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Cattails provide an excellent habitat for blackbird nesting in the spring and roosting in the fall during migration. Blackbirds feed on nearby sunflower in the fall. Annually, 2 to 5% of the crop is lost to predation by blackbirds. Blackbirds have become a major pest for Upper Midwest sunflower growers. Reducing cattail stands located near sunflower fields should reduce losses due to feeding by blackbirds.

Cattail control is difficult due to the large rhizome system that enables the plant to reestablish rapidly after top-growth is killed. Several carbohydrate depletion techniques such as mowing, crushing, burning, and discing have been used to control cattail but with limited success. Herbicides provide the most effective control method.

The objective of this research was to evaluate cattail control with RodeoTM (glyphosate) applied at various rates and cattail growth stages, with several adjuvants, and with or without diammonium sulfate.

MATERIALS AND METHODS

General Procedures

One experiment to evaluate Rodeo (glyphosate) for cattail control was established in a drainage ditch near Fargo, ND, in 1987. Treatments were applied with a backpack sprayer. Three similar experiments were established in Fisk Lake and Dion Marsh near Lakota, ND, in 1990. Treatments were applied with an all-terrain-vehicle-mounted sprayer. Total spray volume was 8 gal/A unless otherwise indicated. The plots were 10 by 30 feet in a randomized complete block design with four replications. Cattail control was determined the following growing seasons by visual evaluations compared to an untreated control (0 percent control = no visible density reduction; 100 percent control = no live stems visible).

Drainage Ditch at Fargo

Rodeo at 1.5, 2.3, and 3 qt/A plus X-77 surfactant at 0.5% v/v was applied in 8 and 24 gal/A total volume on June 19, July 27, and September 3, 1987.

Rodeo Rate and Cattail Growth Stage at Lakota

Rodeo at 1, 1.5, 2, and 2.5 qt/A plus X-77 surfactant at 0.5% v/v was applied to cattail at the 7- to 8-leaf stage on July 5, the flowering stage on July 30, the catkin-development growth stage on August 16, and the mature-catkin growth stage on September 4, 1990.

Diammonium Sulfate at Lakota

Rodeo at 1.0 and 1.5 qt/A was applied alone and with diammonium sulfate at 0.6 and 1.2 lb N/A. Cattail control was compared to that from Rodeo at 2.5 qt/A plus X-77 surfactant at 0.5% v/v (labeled rate). The treatments were applied to cattail at the flowering growth stage on July 31, 1990.

Adjuvants at Lakota

Rodeo at 1.0 and 1.5 qt/A was applied with two spray adjuvants; Li-700 and X-77 at 0.5% v/v. Cattail control was compared to that from Rodeo at 2.5 qt/A plus X-77 surfactant at 0.5% v/v (labeled rate). The treatments were applied to cattail at the flowering growth stage on July 30, 1990.

RESULTS

Drainage Ditch at Fargo

Cattail control 1 yr after treatment was good to excellent with Rodeo at 2.3 and 3 qt/A (88to 93%) and was fair with Rodeo at 1.5 qt/A (76%). Rodeo usually controlled cattail better when applied at 3 qt/A than 2.3 qt/A, but the increased control by the additional herbicide probably was not cost-effective. The best application time appears to be from late July to early September. Spray volume did not influence cattail control, but using 8 gal/A rather than 24 gal/A would reduce surfactant and application costs.

Rodeo rate and cattail growth stage at Lakota.

Generally cattail control was lowest with Rodeo at 1 qt/A (about 68%) and was similar with Rodeo at 1.5 to 2.5 qt/A (80 to 93%). Thus, Rodeo above 1.5 qt/A may not be necessary for cattail control. Cattail control averaged over Rodeo rates tended to be best when Rodeo was applied in late July and poorest when applied in early July, although differences between the last three application dates (July 30, August 16, September 4) were small. Cattail emergence was poor in early 1990 due to drouth conditions, so cattails tended to be small, which may account for the reduced control by Rodeo applied on July 5, 1990.

Diammonium sulfate.

Cattail control on June 27, 1991 at Dion Marsh and Fisk Lake were not homogeneous, so the data were not combined. Cattail control data collected on August 27, 1991 are from the Dion Marsh only, because treatments in Fisk Lake could not be distinguished visually from the untreated check.

Cattail control at Dion Marsh (> 97%) was much greater than at Fisk Lake (30 to 60%). Generally cattail control was better with Rodeo at 1.5 qt/A (75%) than at 1 qt/A (50%) with or without diammonium sulfate. However, diammonium sulfate at 1.2 lb N/A may have antagonized Rodeo at Fisk Lake.

Adjuvants at Lakota.

Cattail control data collected on June 27, 1991 at Dion Marsh and Fisk Lake were not homogeneous, so the data were not combined. Cattail control was less at Fisk Lake (> 90%) than Dion Marsh (15 to 75%). Cattail control tended to be greater with Rodeo at 1.5 qt/A (45%) than 1 qt/A (30%) regardless of the adjuvant. When Rodeo at 1 qt/A was applied, cattail control tended to increase when Li-700 adjuvant was used instead of X-77. However, when Rodeo at 1.5 qt/A or greater was applied, control was similar with all adjuvants evaluated.

DISCUSSION

There are several possible explanations for the differences in cattail growth between Dion Marsh and Fisk Lake. Cattail residue at Fisk Lake was burned in the fall of 1989 so snow cover during the winters of 1989-90 and 1990-91 was reduced; thus, "winter kill" of some cattail roots may have occurred. Cattail density at Fisk Lake increased dramatically from seedlings in July 1991 after several inches of rainfall were received in late June and early July 1991. Fisk Lake is a mud flat and is very shallow where the experiments were established so it dried out rapidly, whereas Dion Marsh is deeper and water did not retreat as fast.

One possible weakness of this research was that Rodeo was applied to long narrow plots, so encroachment of cattail rhizomes from untreated plants adjacent to the plots may have contributed to rapid cattail reestablishment. Perhaps Rodeo at 1.5 qt/A would provide adequate control when encroachment from untreated plants is prevented by treating the entire drainage ditch or wider strips within a marsh. The cost per acre would be reduced by one-third with Rodeo applied at 1.5 qt/A rather than at 2.3 qt/A.

Weed control is the process of preventing weed growth and/or reducing the density to an acceptable level. Cattails have a large rhizome system that enables the plant to regrow after the topgrowth is killed. Depending on effectiveness of the herbicide treatment and marsh site characteristics, especially water depth, cattail reestablishment may occur within 1 yr or may take 3 to 4 yr. Therefore, treatments should be evaluated for 2 to 3 yr after application before strong conclusions are made about the treatment. The research presented in this report is based on 1 yr of data and herbicides were applied during a drought, so the data should be interpreted with caution.

SUMMARY

Generally, Rodeo™ at 1.5 qt/A or greater controlled cattail similarly (80 to 93%) so Rodeo rates above 1.5 qt/A may not be necessary. Cattail control was achieved with Rodeo applied at any time during the growing season, but late July tended to be the optimal time for cattail control. Diammonium sulfate added to Rodeo did not improve cattail control and may be antagonistic to Rodeo. When Rodeo was applied at 1.5 qt/A or greater, cattail control was similar with all adjuvants evaluated.