I would appreciate a little help with my tomatoes. Last year, I planted five plants – two cherry and three large (I cannot remember which variety). The cherry tomatoes produced wonderfully but the others – though they produced lots of flowers – did not set fruit.

I looked closely at the flowers and it seems like there's a clean little cut a quarter of an inch from the blossom.

I have not seen any worms or insects of any kind! What could be making those cuts? Please let me know your thoughts.

– Audrey Morse, Lincoln

That "cut" wasn't made by an insect. It was just the plant dropping the blossom before it was pollinated.

According to UC Master Gardener June Bliele, tomato flower drop can occur – usually early in the season – for many reasons.

Cold nights in the spring, high temperature in the summer, low light intensity and smog can all reduce fruit set. So can dry windy conditions or excess nitrogen fertilizer.

Tomatoes require temperatures above 55 degrees F and under 90 degrees, and a minimum of six hours a day of full sun.

The application of a growth hormone, available at most nurseries, may be of some help when the temperatures are too low, but it will not be effective when applied in the high heat of summer. Be sure to use as directed on the label.

We need some help to figure out what is plaguing our 10-year-old lemon tree's fruit this year.

We have had some freeze-affected lemons that – when opened – show a dry, separated internal structure. But we find in other lemons that were not frozen a very odd material inside.

These lemons on the outside look perfect; no signs of defect in the outer skin. However, when we cut them open, we find in the center a black, moist-looking accumulation. It's only in the center.

The outer parts of the segments are normal, clear and juicy. We looked for a defect in the skin at the stem, which might allow what looks like mold to enter. But we found nothing at the stem or the bottom end.

What in the world is this? We have had this tree's lemons for 10 years through several bad freezes but nothing like this before.

Would you be able to give us an explanation and, more important, how to prevent it from reoccurring now on the good lemons left on the tree and in the future?

– Bill Kassel, Sacramento

In Peggy Mauk's "Questions and Answers to Citrus Management," she identifies the disease in your lemons as Alternaria black rot. This is a fungus condition that typically enters the fruit through the blossom end.

It is wind-born and tends to be a problem when trees are stressed. It occurs more frequently when warm rains follow severe winds. There is no control for this disorder. But it won't kill your tree and may not infect future crops.

Clean up any fallen fruit under your tree and concentrate on keeping the tree healthy, watered and stress-free.

GARDEN QUESTIONS?

Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties.

Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h&g@sacbee.com. Please put "Garden Detective" in the subject field and include your postal address. To contact your UC Extension directly, call:

• Sacramento: (916) 875-6913; 9 a.m.-noon and 1-4 p.m. weekdays

• Amador: (209) 223-6838; 10 a.m.-noon Monday through Thursday; email ceamador.ucdavis.edu

• Butte: (530) 538-7201; 8 a.m.-noon and 1-5 p.m. weekdays

• El Dorado: (530) 621-5512; 9 a.m.-noon weekdays

• Placer: (530) 889-7388; 9 a.m.-noon on Tuesdays, Wednesday and Thursdays or leave a message and calls will be returned

• Nevada: (530) 273-0919; 9 a.m.-noon Tuesdays through Thursday or leave a message

• Shasta, Tehama, Trinity: (530) 225-4605

• Solano: (707) 784-1322; leave a message and calls will be returned

• Sutter, Yuba: (530) 822-7515; 9 a.m.-noon Mondays and Tuesdays and 1-4 p.m. Thursdays

• Yolo: (530) 666-8737; 9-11 a.m. Tuesdays and Fridays, or leave a message and calls will be returned

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