Floating Row Covers
Row covers are flexible, semi-transparent materials used to enclose
one or more rows of plants with the objective of increasing
temperature, providing wind protection and excluding pest insects.
There are two basic types:
-Supported row covers (using wire hoops)
-Lightweight floating row covers
Floating row covers are most often used to keep insects out and
at the same time let air, moisture and light in. The crop provides
support for the cover, which floats on top of the plants as they
grow - thus the name! Examples of floating row covers are ReemayR
and AgribonTM; check local garden centres and catalogues for sizes
and availability.
The principle behind floating row covers is simple: they act as a
physical barrier, preventing adult insects from landing on the crop
to lay eggs. They are often used in organic production,
particularly in vegetables, and they are an excellent way to reduce
the need for insecticides. Some good examples of pests in
Newfoundland which can be controlled with row covers are the
cabbage maggot, the cabbage butterfly and the carrot rust fly. The
cover should be placed over the crop at transplanting. It may not
be necessary to keep the row cover in 
place all season. The critical period
varies with the crop and the pest and is just one more reason why
knowing pest life history is a good idea. You should check under
your row cover periodically to ensure there are no diseases or
insect problems developing.
To use a floating row cover, simply unfold the fabric and place
loosely over the seed or plant bed. The cover should be loose
enough to allow for crop growth but not so loose that it can be
damaged by our sometimes excessive winds! To secure the edges, use
boards, pipes or rocks, or bury the edges in soil. You can help
maintain your row cover by removing any obvious sharp rocks
underneath. This will minimize the potential for the fabric to be
torn by rubbing on the rocks. Floating row covers can be used with
black plastic mulch to control weeds. Speaking of weeds, you may
have to raise the edges to remove them, but replace the seal as
soon as possible so pests don’t get in.
It is essential to practice crop rotation when using row covers.
The cabbage maggot, carrot rust fly and other insects, overwinter
as pupae in the soil underneath their host plants. If you grow
related plants in the same ground the following summer (for example
cabbage one year, broccoli the next), and use row covers, the adult
insects will emerge into essentially a little greenhouse you have
created. Imagine what they will do in that sheltered environment.
To them it’s paradise! Of course there are many reasons for
practicing crop rotation, this is but one.
Another critical point: if the crop requires insect pollination,
you must remove the covers after flowering begins.
If removed with care, floating row covers can be stored and used
for several years. Good luck!
Dr. Peggy Dixon
Peggy is the Entomologist at the Agriculture and Agri-Food
Canada Research Centre, Brookfield Road and is ‘resident bug
expert’ on the NTV gardening series
Homegrown.
