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Stem Injection

steminjectionStem injection applications are done by delivering herbicide directly into the hollow cane of the plant. Injections are made in the lower portion of the Japanese knotweed plant in the first few internodes above the ground level. Delivering herbicide directly into the plant, above the root crown dramatically increases the translocation ability of the herbicide throughout the plants root structure.In previous years, this method lacked an adequate delivery system, although effective, without an adequate delivery system, this method was difficult to employ in the field. In 2004, the J. K. Injection Tool was commercially introduced following several years of testing and has been found to be a very effective tool for the individual stem injections. The needle is inserted perpendicular to the stem, and midway between lower nodes. The applicator squeezes the trigger and the pre-set amount of herbicide is delivered into the stem cavity.

The injection process in riparian areas has been the most effective control method against plant re-growth, and poses limited threats to neighboring vegetation. With this method there is no need to cut canes, or handle viable plant material for disposal. If 40 of 50 canes in an area are injected, expect that the 10 canes NOT injected/treated to survive and spread. Each cane develops its own rhizome system. The injection process is more cost effective compared to making several trips to sites to re-spray foliar applications. Injections can be made anytime during the growing season, with early June being the preferred timing as most canes have developed.

In substitution to the JK injector tool, a simple probe can be used to create a small opening in the stem on either side just below the node. This allows pressurized water to escape while the syringe metered to inject the treatment dose on a downward diagonal through one of the two holes closest to the applicator. The second hole will then allow the pressurized water to escape if the node is full of water. Plants will normally take up the herbicide within 20 minutes of the injection. Plants will be dead within 72hrs, and can be cut and transported with no risk of spreading by fragmentation.

Field Observations:
The inclusion of another control method to the well known practices of foliar application and cut stem has provided new insight to how to effectively control many invasive plant species. The section on field observations outlines aspects of the field research that were of particular interest and value to field operators.

Why inject below the third node for Japanese Knotweed?
During recent test trial periods on Japanese knotweed, evaluators noted that when plants were injected above the third internodes, or segments, that only the upper portion of the canes were affected. The day after application, the area above the injection site had wilted and collapsed. On applications made at the same location within the first two segments, above the J. Knotweed root crown, no herbicide symptoms were observed during the first week. After that period, plants showed herbicide symptomology of leaf curling and yellowing.

This may suggest that injection applications made above the second internode region are unable to completely translocate herbicide to the roots prior to disruption or collapse of the conductive tissue. This phenomenon occurred in the spring time when most photosynthate is moving up in the plant as opposed to later in the year as photosynthate is being sent to the roots and rhizome structures. In those situations, aggressive re-growth occurs later in the same growing season of treatment. For best results, closely adhere to the stem injection system described earlier, especially during late spring and early summer applications.

How effective?
Where application rates were maintained at the recommended 5 cc’s per injection, a control rating project-wide was 98% control.

In the course of making applications, occasionally stems will be overlooked and not treated, but the use of lower rates will require additional significant human and financial resources to be used to obtain satisfactory results. Follow-up is a key element of successful removal of any invasive species. Using the recommended injection rate plus careful application techniques will produce the best results..