- Author: Thomas J Getts
I have gotten quite a few calls about blister beetles this year. There was a newspaper article up in Modoc that caused some stir, and was picked up by a lot of social media pages. So, what are blister beetles and why do we care?
Blister beetles get their name for a reason. They contain the toxin cantharidin, which can be excreted when they are threatened, or crushed which causes bad blisters on the skin. While this is problematic they typically are not drawn to humans, and blisters can be avoided by not handling them. Where they pose a larger problem is as a contaminant of hay, where they can be crushed/killed and incorporated into a bale posing as a potential toxin to be consumed by livestock.
Photo One: Blister Beetle on Musk Thistle next to a Roadway
Let's take a step back. What are blister beetles and why are they a subject of conversation now? There are numerous native blister beetles in California. Some are striped, some are brightly colored, but most of the ones I have been seeing are black or grey. The immature larvae of blister beetles feed on the eggs of grasshoppers or ground dwelling bees. I don't have to tell anyone in the Intermountain region, we have had quite a few bad grasshopper years which has led to an increase in blister beetle populations. Typically, the adults lay eggs right on top of the egg beds of grasshoppers. I'd be on the lookout for blister beetles the rest of this year, and definitely next year as they feast on the eggs underground. (So, they are not all bad as they kill some hoppers!).
Photo Two: Grasshoppers flying away from an ATV in a pasture up in Modoc County
As adults, they can consume forage, but typically they are drawn to flowers and consume pollen. (Different species have different preferences.) I have mainly seen them on roadsides, trail sides, and rangelands where there are flowering plants. In hay fields I have only seen them in “native hay pastures” that have wildflowers. However I have gotten reports of them being on the edges of some alfalfa fields that have started to go to bloom.
For livestock generally they are only problematic when they get caught up in a bale. How many is too many? This is a good question. Numerous extension publications cite research done back in the 80's looking at how many blister beetles it would take to kill a horse (horses are more susceptible to the toxin than cattle of sheep). As with all toxin's it often depends on numerous factors, and there is not a single number of beetles that will kill a horse every time. The amount of toxin per beetle can vary by species of beetle as well as within species of beetle. From the research done in the 80's the cantharidin content per beetle ranges from 0.5mg to 5mg, and is toxic to horses at the tune of 1mg/kg. This means that there can be a huge range of how many beetles it will take to kill a horse (see table one). With that being said while it may take a significant number of beetles to kill a horse, as few as five beetles can start to cause colic.
Table one: Adapted from Capinera et al. 1985. J. Econ. Entomol. 78:1052-55.
So, what do you do about the beetles? One of the best things to do is scout fields before they are cut to make sure you do not have them in the field. While it might be counter your management objectives to maximize yield during the mid-season cuttings, cutting alfalfa or clover before bloom can reduce the incentive of beetles to move into hay fields. It is also important the keep a clean hay field, and reduce the number of weeds that may flower in the field drawing the beetles in. There are insecticides like (Sevin- carbaryl, or Warrior- lambda-cyhalothrin) which are effective at killing blister beetles in forages, but may pose their own drawbacks. While most of the beetles should die and fall down to the ground after an insecticide application, there is still some potential for them to be incorporated into the hay during the cutting and raking process. Likewise, the pre harvest intervals for these materials can delay cutting and could require driving over a lot of hay, if an aerial applicator is not available. Cutting around infested patches or isolating/discarding hay that may be contaminated, could be a prudent strategy. Likewise waiting until the beetles move out of the field could be an option.
Photo Three: Blister beetles on clover in a "native" hay meadow in the Intermountian region
There are over 300 species of blister beetles in North America, and not all have been tested for their Cantharidin content. When haying especially using modern equipment with conditioners, I urge you to be cautious, and take time to scout fields before cutting, especially if that hay is going to the horse market.
For more information there are some excellent extension publications online from UCIPM, Colorado State University and North Dakota State.
Photo Five: Blister Beetle on Feral Rye next to the Susan River in Lassen County
- Author: Thomas J Getts
Ten years ago, Guy Kyser wrote an excellent blog on the identification of Northern California's “Big Three” invasive thistles. I encourage you to check it out, if I recall correctly, it is one of the most viewed blog posts ever posted on the UC Weed blog, which is impressive!
