Common Peach Diseases

Jane E. Stewart Plant Pathologist Colorado State University Colorado climate inhibits some pathogens, and other pathogen behave differently

Foliar Peach Diseases Stem/Root Peach Diseases • Brown rot • Armillaria root rot* • Peach leaf curl • Phytophthora root rot • Shot hole* • Cytospora* • Powdery mildew*

*Important Colorado Diseases Brown rot • Fungal pathogen: Monilinia fructicola

• No. 1 disease in Southeast, but widespread in US

• Hosts include: Prunus spp.

• Typically occurs in areas with high moisture

• Polycyclic disease

Chavez, UGA Brown Rot Symptoms

• Blossom blight, twig and dieback and fruit rot

• Some infections are symptomless until fruit ripens

• Symptoms may occur while in storage

PNWhandbooks.org Identification of Brown Rot

• Mummy berries

• Sporulation – Look for apothecia in winter/early spring in moist areas Intermountainfruit.org – If found, infections are likely to be high

APSnet.org; Sanoamuang & Ganut Disease Cycle of Brown Rot Summer and Fall Spring Protective fungicides to prevent new infections Protective fungicides to prevent new infections

Protective fungicides to prevent new infections

Winter M. Ellis, OSU Management for Brown Rot • Sanitation: Remove infected fruits – Limits inoculum current and next growing season • Control insect damage and wounding • Post harvest: cool fruit rapidly after harvest – Short soak in 122F water

APSnet.org Chemical Management for Brown Rot

• Fungicides are the best option – Sterol Inhibitors: Indar, Elite, Pristine and Gem – Iprodione: Rovral – Spring application – Copper or sulfur

• Spray at full rate and coverage at pink bud, full bloom and petal fall

• Wet conditions: 7-10 days post

• Rotate fungicide classes

• Populations are becoming resistant to sterol inhibitor fungicides Peach Leaf Curl • Fungal pathogen: Taphrina deformans

• Hosts: Peach, plum, nectarine, almond

• Can defoliate trees early in the season

• Found throughout the US Symptoms of Peach Leaf Curl

M.A. Hansen, VA Tech Disease Cycle of Peach Leaf Curl

Spores Spring Summer and Fall penetrates host tissues Healthy and diseased peach New Infections Protective on young leaves Spores on fungicides to prevent new infected leaf and infections fruit Spores overwinter on buds or twigs

Spores Winter Agrios Management for Leaf Peach Curl

• Fungicides are the most effect method of control

• A single application before buds begin to swell can control disease for a season

• Can also apply chemicals in dormant season – Ferbam, Ziram, Chlorothalonil, or copper Shot hole blight

• Fungal pathogen: Thyrostoma carpophilum (Wilsonmyces carpophilus) • Hosts: Peach, apricot, cherry • Common in Intermountain

West Intermountainfruit.org • Polycyclic disease Symptoms of shot hole

Intermountainfruit.org Disease cycle for shot hole

In spring, spores are Fungus overwinters in disseminated via infected buds and lesions Winter wind/rain Protective on small shoots fungicides to Protective prevent new In fall and fungicides to infections winter, prevent new spores Spring infections are Spores can produced infect healthy during tissues. wet Utah State University Extension condition s Fall Later in Summer spring, spores In warm, dry weather infect fruit fungus survives in buds and twigs until wet weather returns

Utah State University, Extension Cultural Controls • Summer rain and sprinkler irrigation promote fruit infections, when fruit is wet for longer periods of time

• If orchard is sprinkler irrigated, reduce canopy wetness by adjusting sprinklers

• Prune cankers and remove/burn infected branches Chemical controls for shot hole

• Similar to leaf peach curl and brown rot

• Bordeaux mixture, Boscalid, Chlorothalonil, Azoyxstrobin

• In orchards with a history, spray at leaf fall to protect against twig infections

• Spring applications during bloom and wet conditions to prevent fruit and leaf infections. Powdery Mildews on Peaches

• Fungal pathogens: Podosphaera pannosa – Infects peach and rose • Podospharea leucotricha – Infects apples and peaches • Polycyclic disease • Obligate pathogen

Utah State University, Extension Symptoms of Powdery Mildew

• Yellowing or distorted leaves

• Stunted shoot growth

• Reduced yield

• Powdery residue on leaves and fruit

Utah State University, Extension Identification

• Conidia

• Cleistothethia

Apsnet.org Disease cycle of Powdery Mildew

• Overwinters on in buds, as buds expand, infection occurs on young leaves

• Sporulation occurs usually at night with relative humidity is higher

• Spore germination occurs when temperatures are between 36-98 F.

APSnet.org H. Larson Management of Powdery Mildews

• Provide good circulation by pruning for increase airflow between trees

• Full sun exposure

• Use lower levels of nitrogen – less succulent, young growth

• Remove nearby rose for peach powdery mildew

• Do not plant peaches next to susceptible apple varieties – Gala, Jonathan, MacIntosh, Rome Beauty

H. Larson Chemical Control for Powdery Mildew

• Conventional: Azoxystrobin (Abound), boscalid + pyraclostrobin (Pristine), thiophanate methyl (Topsin) • Organic: Potassium bicarbonate + horticultural oil, sulfur based

