When my son was 2 years old, he came running in from the backyard in a panic because "there was a monster outside." I summoned my courage and went out, with him leading the way.

He stopped several yards from where we had tomatoes growing, pointed and whispered, “there.” I had to get closer to see this monster, but sure enough, there it was; a 5-inch long, green, hairless caterpillar with a horn-like apparatus on its backside, perched on what was left of a leaf, one of the last on this ragged-looking tomato plant.

Tomato hornworms (Manduca quinquemaculata) can decimate a plant in short order by defoliating it. Their color makes them difficult to detect among the green leaves and stems of a vigorously growing tomato plant. You are more likely to notice the damage, or droppings, than see the hornworm.

In addition to tomato plants, they can also defoliate peppers, eggplant and potatoes; all members of the Solanaceae family. That’s the bad news. The good news is that these creepy looking caterpillars become beautiful moths with a 5-inch wingspan.

The Solanaceae family of vegetables are susceptible to other problems as well. Last week I told you about early blight and Septoria leaf spot. Today, I will tell you about late blight.

Late blight (Phytophthora infestans) is a killer. It is capable of destroying a tomato or potato crop in very little time. Weather plays a part in the spread of the pathogen, as it can travel several miles in the wind, and reproduces rapidly on wet leaves. This is one of the reasons we recommend that you water plants at ground level instead of from overhead. You can’t do much about the rain, though.

Symptoms of late blight include water-soaked-looking lesions on foliage. Dark lesions may appear on the stalk of the plant as well as the leaves and fruit. If the humid, wet weather continues, the lesions on the stems and leaves may develop white, fuzzy spores.

One of the reasons late blight is so deadly is because the reproduction rate is high. From initial exposure to plant death can take just days. As spores are produced, winds carry them to neighboring gardens and farms. This is one reason we request that if your plants have been diagnosed with late blight, they be removed, placed in a plastic bag and disposed of safely.

Please don’t remove plants that you suspect have late blight until you have a positive diagnosis. Several years ago when we experienced an epidemic of late blight, several people uprooted all their tomato plants and then brought us a sample. It was not late blight, which was fortunate, but not for their gardens.

We do not charge for diagnostics or identification of garden problems or pests you may be experiencing. Bring a sample, including diseased sections and healthy sections, in a sealed plastic bag. In the case of insects, living or dead (but not squished) insects can be brought in any container from which they cannot escape. It may take a few days, depending on the volume of samples we have, but we will get back to you with an ID and your options for dealing with the problem.


Jolene Wallace is the consumer horticulture educator for Cornell Cooperative Extension in Clinton County. Contact her at 561-7450 or jmw442@cornell.edu.

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