Driving back home from Quincy yesterday, in the Dixie fire scar on Hwy 70, there were hundreds of native “snowy thistles” growing along the steep slopes clinging to the rocks. This has to be one of my favorite plants since moving to California. Stark white, covered in hairs, with a vibrant pink flower, it looks like something out of a Dr. Suess book! The first time I saw a snowy thistles, I made the person who was driving slam on the brakes and flip a U-turn so I could check them out.
Picture one: Snowy thistle in Surprise valley on a roadside before it bloomed. Look at how dense the white hairs are!
Here in Northeastern California we have a boatload of native thistles, and doing a quick search for thistles on Cal-flora will produce a list of over 20 native thistles, as well as quite a few non-native thistles. It really is important to be able to identify the difference between the good ones and the bad ones.
First, I would like to highlight four of the non-native thistles I get the most questions about controlling, and only one, Bull thistle (Cirsium vulgare) overlaps with Guy's list.
Picture Two: Bull thistle in the Honey lake Valley, observe the onion/bulb shaped seed heads.
Bull thistle is pretty widespread, and while it can form dense patches, often it does not. It typically grows as a biennial, and is around 3 feet tall (sometimes taller). Bull thistle has a deeply serrated leaf, with onion shaped flower heads. I will mention that the head shape/size can really set it apart from the other thistles I'll mention.
The next biennial thistle is Musk thistle (Carduus nutans). Lower leaves on rosettes often have a whitish tinge on the margins. It can grow quite tall (over 6 ft. if moisture is available), and flowers are large and typically perched on individual stalks. The bracts below the flower heads are large and distinctive compared to the other thistles, and the bottom of the flowers are somewhat flattish.
Picture Three: Musk Thistle in a pasture in Sierra valley, look how large and distinct the bracts are at the base of the flower.
Another, Scotch thistle (Onopordum acanthium) is probably the worst of the biennial thistles because of its decades long lived seed bank. When it grows tall people describe it as a “Christmas tree” and folks will literally chop them down with axes if they are not controlled when young. I have seen plants 8 ft. tall with bottom stalks 5-6 inches in diameter. However, it doesn't always grow this tall and under moisture stress will produce seeds on plants only a foot or two high. It has more of a blueish grey tinge to the foliage which are covered in numerous hairs. The main stems are winged. Flowers heads are typically bigger rounder and flatter than Bull thistle, but not as flat as Musk thistle with much smaller bracts. The foliage of the Scotch thistle really sets it apart from the other two.
Picture Four: Scotch thistle in Long Valley, notice the rounder seed heads and hairy blueish grey leaves.
Lastly is Californian thistle. Just kidding… but not really! Cirsium arvense, what we call Canada thistle in the states is called California thistle in New Zealand. It doesn't come from California or Canada, but instead Eurasia, but I guess it is fun to blame your thistle problems on other places! This thistle is the only perennial on the list, and has a deep creeping root system. Leaves are typically smaller than the other three and flowers are much smaller often growing in bunches or clumps on a plant. Flowers are most typically purple, but occasionally you can get white blooms. The underside of the leaves are covered in white hairs. Canada thistle is terribly problematic in both cultivated production and wildlands.
Picture Five: Close up of smaller Canada thistle heads in the Honey Lake Valley. Heads can be onion shaped, to round, but are smaller than the biennial thistle heads above.
Picture Six: Canada thistle in Willow Creek Valley during the Dixie fire in a triticale field. Notice the smaller leaves small seed heads in clumps with purple pink and whitish flowers.
Cal Flora/Cal Photos is a great place to get some pictures of various thistles, native and non-native to make sure you know what you are dealing with. I know quite a few folks that spray or dig all thistles, which is not ideal as the natives can be beautiful and provide good pollinator habitat!
- Author: Thomas Getts
Last year about this time, I posted a blog regarding an ongoing trial investigating various herbicides for Pre-emergent Control of Medusahead. I wanted to follow up on that trial which I “deemed” unsuccessful and share some of the data collected in 2017.
