Tomato problems

Asked June 24, 2016, 12:28 AM EDT

Attached are some pictures of several different tomato plants. I can't figure out the problem that's causing them to curl. Thanks, Tom Porter

Placer County California

1 Response

Your tomato have been damaged by herbicide; this may occur in one of two ways: Spray drift when weeds were treated, or by herbicide carryover in organic materials added to or on the soil, among them manures, composted or not.

Unfortunately, this has been a widespread problem across the country for a number of years.

The underlying situation is that one of several different agricultural herbicides were used against broadleaf weeds in such crops as pastures or grain fields. (Such contamination has also occurred in commercially packaged composts and potting mixes.)

When livestock feed on the grass or grain, these herbicides survive the trip through the animals’ guts and are excreted in the manure which is then composted. In order for the chemicals to be inactivated, the manure must be hot composted for a year before use in gardens.

Here are several helpful resources which describe how the damage occurred; how to verify the contamination via a simple bio-assay; and what you can do to remedy the situation.

- Page 3 of “Herbicide carryover in hay, manure, compost, and grass clippings” describes an easy bio-assay you can do:

- Numerous images of various affected plants as well as informative text (via the menu at left of the page) including a bio-assay are in “Herbicide Contamination Organic Matter”: (

As a safety measure, I now suggest gardeners do a bio-assay prior to using any composted materials obtained from other sources.