Yellow Starthistle Information
Mech control
-hand
-tillage
-mowing
Cultural control
-grazing
-burning
-re-vegetation
Biocontrol
-insects
-biocontrol table
-plant pathogens
Chem control
- risks
--spray
--water
--toxicology
--herbicide
resist
--effects
-herbicides
--preemergence
--postemergence
--late season
--pre- & post-
--imazapic
--clopyralid
--picloram
Management
Cultural control
Cultural control techniques are defined as those practices that require manipulation of the environment either through controlled burning, grazing management, or re-vegetation programs.
Grazing
Proper grazing management can minimize the spread and effectively manage noxious weeds in many rangeland systems, including yellow starthistle infested areas. Different strategies can be used for managing weeds. For example, moderate grazing levels can minimize the impact on native plants and reduce soil disturbance; intensive grazing will counteract inherent dietary preferences of livestock, resulting in equal impacts on all forage species including weeds; and multispecies grazing distributes the impact of livestock grazing more uniformly among desirable and undesirable species (Olson 1999).
Timing can also be critical to the success of grazing. The ideal time to graze is when the noxious species is most susceptible to defoliation or when the impact on the desirable vegetation is minimal. Improperly timed grazing can lead to rapid selection for yellow starthistle. For example, livestock grazing in late winter or early spring will primarily feed on young grasses with an erect growth form, causing little damage to seedling yellow starthistle rosettes. This practice increases light penetration through the canopy and generally stimulates yellow starthistle growth during the late spring and early summer. On the other hand, livestock grazing in the mid- to late summer months will selectively avoid spiny yellow starthistle plants, thus allowing heavy seed production and the next year's survival of the weed.
Thomsen et al. (1989, 1990, 1993) showed that properly timed (May and June) intensive grazing by cattle or goats resulted in reduced growth, canopy cover, survivability, and reproductive capacity of yellow starthistle. The success of this approach was attributed to grazing yellow starthistle after the stems had bolted but before the development of spiny seedheads. Although sheep did not reduce starthistle infestations in the 1993 Thomsen et al. study, they observed many localities outside of the trials where sheep routinely grazed starthistle late in the season and effectively reduced dense stands. Cattle and sheep tend to avoid starthistle once the buds produce spines, whereas goats continue to browse plants even in the flowering stage (Thomsen et al. 1993). For this reason, goats have become a more popular method for controlling yellow starthistle in relatively small infestations.
Thomsen et al. (1989, 1990, 1993) also reported that grazing the weed during the bolting stage could provide palatable high protein forage (8 to 14%). This can be particularly useful in late spring and early summer when other annual species have senesced. It is important to note, however, that grazing alone will not provide long-term management or eradication of yellow starthistle. However, it can be a valuable tool in an integrated management program.
Short periods of intensive grazing have been widely adopted in other countries (DiTomaso 2000). In this system pastures are intensively grazed from 3 to 5 days, often with the use of electric fencing. After livestock are moved to another area of the pasture, the grazed area is allowed to recover for at least a month before grazing is repeated. This system typically results in more uniform and complete forage utilization. In addition, forage is not completely grazed and recovery occurs rapidly. This can increase total season forage production and the stocking capacity of the area.
As an added benefit of short duration intensive grazing, the remaining forage reduces light penetration to the soil surface and can suppress weed establishment and growth. In contrast, conventional grazing practices allow animals to forage grasses and other plants nearly to the soil surface. Yellow starthistle has been shown to be very susceptible to light suppression (Roché et al. 1994). Shading reduces seedling survival rates. In a report by Weber (1985), it was noted that when Roché delayed spring grazing of wheatgrass, starthistle was controlled because ungrazed, taller wheatgrass plants blocked sunlight from the rosettes of starthistle.
Intensive time-controlled grazing can also minimize the grazers' ability to avoid less palatable noxious weed species. High stocking rates may force cattle to graze typically less preferable species, including yellow starthistle. This can result in a more uniform composition of range plant species and more balanced competitive relationships among native and non-indigenous species (Olson 1999). In contrast, conventional grazing or overgrazing can lead to the invasion of yellow starthistle and many other rangeland weeds. Excessive trampling of livestock was shown to increase the density of yellow starthistle (Miller et al. 1998). In some cases, grazing can select for a particular weed or group of weeds. Animals forage around these plants, eliminating its competition. This selective pressure can lead to more rapid infestation.
In contrast, conventional grazing or overgrazing can lead to the invasion of yellow starthistle and many other rangeland weeds. Excessive trampling of livestock was shown to increase the density of yellow starthistle (Miller et al. 1998). In some cases, grazing can select for a less palatable weed or group of weeds. Animals forage around these plants, eliminating their competition. This selective pressure can lead to more rapid infestation. In contrast, grazing can be very non-selective and may endanger sensitive non-target species. Goats are typically browsers and can effectively control certain noxious species. However, when confined they can intensively forage both desirable and undesirable species and may even strip the bark off trees. Livestock can also trample desirable sensitive species and can spread noxious weeds over a wide range when seeds become attached to hair or when they remain intact after passing through the digestive system (DiTomaso 1997).
