Yes, row covers protect from pests when the edges of the fabric are fully sealed to the ground. Open gaps along the sides let bugs crawl right under the cover. A pest exclusion fabric can stop most garden bugs cold once you set it up the right way. Skip the edge seal and your cover does no real work at all against the bugs you want to block out.
I lost a full bed of zucchini to squash vine borer in my first year of growing summer squash. The next year I covered the bed from transplant day through the first yellow flower. I had no borer damage that whole season and pulled in forty pounds of zucchini from six plants. I have used this trick for four years since and not lost a single squash plant to vine borer.
Covers stop bugs through a simple physical block on top of the plants. Bugs cannot crawl through the tight weave of the fabric to reach the leaves below. The mesh grade sets which bugs you can keep out and which slip through. Light covers stop bigger bugs but tiny pests like thrips can get through. Fine mesh stops both big and small bugs at once.
Per Maryland Extension, covers block a long list of pests in the garden. The list runs squash vine borer, cucumber beetles, flea beetles, harlequin bug, rabbits, deer, and birds. That covers most of the pests that kill the most plants in home beds. A cover is the cheapest way to fight all of these at once with no spray.
A squash vine borer barrier is the use case where covers shine the brightest. The moth lays eggs on stems in late June and the grubs bore into the stem and kill the plant in days. Cover your squash from transplant day through the first flower to block the moth from ever reaching your plant. Pull the cover at bloom so bees can do their work on the open flowers.
Seal the edges every three feet with soil, rocks, or sandbags along both long sides of the bed. I use a row of bricks down each side and a few large stones on the corners for extra hold. Bury the edges in a small trench for the tightest seal of all. Tight edges mean no bugs in and no warm air out at night.
Scout your bed for bugs before you put the cover on the plants. Any pest you trap under the cover will breed and feed without natural foes to stop it. I check each plant for eggs, larvae, and adults on the day I plan to cover. If I find any, I pull them off by hand or spray the bed with neem oil and wait a day to install the cover.
Move your crops to a fresh bed each year to dodge bugs that come up from the soil. Cutworms, flea beetles, and potato beetles can sleep in old beds. They hatch out right under your fabric in spring. Garden insect netting plus a yearly crop swap keeps my beds clean year after year. I have used this trick for five years now with zero sprays.
Read the full article: Row Cover Garden Guide: Weights and Timing
