Western Plant Diagnostic Network1

First Detector News A Quarterly Pest Update for WPDN First Detectors Winter 2017 edition, volume 10, number 1

In this Issue Dear First Detectors, We have gone from 5+ years of drought with water-starved Page 1: Editor’s comments trees, vineyards, and gardens to an overabundance of water

Pages 2 – 3: Drought, Rain, in a very short time. The lead article discusses working with Snow, Flooding, and Plants wet soils and the judicious selection of nursery stock. Hawaii is right in the middle of the Pacific and is indeed the crossroads of that ocean. Because it is the crossroads and Pages 4 – 5: Hawaii: was historically isolated, it receives more than its share of Paradise for Invasives invasives plants, , , and plant pathogens. The Hawaii Department of Agriculture (HDOA) has sent a list of Page 6 – 7: Five Fusarium the latest invasive pathogens. Nevada once again Species Isolated from Hemp contributes to the further knowledge of diseases of

Cannabis sativa. And there is yet another invasive Pages 8 – 9: Olive Bark pest of olives in California, this time a woodboring bark Found in California beetle found in Riverside County, California. Monday, March 20th is the first day of spring, time to get Contact us at the WPDN Regional busy in orchards, vineyards, fields, and gardens! Keep an eye Center at UC Davis: out for invasives, who are also waking up! Phone: 530 754 2255 Email: [email protected] Please find the NPDN family of newsletters at Web: https://wpdn.org Editor: Richard W. Hoenisch Newsletters @Copyright Regents of the University of California All Rights Reserved

J. B. Wheatley J. B.

Gypsy moth about to emerge from pupa Western Plant Diagnostic Network News

Drought, Rain, Snow, Flooding, and Plants 2

In the Summer 2016 WPDN newsletter featured Western forest mortality from the effects of five years of drought, warmer winters, and the subsequent explosion of woodboring beetle populations. What a difference a very wet season makes! The West Coast dams and aquifers are being recharged, as well as the Colorado River basin. The Southwest is still parched, but hoping for a good August monsoon season.

With all these blessings, standing water and wet soils can be also be cold and anaerobic or hydric. Trees planted in cold, wet soils may be in anaerobic conditions and experience root rots. Seeds planted into cold soils may sit and wait or may germinate but grow very slowly. In these very early stages of life, seedlings are highly susceptible to soil borne pathogens that cause root rot and damping off, such as Rhizoctonia and Pythium. Signs that trees and crops are infested with Rhizoctonia and Pythium are:

 Plants are stunted.  Root tips are brown and dead.  Plants wilt at mid-day and may recover at night.  Plants yellow and die.  Brown tissue on the outer portion of the root easily pulls off leaving a strand of vascular tissue exposed.

To prevent these early season root rotting pathogens, wait to plant warm season crops and gardens until soils have warmed to the recommended temperature and are moist but not heavily wet. This year, it may be necessary to start seeds indoors and transplant them into the garden when outdoor conditions improve. In addition many simple structures like cold frames and walls of water can help warm soils and protect plants. Black plastic mulch also warms soil in the root zone. By growing plants in a raised bed, gardens have improved drainage even in wet weather. Seeds coated with a fungicide treatment will be protected at the earliest stages of growth.

Tree and vineyard growers should always obtain their planting stock from reliable and certified nurseries. In addition to the soil fungi, plant viruses, not visible in dormant planting material, could infect the woody plant and manifest later in growing trees and vines.

Retail plant nurseries have to stay on top of their pests and disease issues. Choose to buy from places that seem to be always monitoring their product. Despite what appears to be close monitoring, even the most scrupulous shop owner can miss a problem.

It is up to you to check your individual plants for any visible insects or disease problems. Turn the leaves over and inspect for visible insects hiding there. Look for chewed or damaged spots on the leaves and stems, and pick only the individual plants that have nothing. A disease can be in the form of mold, mildew, fuzzy, discoloration, slime, or powder. Lastly, do not buy a flat or 6 pack with a diseased plant in it. More than likely, the other 5 plants have been inoculated. You don’t want to introduce Phytophthora, Fusarium , and Verticillium into your garden soil.

When you do find a plant that seems to be harboring some sort of insect or disease, please let the shop owner know (in a quiet, respectful tone), and do not handle the pot yourself if possible. Plant disease, insect pests, nematodes, mites, weeds, snails, and slugs do spread!

Many years ago one of our UC Davis professors moved to a new house. He was very fond of cactus and replanted his new garden with several species. He inadvertently introduced Phytophthora cactorum on a n infested cactus and it destroyed his entire collection!

