How to identify and manage common ragweed in Christmas tree production – Part 2
Strategies to manage common ragweed in Christmas tree production.
An effective weed management program uses different approaches and practices to keep weed populations in check. It is important to use several strategies to avoid herbicide resistance from developing. As we discussed in Part 1 of this series, proper identification is the first step. Other management options include prevention, along with mechanical, biological and chemical controls.
Using non-chemical control to manage common ragweed
The foremost way to control common ragweed is preventing seed introduction into Christmas tree production areas. Frequent scouting for this weed is essential for control. If already present or established, the weed should be controlled right at emergence or pre-flowering stage by regularly monitoring the field to prevent seed spread at later stages.
Mechanical control of common ragweed includes hand weeding or uprooting, hoeing, mowing or cutting the plants before flowering in Christmas tree production fields. Mulching with hay, wood chips, grass clippings or similar materials can also prevent seed germination or limit growth of germinated seeds. According to Odero et al., 2011, cultural or mechanical methods in combination with chemical control can provide effective control of the weed.
Ground beetles (carabids) act as predators for common ragweed as they eat away seeds lying on the soil surface. In addition, the leaf beetle Ophraella communa can also be helpful for biocontrol of common ragweed by reducing its pollen production by about 82%, according to Schaffner et al., 2020.
Using chemical control to manage common ragweed
Controlling common ragweed by using herbicides is best when seeds have started germinating or the plants are in early stages of development. Among the preemergence herbicides, Princep 4 L provides excellent control. Whereas Aatrex 4 L, Gallery 75 DF, Goaltender 4 SC and Sureguard 51 WDG are also good options as preemergent herbicides that can provide common ragweed control. Postemergence herbicides are generally effective when the common ragweed is in early stage of growth and development before it has attained reproductive maturity. Roundup ultra 4 L is the best option as postemergent herbicide. Goaltender 4 SC, Cobra 2 EC, Garlon 3A and Stinger are other postemergent herbicides that can provide good control of common ragweed.
The chemicals recommended for controlling common ragweed vary in different states in the U.S. since it has developed resistance to few groups of herbicides in different places. According to research from Hill, 2018, common ragweed has been reported to be resistant to glyphosate in Berrien and Montmorency counties, ALS-resistant in Isabella County and resistant to synthetic auxin Clopyralid (Stinger) in Montcalm County. Also according to research from Hill, 2020, it has been reported to be resistant to atrazine (Photosystem –II inhibitor) and cloransulam-methyl, imazamox, and imazethapyr (ALS inhibitors) in Michigan under nursery conditions and resistant to different groups of herbicides in field crops (corn, cotton, soybean) in most of the states of the U.S.
The directed postemergent application of glyphosate along with ammonium sulfate can result in an increased performance for common ragweed control as reported in Florida, according to Odero et al., 2011. In addition, applying 2,4-D, Saflufenacil (Sharpen) and methylated seed oil (1% v/v) can also provide common ragweed control. Adding ammonium sulfate or surfactant can potentially increase the risk of injury to the trees if they come in contact with the herbicide. Always apply as a directed spray, making sure the foliage is thoroughly hardened-off prior to application.
To prevent further resistance development to other groups of herbicides in different regions, repeated use of a single herbicide with the same mode of action should be avoided and integrated weed management strategies need to be adopted by the Christmas tree growers. Combinations of herbicides or rotating herbicides with different modes of actions are recommended to avoid development of herbicide resistance among common ragweed species.