- 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.
- Author: Ben Faber
Having trouble viewing this email? View it as a Web page. The government of Ecuador has requested the U.S. allow avocado to be imported into the continental United States. APHIS has drafted a pathway-initiated risk assessment for this request. The draft document is available for 30 days for stakeholders to review and provide comments. The document and instructions for submitting comments may be accessed through the APHIS Plant Import Information Web page, or this link: http://www.aphis.usda.gov/plant-health/risk-assessment-consultation.
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- Author: Sonia Rios
Education:
Rios completed an M.S. in Plant Science with an emphasis in Weed Science from California State University, Fresno, a B.S. in Plant Science from California State Polytechnic University, Pomona
Experience:
Prior to accepting her advisor position, Rios served as a staff research associate in UCCE Tulare County where she assisted advisors in all phases of applied agricultural research (field and greenhouse research on cereal crops, cotton and weed management). She was involved in approximately 30 – 40 research projects that included research testing in herbicide resistance, variety evaluations, and pest management including evaluating new herbicides and insecticides. Rios has conducted and reported agronomy research experiments through data collection that is statistically analyzed, translated and disseminated to clientele; maintained research plots; prepared educational materials for research reports and University publications that would benefit California growers, industry clientele; assisted regulatory agencies with science-based information; conducted radio interviews; and she was a regular speaker at the Tulare County Pesticide Safety meetings. In addition to working with UC, she was also her main professors' student research assistant that would help with trials on campus, assist undergraduates with their research projects and spent time in the classroom teaching.
Rios had also worked with the United States Department of Food and Agriculture (CDFA) inspecting airplanes for Japanese beetle as an Agriculture Aide I. She also worked with the United States Department of Food and Agriculture (USDA) Forest Service as a Forestry Technician.
Rios will be working in education and applied research program in tree crops production and marketing in Riverside and San Diego Counties. Primary target crops are citrus, avocados and dates, but also include other subtropical and deciduous fruit and nut crops, such as pomegranates, figs, mangos and walnuts.
She will facilitate interactions and information exchange among campus based academic, Cooperative Extension advisors and community stakeholders. Focus is expected on increasing productivity and efficiency of commercial tree crops operations, thus maximizing the return on invested capital, and at the same time, providing consumers with a high quality, safe and reasonably-priced product. The advisor will address emerging production issues in subtropical fruit crops including: horticulture, entomology, plant pathology, integrated pest management, plant nutrition and variety testing. She will be working closely with the subtropical horticulture industries, local growers and members of the subtropical horticulture and nuts and fruits workgroup to identify research areas of highest priority. Her contact information is as follows:
Cooperative Extension Riverside County 21150 Box Springs Road, Suite 202 Moreno Valley, CA 92557-8718
Phone#: 951-683-6491
Email Address: sirios@ucanr.edu
- Author: Ben Faber
Impacts of the recent drought conditions on Central Coast avocado production, and potential impacts of continued drought conditions
Avocados are the most salt and drought sensitive of our fruit tree crops. They are shallow rooted and are not able to exploit large volumes of soil and therefore are not capable of fully using stored rainfall. On the other hand, the avocado is highly dependent on rainfall for leaching accumulated salts resulting from irrigation water. In years with low rainfall, even well irrigated orchards will show salt damage. During flowering there can be extensive leaf drop due to the competition between flowers and leaves when there is salt/drought stress. In order to reduce leaf damage and retain leaves, an excess amount of water is required to leach salts out of the roots zone. The more salts in the water and the less rainfall, the greater leaching fraction. Drought stress often leads to diseases, such as black streak, bacterial canker, and blight (stem, leaf, and fruit). Defoliation leads to sunburned trees and fruit which can be severe economic losses.
Strategies to address drought conditions
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Ensure that the irrigation system is at its greatest potential and is maintained. Avocados are grown on hillsides and pressure regulation is extremely important and is frequently neglected.
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Significantly prune trees to reduce leaf area. Avocado can be a very large tree, and if half the canopy is removed, there can be as much as 1/3 reduction in water use. When trees are about 15 feet tall, removing half the canopy can reduce water use by one half.
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In extreme drought conditions, the canopy can be reduced to just the skeleton branches which are white washed to prevent sunburn. Water use drops to zero, and then gradually as the tree leafs out, water can be slowly reapplied, but at significantly less amounts than with the full canopy. Stumping typically results in three years' worth of crop.
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In orchards that have low producing areas, because of recurrent frost, high winds, shallow soils, disease, etc. the grower could decide to completely remove those trees, thereby saving water.
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White kaolin applied to leaves has been shown to reduce leaf temperatures and water loss. This can be used, but under the direction of the packing house, since if it is applied to fruit, it is very difficult to remove.
Impacts of the recent drought conditions on Central Coast citrus production, and potential impacts of continued drought conditions
Citrus is much less sensitive to salts and drought than avocado, partially because of its greater rooting depth. However, it is much more sensitive than deciduous fruit trees, resulting in smaller fruit and lower prices when drought cannot be addressed with adequate irrigation water. Drought also makes the trees more susceptible to leaf drop, and sunburned fruit.
Strategies to address drought conditions
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The strategies for citrus are very similar to those for avocado. It is much more sensitive to pruning to reduce water use than avocado. Typically removing half the canopy results in half the water use. Because of thus greater control, citrus is rarely stumped.
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By reducing canopy size, production can be maintained, often without loss of fruit size.
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Kaolin clay can effectively reduced water use and can be applied soon after harvest without the problem of coating fruit making its removal difficult at the packing house.
- Author: Ben Faber
Just when you thought we knew all the devastating pests of avocado, along comes another one, this showing up in the Piru area of Ventura County - bagrada bug. The infestation is in huge numbers covering the stems and leaves of the tree, leaving fecal droppings on the backsides of leaves. The insects have caused some defoliation and damage to terminals. They lay their eggs in crevices in the soil and sometimes on the plant. Maybe mulching would help in their control. The orchard will be sprayed soon to control them.
The bagrada bug, Bagrada hilaris, also called the painted bug, is a stink bug that attacks various vegetable crops, weedy mustards and several vegetable crops like cabbage, broccoli and cauliflower. It is particularly devastating to young seedlings and leafy mustard greens.
Bagrada bugs often infest wild mustard weeds, which are pervasive in California on hillsides and in agricultural corridors in late winter to early spring. Populations rapidly increase in the weeds when seasonal temperatures rise. Record numbers of bugs can invade newly planted cole crops after mustard weeds dry out in late summer.
The bagrada bug is an invasive pest species, native to Africa, which has spread to India, Pakistan, parts of Southeast Asia, and Italy. In the United States, it was first found in Los Angeles County in 2008. By 2011, the pest had disseminated throughout Southern California to include San Diego, Imperial, Orange, Riverside, San Bernardino, and Ventura counties. In September 2012, the pest moved northward to Santa Barbara and San Luis Obispo counties and recently (2013) the Bagrada bug was found in Fresno, Tulare, and Monterey counties.
In this case, it appears that with the drought all the mustard on the hillsides has dried up and the only food is the young avocados on the hillside. Interestingly, the neighboring canyon is infested with harlequin bug (Murgantia histronica) another stink bug with similar coloration but about three times larger than the bagrada bug. Once rains return, these pests should retreat back to the wild hillsides.
Images: 1) Dry hillside where infestation is occurring. 2) Defoliation caused by bug. 3) Fecal pellets on underside of leaves. 4) Bagrada adults and nymphs.
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