The main objective of the study was to test various herbicides for medusahead control. I was interested if some of the work conducted at Colorado State with Esplanade (indaziflam) could be replicated with medusahead. In Colorado field trials, single applications of Esplanade had offered three-year control of cheatgrass without litter manipulation prior to application. Could this be replicated with medusahead, notorious for its thick persistent litter layer? Secondly, it was of interest to take a look at Milestone (aminopyralid) applications as a preemergence treatment in the Intermountain Region. Josh Davy, Guy Kyser and Joe DiTomaso had seen excellent success utilizing Milestone for preemergent medusahead control in lower elevation rangelands, as indicated in one of Dr. DiTomaso Blogs and this article from Techline Invasive Plant News.
I implemented two field trials in September of 2016 to investigate if single applications of either of these products could be effective for medusahead control. At the time of application, no medusahead had germinated, so the preemergent activity for each of these products was being tested. One trial was located by Willow Creek near Goose Lake, and the other trial was located further south, just outside of Likely, California.
While initial results from the evaluation in November of 2016 were not great, I wanted to continue to follow the plots. Further evaluations were conducted in June and November of 2017 at both trial locations. Results from both sites at the November 2017 evaluation can be found in Table One below:
Table One: Displays percent medusahead control at both sites in November 2017, 14 months after treatment.
Good control of medusahead was achieved at both study sites in most treatments that contained Esplanade. At the Willow Creek site, Esplanade 7oz/acre alone offered 97 percent control. Where the best treatment at the Likely site was a combination of Method 8oz + Esplanade 7oz/acre which gave 92 percent control (Picture one). Looking at the plots anecdotally, it appeared Esplanade failed to control the medusahead in areas where litter layers were the thickest (Picture two). Milestone 14 oz/acre offered some suppression of medusahead at both sites during the June evaluation (Picture Three), however, almost no control was observed in germinating seedlings during the November 2017 assessments. Panoramic (imazapic) was unsuccessful at both sites.
Picture One: Excellent control of medusahead at the Likely site for the June evaluation of Method 8 oz + Esplanade 7 oz in this replication. Some small perennial grasses are present in the top right corner of the plot, but overall medusahead was largely replaced with bare ground (litter from the previous year).
Picture two: The Likely site in June of 2017 looking at the 7 oz Esplanade treatment. The red circle highlights where medusahead grew through the treatment. Outside of the circle, excellent control was observed and the litter layer from the previous growing season still covered the soil surface. Some perennial grasses are present.
Picture Three: The Likely site in June of 2017, looking down the middle of an untreated check and Milestone at 14 oz. At this evaluation, Milestone offered some suppression of the medusahead. However, by the fall evaluation, medusahead not initially controlled by Milestone took advantage of the lower densities, and individual plants grew much larger and more vigorously than individual plants in the untreated control.
These field trials have certainly seen an interesting set of environmental conditions as one of the wettest winters in recorded history came after application. All of the precipitation certainly could have affected the movement and degradation of herbicides applied. It could be considered a worst case scenario, or a best case scenario to test the effectiveness of the residual activity these products have.
There were populations of perennial grasses at each site with larger populations existing at the Willow Creek site. An assessment of species cover by functional group was conducted, and Table Two displays the results for the Willow Creek site in November 2017. Largely reductions in medusahead were replaced with bare ground, along with small numerical increases in perennial grass cover. Similar results were seen at the Likely site, but perennial grass populations were much lower and more sporadic throughout the plots.
Table Two: Species cover by functional class for the Willow Creek site for the November 2017 site evaluation.
Picture Four: The untreated check for the June assessment at the Willow Creek site. Medusahead was vigorously growing in-between the interspaces of perennial grass species.
Picture Five: Willow Creek, Esplanade 7oz at the June assessment. No medusahead was recorded in this plot. Actively growing grasses are perennial species. Medusahead litter from the previous growing season can be observed in the interspaces of the perennial grasses.
Esplanade has a very long residual activity, and I am planning on monitoring these studies throughout the 2018 growing season. It will be interesting to see if some of the bare ground previously occupied by medusahead will fill in with other species, or if it will refill with medusahead. When resources allow, I would like to re-test both Esplanade and Milestone under different environmental conditions. Please feel free to follow up with me if you have any questions: tjgetts@ucanr.edu.