- Author: Ben Faber
This has been a hot time. Look for irrigation problems, but also look for other weather related problems. This is possibly the most shocking.
If you see your citrus tree suddenly collapse. It happens on a weekend or in a few days, and it has suddenly turned hot with a Santa Ana or Sundowner, it is quite likely "Dry Root Rot". This is a situation where the water conducting tissues, the xylem, have been clogged by fungi and when a sudden demand for water comes from the weather, the tree collapses because it can not support the movement of enough water to satisfy that demand. It is more common along the coast than the Valleyk, but it does occur there, as well.
It starts with some type of wound to the crown roots or stem - gophers or field mice nibbling away at the roots or crown. Or damage from weed whipping or some sort of mechanical damage. This allows entry of the Fusarium fungus that causes the xylem clogging. You can usually see the damaged tissue just below the bark, near the base of the tree. The damage has usually occurred several years prior and takes awhile for the fungus to do its clogging. There's no know cure for this situation. Cut the tree out. It's not particularly contagious as far as we know. The fungus is cosmopolitan, meaning it is found in most orchards, and it just waiting for a wound to invade. You can replant into the orchard, but just avoid causing wounding.
Dry root rot affects all citrus species and varieties.
http://ipm.ucanr.edu/PMG/r107100211.html
Photos:
Collapsed canopy, grapefruit
Dead tissue below the bark
- Author: Akif Eskalen
FUSARIUM DIEBACK AND POLYPHAGOUS SHOT HOLE BORER ON AVOCADO
Akif Eskalen1, Richard Stouthamer2
1Department of Plant Pathology and Microbiology, UC Riverside
2Department of Entomology, UC Riverside
BACKROUND
Polyphagous shot hole borer (PSHB), Euwallacea sp. (#1) (Fig.1) is an invasive beetle that carries three fungal symbionts in a special structure in their mouth called a mycangium. These symbiotic fungi are Fusarium euwallaceae, Graphium euwallaceae and Acremonium pembeum (Freeman et al. 2013, Lynch et al. 2015). The adult female tunnels galleries into a wide variety of host trees, where it lays its eggs and grows the fungi (Fig.2, 3). The fungi cause the Fusarium Dieback (FD) disease, which interrupts the transport of water and nutrients in over 38 tree species that are suitable for beetle reproduction. A separate invasion was recently detected in San Diego county and is now being called Kuroshio shot hole borer (KSHB) and is another closely related species to PSHB (Euwallacea sp. (#5)) carrying two new fungal species - Fusarium and Graphium. Both species have been found causing damage on avocado in the los Angeles basin and San Diego County.
BEETLE BIOLOGY
Adult females of PSHB and KSHB (Fig. 1) are black in color and 1.8-2.5 mm long. Adult males (Fig. 4 ) are brown and smaller than females at 1.5 mm long. More females are produced than males, which are flightless and very rarely leave the galleries. Mature siblings mate with each other so that females are already pregnant when they leave to start their own galleries. Males do not fly, but stay in the host tree.
SYMPTOM AND SIGNS
External Symptoms: Attack symptoms, a host tree's visible response to stress, vary among host species. Staining (Fig. 5), sugary exudate ( also called a sugar volcano) (Fig. 6-7), gumming (Fig.8), and/or frass (Fig. 9) may be noticeable before seeing the tiny beetles. Beneath or near these symptoms, you may also see the beetle's entry/exit holes, which are ~0.85 mm in diameter Fig 10). The abdomen of the female beetle can sometimes be seen sticking out of the hole. Advanced fungal infections will eventually lead to branch dieback, as seen on this Avocado (Fig. 11).
Internal Symptoms: Fungal species associated with the beetle PSHB and KSHB cause brown to black discoloration in infected wood. Discolored wood can easily be seen when bark is scraped away around the entry/exit hole (Fig 10). Cross-sections of cut branches (Fig. 12) show the extent of infection.
KNOWN REPRODUCTIVE HOSTS OF PSHB and KSHB
PSHB attacks hundreds of tree species, but it can only successfully lay its eggs and/or grow the fungi in certain hosts.
