This Week, Tomato Spelled With A Why

This week, I’ve been inundated with questions concerning tomatoes: Why aren’t the plants aren’t setting fruit? Why are the blossoms dropping (this may explain why the fruit isn’t setting)? Why are the top leaves are curling? Why are the lower leaves are curling? Why do the leaves look like they’ve been blasted with a shotgun? Why, why, why?

Where do we start?

Why do blossoms drop and those that remain don’t seem to set fruit? If the night temperatures drop below 55 degrees, blossoms may drop. (And we’ve certainly had our share of sub-55 nights.) Some blossoms may also drop if the daytime temperatures reach high into the 90s.

Spraying with the hormone Blossom Set may help keep the blossoms from dropping during cool spells.

Even though tomatoes are self-pollinating and don’t require bees or other insects to pollinate them, cool weather may slow pollination. When temperatures are cool, it may help to shake the branches gently, spreading the pollen.

Aside from temperature extremes, there are other factors that may contribute to the demise of blossoms: not enough water, not enough sunlight or too much fertilizer, especially nitrogen.

What causes the top leaves to curl, turn a dull yellow and the plant to stop growing? This could be a disease called curly top virus. It is spread by leafhoppers. Since there are no cures for the virus, the infected plants should be pulled and destroyed.

What causes blotches on leaves? Perhaps a disease called late blight. This disease attacks all above-ground parts of the plant, starting on the leaves and moving to the stems and eventually to the fruit. It seems to be worse when weather is cool and rainy or when nights are cool and daytime temperatures are less than 85 degrees.

Prune infected leaves and destroy plants if they are badly infected. Curling or yellowing older leaves may be natural. Older curling leaves may be due to heavy rains or a wide variation between day and night temperatures.

Older leaves that turn yellow may be due to age or a nitrogen deficiency. When the soil is cold, nitrogen isn’t picked up by the plants.

What causes dark, scab-like spots to appear on green tomatoes coupled with dark, greasy spots on the lower leaves? More than likely, this is bacterial spot. It affects green tomatoes rather than red tomatoes. The bacterium will attack all parts of the plant, especially the lower leaves. Fruit does not ripen well. It spreads rapidly when temperatures are between 75 and 85 degrees and after heavy rains.

We can spray for this disease with maneb or copper sulfate. Repeated applications may be necessary. Always read the label for amounts and application instructions. Do not work around plants when they are wet.

What causes the bottom of tomatoes to turn black? This is blossom end rot. It’s not a disease, but a cultural condition resulting from a lack of calcium. Alternating wet and dry soil interrupts the uptake of calcium resulting in the blossom end of the tomato rotting.

To prevent blossom end rot, keep plants evenly moist. Once the soil is sufficiently wet, mulch tomatoes with three to six inches of straw or other such mulching material.

What causes the small holes in the leaves? Tiny insects called flea beetles eat small holes in the leaves, giving them the appearance of being hit by a shotgun blast. You can use pyrethrins to control these pests or mulch the soil with three to four inches of straw.

Of course, later in the season, tomatoes can also be attacked by hornworms, anthracnose, sunscald and growth cracks. Despite all these problems, tomatoes are by far the most popular vegetable in the garden. There is nothing more mouth-watering than a vine-ripened tomato, especially served up in a BLT.

If you would like to know more about tomatoes, their culture and varieties, read “Tomato Favorites” by Lois Hole or “In Praise of Tomatoes: A year in the life of a home tomato grower” by Steven Shepherd. Or you can join the National Tomato Club and get all the juice.

Phyllis Stephens is a horticultural consultant and landscape designer in Spokane.

, DataTimes The following fields overflowed: CREDIT = Phyllis Stephens The Spokesman-Review