Arboriculture & Urban Forestry 33(1): January 2007 57 Table 1. Chemical techniques, location, timing, treatment, carrier, and rate used to control tree-of-heaven. Treatment method Treatment location Stem injection Cut stump Stem injection Stump injection Basal bark Putah Creek Putah Creek Putah Creek Putah Creek University of California, Davis 1998 1998 2001 2001 2001 2001 2001 2001 2001 2001 2001 2001 2001 Year of October Herbicide (trade name) Imazapyr (Stalker) Imazapyr (Habitat) Carrier None None Glyphosate (Roundup Pro) 50% water Imazapyr (Chopper) Triclopyr (Garlon 4) Glyphosate (Roundup Pro) None Imazapyr (Chopper) Triclopyr (Garlon 4) None None Glyphosate (Roundup Pro) None Imazapyr (Chopper) Triclopyr (Garlon 4) Imazapyr (Chopper) Triclopyr (Garlon 4) None None soluble formulation of imazapyr (Habitat [BASF Corp., Re- search Triangle Park, NC]; 239.7 g·ae/L; 2 lb·ae/gal), which is registered for use in riparian areas and adjacent to water. Trees at both sites were treated on 23 October 1998, in au- tumn before leafdrop. In the Putah Creek site in Yolo County, California, we tested four treatment methods for control of tree-of-heaven using three herbicides. Treatments were made shortly before leafdrop in late October 2001. Herbicides tested included the emulsifiable concentrate of imazapyr (Chopper [BASF Corp., Research Triangle Park, NC]; 239.7 g·ae/L; 2 lb·ae/gal), the ester formulation of triclopyr (Garlon 4 [DOW AgroSciences LLC, Indianapolis, IN]; 479.3 g·ae/L; 4 lb·ae/A), and glypho- sate (Roundup Pro [Monsanto Co., St. Louis, MO]; 359.5 g·ae/L; 3 lb·ae/gal). Methods included stem injection, cut stump, stump injection, and basal bark treatments. In addi- tion, we included untreated plants for each treatment. Indi- vidual trees were treated as replicates with six to eight trees per treatment. Trees were represented by three size classes (trunks <8 cm [<3.2 in] diameter, trunks >8 cm [>3.2 in], and multiple trunks). At least two trees from each size category were included in each treatment. Because trees were randomly dispersed along each of these riparian areas, treatments at each site were organized in a complete randomized block design. Individual trees were marked with plastic flagging and numbered with aluminum tags. Treatments Techniques Cut Stump Trees were cut 60 cm (24 in) above the soil surface using a chain saw. The stump cambium was treated with an herbicide solution consisting of 20% v/v Chopper in Hasten crop oil, 20% v/v Garlon 4 in Hasten oil, or 50% v/v Roundup Pro in water (Table 1). The herbicide solution was applied using a laboratory Nalgene squeeze bottle. An average of 5 mL total solution (range from 3 to 25 mL [0.09 to 0.75 fl oz] depend- Rate Undiluted Undiluted 50% 80% Hasten oil 20% 80% Hasten oil 20% Undiluted Undiluted Undiluted Undiluted Undiluted Undiluted 80% Hasten oil 20% 80% Hasten oil 20% ing on tree size) was used per stump (3.6 cm [≈1.4 in] diam- eter average stump size), which wet the cambial ring short of runoff down the stem. Stumps were treated at four intervals after cutting (0, 15, 30, and 60 min). Stem Injection The stem injection technique, also known as hack-and-squirt, consisted of making a downward angled 4 to 8 cm long (1.6 to 3.2 in) hatchet mark (hack) in the bark 30 to 45 cm (12 to 18 in) above the soil surface and then injecting 1 mL [0.03 fl oz] of undiluted herbicide (Chopper, Garlon 4, or Roundup Pro) into the mark using a disposable 10 mL (0.30 fl oz) pipette and pipette pump (Table 1). The standard rate was one hack and herbicide treatment for every 8 cm (3.2 in) in trunk diameter. For the tree clumps, the standard dose was based on the accumulated stem diameter (total of all stems) of all trunks, but applications were made at lower rates of one-half or one-fourth the standard rate. These lower rates were used because it was considered impractical to apply herbicide to each stem within every clump. For example, a clump with four 8 cm (3.2 in) stems (standard rate of four injections, one on each stem) would receive either two injections, one each on two stems (one-half rate) or one injection on one stem (one-fourth rate). We also established control trees of all sizes, which were also marked with the hatchet but were not treated. Stump Injection Trees were cut with a chainsaw similar to the cut stump treatment. A hatchet mark and undiluted herbicide treatment (Chopper, Garlon 4, or Roundup Pro) was then made to the stump as described for the stem injection treatment (Table 1). The herbicide application was performed either immediately, 1 hr, 1 day, or 1 week after the tree was cut to test whether a delay between cutting and treatment would affect efficacy. Basal Bark Similar to the stem injection treatment, this technique left the tree standing. Only imazapyr and triclopyr were used in this ©2007 International Society of Arboriculture
January 2007
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