It’s not Scab! Other leaf & nut diseases of pecans

1. It’s not Scab!Other leaf & nut diseases of pecans Monte Nesbitt, Extension Horticulture Texas A&M University

2. Diseases not easily confused with Scab.

3. Powdery Mildew-Microsphaeraalni Damage: Foliage and Nuts T. A. Lee

4. Conditions-Damage-Control • Hot & humid • July is popular month for appearance • Growing nuts can be stunted from heavy presence. • Light infections cause no damage. • Cultivar differences presumed to exist, but not well documented. • Early season Scab fungicide programs control by default. • Responds well to sulfur and many other fungicides, especially Group 3 and 11.

5. Downy Spot-Mycosphaerellacaryigena Damage: Foliage Only. Leaf loss can reduce nut quality.

6. Conditions-Damage-Control • Frequent rainfall & high humidity in pre-pollination period • Damage (Frosty spots) appear in June, followed by defoliation that extends through growing season. • Cultivar differences have been documented • Early season fungicide and timing are critical to break disease cycle on early season foliage. Combo products that contain Group 3 & 11 are good choices. Group 1 (thiophanate methyl) also known to provide control.

7. Most susceptible -- Western, Pawnee, Desirable, Delmas, Moneymaker, Stuart • Moderately susceptible -- Wichita, GraBohls, Cheyenne, Barton • Moderately resistant -- Choctaw, Mohawk, Kiowa, GraKing, Success, Cape Fear Wichita Western Photo/slide by Mark Black

8. Zonate Leaf Spot-Cristulariellapyramidalis • Bulls-Eye target lesions, contributing to late season poor leaf condition and retention. • Inoculum enters from wooded areas, hedgerows around orchard. • Hosted on maple, magnolia, box elder, other. • Cooler, wet conditions in late summer drive disease development. • 40-81 F, >90 % RH • Uncommon conditions & occurrence • Fungicides must continue after scab program ends if conditions are favorable. • TPTH and dodine not very effective.

9. Diseases more frequently confused with Scab.

10. Vein Spot-Gnomonianerviseda Photo: OKStateUniv.

11. Distinguished from Scab by location on leaf—confined to veins or rachis, and by glossy/slick appearance. • Moderate infection can cause premature leaflet defoliation. • Control efforts should mimic that for Downy Spot.

12. Brown Leaf Spot-Cercosporafusca Infection of foliage on weak trees in June and July. Rare problem where trees are fertilized properly, given adequate spacing and receive any fungicide treatment. Distinguished from Scab by reddish-brown color, larger lesions that extend across lateral veins. Other Leaf Spots Liver Spot Gnomonia Leaf Spot

13. Complex of Nursery Blight and Leaf Blotch

14. Nursery Blight-Elsinoerandii Leaf Blotch-Mycosphaerelladendroides Primarily a nursery/young tree problem. Small reddish lesions on both leaf surfaces, becoming gray on upper surface and coalescing into lesion masses. Leaves, become ragged, perforated and weak. Weak parasitic fungus only attacking pecans weakened by crowding and poor fertility. Olive green spores, give rise to black pimple-like fruiting bodies that coalesce into dull black to gray masses. Early defoliation results in severe cases.

15. Neofusicoccum (Terminal Dieback)—new problem occurring in unusually wet Spring/Summers

16. Downy Spot Scab Neofusicoccum

17. Fungicides are timed to coat new leaf and nut tissue with protective fungicide. Basic Program Budbreak to Post-Pollination: Sterol Inhibitor or Strobie every 10-14 days. Post-Pollination to Shell Hardening: TPTH every 14-21 days.

18. Simplified East Texas Pecan Spray Guide

20. RESISTANCE MANAGEMENT • Chemicals with narrow mode of action that are repeatedly exposed to fungi ultimately can become non-effective as they develop tolerance and continue reproducing. • Follow EPA Guidelines and restrictions on annual product use per acre---All Orchards! • Rotate Fungicides • Spray with tank mixes with multiple modes of action • Use Products with Reduced risk of resistance.

21. Pecan “diseases” not responding to early-season fungicide use or to fungicides at all!

22. Pecan Bacterial Leaf Scorch--Xylellafastidiosa(bacteria) A chronic bacterial disease that can cause leaf scorching, drop and devigored trees with yield loss. • Symptoms of PBLS • Begins with necroses of leaflet tips and margins, later progressing in a uniform pattern toward the leaf base and midribs. • Lesions aretan to light brown in color when spreading through leaflet tissue. • Defoliation can be severe and may occur on individual limbs or systemically across the entire plant. Slide Credit: Angelyn Hilton

23. Symptoms of PBLS • Symptoms can be expressed every year • Most prominent late in the growing season PBLS in pecan leaflets Rebecca Melanson, Mississippi State University Extension Bare rachises remain after defoliation Rebecca Melanson, Mississippi State University Extension Systemic PBLS symptoms in mature pecan Rebecca Melanson, Mississippi State University Extension Slide Credit: Angelyn Hilton

24. Stress-related Shuck Dieback, Sprouting Scab Stress J. W. Stewart Stein

25. Stem-End Blight • Also called Anthracnose • Prevalent on ‘Success’ and Success progeny. • A brown to black lesion develops on the proximal or stem end of the shuck and then progresses to turn portions or even the entire shuck black in color and stick to the shell. • Earlier than shuck dieback, associated with water stage (July-August), causing embryo to die at that time (Stein and McEachern, 1984). • Fungi including Glomorellacingulata (Brenneman and Reilly, 1989), Botryosphaeriaribis (Johnson, 1980) and Phomopsis sp. (Reilly, 1994) have been linked to this problem. • Fungicide (benomyl) usage during water stage has reduced the incidence of the problem (Johnson, 1980; Sanderlin, 1998). • Recent fungicide work with new fungicides has not been done to corroborate previous efficacy of benomyl during water stage. Photos: Auburn Univ.

26. Concluding Points • Familiarity with the full catalog of pecan diseases can help pecan growers identify and manage emerging problems. • Those growers making preventative or weather-based sprays for Scab control usually control secondary/minor diseases by default. • Growers in Central Texas, who spray fungicides infrequently, are at some risk for problems with Downy Spot, Vein Spot and other minor fungal problems. • Good orchard management (sunlight, fertility, water, crop thinning) and sanitation contribute to overall tree health and elimination of many pecan disease problems.

27. NEED MORE HELP? • Texas Plant Disease Diagnostic Clinic • (College Station) • http://plantclinic.tamu.edu • 979-845-8032