• Spray early spring (7-10 days) until symptoms are moderate

• Alternate chemicals to prevent fungicide resistance

H. Larson Stem/Root Peach Diseases • Armillaria root rot* • Phytophthora rot • Cytospora*

*Important Colorado Diseases Armillaria Root Rot

• Fungal pathogen: Armillaria mellea

• Hosts: Many hardwoods

• Persists on decaying roots and debris, infects new

Guido Schnabel • Occupies large areas Humongous fungus Symptoms

• Height growth is reduced • Thin crown • Yellow leaves • Sap on the root collar • Reduced root system • Circle of diseased trees Identification

Honey mushrooms

Mycelial Fans

Rhizomorphs Conditions that promote disease • Poorly drained soils and excess irrigation – Furrow irrigated orchards

• Areas of lower elevation a field

• Planting new stock in the same areas

Rootstock Working Group, rootstocks.net Cultural Management Options

• Avoid excess watering • Armillaria can exists for many years; Sanitize to remove diseased roots before replanting • Avoid wounding roots; Shade exposed crowns from sunburn

• Root collar excavation to expose crowns to air and to limit spread to the stem

• Keep trees healthy Root collar excavation

Guido Schnabel, Clemson University Phytophthora Root Crown and Collar Rot

• Caused by pathogens: Phytophthora cactorum and Phytophthora spp.

• Hosts: Peach, apple, cherry, apricot T. Burr, Cornell • Soilborne pathogens Symptoms of Phytophthora Root Rot

• Stunted growth • Scorched leaves, dry leaves that remain on tree • Reduced root system • Circle of diseased trees

T. Burr, Cornell Identification of Phytopththora root rot

Oospores of P. cactorum, Cating et al. 2010

M. Murray, UT Disease cycle of Phytophthora root rot

Several hundred oospores can be produced per Optimum temperature inch length of infected root!! 50-60ºF

Swim to the Penetrate root tips – root optimum temperature 50-64ºF

In soil and roots resistant structure

Wolfgang Oßwald et al. 2004 Management of Phytophthora Root Rot

• Avoid excess watering, especially in the fall and spring. Good temperatures for fungal infection and less use by the tree • Plant trees on a good site. Good drainage and evenly sloped

• Plant trees shallow on a mound • Move easily on nursery stock so ensure clean material • Select resistant root stocks • Soil drenches of mefenoxam (Ridomil Gold) Cytospora Canker

• Caused by Cytospora spp. • Common on all stone fruits and many other tree species (urban and forests) • Associated with stress (drought, pH, cold damage) • Most significant disease in Colorado peaches Cytospora Disease Cycle

• Fungus grows in bark tissue through open wounds, and can can also enter buds

• Kills by girdling branches

or trunk of tree Alan Biggs • Attacks tree during conditions when temperatures are warm and moisture is available

• Trees affected by drought, late spring frosts, insect and fungi defoliation, sunscald, herbicides, or mechanical injury are susceptible to Cytospora infection Survey of Orchards

• Estimated incidence and severity of Cytospora in major peach production areas of Western Colorado

• March/April 2015

• Conducted in Grand Valley, North Fork and Olathe areas – Focus on gathering data from a widespread area and range of orchard management Methods

• Surveyed by orchard and variety • Recorded presence/absence for every 10th tree

• Counted and rated infection K. Kimbrough severity for every 50th tree • Interviewed growers • Collections of Cytospora isolates Results • Surveyed: – 200 acres – 42 varieties – 2-32 year old orchards (11 yr mean)

• 100% of orchards surveyed infected (mean 75% infected) • Ave number of infections per tree was 5.2 (range 0-27) • Potential relationships between practices and infection, but are inconclusive at this time Species differ biologically

• Three species have been identified on peach within the US: – Cytospora leucostoma – Cytospora paraleucostoma – Cytospora cinctum

• Only 1 species has been identified in Colorado – Cytospora leucostoma Symptoms of Cytospora canker

Larson & Pokharel Identification of Cytospora Disease cycle Crotches with narrow branch Unhealed angles pruning stub Shaded winter Leaf scars, damaged twig damaged buds

Humid, Poorly wet Conidia spread by rain; germinate healed and infect injured and dead wound tissues, expands as cankers

Canker rings formed by Fungus persists and infection and forms fruiting host callus structures in dead formation wood and cankers Biggs and Grove 2006. High inoculation levels correlated with high rainfall events (Watapo, WA)

1993 1994 1995

Grove and Biggs 2006. Plant Disease Spread of spores from cankers

ž Maximum spread 2 ft from rain splash

ž More inoculum further at angles higher than 90 degrees from canker

ž Rain splash is important for inoculum spread

ž Are there long distance spread mechanisms? — Wind — Insects — Humans

Grove and Biggs 2006. Plant Disease Healthy trees • To help a tree resist infection: – Prepare soil before planting – Fertilize, water properly for winter and summer – Avoid injury to the trunk and limbs – Prune correctly

• Slow growth in Fall: – Fertilize in late winter or early spring – Avoid excessive nitrogen fertilization, which causes vigorous growth – Trees need to harden off in fall to prevent cold-injury Management Tools

• Manage tree stress

• Remove cankers – Pruning

• Reduce inoculum levels – Pruning – Chemical treatments Chemical Management options

Stephan will present these! Summary foliar fruit diseases Summary soil borne pathogens Armillaria Root Rot Avoid excess watering, sanitize sites before replanting, avoid wounding roots, root collar excavation method, keep trees healthy Phytophthora Root Rot Avoid excess watering, plant trees on a good site, plant shallow on a mound, use clean nursery stock, resistant cultivars in available,

drench with mefenoxa T. Burr, Cornell Questions?