- Author: Patrick Moran
Editor: Guy B Kyser
The giant invasive grass arundo (Arundo donax), one of the weeds targeted under the USDA-ARS-funded Delta Region Areawide Aquatic Weed Project (DRAAWP), has been re-acquainted with one of its natural enemies imported from arundo's native range. A tiny insect called the arundo armored scale (Rhizaspidiotus donacis) has been successfully released in the Sacramento River watershed and in the Delta.
Arundo forms dense stands across at least 10,000 acres in California, and over 100,000 acres in other arid riparian areas such as the Lower Rio Grande Valley of Texas and Mexico. Other control methods such as herbicide application, mechanical removal, mowing or burning have been used to reduce arundo populations in California, costing tens of millions of dollars. However, arundo is a tough plant and takes advantage of human disturbance and fire in riparian habitats along creeks, sloughs, rivers and reservoirs. Arundo populations in California thus exceed the capacity of these other control methods. In the absence of control, arundo consumes and wastes scarce water – a single plant can consume as much water as corn when growing in moist soil under hot, sunny conditions. Dense arundo stands block access to water for irrigation and recreation, and also obstruct flood control structures such as drainage ditches. Arundo also displaces native plants and animals and alters geomorphology and water flow dynamics in riparian habitats in ways that make it difficult for the natives to come back even if the arundo is controlled.
Biological control of invasive weeds focuses on the characterization, release and evaluation of insects (or plant pathogens) from the weed's native range into areas where the weed is non-native. The arundo armored scale was collected originally in southern France, Spain, and Italy. Studies by Spanish collaborators showed that, even in its native range with its own natural enemies, the arundo armored scale reduces shoot growth and rhizome size by 50%.
Biological control agents undergo rigorous testing to ensure they are not a threat to native plants or crops. After a permit review process, the USDA granted a permit for field release of arundo armored scale in 2010. (This is one of two insects that have been released for biological control of arundo in North America.) Since 2011, this biological control agent has been released in the Lower Rio Grande Basin. Initial releases of this agent in California began in 2014, and it was found that the scale insect had become established at one site in the northern Sacramento Valley by November of that year.
Armored scales are small insects that spend most of their lives in an immobile state, covered by their waxy secretions (‘armor'). Adult females produce ‘crawlers' that disperse locally (typically just a few feet) to find new buds coming up from the arundo rhizomes or lateral shoot buds above ground. The crawlers then lose their legs and antennae and insert their stylet-like mouthparts into the arundo tissue to feed on the fluids in the plant's vascular system. Crawlers molt to a second immature phase, and about six to eight weeks later, short-lived adult males emerge from their armor and mate with the immobile adult females. The females continue to feed and slowly develop embryos. A new generation of crawlers then emerges from the females. The life cycle takes four to six months.
Top row, left to right: Tiny (0.5 mm) crawlers emerge from females and settle on rhizomes or lateral shoots. Second-instar immature scales continue to feed and expand. Winged adult males emerge from their oyster-like scale covering. Females (armored scale cover removed) are shriveled and skinny right after molting. Mature females are plump and turn a darker color when they are full of crawlers ready to emerge. Bottom row, left to right: Adult females form aggregations on arundo rhizomes and shoots. The presence of armored scale populations causes shoot distortion and reduces both shoot growth and rhizome size.
In 2015, we tested a new release technique using arundo ‘microplants'. We soaked arundo shoot fragments in water for one month, then planted them in pots where they produced new shoot buds and roots. Armored scale crawlers were released onto the microplants. After about six months, we planted the infested microplants at field sites in the Delta – Andrus Island on the Sacramento River, and at Big Break near Oakley – and along Stony Creek in Glenn and Butte Counties north of the Delta. We established the microplants adjacent to large arundo shoots, and we cut off some of the established shoots to encourage production of new rhizome buds and lateral shoots. We watered the microplants as needed to keep them alive for about 6 months.
Left to right: Microplant with gelatin capsules used to isolate scale crawlers from females (capsules had been opened and crawlers poured onto the base of the plant). Greenhouse bench with arundo microplants. Field plot with arundo shoots cut back to promote new shoot and rhizome growth. Base of an arundo shoot at the field site (arrow indicates location of adult female scales that developed from crawlers that had previously came out of the females on the microplants.
