Ponderosa pine has many unique attributes that make it useful for reforestation in valley fringe areas. Unlike Douglas fir, many of the common forest herbicides can severely injure or kill pine seedlings if landowners are not careful. Here are a few tips to control competing vegetation in pine plantations without undue pine hazard.
Directed Spraying and Stem
Many products can be used as a directed spray around seedlings but not contacting them directly. Glyphosate products like Accord and Rodeo can be used to control competing grasses and forbs in the spring through summer. Avoid contact with the foliage especially after bud break. Products like 2,4-D and Garlon can injure seedlings if sprayed directly but are useful for controlling broadleaved weeds (2,4-D) and blackberries in late summer or Scotch Broom in the spring (Garlon).
For maple sprout clumps and trees, stem treatments like hack and squirt with imazapyr (Arsenal or Polaris) are very useful and quite effective. Make small cuts in the stems or tree trunks with an ax or machete and use a 50/50 mix of imazapyr (Arsenal AC) and water. Usually one cut per two inches of diameter is sufficient and place one milliliter (cc) of mixture in the cut with a squirt bottle. Small trees and even brush species can be treated with this method. Landowners can also cut unwanted trees and brush and treat the stump with herbicides like triclopyr amine (Garlon 3A) or glyphosate. A 50/50 mix in water is sufficient if the outer cambium ring or any other exposed cambium is treated right after cutting.
Broadcast Over the Top Release
Some herbicides can be used safely over the top of pine seedlings if correct use rates and seasons are followed and the spray equipment is carefully calibrated. Velpar is used to control unwanted grass and forbs in the spring before bud break and is well tolerated by pine. Oust is also used to control weeds and grasses at low rates of 2 ounces per acre or less. Atrazine is very safe over pine but is a restricted use herbicide and requires a license to buy and apply. Transline is a very useful material that has no effect on pine but controls many thistles, some broadleaves and elderberry. Late summer release treatments can be made after pine growth has hardened off in September with glyphosate products like Rodeo.
Many deciduous brush species can be controlled during this time. Oust (sulfometuron) can also be added to help control herbaceous weeds, salmonberry, and slow down blackberries. Pine is usually tolerant of fall applications of glyphosate but at times shows minor injury.
Site Preparation Treatments
The best way to control vegetation in pine plantations in western Oregon is to control it before planting pines. Site preparation applications of glyphosate, imazapyr (Chopper or Polaris ), metsulfuron (Escort) and/or Oust can be made in late summer when brush is sensitive to those products. Planting pines the following year gives them a head start and can many times eliminate the need to do any brush control treatments for several years.
Remember to always read and follow the label on the product jug you are using and if in doubt contact someone that can help you interpret the correct rates and timings. Improper use can result in a fine from the Department of Agriculture. By carefully using the right herbicide in the right spot, landowners can keep their pine plantations growing strong into the future.
Last Updated 02/11/12