The issue: Curlycup Gumweed
Curlycup gumweed (Grindelia squarrosa) is a native biennial that is very drought tolerant. Its presence is an indicator of poor growing conditions. It can be found in dry rangeland, waste places, roadsides, abandoned crop lands and poorly managed pastures. It can accumulate excess selenium in high selenium soils, but this is only an issue when livestock are starved into eating it.
The first-year growth is a rosette while the taproot develops. The second season it will send up a flowering stalk. In warm climates it may be a sort-lived perennial.
The flower is yellow and the gummy bracts curved back. The leaves on the stalk are long, fairly narrow and usually clasp the stem. The leaves also have a gummy substance on them.
Gumweed spreads only by seed, but it does develop rhizomes, which can form a cluster of plants.
Integrated pest management options:
· Prevention: Keep ditch banks free of seed-producing plants; clean all equipment and vehicles of weed chaff; feed weed-free hay; manage pastures for good competition; establish desirable plants in disturbance areas.
· Mechanical: Remove at least two inches below the crown.
· Cultural: Gumweed is not competitive in good growing conditions. Irrigate and fertilize for good competition.
· Biological: None.
· Chemical: Apply broadleaf herbicides on the rosettes in the fall. Glyphosate has NOT been effective. High temperatures greater than 85 degrees within 72 hours after application may cause some herbicides to volatilize and drift to non-target plants. Be sure the target weed and crop or landscape situations are listed on the product label. Always read and follow herbicide label directions.
Curlycup gumweed can take several years to get under control — a long-term program is essential. Combine different IPM options over a period of years to help improve the effectiveness of your efforts.