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Margaret Lauterbach: Gardeners are reporting tomato plant deaths

For several years, I exerted extra efforts to thickly mulch tomato plants with our own grass clippings. This year I had other obligations, so I did not mulch them, and I’m seeing the real value of that mulch: I’ve lost four plants and am losing a fifth in my tomato patch of 39 plants, chalking the losses up to blight. Missing the thick mulch, rains now can splash water and disease organisms from the soil onto plants, infections previously prevented by the mulch.

Many folks in the Valley are reporting deaths of tomato plants. Liz Vavricka, plant pathologist with the Idaho Department of Agriculture, thinks it could be a seed-borne problem instead of blight. Most of the dead plants she’s examined were killed by bacterial blight.

(Dr. Krishna Mohan, plant pathologist with the University of Idaho extension service in Parma, retired last spring, and Vavricka agreed to fill in, diagnosing problems until a replacement is hired for Dr. Mohan.)

She said all but one of the dead tomato plants she’s seen this year have been killed by one of the Clavibacter michiganensis subspecies of bacteria. These bacteria attack plants at wound sites, water-emitting pores or are already resident in the seeds of the tomato when planted. When bacteria build up sufficiently in a plant, they clog the whole vascular system of the plant, causing its death.

That is, even though the disease starts with the seed, it’s not toxic enough to kill the seedling or even the small version of the plant, but by the time the plant grows larger, bacteria have multiplied enough to do the damage.

Fungus diseases such as Verticillium and Fusarium also attack the vascular system of the plants, but those should show as a dark interior ring just below the surface of the outer sheath of tissue. There was no indication of either of those soil-borne diseases in my plants.

Vavricka advised destroying the plants (not composting them, but sending them to the landfill), and destroying any leftover seeds of the variety showing such symptoms. She said these bacteria are causing major problems among tomato seed vendors.

In my garden, the plant leaves cupped, turned yellow and died rather rapidly. I examined the undersides of leaves to see if the cause might be psillids, but I never saw a single tiny insect. Veins had not turned purplish or leaves leathery, so no signs of curly top virus. All of the images I’ve been able to find of tomato plants killed by the C.michiganensis bacteria have shown brown, crisp leaves. There are numerous allusions online to psyllid yellows, but few images. Cupped leaves are one indication of psyllid poisoning, apparently. I did not use a hand lens to look for insects on my plants, but should have. Psillid yellows may be a cause of death of some tomato plants, at least in my garden.

Squash bugs

In the past few years I’ve had terrible infestations of squash bugs. This year it’s not as bad, and I credit these reasons: 1) I’m mainly growing winter squash, less attractive to squash bugs than summer squash, 2) I’m growing them in other locations than in the past and those growing in one of my raised beds are planted with cucumbers, and squash bugs are not very fond of them, 3) the summer squash I’m growing is only one variety: Zapallito del Tronco.

Zapallito del Tronco squash is often sold as a winter squash, because you can let it grow large and use it as a winter squash. If you pick it when it’s hardball or softball size at the most, the flesh is tender, the texture almost avocado-like. The fruits are green, shaped like small pumpkins. Seed is hard to find, but two sources I know of are Irish Eyes Garden Seeds in Ellensburg, Wash., and Sand Hill Preservation Center, Calamus, Iowa. I don’t know whether squash bugs don’t move in quickly on that summer squash because it is usable as a winter squash, or because they just don’t like it. It has an upright growth like summer squash. I decided to grow it for summer squash this year because in the past I’ve noticed that’s the last one squash bugs attack.

Look at your winter squashes now, and try penetrating them with a thumbnail. I’ve picked several butternuts and the three large climbing zucchini a week ago because I couldn’t penetrate them with a thumbnail. Last year I picked several about this early for the same reason, and the plants proceeded to set an entire new crop that matured in our long autumn. Mind you, we may not have that luxury this year; I keep hearing reports that fall is coming early in the high country.

Send garden questions to melauter@earthlink.net or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.