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
Biological control (continued)
Plant pathogens
Plant pathogens are not typically used as weed biological control tools. However, at least two pathogens have been commercially available for control of agricultural weeds (Collego® [Colletotrichum gloeosporioides f. sp. aeschynomene] and DeVine® [Phytophthora palmivora]). Although no pathogens have yet been released for the control of yellow starthistle, a number of species have been evaluated including Fusarium oxysporum f. sp. carthami, Verticillium dahliae, Phytophthora spp., Botrytis cinerea, Sclerotinia sclerotiorum, Sclerotina minor, Ascochyta n. sp., Colletotrichum gloeosporioides, and Puccinia jaceae. Some of these pathogens have shown promise.
Under laboratory conditions, Klisiewicz (1986) looked at the effect of several pathogenic fungi on yellow starthistle rosettes. The species evaluated included Fusarium oxysporum f. sp. carthami, Verticillium dahliae, Phytophthora spp., Botrytis cinerea, and Sclerotinia sclerotiorum. Starthistle plants developed symptoms from all these organisms and, with the exception of B. cinerea, the diseases were frequently lethal. However, these pathogens are not host specific and, thus, have the potential to attack other economically or ecologically important plant species.
An undetermined or perhaps new species of Ascophyta n. sp., as well as Sclerotinia minor, and Colletotrichum gloeosporioides were evaluated by CDFA scientists (Pitcairn et al. 2000b, Woods 1996, Woods and Fogle 1999). All three of these species are already naturally present in California. Seedlings of yellow starthistle are susceptible to Ascophyta n. sp. under cool conditions typical of the winter months (Woods 1996). In addition, the pathogen appears to be fairly host specific. However, it has been difficult to maintain a high level of virulence in laboratory cultures (Woods and Fogle 1999). Sclerotinia minor has also been able to cause high mortality rates in starthistle seedlings; particularly in areas were skeletons of previous years starthistle plants provide shading. Unlike Ascophyta n. sp., Sclerotinia minor is not host specific and is able to infect important crops including lettuce (Pitcairn et al. 2000b). The host specificity of the isolate of Colletotrichum gloeosporioides has not yet been determined, but this fungus appears to be quite common in California and may have a significant impact on yellow starthistle (Pitcairn et al. 2000b). In contrast to Ascophyta n. sp., it is most aggressive at warmer temperatures, causing symptoms characterized by wilting and yellowing (Woods and Fogle 1999). It is possible to isolate a host specific form of the pathogen that might be used as a mycoherbicide in starthistle infested grasslands.
The most widely studied pathogen of yellow starthistle control is the Mediterranean rust fungus Puccinia jaceae. This work was initiated in 1978 from isolates collected in Turkey. At the time, these isolates were not specific to yellow starthistle (Bruckart 1989, Shishkoff and Bruckart 1993, 1996) and also attacked safflower (Bruckart and Dowler 1986). However, the pathogen was most aggressive on rosettes of yellow starthistle and bachelor buttons, also known as cornflower (Centaurea cyanus). Puccinia jaceae is well suited to environmental conditions found in California and other areas of infestation in North America (Bennett et al. 1991). It can attack the leaves and stem of starthistle, causing enough stress to reduce flowerhead and seed production. Additional experiments are currently underway at the USDA-ARS Foreign Disease Introduction Laboratory in Fort Dietrick, Maryland, and the organism may be available for introduction in 2001 or 2002 (Pitcairn 1999).
