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Dogfennel, Smutgrass, and Blackberry and Dewberry Control and Costs

February, 2015
James McWhorter, Highlands County Livestock Extension Agent

Controlling weeds in South Florida pastures is a constant battle for cattlemen. Growing seasons in South Florida allow for production of large amounts of forage biomass, but, unfortunately, allow weeds to thrive. Starting a plan early can let cattlemen develop a weed control budget to better manage the cost of weed control while improving the effectiveness of the program. This article will cover three problematic weeds in South Florida and will provide an estimated cost of controlling these weeds. Dogfennel, smutgrass, and blackberry and dewberry are not the only weeds a rancher will need to control, so for questions about other pasture weeds, contact your County Extension Office.

Dogfennel
Dogfennel can begin growing from seed and rootstock as early as February. By April, plants can be 6 to 12 inches tall. Smaller dogfennel plants are much easier to control than larger ones, so controlling dogfennel early is crucial. Dogfennel, less than 20 inches in height, can be controlled with 4 pt/A 2,4-D amine, or 1.5 qt/A Weedmaster (dicamba + 2,4-D amine). Once the plants reach 20 inches in height 2,4-D and Weedmaster become less effective. Once plants become taller than 36 inches, other options should be considered. Pasturegard at 3 pt/A is an effective option, however, if other weeds are present, a combination of Pasturegard and GrazonNext is a better option. Applying GrazonNext at 2 pt/A with PastureGard at 1 pt/A (PastureGard HL at 0.5pt/A) will effectively treat dogfennel and other pasture weeds like tropical soda apple. The herbicides used to treat dogfennel are safe for forages with the exception of 2,4-D. 2,4-D should not be applied to limpograss from May 1 and November 1 or severe injury could be sustained.

Environment conditions can alter the effectiveness of dogfennel control. Drought conditions can prevent the herbicides from realizing their full effectiveness. Dogfennel in drought conditions can “hardnen-off” to prevent moisture loss and not allow the herbicide to work properly. If the dogfennel plant is not wilting during the day, the plant is preventing moisture from leaving the plant, so sprayings should be delayed until the dry conditions pass.

Smutgrass
Two types of smutgrass can be found in Florida: small smutgrass and giant smutgrass. An easy way to tell the difference is the size of the bunch and the seedhead. Small smutgrass has a bunch that averages 8 – 10 inches in diameter and has a compact seed head that is usually infected with black fungus. Giant smutgrass has a 12 – 18 inch bunch and has an open seed head with panicle branches directed upward.

Chemical control for giant and small grass are the same. Velpar at 2 qt/A is effective for controlling smutgrass. Velpar should be applied from June through September. Velpar has very little leaf activity with smutgrass and the herbicide has to be absorbed through the roots, so rainfall after spraying is required to realize the full benefit. If rainfall does not occur within a two week period after spraying, the treatment will likely fail.

Velpar has no grazing restriction for treatments less than 4.5 qt/A, but there is a 38 day haying restriction.  Oak trees are very sensitive to Veplar, so stay 100ft from any oak trees while spraying Velpar. Bahia and Bermudagrass will yellow after spraying with Velpar, but will recover in about 40 days. The greatest restriction for ranchers with Velpar is the price. Velpar is a very expensive herbicide to apply, so ranchers should decide before spraying if it’s worth the cost.

Blackberry and Dewberry           
Blackberry and dewberry plants are usually found in fence rows, ditch banks, and pastures. Blackberry has upright growth and commonly reaches 3 – 6 feet in height with hard thorns and no hair while dewberry has low, vine-like growth that rarely reaches 2 feet in height with slender thorns and red hairs on the stem.  Blackberry and dewberry can be easily overlooked, but if untreated for long periods of time, large thickets can form and can injure cattle and other livestock. Thorns can scratch and cause infection on bulls’ reproductive organs that can lead to a complete loss of reproduction performance. Lactating cows are also at risk. Infections on the udder can lead to lower milk production. Blackberry and dewberry can reduce grazing in portions of pastures if they allowed to grow into hard to control thickets.

Controlling blackberry and dewberry should include mowing and herbicide applications. Large thickets often have dead canes that interfere with the application of herbicides. Mowing will eliminate the dead canes while the live canes will regrow allowing the herbicide full contact with the live canes. Herbicide should be applied 6 months after mowing. Herbicide application directly after mowing is often ineffective. After spraying, it is good practice to mow again to remove the dead canes and allow for grazing, but canes should not be mowed for 6 weeks after spraying to allow the herbicide sufficient time to act.

PastureGard at 2pt/A is an effective control when blackberry and dewberry are blooming and will treat other pasture weeds, but often, retreatment is required for 100% control. Research has shown fall applications are generally more effective than spring applications. Telar at 1oz/A is also effective on blackberry, but will not target other pasture weeds. PastureGard and Telar are both safe to use on bahia and bermuda pastures.

Cost of Control
The following tables were developed using the 2014 Machinery and Equipment Budget produced by IFAS. The budgets account for fuel, labor, maintenance, and annual repairs for tractors and implements. The cost of chemicals were added based on prices gathered by the author in late fall of 2014. The tables show the cost per acre (with machinery included: 75hp tractor with 25ft boomless sprayer and a 40ft boomless sprayer) of treating each problem weed.

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