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What to Look for in a Healthy Plant

1. Quality of Nursery or Garden Center: Take in an overview of the plant department. Look to see that the majority of the plants seem healthy and well cared for. If there are a lot of wilted or browned plants in one section, chances are good the rest of the plants are not being given great

care. 2. Foliage : Evaluate the condition of your specific plant. Are the leaves green, shiny and lush? Steer clear of any plants that are wilting or yellowing. Stressed plants may not recover. This is especially important if you are buying annuals and vegetables. These plants won't have time to rally.

3. Shape: Consider the shape of the plant. Is it compact and full, with multiple stems? Taller is often not better. It could mean the plant has been straining for light and has grown thin and spindly.

4. Insects & Disease: Inspect closely for signs of insects or disease. Check both sides of the leaves and the potting soil. Signs can include: blackened areas, holes, spots, mushy areas, stickiness and

distortions.

5. Root System: Don’t neglect the roots. If the plant is pot bound and the roots are growing out of the bottom, the plant may be stressed and take time to recover. If there aren’t many roots and the plant lifts out very easily, it was probably recently repotted and could use more time to become

garden worthy.

6. Stem Damage: If the plant has a thick or woody stem, make sure there are no cracks or scars. Even prior damage can weaken a plant.

7. Weeds : Weeds in the pot are competing with the plant for nutrients. They also signal some neglect on the part of the nursery staff. The last thing you want is introduce a new weed into your garden.

8. Root Ball: When buying a balled-and-burlapped tree or shrub, the root ball should feel solid. If it appears broken, there’s a good chance the roots have had a chance to dry out and the plant will suffer.

9. Buds & Flowers: Although it's tempting to want to buy a plant that is already covered in flowers, plants in bud will transplant and thrive better than plants in flower. Besides, the existing flowers will fade quickly. You'll get a longer bloom time at home if you purchase a plant that is in bud.

10. When all is said and done: Allow ample time when shopping for landscape garden or vegetable nursery plants. Taking a little extra time to choose your new plants carefully is sure to result in your buying beautiful, healthy specimens.

Western Plant Diagnostic Network News GreenNursery Thumb

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Hawai’i: Paradise Is Also Paradise for Invasives!

In the Winter 2016 edition, page 9, we discussed a fungal disease on the native Hawaiian tree, Ohi’a lehua,

Metrosideros polymorpha, in the family Myrtaceae, called Rapid Ohi’a Death, or ROD. This disease is caused by a , Ceratocystis fimbriata. This disease was originally described in Hawai’I on sweet potato in 1890. It is an invasive species that eventually began to infect O’hia. Please see Rapid O'hia Death Update from the University of Hawaii, Manoa. This map traces the disease from 2014 to February 2017.

The Hawaiian Islands, like Guam, the Samoan Islands, the Marianas, and islands in general, are targets of invasive species. Because islands developed their own particular ecologies, invasives tend to take over these fragile ecologies.

Oftentimes the introduced species is better equipped to survive and competes with the native species for food, light or other resources. For example, the strawberry guava tree is one of Hawaii's worst invasive species. It is dangerous

because it crowds out native plant species, breaks up natural areas, disrupts native communities, alters native ecosystem processes like water production, and provides refuge for alien fruit flies that are a major pest of Hawaiian agriculture.

An excellent book on island ecologies is: Invasive Species, by Daniel Simberloff. The Hawaiian Islands have been ground zero for invasives. Mosquitoes were introduced, supposedly in water casks brought in by ships. Hawaii has a growing invasive species crisis affecting the islands' endangered plants and animals, overall environmental and human health, and the viability of its tourism and agriculture-based economy. Invasive species occur globally, but Hawaii is more susceptible to invasive species because it is an island. The entire island chain of Hawaii has been devastated by invasive insects, plants, hoofed animals such as deer, goats and pigs and others pests. Feral pigs eat endangered bird's eggs and trample fragile native plants, the rosy wolfsnail and the giant African snail, both from Africa gorge themselves on the island's native snails, weeds such as Australian tree fern and Miconia calvescens plants shade out native plants, and coqui tree frogs aggravate tourists, eat native insects and decrease home values with their piercing calls. Among the Hawaiian Islands invasives are: little fire , borer beetle, Asiatic rhinoceros beetle , small hive beetle, Indian myna , papaya ringspot virus, and Lantana camara. Hawaii has so far avoided snake species through rigorous quarantines and inspection. The brown tree snake has destroyed the native bird population of Guam and is not wanted in Hawaii! On the following page are a list and descriptions of some of the latest diseases to find paradise.

