For the last 44 years, the pesticide use in all commercial agriculture categories is regulated by the Environmental Protection Agency. That includes food crops (conventional and organic), golf courses, parks and the seed crops that are produced in Hawaii and elsewhere. Every product has to be "used according to label requirements," and those requirements are customized to mitigate any potential risks to workers (health), the environment (effects on non-target organisms), the neighboring farms (pest-resistance management) and consumers (health).
If the particular chemical could be harmful to delicate aquatic organisms, like fish or invertebrates, the EPA label has specific restrictions about keeping it away from water. If the specific chemical has the potential to move into the groundwater, the EPA label has restrictions about what kinds of porous soils need to be avoided. If the chemical has potential toxic effects on humans, there are specific buffer distances that have to be followed and specific rules about how to limit spray drift (e.g., nozzles that control droplet size). If a pesticide is going to be used in close proximity to human activities (e.g., golf courses, parks, urban pest control), there are EPA label restrictions to ensure that only sufficiently low-hazard materials are used.
All of the people who are licensed to use pesticides in commercial settings have to get training about how to read and follow the label instructions. Those who are licensed to use "restricted-use pesticides" must get the highest level of training and take continuing classes to maintain that license. The goal of all of these efforts is to ensure that there are no significant risks to the environment or the community.
The seed-nursery industry you mention also makes several positive contributions to the neighboring communities. It provides many jobs for residents of communities that grew in the era of sugarcane or pineapple plantations. It is good to diversify jobs beyond the hospitality industry in a place like Hawaii. The seed companies also maintain the 100-plus-year-old irrigation system that makes agriculture possible in places like the dry side of Kauai. These companies also provide the critical mass that allows the continued function of supporting ag industries associated with equipment, fertilizer, seed and chemicals. That in turn makes it possible for other types of farms to have that critical infrastructure. The land that is tended as seed nurseries is also protected from the invasive weed species that tend to take over land that is no longer farmed. Even if past farmland is going to be converted back to more natural vegetation, that is easier if the pool of invasive weeds is reduced.
Finally, no one is "spraying around the clock."