Pecan Diseases and Nematodes

Transcription

1 Pecan Diseases and Nematodes Western Pecan Production Short Course September 27, 2012 Natalie Goldberg Extension Plant Pathologist

2 Diseases of Pecan Phymatotrichum root rot Root-knot nematode Powdery mildew Crown gall Sooty mold Pecan scab Pecan bacterial leaf scorch

3 Phymatotrichum Root Rot Also known as Cotton root rot or Texas root rot Caused by the soil-borne fungus, Phymatotrichopsis omnivorum Extremely large host range over 2,300 broadleaf plants Limited geographically

4 Distribution of Phymatotrichum

5 Field Patterns of Phymatotrichum Root Rot Within the geographical boundaries, the fungus is isolated Found in soils that are high is alkalinity (ph) and low in organic matter

6 Phymatotrichum Root Rot Found at evaluations below 5000 ft. Old (abandoned) cotton or alfalfa land Uncultivated land near arroyos and rivers; covered with mesquite or creosote

7 Phymatotrichum Root Rot Spread of the fungus is very limited no viable spores. The only real significant spread is by root to root contact In Orchards, spread is related to distance between trees and location of the fungus

8 Phymatotrichum Root Rot Invades plant through the roots Grows into the xylem vessels (water conducting tissue) Rots infected roots and xylem vessels Overall symptoms are of water and nutrient stress Plants typically show symptoms in the heat of the summer Toxin production by the fungus may contribute to the rapid development of symptoms

9 Phymatotrichum Root Rot Symptoms Slight yellowing (may turn bronze in color) Leaves wilt and then die; clinging to the plant Highly susceptible hosts, such as apple, stone fruits and pistachios, die quickly after initial symptoms Moderately tolerant hosts, such as pecan, may take several years to completely die

10 Phymatotrichum Root Rot Symptoms If trees do not die in the first year, each year the canopy gets thinner with fewer, smaller leaves

11 Phymatotrichum Root Rot Early symptoms may be confused for zinc deficiency, nematode injury or drought stress. - Zinc Nematode Phymatotrichum

12 Phymatotrichum Root Rot Symptoms

13 Phymatotrichum Root Rot Symptoms Reddish-brown lesion around the collar of the tree

14 Phymatotrichum Root Rot Signs Whitish-tan spore mats produced during wet conditions

15 Phymatotrichum Root Rot Signs Fungal strands on roots resemble threads (visible with a hand lens).

16 Phymatotrichum Root Rot Signs Unique cruciform hyphae visible with microscope

17 Management Management is very difficult if not impossible Extensive dicotyledonous host range non-specific attack of susceptible hosts Survival on native vegetation Overwintering structures found over 12 feet deep in soil - indefinite survival in soil No resistant cultivars

18 Management Avoid land known to be infested with the fungus. Avoid old, abandoned cotton or alfalfa fields Get field history on previously cultivated land Attempt to change soil conditions Fumigation of soil only delays the onset of disease in future planting

19 Management Remove of infected trees do not replant Grass cover crops on orchard floor

20 Pecan Root-Knot Nematode Caused by Meloidogyne partityla First discovered in Texas in 1996 Found in New Mexico in the late 1990 s confirmed as M. partityla in October 2000 Now also found in Georgia, Arizona, Florida, and Oklahoma

21 Pecan Root-Knot Nematode Restricted to Pecan, Hickory and Walnut Introduced into new areas on transplants! Once established in an orchard, management is difficult

22 Pecan Root-Knot Nematode Trees in decline may appear to be zinc deficient, freeze damaged, diseased or neglected -Zinc Nematode Phymatotrichum

23 Pecan Root-Knot Nematode Infects small feeder roots Doesn t kill trees, but causes trees to decline, significantly reducing yield

24 Pecan Root-Knot Nematode Prevention is the key to management of pecan nematodes Avoid land known to be infested Be very careful in purchasing new trees and in transplanting mature trees Prune affected trees to reduce size and eliminate dead/dying branches Infested orchards should be watered and fertilized properly to avoid any added stress on the trees

25 Powdery Mildew Caused by the fungus, Microsphaera penicillata A disease of minor importance in New Mexico Occurs rarely Usually doesn t cause widespread infection High humidity and cool summer nights are required for development of the disease Dense canopy (poor airflow) New Mexico State University

26 Powdery Mildew White powdery growth on leaves (rarely) and nuts Russet appearance results after the white mildew is gone Reduced nut size and yield In NM no treatment is recommended

27 Crown Gall Caused by the soil-borne bacterium, Agrobacterium tumefaciens Causes the development of abnormal woody galls on crowns or roots Severe infections result in poor growth, severe dieback and, eventually, death No treatment after infection avoid infected trees and injuries after planting

28 Sooty Mold Conspicuous black mold on leaves, stems and nuts Fungus is not pathogenic no direct harm to the plant Indirect damage from blocking sunlight from reaching leaves Grows on honeydew produced by aphids (yellow aphid complex)

29 Pecan Scab Caused by the fungus, Cladosporium caryigenum Damaging disease in many growing areas in the U.S. Reduced crop Early infection can result in complete loss of crop, poor leaf growth and premature defoliation Not known to occur in New Mexico

30 Pecan Scab Conditions for disease: frequent rain, high humidity and temperatures over 70 F Infects leaves, stems and nuts Small dark spots, enlarge and coalesce to form large blotches hull turns black Preventative fungicide applications are required where the disease is common

31 Pecan Bacterial Leaf Scorch Caused by the bacterium, Xylella fastidiosa Other diseases caused by this bacterium include, Pierce s disease in grapes, leaf scorch in ornamental plants, and alfalfa dwarf Occurs in the Southeastern U.S. but is not known to occur in the West Other diseases caused by this pathogen are common in the Western U.S. Genetic variation in the pathogen may account for the lack of disease in pecan in the West.

32 Pecan Bacterial Leaf Scorch Bacterium plugs the xylem vessels Results in water stress in the leaves Transmitted by xylemfeeding insects, primarily sharpshooters Disease results in reduced tree growth and poor nut production no effective treatments are known

33 NMSU Plant Diagnostic Clinic Diagnosis is a team effort Grower Submitting Agent (County Extension Agent) Diagnostic Lab (Natalie Goldberg and Jason French; ) NMSU Plant Diagnostic Clinic: Forms and information for submitting samples Publications, presentations, links, etc. Image gallery (work in progress) New Mexico State University