Almost one year after planting, in November 2016, we sampled arundo rhizomes and shoots from the areas where the now-dead microplants were placed. At the Sacramento River site, 150 females were found, and at a site on Stony Creek in Butte County, 72 females were found. The females were placed in gelatin capsules to capture crawlers. A total of 1,668 crawlers emerged by early January 2017. Since there are still many more arundo shoots around the microplant sites, these results indicate that the arundo armored scale has established reproductive populations at three sites in California. This is the first establishment of this biocontrol agent in the state. Additional releases are planned throughout the Delta and surrounding watersheds. Along with the arundo wasp (Tetramesa romana), the arundo armored scale is expected to significantly reduce the potential for arundo to grow, disperse and form damaging populations that threaten water resources.
This work is conducted under the USDA-ARS-funded Delta Region Areawide Aquatic Weed Project (DRAAWP). This portion of the project is led by Dr. Patrick Moran (Patrick.Moran@ars.usda.gov) of the USDA-ARS Exotic and Invasive Weeds Research Unit, Albany, CA. Dr. Moran is working with a postdoctoral researcher, Dr. Ellyn Bitume (Ellyn.Bitume@ars.usda.gov), on this project. Contact us if you have questions. The Sacramento-San Joaquin Delta Conservancy (Beckye Stanton) is collaborating with USDA-ARS to identify field sites in the Delta, connect with landowners, and integrate biological control with their chemical arundo control program. Dr. Moran cooperates with landowners and local Reclamation Districts to obtain access to field sites.
- Author: Ben Faber
At the recent HLB Conference in Florida a paper was given that reinforces the need for appropriate soil and water pH to maximize root density and tree health. The industry there is dominated by a range of rootstocks and by Valencia-like varieties. Jim Graham and colleagues have shown that pH contributes to orchard health in their HLB situation. This should be a reminder for California growers for general tree health. Florida soils tend to be more coarse than soils found in many California orchards. It's much harder to change soil pH with acidified irrigation water with heavier textured soils.
4.b.1 Soil and water acidification sustain root density of huanglongbing-infected trees in Florida
Jim GRAHAM, Kayla GERBERICH, Diane BRIGHT, Evan JOHNSON
University of Florida, Citrus Research and Education Center, Lake Alfred, Florida, USA
Abstract: Early symptoms of HLB include fibrous root loss and leaf blotchy mottle, followed by premature fruit and leaf drop, and yield decline. As a consequence of initial bacterial infection of fibrous roots, a 30-50% reduction in fibrous root density and elevated soil Phytophthora populations were detected in field surveys. Continued sampling of Hamlin and Valencia orange trees on Swingle citrumelo rootstock in different stages of HLB decline revealed that root loss occurs in two stages. The second phase of root loss (70-80%) begins at the early stage of tree canopy thinning resulting from leaf drop and branch dieback. A more extensive survey of HLB-affected groves indicated that greater decline in fibrous root health and expression of HLB symptoms is observed where irrigation water is high in bicarbonates (> 100 ppm) and/or soil pH > 6.5. HLB symptom expression of trees on different rootstocks follows the known intolerance to bicarbonate (Swingle citrumelo > Carrizo citrange > sour orange > Cleopatra mandarin). Acidification of irrigation water in central ridge and south central flatwoods Valencia orange groves on Swingle citrumelo rootstock for three seasons has maintained soil pH below 6.5 on the flatwoods and 6.0 on ridge. Over the last three seasons of survey, root density as an index of root heath has been sustained. Phytophthora populations remain below the damaging level in ridge groves and in flatwoods increase to damaging levels coincident with the fall root flush but drop back to non-damaging levels for remainder of the season. Compared to the 2013-14 season, yields in the ridge blocks have increased up to 4% and on the flatwoods have increased up to 22%.Growers using acidification treatments with sulfuric and/or N-phuric acid for the last 3 seasons report an average cost of $60 per acre. This cost will analyzed in relation to yield response to provide a cost benefit of acidification
Non-Technical Summary: Managements have been implemented to reduce soil, nutrient and water stress, and Phytophthora root rot. They include frequent irrigation cycles, fertigation and acidification of irrigation water and soil to reduce rhizosphere pH, and fungicides. Root density of trees under these practices fluctuates seasonally and annually but has not declined over the past 3 years. Trees managed with soil acidification and fertigation have steadily recovered in health and yield.
