- Author: Jim Downer
As we continue an historic drought in California, trees all over Southern California are showing symptoms of stress, and in some cases have died due to drought and pests that attack drought stressed trees. Despite recent and significant rainstorms, it is likely that trees will again be stressed later in the irrigation season. Trees and other woody plants in nurseries also bear the burden of drought stress as irrigation waters become increasingly salty because of drought effects on wells and reliance on stored water in reservoirs continues.
The Polyphagous shot hole borer is a serious pest of nursery and landscape trees and threatens many species. As such, counties adjacent to Los Angeles are at risk of invasion by this new exotic pest and we are watching and monitoring trees for possible extant new detections. The drought has stressed many of the signature trees that could be attacked by PSHB and these trees are often attacked by native or established pests. In some cases these beetles closely resemble PSHB and cause symtpoms of bleeding and in some cases cambial discoloration and gallery formation similar to that of PSHB.
On coast live oak (Quercus agrifolia) there are two look alike beetles the western oak bark beetle (Pseudopityophthorus pubipenis) and the Oak ambrosia beetle (Monarthrum scutellare). The western oak bark beetle is common in Southern California and the ambrosia beetle more common in the northern half of the state but both have been detected throughout California. As with many beetle/tree interactions both of these are attracted to drought stressed trees. When attacked coast live oak bleeds heavily and these insects often attack in larger numbers uniformly along the main stems or trunk. Examination of the cambium of Oak Bark Beetle attacked trees reveals small galleries and little or no necrotic tissue.
Prunus spp such as peach, nectarine, plum and apricot are common in back yards and retail nurseries. This year we are seeing much increased attack of these trees by the European fruit borer or shot hole borer (Scolytus rugulosus) a beetle very similar in stature to PSHB. The insect is the same size as PSHB and makes numerous holes and causes excessive bleeding in Prunus. This insect also seems to carry a fungal pathogen resulting in cambial necrosis.
One other insect that could be mistaken for PSHB is the walnut twig borer which vectors Thousand Cankers Disease of walnuts (both native and English). This beetle (Pityophthorus juglandis) carries with it a fungus Geosmithia morbida, that causes extensive cambial necrosis, and ultimately twig and branch dieback results from its presence.
- Author: Sonia Rios
The California Avocado Commission is joining forces with Kevin Turner, UC Cooperative Extension goldspotted oak borer (GSOB) program coordinator (http://ucanr.edu/sites/gsobinfo/) in producing and distributing a number of roadside signs to help control the movement of pest infested firewood.
They are asking for avocado grower's participation in areas that are susceptible to the GSOB and/or the Polyphagous Shot Hole Borer (PSHB). GSOB susceptible areas include oak woodlands and forests while PSHB environments include avocado groves. Some of these susceptible locations are primarily focused in the Fallbrook, Escondido, Valley Center, and Alpine areas. Eventually signs will be developed that will feature both the GSOB and the PSHB and discourage movement of oak and avocado wood.
The signs can go in a variety of frame designs. Most signs are 4' x 8'and are normally inserted into a redwood frame, but can be as simple as posts and a piece of exterior plywood onto which the thin aluminum sheet sign can be attached. The signs should be placed visibly along major roadways or busy streets.
If you would like to participate by permitting signs to be placed on your property along major streets, please contact:
Kevin Turner, GSOB Program Coordinator, UCCE/UCR
kevint@ucr.edu
951-827-5115
951-452-6427 cell
- Author: Ben Faber
Polyphagous Shot Hole Borer can go to over 100 and counting hosts, but the Fusarium that the ambrosia beetle carries can not reproduce on all tree species. It is this fungus that ultimately kills the tree. There are now though thirty-seven hosts on which the beetle will attack and the Fusarium will grow. Here is the current list, 14 of which are California natives:
Known Suitable Reproductive Host Trees:
*Native species to California
- Author: Ben Faber
From The Packer:
South Florida university researchers are using dogs and drones to sniff out a disease that's killing the region's avocado trees.
The Florida International University researchers are sending dutch sheppards and belgian malinois into avocado groves to locate trees infected by the lethal laurel wilt disease, which is spread by the redbay ambrosia beetle.
Detection is a major problem and trees can start to wilt within two weeks.
By the time infected trees are detected, the fungus has likely spread to nearby trees via root grafting, said DeEtta Mills, a biological sciences professor.
She and Kenneth Furton, a university provost and forensic chemist, are leading research that trains and deploys five dogs into Miami-area groves.
Drones flying above the groves can detect symptomatic trees, which signal researchers to direct the dogs to infected areas.
The dogs run through the groves and with their powerful noses, have been 90% accurate in locating infected trees, Mills said.
Because of permitting paperwork delays by the Federal Aviation Administration, the researchers haven't been able to use the drones.
The researchers hope to receive approval for drones by August and are relying on growers to point them to infected trees.
The drones provide higher accuracy and can better cover larger areas because running the dogs too long can overheat them and wear them out, Mills said.
Their heavy panting can dull their sniffing senses so after about 20 minutes, the researchers return them to kennels in air conditioned vans, Mills said.
The dogs are trained with diseased wood and infected tree samples detected by the dogs are sent to researchers who examine DNA to verify contamination, she said.
“These dogs, they love to do this and it's amazing to watch them,” Mills said. “These ‘girls' come out of the kennels of the van and ask us where we would like to send them and what we would like them to do. They're extremely highly-driven dogs. If we can get permission to use the drones, it will help us identify areas we need to go in with the dogs and help us verify infection much faster so the dogs won't have to cover as much ground.”
Canine detection is another way of helping save the state's multi-million dollar avocado industry and ultimately, the North American industry.
Florida growers have lost about 4,000 of nearly 800,000 trees and the disease has spread throughout the Mid-Atlantic and into Mississippi.
If it travels farther west, the dogs and drones detection system could also help growers in California and Mexico protect their much larger production, she said.
The Miami university is also working with University of Florida researchers and growers.
N.B. These techniques could also be used to trace Polyphagous Shot Hole Borer infested trees, as well.
- Author: Ben Faber
Polyphagous Shothole Borer which is an ambrosia beetle that normally feeds on dead trees is going after live trees - over 100 species including sycamore, alder and coast live oak. It also goes after avocado. The California Avocado Commission has sponsored the placement of traps that have lures for PSHB. The traps are near avocado orchards but also likely spots where they might show up, such as campsite where people would bring firewood that might be infested with the beetle. The map here shows where the traps are located and where PSHB have been trapped. There are also traps in Santa Barbara County which are not yet shown on this map.