S. Ferreira S. Papaya fruit infected

with papaya ringspot

virus Hugh Erle Smith Erle Hugh

Western Plant Diagnostic Network News Coqui frog

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The following recently found diseases are new to the State of Hawaii:

Colletotrichum queenslandicum on Ti leaf, Cordyline fruticosa.

Paracercospora egenula causing leaf spot of eggplant, Solanum melongena) Nelson Scot Erysiphe pisi var. pisi on Trifolium sp.

Erysiphe russellii on Oxalis

Erysiphe sedi on Kalanchoe Bryophyllum pinnatum

Pucciniastrum boehmeriae on Boehmeria grandis, false nettle, ‘akolea * False nettle with rust

Puccinia crepidis-japonicae rust on Youngia japonica (leaves are edible) see rust fungi

Erysiphe quericola on Murraya paniculata, * Orange Jassamine, Chinese box

Golovinomyces sordidus on Plantago lanceolata

Pseudoidium poinsettiae on Euphorbia cyathophora dwarf poinsettia

*New to the United States

Please note: Erysiphe is one of the genera of powdery mildews. It names the powdery mildew

family, . Other genera include Podosphaera xanthii on cucurbits, Podosphaera leucotricha on apples and pears, Blumeria graminis on wheat, Leveillula taurica on onions and artichokes, and diffusa on . And then there are multiple races of these pathogens! For grape growers, what was known as powdery mildew on grapes, Uncinula necator, is now called Erysiphe necator. Of course this is done to keep us all on our toes!!!

Grape IPM Ontario

University State Ohio The

Late stage of powdery mildew on squash Powdery mildew on grapes Podosphaera xanthii Erysiphe necator

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Five Fusarium Species Found to Be Associated with Hemp Root Rot Disease

(This is a follow-up article from the Fall 2016 newsletter, page 10) Jennifer Schoener, Russ Wilhelm, Rylee Rawson, Patrick Schmitz, and Shouhua Wang* Nevada Department of Agriculture Plant Pathology Laboratory (NDA-PPL) *Contact: [email protected] Industrial hemp (Cannabis sativa L.) is a highly regulated emerging economic crop in the United States. Planting a hemp crop in existing farmlands can be challenging, due to many pathogens that may have accumulated over years of crop production. Successful management of hemp diseases and pests is the key to maintaining crop health and production sustainability. Unfortunately, information on hemp diseases and their management is scarce, which may impede farmers from producing a healthy crop. Here we summarize a new detection of hemp root rot disease that caused high mortality rate of a hemp crop in Nevada. Our diagnostic data suggests five Fusarium species were involved in the disease development. In a hemp field, affected plants exhibited slow growth, stunting, and wilting, similar to symptoms caused by drought stress. During mid-summer, a large number of plants wilted, with the crop mortality rate up to 70% (Fig. A). Among the three varieties planted, the “Canda” variety was most affected, followed by the “Futura-75” and “Joey” varieties. The diseased plants had extensive root rot with very limited lateral root growth.

A C E

D

B F Please find the legend on the following page Western Plant Diagnostic Network News

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Legend

Pink patches were visible on the surface of taproot of many plants (Fig. B). Figure A. Disease patch in a field showing high mortality of plants. B. Infected root with pink spots (left) versus a healthy root (right). C. Typical Fusarium colonies grown from the root tissue on potato dextrose agar (PDA) plates showing mixed Fusarium species from a single root (one root per plate) or a single piece of root tissue. D. Frequencies of recovery of each Fusarium species from the hemp root during two sampling periods. E. Colony characters of Fusarium oxysporum (upper left) Fusarium solani (upper right), Fusarium redolens (middle left), Fusarium tricinctum (middle right), and Fusarium equiseti (bottom) on PDA. F. Antagonism of Trichoderma virens CsR-34 on F. oxysporum (12 o’clock), F. solani (3 o’clock), F. redolens (5 o’clock), F. tricinctum (9 o’clock), and F. equiseti (11 o’clock) (7 days on PDA at 22 ºC). All plants examined in the lab were found to be infected with multiple Fusarium species, characterized by different colony characters (Fig. C). DNA sequence analysis preliminarily classified all obtained isolates into five species of Fusarium, which was consistent with morphology-based grouping (Fig. E). F. oxysporum was the most prevalent species with a frequency of isolation of 82%. Recovery of F. solani from roots was 29%, F. redolens 6%, F. tricinctum 18%, and F. equiseti 29% (Fig. D). We noticed F. tricinctum was recovered at a higher rate from the late season samples or from the dead root tissue. While the role of each species in the disease development remains to be investigated, we speculate that F. oxysporum, F. solani, and F. redolens are the major or primary pathogens that co-infect the root system causing root rot and plant mortality. F. tricinctum and F. equiseti appear to be opportunistic and secondary, respectively. In addition to the five Fusarium species, Trichoderma virens was isolated from diseased hemp roots as well. One of the isolates, named Trichoderma virens CsR-34, was found to potentially be a biocontrol agent against the five Fusarium species isolated from diseased hemp roots. In a PDA plate, T. virens CsR-34 appeared to kill F. solani in 2 weeks, and inhibited or weakened colony growth of F. oxysporum and F. redolens (Fig. F). However, little is known about if and how T. virens CsR-34 affects or suppresses the disease in the field. T. virens CsR-34, if under further studies, could be proved to be a unique agent for controlling Fusarium root rot on hemp crops in the irrigated agricultural system. Control of hemp root rot caused by multiple Fusarium species may be difficult and requires an integrated approach. The NDA-PPL’s detections of Fusarium wilt from indoor medical Marijuana plants and Fusarium root rot from the industrial hemp crop suggest that Cannabis species are prone to Fusarium infection. Therefore, it is recommended that an industrial hemp crop be cultivated on a new farmland or field free from Fusarium pathogens. When disease-free fields are not available, application of a fungicide is an option for the disease management. Introduction of Trichoderma virens biocontrol agents into the soil may provide a long-term suppressive effect on various Fusarium pathogens.

