At least a few times a year, we come across the scene of a minor crime on the farm. It’s almost always theft of small, easy-to-transport items like chainsaws or other valuable tools. Occasionally, someone will steal a farm pickup truck and take it for a joyride. Earlier this year, someone made it just a few hundred feet down the road before driving one into the irrigation canal. On those occasions, we call the sheriff and file a police report.
But at least a few times a year, we have a different type of crime scene to investigate. In those cases, the victims are our crops, and the perpetrators are unknown pests or diseases.
As farmers, we expect to have to deal with insects, mildews, and weeds all the time — it’s part of the job. We are pretty familiar with the most common threats to the crops we grow, as well as with the tools available to us to deal with them.
So it’s a little shocking to walk into a field of plants and see symptoms or damage that you’ve never seen before. There’s a feeling of panic and fear. “What is happening here?” “What am I going to do?”
A couple of weeks ago, I was doing a routine check of our pepper field for powdery mildew, an easy-to-control fungal disease that occurs when temperatures are cool this time of year. I had noticed the plants were no longer the nice dark green color they had been. But instead of the mildew, a faint white mold on the undersides of the leaves, I found large lesions on the leaf surfaces. Looking closer, I noticed faint yellow squiggles running through the leaves.
This is a classic symptom of “leafminers”, impossibly tiny worms that burrow into plant leaves and tunnel their way between the layers. They are a fairly common pest around the farm. The difference this time was they were in literally every leaf of every plant, and the leaves were falling off. While it’s never a good thing for plants to defoliate, the timing for the peppers was particularly bad because hot weather causes the fruit to get sunburned.
While there are plenty of synthetic pesticides can kill pests that infest the inside of a plant, it’s much harder to do organically. We sprayed a pesticide that will kill the worms when they exit the leaves on their way to the ground,. This won’t help save the leaves that are already infested. But it will keep the worms from pupating into flies that would then return to lay more eggs in the plant.
Occasionally we have a farm “crime scene” that we can’t figure out ourselves. In those cases, we have to call in the special detectives: our local UC Extension Farm Advisors. In our area, we have one farm advisor for Vegetable Crops and another for Tree Crops. In addition to their individual expertise, the farm advisors also have the full resources of the University of California at their disposal: other experts in insects and plant diseases as well as labs for testing when necessary.
It’s never good when you have to call the Detectives. They rarely find the guilty party right away, and sometimes can take as much as a month to get you the answer of who or what is causing the problem. By then, the victimized crop is often on life-support or dead. Whatever solution they suggest — if there is one at all — can only be applied to future crops.
But at least we can try to prevent it from happening again, or recognize it the next time it does.