- Author: Joseph DiTomaso
In 1997-1998, the big El Nino year in California, yellow starthistle (Centaurea solstitialis) (YST) infestations throughout the state were probably the largest that I have seen in my time in California. Not only were the infestations the densest, but the size of the plants often exceeded six feet tall. The reason for this is that water uptake by the roots of YST in the Sacramento Valley and surrounding foothills is highest between March and June in both shallow and deep soils. In contrast, water uptake by annual grasses is highest earlier in the season and only in shallow soils. During the El Nino year of 1997-1998, there was plenty of available soil water long after grasses had completed their life cycle and the extensive...
- Author: Joseph DiTomaso
Yellow starthistle (Centaurea solstitialis) (YST) is the most pervasive invasive and noxious weed in California. Previous work showed that YST uses substantially more water than forage annual grasses it typically displaces. Soil moisture was 20% higher in annual grass test sites compared to YST test sites. Because yellow starthistle is found (sometimes in very extensive stands) on millions of acres of California, it is possible that removal of the thistle could substantially increase groundwater recharge and subsequent surface runoff. This could greatly improve range conditions, wildlife habitat and water supply, especially in the Sacramento Valley where groundwater levels are generally still...
- Author: Joseph DiTomaso
Croftonweed (also called thoroughwort) goes by the scientific name Ageratina adenophora or Eupatorium adenophorum. It is native to Mexico and has been introduced to a number of areas around the world. In China, it is the most important invasive plant of tropical forests in the Yunnan area, where it was introduced in the middle of the 19th century. Not only does it cause significant ecological and agricultural damage, but it is considered highly poisonous to cattle and horses, causing chronic lung toxicity. In addition to China, it is an important invasive plant in Hawaii, India, Australia, New Zealand, South Africa, and many other areas of Asia. The plant is a perennial herb or subshrub that grows from 3 to...
- Author: Joseph DiTomaso
So far, this year is beginning to look like a strong El Nino weather pattern throughout much of California. The last time we had a very strong El Nino was the winter of 1997-1998. For those of you that remember back then, yellow starthistle (Centaurea solstitialis) infestations were enormous, both in terms of cover and height. For example, the attached photo was taken in Calaveras County in the summer of 1998, after the El Nino winter. In this case, yellow starthistle probably covered 80% or more of the area and was at least four feet tall, sometimes even six feet in height. The reason yellow starthistle does so well under these conditions is that high rainfall recharges the deep soil moisture, which is where yellow starthistle...