Riparian Restoration
APPENDIXES
Appendix D: Pest and Weed Control
Pests
A number of products on the market can protect seedlings from being eaten by mammals and insects. Screen will keep some insects away. Plastic tubes and/or wire will prevent or discourage browsing. Tree mats and brush blankets® are both designed to cover the ground directly around the plant to discourage competing weed growth. Mats or blankets may be crafted of cardboard. See figure D1.
Products can be found on the Web through a search engine; use the following key words to search: tree mat, tree guard, brush blanket, tree shelter.
Use 3- to 4-foot plant collars or tubes on trees and shrubs if browsing animals and rodents are a problem. See figure D2. Tubes are made of translucent material or of mesh. Growing tubes generally should not be taller than 3 to 4 feet. The tree becomes very spindly when a taller tube is used. If the tree still needs protection, construct a 6-foottall wire cage for the plant that is wide enough to avoid interference with its branch structure. See figure D3. At some point, the tree will have to be without protection. Depending on the species, it may not matter that it is browsed when only 3 feet tall.
Figure D3—Collar and screen method
The “planting collar” was developed at the University of California, Davis. See figure D4. A description from Pacific Gas and Electric says, “The planting collar is used to aid establishment of adapted woody plant species in non-irrigated extensive natural and landscaped areas. It is most effective at difficult [to reach] disturbed sites with well-drained soils where plants are to survive and grow under the existing environmental conditions” (Griggs and Stanley 2000). The collar increases the soil temperature to promote root growth and protects roots. It also concentrates moisture at the root zone. The attached screen protects against browsing and insect infestation during the first growing season. The collar is not appropriate in clay soils because of frost heaving or on flood plains (Griggs and Stanley 2000).
Figure D4—Liner planting with planter and screen
A chicken-wire basket can be installed around the roots of a plant to protect against rodents. Be sure the soil has a high enough mineral content to rust the baskets or the baskets will girdle the plants and kill them. Do not use stainless steel wire. (Flooding kills some rodent populations. If an area floods near planting time, rodents may not be a problem for a while.)
Weeds
Generally, weeds outcompete plants by using the soil moisture (Lardner 1999). One of the objectives in weeding is to shift the balance to more native plants and fewer weeds. This shift allows native plants a chance to grow and to take over. Mulch is a good medium to suppress weeds without resorting to herbicides; there will always be some weed growth while the plants are becoming established. Some weed growth can hide the new plants from browsing animals.
Weed before site work begins. If there are few weeds, dig them out; otherwise use the herbicide Rodeo® where appropriate. Rodeo® breaks down faster than other herbicides, and it has been approved by the EPA for use near water (Roundup® has not). Begin weeding (when no crust is present) as soon as the weeds appear. If possible, find the source and eradicate it.
If you choose to pull up weeds, know when they will drop their seeds and avoid disturbing them during this period. Disturbance may cause seeds to disperse farther than usual. Before seed heads have opened, cut them off and place them in a plastic bag. Ask your State’s weed abatement office for advice on destroying weed seeds.
The Bradley method for eliminating exotic plants advocates pulling errant weeds and those on the edges of a mixture of native and exotic plants. Although labor intensive, this technique has been successfully used. For more information see: http:// www.edgehill.net/bradley.htm
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