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Olive Found in California 8

Phloeotribus scarabaeoides (Bernard) Order Coleoptera, Family , Subfamily Scolytinae G. Daniels Bugwood G.Daniels Dr. Gevork Arakelian, our intrepid entomologist with the Los Angeles Agricultural Commissioner Department, reports yet another invasive, this time the woodboring olive bark beetle (OBB). On October 18, 2016, Dr. Andrew Cline of the California Department of Food and Agriculture (CDFA) positively identified a sample of bark obtained from an olive tree at a grape vineyard in Riverside County as Phloeotribus scarabaeoides , the olive bark beetle (OBB). This is the first record of OBB in the Western Hemisphere and a pest rating proposal is required to assign a permanent pest rating. As one can see from the map below, OBB is native to the Mediterranean basin, as is the olive tree.

Hosts and damage: Attacks olive trees. They were recorded also on ligustrum (privet), ash, common lilac (all Oleaceae ) and oleander Apocynaceae . Olive bark beetles may have several generations per year. Adult female enters the bark and bores a tunnel where she lays up to 60 eggs. Hatched larvae excavate new galleries underneath the bark often completely girdling and weakening branches. Severe infestations may stunt the growth of young trees and reduce number of flowers and olive fruits. Please see the CDFA report

at: Olive bark beetle in CA and Dr. Arakelian’s alert at: Olive bark beetle invades California and on page nine please see Dr. Arakelian’s pest alert. Other articles are: Olive tree protected from olive bark beetle (Spain) and Phloeotribus scarabaeoides (Hebrew University). The following points are from this article by Uri Gerson and Shalom Applebaum.

Life history: In spring the adults start to bore galleries at the bases of young twigs of weakened trees or in broken branches and logs, and lay their eggs there. The emerging larvae excavate their own galleries, usually perpendicular to the maternal gallery. The pest prefers trees that stand in drier and shallow soil, which are usually weaker. It raises 3 annual generations. The commerce in infested olive logs aids the pest’s dispersal.

Economic importance: Severe infestations may reduce the number of flowers and olive fruits, and the resulting damage can reach 70% of the crop. Olive orchards may become completely unproductive within 5 years of such infestations. Tree survival in young groves may be endangered, and olive oil quality can be affected.

Monitoring: The density of the galleries produced in young olive branches can be used to indicate severity of infestation. Decrease in olive yield can be expected when there are >3 pest galleries/meter branch.

Horticultural methods: Appropriate fertilization, pruning and the removal or burning of infested branches.

Chemical control: Treating trees with pesticides (like pyrethroids before the emergence of the adult beetles, which are attracted ethylene. Beetle numbers were reduced in an olive grove surrounded by a barrier of trap-trees that were sprayed with a mixture of ethylene and a pyrethroid. Ethylene can also be used in lure- and-trap control systems.

Biological control: The beetle is attacked by several bethylid , braconid , eurytomid, and pteromalid endoparasitoids , whose abundance and controlling effects vary from year to year and from region to region. The dominant natural enemy is the pteromalid Cheiropachus quadrum, which can reduce pest populations by 30-50%. Natural enemies might be adversely affected by the application of pyrethroids.

Native range of the OBB in the Mideast. It Western Plant Diagnostic Network News has spread around the Mediterranean

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