Catch my Drift? Herbicide Drift, Curling Tomato Leaves, and Food Safety

There’s all kinds of maladies that can strike your garden plants throughout the season- diseases, insects, negligence, and more.  But one common issue we are seeing more and more here in the corn belt and other places with lots of crop production is herbicide drift.  Of course, you don’t have to have a corn or soy field nearby to have issues with drift – it can happen anywhere and anytime an herbicide is applied and proper precautions aren’t taken, even when you or a neighbor are just treating a small area in the yard.  There are other avenues of herbicide damage on plants as well, such as using herbicide-treated grass clippings as mulch in the garden.

 A wide variety of plants can be damaged by herbicide drift from a variety of different products – trees, shrubs, roses, vegetables, and more.  The damage can be slight to severe, and unless the dose is large most plants will grow out of the damage.  Vegetables and fruits, though, are of particular concern due to the potential food safety risk from residues of unknown herbicides on the plants.  Therefore, it is especially important to be able to identify signs of herbicide drift and take the appropriate course of action which is usually and unfortunately removal of the plant from the garden. 

I have to remove the plants!?!?

Yes, you read correctly, I said removal of the plant!  I, along with many of my extension colleagues, encourage gardeners who have drift or herbicide damage on their plants to remove them from their gardens. Why take such a drastic measure, especially if the plant may actually recover and “grow out” of the damage?  The answer is mainly one of safety.  Since it is likely impossible to know exactly which chemical or product formulation was used there’s no way of knowing if the product is safe to use on consumable crops, whether its residue is safe, or whether it is systemic and has a residual effect.  A gardener cannot know if there is a pre-harvest interval where the crop will be safe after a certain passage of time or if it will never be safe.  And even if you do know the product (let’s say you were the one that used it or you know what is being used by the neighbors) it is likely that there won’t be safety information for use on fruit and vegetable crops, since we don’t typically apply herbicides to plants we want to keep growing.  You should also remember that application of such herbicides to fruit and vegetable crops, even if accidental, technically constitutes an off-label (and illegal) application of an herbicide to a non-target crop or pest. 

What are the most likely fruit and vegetable plants to be damaged from herbicide drift?

While just about any plant can be damaged by herbicide drift if enough herbicide gets on the plant, there are a few plants that seem to be more susceptible to herbicide drift.  This means that these plants exhibit damage with smaller doses of herbicides than others and will show damage while other plants nearby remain unfazed.  The plant that we get the most calls about are tomatoes.  This is the vegetable garden crop that is the most susceptible to herbicide drift and just so happens to be the most widely planted crop in the garden.  The other edible crop that seems to be highly susceptible to herbicide drift is grape.  While grapes aren’t nearly as common as tomatoes in home gardens, wineries in regions with high herbicide use rates are struggling to keep their vineyards going due to the damage.

I live nowhere near a big farm, how do I keep getting drift damage?

Of course, drift can come from anywhere, even a small application of herbicide on a neighborhood lawn or garden.  But under the right weather conditions (high temps and wind) some herbicides like dicamba can volatilize and drift for 2-3 miles or more.  Even if you think you live nowhere near a farm or other area where herbicides might be used you can get drift from miles away.  This makes it hard to pinpoint where the damage is coming from in order to sleuth out what exactly was used.  This is especially tricky here in our area where the city of Omaha is surrounded on all sides by farmland, and even has pockets of productions fields sandwiched between residential areas.  Unfortunately, one of the prime herbicide application times in our region is shortly after most gardeners plant their tomatoes so we get lots of calls and questions that end up being drift.  Thankfully there’s usually still time to replant tomatoes, but it isn’t fun telling people that started plants of their favorite or special varieties that they’ll have to rip them out and go buy new plants. 

The kicker is that drift can be random.  It can be one or two plants out of a bed of twenty, or one plant on one side of the garden and another somewhere else, or an entire field full of plants.  It just really depends on the wind patterns and concentration of herbicide. 

Is it drift?  Or is it something else? 

At first glance it can be hard to tell if an issue is drift or something else since the signs can look like some other problem until you get up close.  There are a wide variety of herbicides on the market and therefore there can be lots of different signs.  The most common types of damage you’ll see are light/white colored and necrotic spots from exposure to broad-spectrum herbicides like glyphosate, and curling, twisting, stunting, yellowing, and epinasty from broadleaf herbicides like 2,4-D and dicamba.  Epinasty is an unusual, twisting growth pattern on the leaves that result when one layer of the leaf (usually the upper layer) grows faster than the other.  You can get weird strappy looking leaves, weird margins, and other irregular growth patterns.  The damage from broadleaf herbicides can sometimes be mistaken for heat or drought damage, viral diseases, or even excess watering, all of which cause leaf curling of some sort.  I’ll share a few tomato pictures below to demonstrate herbicide damage vs other types of leaf curling.  For a great pictorial guide to herbicide damage symptoms, check out this resource form the University of Tennessee. 

Can you avoid drift?

Unfortunately, you can only control drift from the herbicides you apply yourself.  Pesticides such as herbicides can be used safely and effectively if used appropriately.  Reading and following the label instruction is important and is the law, paying special attention to wind speed, temperature, and application equipment, e.g., how fine of a mist does the nozzle create.  Drift from the neighbors’ lawn treatment or a nearby farm is really outside of your control, so being watchful for signs of drift is important.  Sheltering susceptible crops, like tomatoes, using something as a windbreak might be helpful.  As this journal article points out, a windbreak or vegetative buffer around wetlands offers some protection and I noticed a similar effect recently in one of our Master Gardener project gardens.  Our Master Gardeners grow thousands of pounds of produce a year for local food banks, and on a recent visit I noticed that about 25 percent of their tomato plants were showing signs of drift (and they were removed and replaced).  The pattern was interesting – the only plants damaged were the ones on the outside edge of the garden and the ones along wide walkways in the garden.  But plants in the interior were spared.  So perhaps planting less susceptible crops on the exterior of the garden and along walkways to act as buffers might work. 

And while it isn’t useful for home gardeners, specialty crop producers (like those all-important wineries) and beekeepers can register for a program called DriftWatch where they can be informed when spraying will take place on local farms.