- Author: Kurt J. Hembree
- Posted by: Gale Perez
While both horseweed and hairy fleabane have been here since farming began in the region, it's only since about 2003 that they have become such an obvious problem, particularly in tree and vine systems and non-crop areas.
In the past, the traditional use of combinations of pre- and postemergence herbicides and/or cultivation was adequate to manage them. However, recent changes in environmental regulations, economics, herbicide use patterns (toward more postemergence-only programs), treatment timing, and glyphosate-resistant biotypes have all contributed to the problem. Other factors contributing to their spread include, high seed production, wind dissemination, lack of seed dormancy requirement, preference for undisturbed areas...
Here's an article from the San Joaquin County Field Notes newsletter (Feb. 2014.)
Dormant Weed Control in Tree Nut Crops 2014
Mick Canevari, Farm Advisor Emeritus
Brent Holtz, Pomology Farm Advisor and UCCE County Director
Brad Hanson, Extension Weed Specialist, UC Davis
Current dry weather has preempted most normal winter weed germination and growth while prolonged periods of dry soil has caused some early weeds to desiccate and die. In most tree and vine herbicide trials conducted so far this winter—the...
- Author: Lynn M. Sosnoskie
- Author: Brad Hanson
- Author: Ted Webster
- Author: Stanley Culpepper
Weed control failures can and do occur.
Weed control failures occur for many reasons, including improper treatment applications and plant size and development at the time of treatment.
Plants that aren't completely controlled can produce viable seed and re-infest fields.
Insufficient control of herbicide-resistant weeds could facilitate the establishment and spread of undesirable traits.
Weed pressure, and the resulting competition for water and nutrients, can significantly impact crop establishment, growth, yield and harvest. Furthermore, there is some concern among growers that non-managed weeds may support...
- Author: Marie Jasieniuk
Horseweed and hairy fleabane are closely related annual weeds that are widespread in Central Valley orchards and vineyards where many populations have evolved resistance to glyphosate. Interestingly, however, the geographic distribution of glyphosate resistance differs markedly between the two weeds.
A survey of 42 horseweed populations across the Central Valley in 2010 showed that glyphosate-resistant plants were abundant across the southern part of the Valley but that horseweed in the northern part of the Valley was still largely susceptible. In contrast, a survey (unpublished) of 35 hairy fleabane populations in the same general...
- Author: Richard Smith
- Author: Larry Bettiga
- Author: Brad Hanson
Marestail (Conyza canadensis; aka horseweed) and hairy fleabane (C. bonariensis; aka flax leaf fleabane) are serious weed problems in vineyards in Monterey County. Both plants are summer annuals that germinate in the fall at the onset of the rainy season (October – February), or germinate in the spring (March – May). Seeds of both species are not long lived (2-3 years) and are ready to germinate when conditions allow as soon as they mature on the plant; they germinate on the soil surface or from no greater than 0.2 inch deep. The seedlings of the two species look very similar to each other until they bolt at which time they can be easily distinguished (for detailed information on these species go to:...