Johnson, Jerral D.; McEachern, George Ray (Texas Agricultural Extension Service, 1997) After spore dissemination is complete, lesions visible on both surfaces of the leaf are 1/8 to 1/4 inch in diameter and greenish-yellow. Wichita is the most productive pecan grown in Texas and is ideally adapted to central and west Texas. – Pink mold (Secondary diseases, behind scab lurks pink fungus) Crop sanitation Adjacent lesions on the nuts may coalesce forming large, sunken, black lesions. This can result in 1 to 4 feet of die back. Fungicides at budbreak will reduce the primary infections. This represents a ten year average and should be reviewed with the realization that any one year can vary greatly from this average. Apply zinc foliar sprays frequently at the beginning of the season. Wind and rain spread spores of the disease organism. 11-11:30 a.m. – Pecan scab and bacterial leaf scorch update, Young-ki Jo, Ph.D., AgriLife Extension specialist in plant pathology and microbiology, College Station. When nuts are cut open, the liquid in the kernel has turned brown. Replanting is not recommended in those sites where trees have been lost to this fungus. The fungus [funlfsc2] causes premature defoliation in the fall. These pecan cultivars do not produce the largest pecans. White powdery fungus, high temperatures, dry conditions, immature foliage – Powdery mildew (Fungus – Microsphaera alvi) – When pecans become infected with this fungus [powmil], they appear to be covered with a white, powdery material. Primary lesions develop on the lower leaf surfaces as small dots which gradually enlarge and become reddish-brown with a grayish cast. Scab risk • Region – east to west gradient LA to CA • Site, Management – fungus life cycle • Variety – minimize susceptible, maximize resistant, diversity • Weather – frequent rains, mild temperatures • AU-Pecan ( ≥0.1” rains and % rain chance for 5 days; by variety scab resistance level Modeling efforts and basic biological studies on pecan nut casebearer, pecan weevil, hickory shuckworm, pecan aphids, pecan scab and other pests began to be implemented into management programs. Other actions to minimize pecan scab are proper pruning and wide spacing between the trees, which can improve air circulation and speed leaf drying. Bunching in severely affected trees may involve all main limbs which produce thick masses of sucker-like growth and few, if any, nuts. 3). The long cycle time for pecan trees plus financial considerations dictate that new varieties go through an extensive vetting process before being widely planted. Domestication of pecan began in the late 1800’s and much genetic potential remains to be capitalized upon. The fungus develops on the outside of the shuck and only feeds on the outer layer of plant cells. Pecan Scab. If the rows are planted perpendicular to the prevailing wind, the outer rows will block movement to the inner orchard. Delayed harvest can cause this problem. Table 1 shows the critical periods for scab development during the growing season. 1st Stuart then Success, Western, Desirable, Wichita, Cheyenne and now is Pawnee. The only spraying I ommited was for pecan husk scab. Recommended for trial plantings on the basis of resistance to pecan scab and nut quality. Pecan scab is the name for the disease associated with Fusicladium effusum.It was first described from Carya tomentosa (=C. – Leaf blotch (Weak trees, old foliage) Losses to this fungus can be reduced, but complete eradication has not been achieved. Although it has serious scab problems in the humid areas and freeze problems in the far north, the tree is very vigorous, productive and begins to bear in only 5 to 7 years. Spray applications are then made based on this accumulation. The fungus sometimes invades the kernel of thin shelled pecan varieties causing “pink rot” which is characterized by an oily appearance of the nut shell and a rancid odor. and B.D. Scab is most severe during times of above-average rainfall. 1 Response . It has also been associated with young trees at the graft union and on older trees where limbs are pruned out. Pecans (Carya illinoensis) are common as a shade and nut tree in the southeastern U.S., where they also grow wild in native bottomland forests. In central Texas, it may begin at budbreak or may be delayed until the prepollination spray depending upon the weather. The fungus girdles the trunk near the soil line. Figure 3. pecan scab (Venturia effusa ) (G. Winter) Rossman & W.C. Allen 2016 by Clemson University – USDA Cooperative Extension Slide Series, (CC BY 3.0). 3). 2132 TAMU College Station, TX 77843-2132; AgriLife Bookstore. For diseases on pecan trees, begin spraying Benlate for control of scab. Gary Veal, Technical Sales Agronomist with Plant Food Systems, Inc. says his company has worked closely with UGA and USDA researchers…Continue reading Wichita develops "V" limb angles that split and require careful training. Hoefnagels, M.H. The first spray should be applied after pollination when the tips of the nutlets have turned brown, and the second spray application should be made 3 to 4 weeks later. Pecan Scab occurs on leaves, twigs, and nut shucks. In humid east Texas, the accumulation of hours should begin at the budbreak application. Later in the season, lesions turn brown due to the death of leaf cells in the disease area. Unfortunately, once the fungus has invaded the tissues, it becomes protected from most fungicides and can continue to produce spores. Early detection of the first symptom of bunch and pruning out of the affected branch may prevent spread of the disease throughout the tree. In susceptible cultivars, the foliage is vulnerable also to downy spot fungus. The disease has not been observed to cause significant