato Famine in 1840. It is a fast-acting disease that affects the foliage, fruits and tubers of tomatoes and potatoes. It produces millions of spores that easily blow on the wind to new areas up to 50 miles away.

Late Blight has been in our area before, but this time it's much earlier in the growing season.

Vegetable specialists in our office and at the University feel sure that Late Blight is in our area. Since it is a very serious disease, we encourage homeowners to take protective action against Late Blight. We recommend that commercial growers do the same.


Gardeners should scout their gardens looking for Late Blight symptoms.

Keep in mind that spots and dead leaves are not unusual and are not Late Blight. What you are looking for, especially on the lower part of your plants, are leaf lesions that look like water-soaked spots.

These will enlarge rapidly into pale green to brown lesions and cover large areas of the leaf. In moist weather, the underside of the leaf may be covered in gray or white mold.

Fruit lesions appear as dark, firm, greasy-looking spots that may cover the entire fruit.

You can find photos of Late Blight on the Web. One good Web site is

If you find Late Blight in your garden, the plant should be destroyed and not put in a compost pile.

We recommend that gardeners use a protective spray on their potatoes and tomatoes in their garden. Be sure to get good coverage of the lower leaves of the plant.

Use a product that has Chlorothanil, such as Fung-onil, Daconil, Bravo or a product that has fixed copper, such as Liquid Copper, Kocida, Tri-Basic or Champion.

Follow the schedule that is on the label and if we have heavy rains, you may want to reapply your spray sooner than your schedule calls for.

Squash vine borer

If you have squash, pumpkins or gourds that wilt in your garden, you know it can't be a result of drought right now.

One possible reason is the squash vine borer. Caterpillars of the moth will bore into the stalk of pumpkins, squash and gourds and feed on the tissue.

This will cause the vines to weaken and collapse. They can destroy a pumpkin patch very rapidly.

The dull red eggs are laid by a moth that may look like a wasp.

When the eggs hatch, the caterpillar bores into the stem and leaves sawdust-like material at the entrance to the hole.

Homeowners spotting the sawdust material may have some success controlling the borer by immediately using a sharp knife to split open the vine and cover it with soil. Be sure the knife is clean when you make your cuts.

The borers can be prevented by using a protective spray of carbaryl (Sevin). The spray should be applied on the stem as soon as the sawdust-like material is noticed to prevent any further borer action.

Repeat the spray in seven days. There can be more than one generation, so keep monitoring through August.

Be careful of the use of Sevin around pollinators, as it can be very hard on bees. Time your sprays when there are no blooms in the area.

Bob Kessler is an Extension agent, specializing in farm and garden, for Penn State University. He is based in Franklin County, Pa. He can be reached weekdays at 1-717-263-9226.

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