Burning the Late Bloomers: Using Fire to Treat Medusahead
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Pre
scribed fire is often thought of in the context of fuels reduction; ho
wever, it can also be used to meet a wide range of other objectives, including invasive species control. In recent years, prescribed fire has shown promise for controlling medusa
head (Taeniatherum caput-medusae), an annual grass from the Mediterranean that is considered one of the worst invasives in western rangelands. Medusahead
rapidly spreads throughout areas where it is found, suppressing growth of desirable grasses and forbs. It has a high silica content,
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Medusahead goes to seed after most grasses turn brown, making it vulnerable to late spring burning. Photo by L. Quinn-Davidson, UCCE.
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which not only makes it unpalatabl
e to livestock, but also results in the development of a persistent, silica-rich thatch that further precludes growth of other plants. Medusahead
is also quite versatile, enjoying the intense heat and thin, rocky soils of California's Central Valley as well as the cool climate and relatively rich soils of coastal areas.
Previous studies have tested various control options for medusahead, including grazing, herbicides, and fire. Grazing has the benefit of trampling, which can temporarily reduce medusahead cover, but the grass is so distasteful that control via consumption is not a realistic option. In a grazed pasture, you can often tell where the medusahead is by looking for islands of untouched grass amid areas that have been fully grazed. Herbicides have been shown to be effective, especially when used in conjunction with prescribed fire. One study showed that medusahead in a sagebrush-steppe ecosystem was best controlled with burning followed by application of imazapic, an herbicide that targets broad-leafed plants (Davies 2010). This treatment not only controlled the medusahead, but it also resulted in greater establishment of perennial bunchgrasses.
Several studies have shown that fire alone can greatly reduce medusahead cover in the years immediately following treatment. A 1998 paper by Pollak and Kan showed that late spring burning on the Jepson Creek Preserve (central CA) reduced the cover of medusahead and other non-native annual grasses and increased the cover of native species and important range forbs. Another paper showed that successful medusahead control was related to the amount of non-medusahead biomass in the unit before a burn (Kyser et al. 2008), as more productive sites provided more combustible fuels, allowing for increased fire intensity. Timing is also an important consideration when using prescribed fire to control medusahead. A late-season grass, it flowers and goes to seed long after other grasses have turned brown. In an unburned system, this gives medusahead an advantage as it can continue to grow and produce seed without competition from early-season grasses. This also means that there is a window when it is the only plant vulnerable to fire and it is surrounded by dry fuels.
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Pitch Canker in California and Systemic Induced Resistance
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Pine pitch canker (caused by Fusarium circinatum) has threatened coastal pines since its discovery in California in 1986 near Santa Cruz. It is believed this invasive fungus originated in Mexico and entered California from the southeastern US. Since its introduction into California, it has spread rapidly and has resulted in substantial Monterey and bishop pine (other pine species, including shore pine, are also susceptible) mortality.
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Pt Reyes National Seashore bishop pine landscape-scale dieback and mortality caused by F. circinatum, 2017. Photo by C. Lee, Cal Fire.
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On a positive note, the UC Davis Gordon lab discovered that Monterey pines infected by the pitch canker pathogen can develop "systemic induced resistance" (SIR) to the pathogen. In some ways, SIR resembles a human immune response: initial infection of the tree activates a physiological pathway that leads to increased resistance to subsequent infections caused by windblown or insect-borne spores. However, despite the existence of SIR, F. circinatum continues to infect new areas within its 18-coastal-county Zone of Infestation. Within the past decade, the pathogen has invaded dense stands of bishop pine in coastal Marin and Sonoma Counties and is found as far north as southern Mendocino County. Branch tip dieback and tree-killing stem lesions are found in abundance in these stands. Time and further research will tell whether SIR is a phenomenon that bishop pine shares with Monterey pine. Hopefully so, as pitch canker adds to a growing list of other ecological and pathological issues affecting bishop pine along California's North Coast.
For more information, go to the UC IPM Pitch Canker Guidelines, Cal Fire Tree Note #32: Pitch Canker Disease in California, UC Davis Gordon Lab, and Pitch Canker Task Force.
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When buying firewood for camping or home heating this winter, remember to buy wood sourced local to where you will be using it, helping to minimize the spread of pests and diseases -
Buy It Where You Burn It. For a list of local firewood dealers, go to
firewoodscout.org.
Sincerely,
Katie Harrell
Communications Director
California Forest Pest Council
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