http://www.icc2016.com/images/icc2016/downloads/Abstract_Book_ICC_2016.pdf
- Author: Ben Faber
At a recent CA Avocado Society meeting there was a discussion about bout flowmeters and their selection. Flowmeters measure the volume of water moving through a full-flowing closed pipe and as such are one of the key components of an irrigation system whether drip, microsprinkler or full pressure systems. They are essential for managing irrigation efficiently and for monitoring the performance of the irrigation system. Managing irrigation efficiently requires: (1) knowing how much water the crop has used since the last irrigation (irrigation schedu7ling); and (2) operating the irrigation system to apply only the amount of water desired. A flowmeter gives the grower the information needed to apply only the amount of water required.
A critically overlooked benefit of a flowmeter is that it makes it possible to identify changes in flowrate during the season (measured at the same pressure), which may indicate problems such as clogging of emitters or filters, leaks in the system or problems with the pump or well.
There are several types of flowmeters and each has their pluses and minuses. Propeller meters are the most commonly used, but can pose two potential difficulties: debris in the water and a small loss of pressure which can be a problem with low flow systems. Alternatives are magnetic meters, ultrasonic, turbine and venture meters. Proper selection is based on pipe size, range of flow and pressure loss. But as with everything it depends on proper installation and maintenance.
Attached is a nice little overview by Larry Schwankl on how to choose a flowmeter for your situation.
flow meters
- Author: Ben Faber
A call from a small grower, surprised at the sudden decline of the avocado trees. It must be a disease was the grower's thought. Well driving up to the site, there were numerous trees with canopies indicating drought stress. In fact most of the trees looked like they had had the water turned off. When I got to the orchard, all the trees had a similar look (see photo below). The fringe of the canopy had turned brown/red where the leaves had collapsed rapidly, while the interior leaves were often still green. All the trees had a similar cast. It turns out the water district had required a cutback just when temperatures were going into the 100's. NO water, no cooling effect of transpiration and the outer fringe of leaves collapsed. This is called the “clothesline” effect. It's like a sheet on a clothesline where the margins of the sheet dry first and gradually the body of the sheet dries. The same thing happens in a canopy. The outside leaves are the first to dry out and then the rest of the canopy goes. When you see a whole orchard go down suddenly, that does not fit into a disease pattern. There's usually an epicenter where it starts – where it's colder, wetter, dryer, hotter, more overgrown, etc. and spreads out from there if it is going to spread. It turns out that the automatic irrigation system had gone down and the grower hadn't noticed until too late. When you see reddish tinged leaves, it means the leaves went down fast. When they are brown, it means they slowly went down over weeks or months.
With all the dead points in the tree, it is now open to disease – twig/leaf blight caused by one of the Botryosphaerias. These decay fungi are everywhere in an orchard decaying organic material on the orchard floor. With the dead material in the tree, now the tree becomes a potential feast for the fungi. The dead stuff has to come out, or the fungus will start eating into the tree. I suggested that instead of pruning out all those little points of death, that they cut back the whole canopy to major scaffold branches. In doing so, it would rapidly and cheaply remove the dead material and reduce the water demand.
- Author: Ben Faber
In a recent meeting the topic of where to go for irrigation information came up. Well there's no substitute for attending a class in irrigation, such as offered at Cal Poly SLO (http://www.itrc.org/classes/iseclass.htm ,
but here's some written sources to get you started thinking.
http://ciwr.ucanr.edu/california_drought_expertise/droughttips/
http://www.salinitymanagement.org/Salinity%20Management%20Guide/ei/ei_1.html
http://www.avocadosource.com/tools/IrrigationCalculator.asp
http://lawr.ucdavis.edu/cooperative-extension/irrigation/manuals
http://lawr.ucdavis.edu/cooperative-extension/irrigation/drought-tips
http://biomet.ucdavis.edu/index.php/evapotranspiration-mainmenu-32
http://www.fresnostate.edu/jcast/cit/goods/
http://edis.ifas.ufl.edu/topic_citrus_irrigation
http://edis.ifas.ufl.edu/results.html?q=irrigation&x=0&y=0#gsc.tab=0&gsc.q=irrigation&gsc.page=1
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