Garden Detective

Triple-digit days can lead to tomato problems

The infamous tomato hornworm is the larval form of a large night-flying moth, the hawk moth.
The infamous tomato hornworm is the larval form of a large night-flying moth, the hawk moth. MCT

Experts tackle readers’ garden questions.

Q: I was quite saddened and disappointed this morning when I went out to water my tomato plants and found so many with blossom end rot – little tomatoes and large ones. My plants are all in pots (about eight of them), one big barrel, four in large pots and the rest in pots a bit smaller. I don’t feel I am watering them too much. Most of them I do by hand watering every morning and a few are on a drip. I don’t know what to do to stop this problem. The leaves are curling and drying out. I have read about this on the internet, but again, I don’t feel I am overwatering. Every day, the dirt is dry.

Also, another big problem is I must have several nasty worms out there, because I see their droppings and the leaves being eaten up. We are out there with a magnifying glass and a flashlight trying to find the culprits but have had no luck so far.

Laura Courson, Sacramento

Bee garden writer Debbie Arrington: There will be a lot of blossom end rot after our recent heat wave.

Your tomatoes are not getting enough water. The heat and lack of water is also burning and curling their leaves.

This is really common with tomatoes grown in containers. During triple-digit weather, your tomato plants each need a gallon a day, preferably in the early morning. Your drip system is not giving them enough moisture.

Blossom end rot, which looks like a brown spot or lesion on the blossom end of a tomato, is linked to calcium deficiency. Calcium is water soluble and the plant needs moisture in the soil to access the calcium it needs to form the tomato’s skin and plump cells. When it can’t reach that calcium, the brown spots occur.

In our area, blossom end rot is almost always due to inconsistent soil moisture while the fruit is forming, usually because there was not enough water instead of too much. The soil should be kept evenly moist (not soggy) and not allowed to dry out completely. (On the other extreme, this problem can also occur if the plant is basically standing in water all the time.)

Give your tomato plants a deep soaking, then cover their soil with mulch to retain moisture. Make sure the water is getting into the root ball and not just running down the insides of the pot. Then, as long as the weather is above 95 degrees, water them with a gallon a day. Once temperatures cool off, water them every other day.

The key is consistency. The next round of fruit should be fine.

Find more information on blossom end rot at the University of California’s integrated pest management website, ipm.ucdavis.edu.

As for the caterpillar, it sounds like a tomato hornworm. Green in color, hornworms camouflage themselves amazingly well and eat day and night. This is one of the largest caterpillars we encounter, often growing to 4 inches long. One hornworm can defoliate the whole tomato plant!

You don’t need a flashlight to find one, just patience and a garden hose. They often hide under leaves or go vertical along a stem. Look for the dark frass (or bug poop) on leaves, then spray water on the plant in that general vicinity. The hornworm will start thrashing around to escape the water spray and give away its location. Then, dispose of the hornworm as you see fit.

The hornworm becomes a large brown hawk moth; it’s equally impressive with a 5-inch wingspan. More information on hornworm control is available at the UC IPM website.

Bee garden writer Debbie Arrington is a consulting rosarian and lifelong gardener. 916-321-1075, @debarrington

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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 UC Extension directly, call:

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