Known Suitable Reproductive Host Trees of PSHB:
- Avocado (Persea americana)
- Box elder (Acer negundo)
- California Sycamore (Platanus racemosa)
- Big leaf maple (Acer macrophyllum)
- Evergreen Maple (Acer paxii)
- Trident maple (Acer buergerianum)
- Japanese maple (Acer palmatum)
- Castor bean (Ricinus communis)
- Mexican sycamore (Platanus mexicana)
- Red Willow (Salix laevigata)
- Mimosa (Albizia julibrissin)
- English Oak (Quercus robur)
- Coast live oak (Quercus agrifolia)
- London plane (Platanus x acerifolia)
- Cottonwood (Populus fremontii)
- Black cottonwood (Populus trichocarpa)
- White Alder (Alnus rhambifolia)
- Titoki (Alectryon excelsus)
- Engelmann Oak (Quercus engelmannii)
- Cork Oak (Quercus suber)
- Valley oak (Quercus lobata)
- Coral tree (Erythrina corallodendon)
- Blue palo verde (Cercidium floridum)
- Palo verde (Parkinsonia aculeata)
- Moreton Bay Chestnut (Castanospermum australe)
- Brea (Cercidium sonorae)
- Mesquite (Prosopis articulata)
- Weeping willow (Salix babylonica)
- Chinese holly (Ilex cornuta)
- Camelia (Camellia semiserrata)
- Acacia (Acacia spp.)
- Liquidambar (Liquidambar styraciflua)
- Red Flowering Gum (Eucalyptus ficifolia)
- Japanese wisteria (Wisteria floribunda)
- Goodding's black willow (Salix gooddingii)
- Tree of heaven (Alianthus altissima)
- Kurrajong (Brachychiton populneus)
- Black mission fig (Ficus carica)
Known Suitable Reproductive Host Trees of KSHB:
- Avocado (Persea americana)
- California Sycamore (Platanus racemosa)
- Big leaf maple (Acer macrophyllum)
- Coast live oak (Quercus agrifolia)
- Cork oak (Quercus suber)
- Coral tree (Erythrina humeana)
COMMENTS OF THE PEST AND DISEASE COMPLEX
Fusarium dieback (FD) is a new, invasive, beetle-vectored disease that has caused damage on avocado and other host trees in urban forests and wild lands in the Los Angeles basin since early 2012, and Orange and San Diego County since early 2013. This pest/disease complex has also impacted the avocado growing regions of Israel since 2009. DNA analyses of polyphagous shot hole borer (PSHB) beetles indicate that those from San Diego County are different from those in Los Angeles.and these beetles are now being called Kuroshio shot hole borer (KSHB) and are genetically similar to a beetle population in Taiwan. The beetles from Israel and the Los Angeles basin are genetically similar to those from Vietnam (Stouthamer unpublished data). Other studies have shown that species of Euwallacea, as well as thefusariumfungi they cultivate, are genetically distinct, including those from the Los Angeles basin (which are identical to those in Israel) and San Diego (O'Donnell 2014). These results indicate that at least two introductions into California have occurred. Each beetle carries its own novel pathogenic fungal species of Fusarium and Graphium, while the beetle from Los Angeles additionally carries a species of Acremonium (Lynch et al. in press).
Rapid spread of the beetle/fungi throughout various land use areas is attributed to the diverse range and quantity of suitable hosts in Southern California (Eskalen et al., 2013). Establishment of the beetle is a source of concern for the avocado industry, of which 90% of the United States crop is produced in California (California Avocado Commission). Several commercial avocado groves in Los Angeles County have been infested since 2012. The second invasion in San Diego County was not detected in commercial avocado groves until October 2014, one year after the initial finding on sycamore in El Cajon. Since then, 20 commercial avocado groves in San Diego County have been confirmed infested.
MANAGEMENT
Currently there are no control measures to control this pest. Early detection of infestation helps reduce the population of the beetle by removing infested branches where beetle can reproduce their offspring.
-If the infestation is on the branch collar, cut into branch collar and spray pruning wounds with a registered product of Bacillus subtilus.
-Chip infested wood on-site to a size of one inch or smaller. If the branch is too large to chip, solarize them under a clear tarp for several months
-Sterilize tools to prevent the spread of the disease with either 25% household bleach, Lysol® cleaning solution, or 70% ethyl alcohol.
-Avoid movement of infested firewood and chipping material out of infested area.
