Almond Foliar and Bloom Disease ControlDavid Doll Farm Advisor Merced County November 14, 2011

Almond Bloom DiseasesTrees are susceptible to many fungi, blossoms are highly susceptibleRainy conditions favor disease Rainy periods occur during bloom!

Almond Bloom DiseasesDisease control is dependent upon:Fungicide Used Timing Coverage

Growers need to assess which diseases are present and select the fungicide Rotation of fungicides is advised to reduce resistance

Almond Bloom DiseasesA typical bloom spray includes a spray at 520% bloom, and one at 80%- full bloom.Persistent rainy conditions may require a third spray - 10 days without protection

Almond Bloom DiseasesThree main diseases: 1. Brown Rot Blossom Blight 2. Shothole 3. Jacket RotOther diseases: Scab, Rust, and Anthracnose

Brown Rot Monilinia laxaAlmost always sprayed for at least once full bloomAttacks anthers and pistils of opened flowers Moves into and kills the spur, can move into shoot Young fruit are also susceptible

All varieties are susceptible; Butte and Carmel are most susceptible

A conventional Butte orchard that missed a full bloom brown rot spray had over 50% blossom blight despite no rain!

Early Spring Diseases 3 Main Disease: Green Jacket Rot Anthracnose Shot Hole

Tend to be more severe in wet weather Require retreatment of trees every 10-14 days if rain persists Once established, can become a re-occuring problem

Green Fruit/Jacket RotCaused by three fungi - Monilinia laxa - Botrytus cinerea - Sclerotinia sclerotiorium Timing of infection is from flower opening to petal fall symptoms are observed later Cultivars that form tight clusters are most susceptible: Butte, Ne Plus, Carmel, Merced

Poor control with DMIs (Bumper, Tilt, Quash, etc.)!!!

Almond AnthracnoseColletotrichum acutatumInfected nuts show round, orangish, sunken lesions on the hull. Symptoms may appear 3 weeks after petal fall; Profuse gumming occurs as the infection progresses into the kernel.

Almond AnthracnoseColletotrichum acutatumSymptoms include spur and limb dieback. Leaves on infected spurs develop marginal necrosis, beginning with water-soaked areas that fade in color; leaves die but remain attached to branches.

Control: Bloom to summer if wet

Shot Hole Wilsonomyces carpophilusRequires water for completion of lifecycle Causes lesions on fruit and leaves; heavy fruit infection causes fruit drop Around the first of May, the hull becomes resistant to the disease Post-bloom fungicide applications (Petal Fall to 2-5 weeks after bloom)

Shot Hole Wilsonomyces carpophilusSpots occur on leaves, fruit, twigs, and flowers; Spots on young leaves usually fall out, leaving a hole (the shot hole); older leaves retain their lesions. Fruit spots are small with purplish margins, slightly corky, and raised.

Shot Hole Wilsonomyces carpophilusThe fungus survives on infected twigs and as spores in healthy buds Spores are moved by water to new sites; prolonged periods of wetness, either due to rain or sprinkler irrigation

Summer Diseases 3 Major Diseases Of Concern Scab Rust Alternaria

Becoming more of a problem with increased planting densities Documented cases of resistance formation Biggest concern to many almond growers

Almond Scab - Cladosporium carpophilum

Gray-black, oil-like soft looking spots form on leaves, fruit, and twigs

Almond Scab - Cladosporium carpophilumYoung lesions are indistinct small yellow specks, best seen by holding a leaf up to the light.Lesions usually are not visible until late spring or early summer.

Almond Scab - Cladosporium carpophilumThe fungus survives in twig lesions, and spores are spread by wind or rain. Scab is favored by prolonged wet spring weather

Almond Scab - Cladosporium carpophilumSevere scab infections can cause early defoliation If left uncontrolled for several years, infected trees become weakened.Control: Fungicides 2-5 weeks after petal fall

Late Season Scab Defoliation

Scab Control No History of Disease Make an application 2-5 weeks post petal fall Use of DMI or strobilurin Micronized sulfur sprays made monthly may help suppress, but not the most effective History of Disease Dormant application of copper and oil, or chlorothalinil Follow same spray program listed under the no history

Almond Rust - Tranzchelia discolorRust occurs sporadically throughout almondgrowing areas in California. It often is serious on young orchards where bloom sprays have not been applied.

Almond Rust - Tranzchelia discolorRust appears as small, yellow spots on the upper surface of leaves.

On the lower surface - a rusty red appearance when erupt through the surface.

Almond Rust - Tranzchelia discolorRust ManagementHistory of rust: Apply fungicides in late spring and summer for prevention 5 weeks after petal fall and forward 2-3 applications may be needed in orchards that have had severe rust problems. To be effective, fungicide must be applied before rust symptoms are visible. Micronized sulfur works well on rust, apply when not using oil To prevent the inoculum from increasing, apply zinc sulfate (20-40 lb/acre) in late October to early November to hasten leaf fall.

Almond Bloom Diseases

Fungicides to Consider at Various Timings Delayed Dormant: Copper and Oil Liquid Lime Sulfur Bravo and Oil (reg pend)

2-5 Weeks Post Petal Fall (SCAB) DMIs (Bumper, Tilt, Indar, etc.) Strobilurin (Gem, Abound) Combos (Pristine, Quadris Top, Inspire Super

Bloom 80%-100%: Rovral + oil Scala

Petal Fall Bravo (no oil) Captan (no oil) Strobilurin DMI

5 Weeks forward (RUST) Sulfur (not with oil!) Strobilurin

Further Resources UC IPM Website Almond Doctor Blog Local Extension Office Chemical PCA