ROBERT K. LYONS, Texas Agricultural Extension Service, Uvalde, TX 78802-1849
Leaf sprays can be as effective as any other individual plant treatment for brush control and are more efficient in some cases. Generally, expected control is 76% or greater when individual brush species suited to leaf sprays are targeted. Lower control occur in mixed brush situations. Leaf sprays can be applied either with backpack sprayers or with 4-wheel all-terrain vehicles. Spray guns should be equipped with a nozzle capable of delivering a course spray (large droplets). A fantype nozzle may be best for large pricklypear plants, while an adjustable cone nozzle (X6 to X8) will be more efficient for smaller plants.
Leaf sprays are more efficient than stem sprays with multistemmed plants and in dense grass. Because each stem must be treated with stem sprays, multistemmed plants usually take more time to treat than with leaf sprays. In dense grass, additional time is required to push the grass down so that stems can be treated to the ground line.
When to spray
Season and plant growth stage are more critical with leaf sprays than with most other treatment methods. Leaf sprays are generally applied when leaves are mature and growing conditions are favorable. Treatment timing varies somewhat with the brush species. For example, mesquite leaf sprays should begin when leaves change from light pea green to a uniform dark green. This color change usually corresponds to when the soil temperature is 75o F at 12 inches deep. The mesquite spray period lasts through September except in South and East Texas where the cutoff date is July 31. In contrast, cedar can be sprayed from late spring through summer when cedar is actively growing. Pricklypear and other cacti can be sprayed year-round except in extremely cold weather and both sides of every pad should be sprayed until pads or stems are almost wet, but not to the point of runoff. Leaf sprays should not be applied when foliage is wet. Anything that reduces the amount of plant leaf material reduces the potential effectiveness of leaf sprays. For example, hail damage, insect damage, or drought make leaf sprays risky.
Suitable species
Not all brush species are suited to leaf sprays. Species with small leaf area and leaf quantity such as whitebrush may not be good candidates. In addition, control may not be satisfactory in species with heavy waxy coatings on the leaves such as algerita or Texas mountain laurel.
Plant size and density
Plant size and density determine the cost of leaf sprays. Plant size suitable for leaf sprays varies with species. However, plants smaller than the maximum suggested size are always more economical to control. With mesquite, plants should be less than 8 feet tall. Cedar should be less than 3 feet tall because of its dense foliage. In demonstrations, mesquite treatment costs have ranged from $0.04 to $0.17 per plant compared to $0.07 to $0.19 for cedar. As density increases, cost per acre increases.
Selectivity
Leaf sprays can be very selective if used properly. The main concern is chemical drift. Under calm conditions, leaf sprays can be used safely to control individual brush species and plants while leaving others. Leaf sprays should not be sprayed immediately upwind of desirable trees, shrubs, or susceptible crops. Herbicides used can also affect selectivity. For example, Tordon 22K (active ingredient picloram) is active in the soil and could potentially cause problems if treatments are applied under the dripline of desirable woody plants.
Spray mixes
Herbicides in the spray mixes will depend on target brush species. However, for individual plant treatments, there are some constants in the spray mix. HiLite Blue DyeTM is a standard part of the mix to mark treated plants and avoid retreatment. Another standard part of the spray mix is a surfactant or diesel and an emulsifier. When using diesel, an emulsifier is essential. Finally, water is used as the carrier for all leaf sprays.
MENTION OF A TRADEMARK OR A PROPRIETARY PRODUCT DOES NOT CONSTITUTE A GUARANTEE NOR A WARRANTY OF THE PRODUCT BY THE TEXAS AGRICULTURAL EXTENSION SERVICE AND DOES NOT IMPLY ITS APPROVAL TO THE EXCLUSION OF OTHER PRODUCTS THAT ALSO MAY BE SUITABLE.
Comments: Dale Rollins, Professor and Extension Wildlife SpecialistUpdated: Mar. 18, 1997