-For more information visit http://eskalenlab.ucr.edu
The insect and the damage on avocado
- Author: Ben Faber
- Author: Craig Kallsen
- Author: Akif Eskalen
Dry Root Rot is a pretty fantastic disease symptom that is usually seen in lemon, but can be seen in orange, as well.
Craig Kallsen, UCCE Citrus Advisor in Kern Co. comments on a disease sample:
I have seen a lot of dry root rot over the years. It usually is something that damages or weakens the root system which allows a Fusarium species to colonize the rootstock. It is very common in older lemon groves that froze at some point in their past. Also common in groves that suffered a lot of gopher damage or where the wraps got too hot in the sun burning the bark and cambium. I have also seen it in cases of fertilizer or other soil-applied chemical burn. I have no doubt that graft incompatibility could do it too.
Akif Eskalen, UCCE Plant Pathology Specialist chimes in on a disease sample submitted:
As you can see from the attached picture there is a weird callus formation and symptoms of incompatibility at the graft union which I think is the primary cause of decline. We didn't observe any discoloration in the scion, however rootstock was completely discolored where we isolated Fusarium solani the causal fungus of Dry Root Rot. Dry root rot caused by either Fusarium solani and/or Fusarium spp. When there is a disconnection at the graft union, the phloem can not transfer enough carbohydrate to the rootstock to feed feeder roots. Fusarium fungal species are present in the soil and they can attack and easily colonize on starch depleted roots and cause DRR.
We still don't know what is causing the graft incompatibility on these plants. That needs to be investigated.
It's still not clear how and why citrus becomes affected.
- 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.
- Author: Akif Eskalen
The Polyphagous Shot Hole Borer (PSHB), Euwallacea sp. #1, is an invasive beetle that carries three fungi: Fusarium euwallaceae, Graphium sp. , and Acremonium sp. The adult female tunnels galleries into a wide variety of host trees, where it lays its eggs and grows the fungi. The fungi cause the Fusarium Dieback (FD) disease, which interrupts the transport of water and nutrients in over 35 tree species that are suitable for beetle reproduction.
Once the beetle/fungal complex has killed the host tree, pregnant females fly in search of a new host.
A separate invasion was recently detected in commercial avocado groves and landscape trees in San Diego county. It has been determined that the damage has been caused by another closely related species of PSHB (Euwallacea sp. #2), carrying a new species of Fusarium and Graphium. The beetle in LA, Orange, Riverside, and San Bernardino Counties are morphologically indistinguishable, but genetically distinct from the beetle found in San Diego County.
Signs and Symptoms
Attack symptoms, a host tree's visible response to stress, vary among host species. Staining, sugary exudate (B), gumming, and/or frass may be noticeable before the tiny beetles (females are typically 1.8-2.5 mm long). Beneath or near these symptoms, you may also see the beetle's entry/exit holes, which are ~0.85 mm in diameter. The abdomen of the female beetle can sometimes be seen sticking out of the hole.
Sugary exudate on trunks or branches may indicate a PSHB attack (photos A-E). Note that exudate may be washed off after rain events and therefore may not always be present on a
heavily infested branch.
Hosts
PSHB attacks hundreds of tree species, but it can only successfully lay its eggs and/or grow the fungi in certain hosts. These include: Avocado, Box elder, California sycamore, Coast live oak, White alder, Japanese maple, and Red willow. Visit eskalenlab.ucr.edu for the full list.
Fusarium dieback pathogens cause brown to black discoloration in infected wood. Scraping away bark over the entry/exit hole reveals dark staining around the gallery, and cross sections of cut branches show the extent of infection. Advanced infections eventually lead to branch dieback and death of the tree
How to report a suspect tree
Please report suspected tree infestations to UC Riverside (eskalenlab@gmail.com).
Submit the following information:
•Contact information (name, city, phone number, email)
•Suspect tree species
•Description of suspect tree's location (and/or GPS coordinates)
•Description of suspect tree's symptoms
•Photos of suspect tree and close-up photos of symptoms (see examples)
Take photos of suspect trees from several distances. Include photos of:
1. the trunk or symptomatic branches;
2. the symptoms (close-up); and
3. the entry/exit hole, if visible, with a ballpoint pen for scale (remove exudate if necessary). If dieback is observed, take a picture of the entire tree.