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Plant Answer Line Question

Keywords: Verticillium, Tomatoes--Diseases and pests

I was just outside checking on the slow ripening progress of my tomato plants and noticed something that has me concerned. There seems to be a fungus or mold at the very base of my "super fantastic" tomato plant. Other than this issue and the slow ripening the plant seems to be doing okay. I haven't noticed this fungus/mold before so I don't know if has just appeared and is spreading rapidly or if it has been there all along. Do you know what it is? Will it spread through the entire plant? Will it spread to the other tomato plants and veggies in this bed? Should I remove the entire plant?


This sounds a lot like Fusarium wilt, but it could also be Verticillium (another fungal problem) or even walnut toxicity (do you have any black walnut trees within 50 feet of your plants?). It might even be excessive watering which is causing the problem.

According to The Organic Gardener's Handbook of Natural Insect and Disease Control edited by Barbara Ellis (Rodale, 1996), you can cut open a stem near the soil line and look for internal discoloration. Verticillium affects the whole plant, while Fusarium will start by infecting individual shoots and then spread. Tomato Fusarium only affects tomatoes, while there are numerous plants which are susceptible to Verticillium. The best thing to do if your plant is suffering from these fungal diseases is to destroy them, so you may want to take a sample to a Master Gardener Clinic for diagnosis before you do anything drastic.

General resources on tomato problems:

Recognizing Tomato Problems from Colorado State University Extension.

Vegetable MD Online from Cornell University.

University of California, Davis Integrated Pest Management has excellent pictures of the insides of the stems, for comparison.

Date 2019-05-03
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Plant Answer Line Question

Keywords: Tomatoes--Care and maintenance, Lycopersicon, Tomatoes--Diseases and pests

It's midsummer, and I have a bunch of healthy-looking green tomato plants without any fruit. Shortly after I planted the starts, the flowers developed, and promptly fell off, taking a bit of the stem-end with them. The spot where I've planted them is in full sun, they have good soil, and they get watered as they should. Any idea what might be going wrong?


The problem which most closely resembles your description of what is happening with your tomato plants (flowers falling off shortly after planting, and taking a bit of the stem as they drop) is called 'blossom drop.' According to D. G. Hessayon's Vegetable Expert (PBI, 1990), blossom drop occurs when pollination fails to take place, and there is dryness at the roots or in the air. There is no treatment for this malady, but watering regularly, spraying flowers in the morning, and tapping the plants to aid pollination are preventive measures. Attracting beneficial insects to your garden will also help with pollination.

Here are links to more information that may be useful to you:

  • University of California Integrated Pest Management pages on tomato problems and pollination
  • Washington State University - Spokane County Extension: Why Blossoms Fail. Note also that WSU Extension in Spokane County says cool night temperatures may cause blossom drop.
  • University of Illinois Extension: "Tomato blossom drop is very common with high summer temperatures. Tomatoes will drop blossoms when daytime temperatures in the summer are above 90 degrees F. Blossoms will also drop earlier in the growing season when night temperatures drop below 55 degrees F."
  • This article from about.com provides a lot of detail about the problem and how to prevent it:
    Blossom drop can be attributed to several causes, most often related to either temperature and/or stress.
    1. Temperature too high or too low
    2. Lack of pollination
    3. Nitrogen: too much or too little
    4. Humidity too high or low humidity
    5. Lack of water
    6. Stress from insect damage or disease
    7. Too heavy fruit set

    This article recommends planting varieties known to do well in your climate, ensuring pollination, avoiding over-fertilizing, taking note of humidity levels, and watering deeply once a week in dry weather.

Date 2019-05-23
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Plant Answer Line Question

Keywords: Tomatoes--Diseases and pests, Nicotiana, Honeybees and pollinators

I am about to plant Nicotiana mutabilis seeds, and I wonder: if neonicotinoid insecticides are harmful to bees, is the pollen in Nicotiana also harmful? Also, is it a bad idea to plant Nicotiana near my tomatoes (could it spread tobacco mosaic virus)?


Although neonicotinoids are not currently implicated as a direct cause of Colony Collapse Disorder, the Xerces Society for Invertebrate Conservation's "Are Neonicotinoids Killing Bees?" says that "recent research suggests that neonicotinoids may make honey bees more susceptible to parasites and pathogens, including the intestinal parasite Nosema, which has been implicated as one causative factor in CCD." The brief summary of the full report on this issue is well worth reading.

I doubt whether the pollen or nectar of the ornamental plant Nicotiana has the same properties as a formulated systemic pesticide which contains a synthetic form of nicotine. For an example of the ingredients in a neonicotinoid pesticide, see this fact sheet for Imidacloprid from the National Pesticide Information Center. I found a scientific article ("The effects of nectar-nicotine on colony fitness of caged honeybees" by N. Singaravelan et al., in Journal of Chemical Ecology, January 2006) which says that the floral nectar of Nicotiana species and of Tilia cordata contains trace amounts of nicotine. The authors concluded that "results indicate that honeybees can cope with naturally occurring concentrations of nicotine, without notable mortality, even when consumed in large quantities for more than 3 weeks."

As for your other question, Nicotiana does sometimes get tobacco mosaic virus, though the National Garden Bureau (in a link no longer available online) says the plant seldom has much trouble from it. Still, it is probably a good idea to keep some distance between your Nicotiana and your tomatoes (and any other solanaceous plants, like potato, eggplant, pepper) just to be on the safe side, or at least be sure to change gloves and clean tools after handling the plants. The main method of transmission of tobacco mosaic virus is "mechanical," that is, by handling a plant with the virus and then handling plants that are susceptible to it.

