Talk about only looking at one side of the coin! There are harmful nematodes and beneficial nematodes. Just like bacteria. There are a plethora of beneficial bacteria in your digestive system now, but there are also bacteria that will make you very sick if introduced into your digestive system, or into your body in general. Bacteria that will turn milk into yogurt, and bacterial that will turn milk into a dangerous rotten cup of botulism.
I have not looked at this product in detail, but if it is formulated properly it will kill off the specific nematodes that are harmful to the crop being grown, and not kill the non-harmful and even beneficial little critters. Most agricultural chemicals are formulated this way. There are herbicides that you can apply that will kill most everything except corn, and others you can apply that potato plants will tolerate just fine but will kill corn. Just like the drug industry, every chemical has benefits and potential side effects. Farmers attend classes put on by various entities (for-profit and non-profit, both government and private) on how to wisely manage and minimize the use of chemicals. Unless you're meaning a city-slicker who bought 5 acres for their horses when you say "farmer," most farmers don't just go blindly put chemicals on the soil because the saw an ad in a magazine this afternoon.
As for early adoption of technology being a lust for shiny things, sorry, that just isn't the case. Farmers are actually very hesitant to try new technology until it has been proven. As the GP said, farmers have been using GPS systems in their machinery years before they became common in everybody's cars, but they weren't a $49.95 box they could buy at Walmart either. These systems cost tens of thousands of dollars by the time they were installed, so they had to be proven to be beneficial. That GPS system may allow a tractor to drive in straighter rows down the field with better accuracy than a human driver. Spacing rows an extra 2 inches apart on each pass of the tractor, multiplied by hundreds of passes on a field, works out to a lot of wasted space, which means a lot of fuel wasted, time wasted, and a greater environmental impact. While farmers may have been an early adopter of GPS compared to the consumer market, rest assured that years of testing and proving were done before the farmer was convinced it would pay for itself. Those yield maps you talk about enable farmers to apply as little chemical as possible to each individual area of a field, thereby altering the "natural" soil balance as little as possible. This also saves money on the expensive chemicals, and lessens the needed chemicals in following years when different crops are grown in order to keep the soil as balanced as possible.
I grew up on a farm and decided I wanted to pursue another career when I graduated from school. I know from first-hand experience what kind of planning goes into making a farm work. It isn't just throwing out a handfull of seeds, applying a dozen chemicals, and reaping the rewards. Farming is a very difficult vocation not only in the physical sense, but the intellectual sense as well. The only "dumb" farmers I've ever known didn't farm for very long before they went broke and went on to other work. I know my family sure would like to get all these subsidies that all farmers are supposed to be getting, but unless you're a multi-thousand acre corporate farm, they're few and far between.
With that said I wholeheartedly agree that we as a society use too much corn syrup and chemicals in our foods. There are a few recipes in the standard Betty Crocker Cookbook (even 30+ year old versions) that call for Kero (corn) Syrup, but they're all for treats that should be eaten sparingly anyway. I fully believe the preservatives and "chemicals used in the manufacturing process" of foods and food prep products are not good for us. This is not a result of the "dumb farmers" though, they are doing it as little as possible.