Twisted tomato plants are distorted from afar

A gardener I know asked me to look at her tomato plants. She was concerned they were diseased or perhaps she may have damaged them by applying fertilizer during a hot, dry day.

One look and I could see immediately by the tell-tale symptoms that the tomato plants were damaged by a weed killer, specifically the herbicide 2,4-D.

Plants produce growth hormones called auxins that are necessary for plant growth and development. The formation of stems, leaves, flowers, roots and all other plant parts is regulated by auxins. These plant hormones do their work at extremely minute concentrations.

2,4-D is a synthetic plant auxin and as such, works by disrupting normal plant functions. It was developed in the 1940’s to kill broadleaf weeds such as pigweed, lambsquarters, dandelions, etc. while leaving grasses such as corn and turfgrass unharmed.

This chemical is found in a lot of weed killer formulations used by both farmers and homeowners. Farmers traditionally use it on corn while homeowners apply it to their lawns as a weed killer, often in the form of “weed and feed”.

“How”, my gardener friend asked, “did herbicide get on my tomatoes?” The short answer is “drift”. The herbicide drifted through the air from somewhere over to her garden where it did its damage on what researchers call “off-target crops,” in this case her tomatoes.

There are different types of 2,4-D --  most are quite safe, but others, under certain circumstances, can volatilize into vapor.

The 2,4-D volatilized vapor particles rise into the air and float in place. If the air gently moves as a mass, it will carry the herbicide with it. Warm air and calm winds create the perfect conditions for herbicides to slowly drift without dissipating. Ultra-fine droplets formed during spraying can be suspended in the air  drift and often causing more severe damage than vapors.

Farmers usually allow a 200-300 feet safety buffer zone between their target crops and other off-target crops. Most drift occurs well within an eighth of a mile. If the weather conditions are just right, drift from farms can travel several miles. Distances that long are quite rare however. This most often  occurs during the calm of the evening.

Since auxins work at such low concentrations, it doesn’t take very much 2,4-D to cause damage especially on very sensitive crops like tomatoes or grapes.

In the case of my gardener friend, it was a mystery where the herbicide drifted from. Since she lives in the country, the nearest neighbor is 300 or 400 feet away with heavy shrub growth between them.

We finally concluded it came from the neighbor across the street. He is very fastidious about his grass and has not a single dandelion on his property. He must have sprayed a liquid formulation onto his lawn that then volatilized and eventually drifted over. However that is all conjecture and circumstantial evidence.

It’s early in the season and her tomato plants probably were exposed to a small dose, so hopefully they will grow out of it with a just small reduction in yield. I hope that is the case since some of those plants are rare heirloom varieties not available to the general public.

We also see this kind of damage on vegetable plants when gardeners use grass clippings from treated laws as a mulch around their plants. Be very careful when others offer you grass clippings to use in your garden, even if they insist the lawn has not been treated.