Broccoli not growing well and showing leaf damage
We have a client who is having issues with her broccoli plants. She dusted just the leaves with Sevn which had "no effect" on it. The heads not producing well although the plant is of decent size. The rest of the garden (green beans, eggplant and zucchini) are all doing well.
Van Buren County Michigan
The creature you have is cabbage worm, and it likes to eat from most members of the Cole crops, e.g. broccoli, cabbage, kohlrabi etc. The green caterpillar is causing the holes in your broccoli. At this stage of the growing season, it's probably best if you just try to collect/crush the caterpillars rather than trying to apply anything else as the insect is nearing the end of its cycle.
This started in April when white moths laid eggs and then, these hatched into the caterpillars. Something you can do to help prevent this next year is to be sure to remove and destroy any of the dead Cole crop material so they are not able to overwinter. You can also after planting transplants in the spring, place the lightest weight row cover (secure and use wire hoops) over your broccoli, so the moths cannot lay their eggs.
Here is a brief Illinois Extension resource that explains this: https://web.extension.illinois.edu/vegproblems/impcabbage.cfm
For a more detailed description, here's a resource from Maryland Extension: https://extension.umd.edu/hgic/topics/imported-cabbageworm-vegetables
Thanks for the info! Do you have any idea why her plants are producing well this year? Is it in response to the cabbage worm?
Yes, it could very well be because of the cabbage worm. Especially if they have defoliated the plants repeatedly, and the plant isn't able to grow and then, produce enough leaves and then, broccoli florets.