Date 2020-01-18
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Plant Answer Line Question

Keywords: Tomatoes--Diseases and pests, Mosaic diseases

My unripe green tomatoes ('Old German' variety) have developed a very weird appearance: lots of lumps and bumps, and nooks and crannies, plus strange discolored blotches. What is causing this? And will I be able to salvage (and eat!) them?


There may be more than one problem here. I definitely see a physiological disorder called cat-facing in the photo you sent us. University of Massachusetts Extension provides this information about it:
"Cat-facing is a physiological disorder of tomatoes. Cat-face originates in the early stages of flower bud development and is the result of abnormal development of plant tissue between the style and ovary which results in misshapen fruit. Other impediments to flower bud development can also result in cat-facing. The syndrome is related to unfavorable growing conditions, in particular several days below 60 F when the plants are young. High levels of soil nitrogen and excessive pruning aggravate the problem. Accidental exposure to phenoxy herbicides can also lead to malformed fruit. Cat face is more prevalent on large-fruited, fresh market tomato varieties. Good growing practices, especially temperature control, should be followed in greenhouse production of field transplants. Excess nitrogen, aggressive pruning, and accidental exposure to hormonal herbicides should be avoided."

The book Epic Tomatoes by Craig LeHoullier (Storey Publishing, 2015) says that catfacing occurs more often in large varieties that also have large blossoms. Some older varieties (heirlooms) have this tendency. Plants put out in the garden when it is too cool can also develop this appearance later. And too much nitrogen worsens it. As early as the 19th century, plant breeders were attempting to breed out this characteristic in favor of more uniform, smooth-looking fruit, but many heirloom tomatoes much-sought for their flavor tend to have this bumpy look. A little bit of catfacing shouldn't render your tomatoes unusable. I have grown Cherokee Purple tomatoes that often have some cat-facing, but they are still delicious.

Depending on the cause of the spots, the tomatoes may or may not develop to the point of ripeness and if they do, there may be some parts that rot and some parts which are still edible. Also depending on the cause, you may decide to pull out any affect plants and dispose of them.

It's possible that those discolored spots are due to sunscald, but the pattern of the discoloration looks more like a virus. LeHoullier says that plants which are heavily pruned or have lost a lot of foliage are more vulnerable to sunscald. However, the discoloration on your tomatoes resembles a mosaic virus, such as tobacco mosaic virus. If you are growing Nicotiana in your garden, debris from that plant as well as tomato plant contact with any tobacco products (cigarettes, or the hands that have held them, etc.) could introduce the virus to your tomatoes through any small wound—such as a pruning wound or accidental damage to plant tissue.

Washington State University Extension’s HortSense webpage has useful information on mosaic viruses as does University of Minnesota Extension.

Still, the best thing to do is bring samples to your local Master Gardener Clinic. Many tomato problems look similar (viral, bacterial, stink bug damage, hornworm feeding). There is a good visual guide from Missouri Botanical Garden but an in-person diagnosis is best.

Date 2019-10-30
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Plant Answer Line Question

Keywords: Tomatoes--Diseases and pests, Soil amendments, Plant-water relationships

It's summer and my husband wants to add lime to our soil because some of our tomatoes have blossom-end rot. He thinks this will correct the problem. I think we would do better to make sure our tomatoes aren't drying out, and then work in soil amendments next time around. Also, couldn’t we use eggshells for calcium instead of lime? We have a ready supply from our backyard chickens!


I think you are on the right track. Blossom End Rot (BER) is a physiological disorder that tends to affect larger tomatoes rather than smaller ones. According to Craig LeHoullier’s book Epic Tomatoes (Storey Publishing, 2015), some varieties are especially susceptible: "Roma/paste varieties, and some of the longer indeterminate sauce types like Opalka and Speckled Roman. Adverse growing conditions [such as drought stress or low calcium levels] can make it problematic for many other varieties as well."

All print and web sources I consulted mention environmental conditions as a cause of this problem. It starts through the supply of water and calcium in the developing fruits. The effects may be seen on plants exposed to a period of drought during rapid growth; root damage; heavy, wet, or cold soil; excess salt in the soil.

A soil test is the ideal starting point to make sure the pH is adequate for tomatoes. Epic Tomatoes recommends amending the soil with lime if necessary. (Washington State University Extension says the time to do this is 2-4 months before planting, not in the middle of summer!) Mulch around the base of the plants to conserve soil moisture during hot spells and water regularly. Another reason a soil test is a good idea is mentioned by British Columbia author Linda Gilkeson in her book Backyard Bounty (New Society Publishers, 2011):
"Your soil might have enough calcium, but it isn't available, or the plant can't take it up fast enough. This is often because the movement of calcium inside the plant has been inhibited by drought stress, possibly from irregular watering. This is often seen on tomatoes in containers that experience alternating dry and wet soil. It can also be caused when plants grow too fast as a result of too much nitrogen fertilizer."

Since you prefer not to use lime (the dry powdery texture of calcium carbonate can be irritating to the skin and eyes), you will be pleased to know that the use of eggshells is mentioned by Mike McGrath in You Bet Your Tomatoes! (Rodale Press, 2002). At planting time you can "put some crushed-up eggshells into the planting hole." Make sure the eggshells are ground to a fine consistency.

Don't forget that those damaged tomatoes can still be used--just cut off the bad parts!

Date 2020-01-31
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