Herbicides Don’t Just Kill Weeds
In the last post, we looked at biological cascades in ecosystems. We saw that seemingly unrelated activities are linked together through complex food webs. Living creatures that seem unrelated at first glance turn out to be so dependent on one another that what benefits one species can benefit many. Likewise, what hurts one can hurt many.
Days after writing that post, I personally witnessed a disaster I had only heard others experience in the past. First, the alfalfa in neighboring farms wilted suddenly. Then, we saw leaves on the new saplings in our orchard turn yellow. Soon, the apple trees began growing long, yellow shoots. The peach leaves turned brown. The plants in the vegetable garden each responded differently, but all of them looked bad.
The leading hypothesis is that that the crop dusters many of us saw flying days earlier sprayed herbicide mixes used for shrub control on the surrounding rangelands. A temperature inversion and a change in wind direction carried the spray into the valley, where farming is dominated by small acreage farmers that produce hay and vegetable crops.
While the details of the cause are still under investigation, the most likely conclusion is that our farm, our neighbors, and even households in the nearby village were unintended targets of herbicide spray drift.
The Resulting Cascade of Negative Effects
The suspect herbicides include four commercial products commonly used for mesquite control. All four products use ingredients that mimic plant auxins. Plant auxins are hormones. These are powerful growth regulators. When applied in excess, they can lead to distorted growth.
The naturally occuring auxin, indole-3-acetic acid (IAA), is released by plants in small doses to promote things like cell division, DNA production, and osmoregulation (water movement) in plants. IAA does its job quickly, and a little bit goes a long way. So to protect plants from toxic auxin overloads, plants produce enzymes that transform excess IAA into benign products. Unfortunately, these enzymes aren’t very good at removing the synthetic auxins found in herbicides. These chemicals stay in the environment for a long time. They dissolve in water, so they can quickly accumulate in water bodies where they are also toxic to fish.
In the incident we witnessed this summer, the herbicide that is believed to have drifted into our valley appears responsible for damage to numerous trees, flowers, and gardens belonging to village residents. Damage was seen on vegetable gardens and small farms that local families rely on for fresh produce. All of the trees in our orchard were damaged, in addition to the hay and produce crops of farmers up and down the valley. We are told that the chemicals can stay in the soil for 18 months, which means the economic impact of this incident will be felt for at least 2 growing seasons.
Plants that were flowering suddenly died. This means bees, butterflies, and birds that were not directly poisoned by the herbicide suddenly found themselves without a food source. Local hives reported a loss of bees.
On our farm, we noticed a change in the numbers of birds and the diversity of insects present on the farm. We saw more pests and fewer beneficials. This is understandable when you realize that healthy plants synthesize a symphony of natural chemicals designed to attract the good bugs and repel the bad ones.
Responding to a suspected herbicide spray incident is challenging. Companies that might be responsible are reluctant to speak up, and when different companies were spraying, it can be anyone’s guess whose spray drifted off target. Crops can be tested, but lab tests are expensive. And since different herbicides require different sampling and testing procedures, it can be risky to test without knowing what you are testing for.
Plants also respond differently. When we saw our neighbor’s alfalfa wilt, our trees looked good, so we thought we had been missed. It took two weeks for our trees to show clear signs. By then, it had rained, and we had irrigated. So it seemed unlikely that samples sent to a lab would reveal substantial loads of herbicide.
We spoke to several experts. Not surprisingly, we got several conflicting pieces of advice about how to mitigate the damage. Should we prune effected shoots? Should we change our management? Should we cut our losses and remove the trees? If so, how long will it be before we can safely replant? Everyone had an opinion.
As of the moment, we have applied a foliar spray containing fulvic acid, trace minerals, and a mixture of biologicals. We are hopeful that this mixture will treat what appears to be herbicide-induced mineral deficiencies and foster decomposition of residual herbicides. We are also hopeful that our efforts to diversify with cover crops and build soil health have provided some resilience that will carry us through this disaster.
We will wait for our blossom count next spring to tell us how permanent the damage might be.
These direct and indirect impacts of herbicide drift on plants, bees, birds, bugs, farms, farm incomes, and families in the village provide a clear illustration of biological cascades in action. If all goes well, the direct effects on plants will be compensated by the insurance companies. But how does one measure the loss of the farmer who says, “I’m not going through this again,” and closes shop? How does one assess the value of the insect and soil microbial populations, whose compositions have been transformed, perhaps permanently, by this event? As I consider the impacts of these herbicides on soil life and on the forbs growing on rangelands, I find it amazing that any rancher would consider broadcast herbicide spraying a good investment. Do they think cattle will gain more weight on a range that is devoid of broadleaf forbs? I get the value of mesquite control, but are the tradeoff’s worth the risk?
Many experts today see holistic management as the way of the future. As we recognize the cascades of damage that agrochemicals can produce, we can only hope that the future arrives quickly.