economic losses in Texas. – Shuck die back ( Physiological, nut drop, variety reaction) Diseased plants can be submitted for disease identification to the Texas A&M Plant Disease Diagnostic Lab at An effective control for cotton root rot disease has not been developed. Mason 2016. Pecans should be dried before sacking. It is a disease that destroys pecan crops, especially in the southeastern United States. – Fungal twig die back (Black pustules, drought) Scab is a fungus which invades the young rapidly growing shoots and leaves and later the developing nuts. Another reason to concentrate on insect control is the fact that pecan fungicides are available only in commercial-size packages. The fungus produces a great abundance of spores on the surface of these primary infection sites and become visible to the naked eye within 7 – 9 days depending and then spreads throughout the trees infecting young shoots, leaves, and nuts [scab3]. Therefore, thorough coverage of leaf, nut, and shoot surfaces with a fungicide must be maintained during the season to prevent secondary infections following rains providing wetting periods sufficient to allow germination and penetration. Defoliation, susceptible varieties, leaf curling – Fungal leaf scorch (Fungus – several) – Although all varieties are susceptible to this group of fungi [funlfsc1], Shoshoni, Chickasaw, Cheyenne, Shawnee, and Stuart appear to be some of the most susceptible. If the fungus invades the kernel, it becomes oily and produces a rancid odor. 1-1:15 p.m. – Texas Pecan Growers Association announcements, Blair Krebs, TPGA executive director, Bryan. Poor air circulation slows down the drying of foliage and increases the potential infection periods within an orchard. infections occur (e.g. Several other diseases can infest pecans, including bacterial leaf scorch, downy spot, powdery mildew, shuck dieback, and stem-end blight. Dr. George Ray McEachern (TAMU) says: Varieties will continue to change. Comparison of different areas of Texas using days above 90 deg. To maintain control, they must be applied early and then reapplied. Fungicides applied for scab plus orchard sanitation will help reduce losses due to this disease. – Articularia leaf mold (Minor leaf disease, white tufts, weak trees) It is difficult for homeowners to properly manage pest problems so that large pecans can fill out properly. LJ Grauke , Research Horticulturist & Curator USDA-ARS Pecan Genetics Route 2 Box 133 Somerville, TX 77879 tele: 409-272-1402 fax: 409-272-1401 Where possible, the rows should run with the prevailing wind. Based on work in Georgia, 70 degree F appears to be the lower temperature limit at which spores are formed. The Problem A problem that researchers face in the field is categorizing the infection level of pecan Pruning to remove low hanging limbs can also help to reduce the disease build-up within an orchard. Weak trees, old foliage – Leaf blotch (Fungus – Mycosphaerella dendroides) occurs mainly in trees of poor vigor. Galls can be formed on any below-ground tissue. Pecan scam disease is caused by the fungus Fusicladium effusum. scab in the low-mid canopy (≤35 ft) • Above 40 ft, there was no significant effect of fungicide on scab severity 30 Treatment <15.0 ft Tree height Vertical distribution of scab in the pecan canopy 15-25 ft 25-35 ft 35-40 ft >40 ft August 15 Within each column of charts, bars with the different letters are significantly different (P=0.05). Losses to this fungus should not be confused with other drops that occur in the fall due to other pathogens and physiological problems. The black pecan aphid also increases in severity as densely shaded areas become more prevalent, as occurs in orchards needing thinning. Q: Each year I have a problem with my pecan tree that is now about 11 years old. Most pecan varieties which are maintained in a vigorous state of growth are not as susceptible to this disease. The accumulation of hours begins at that time. Limiting fungicide applications The nuts that drop do show some scab on them but look healthy and have plenty of moisture in them. This infection often resembles pecan scab lesions. Resistant varieties should be planted which have a scab resistance level to ensure that over a ten year period they can be grown with little chance of significant crop loss. Experiments for the Control of Pecan Scab Disease.. Texas Agricultural Experiment Station. For example, resistance can delay the occurrence of scab during periods of inclement weather when spraying is not possible. Pruning to open up the tree for better air circulation will help reduce scab occurrence by reducing the number of infection periods occurring during the year. Moneymaker and Stuart varieties are most susceptible to downy spot disease although all pecan varieties are moderately to slightly susceptible. Pecan Scab, a disease cased by the fungal pathogen Fusicladium effusum, can drastically reduce nut yield. The following 8-spray fungicide schedule is provided as an example of one option to use for pecan scab management in light of the emerging scab insensitivity issues surrounding some of our fungicides. Texas east of the Pecos River generally experiences one population peak in late July. Pecan scab Pecan scab is a common fungal disease of pecans. Tested by Auburn University, Mississippi State University and the University of Georgia. A thin film of the fungicide prevents the scab fungus from developing by killing spores before they can invade susceptible tissues. Plant tissues are most susceptible when young and actively growing. The Texas A&M Department of Horticultural Sciences offers two undergraduate and three graduate degrees that prepare students for a myriad of diverse career opportunities.. Our mission is to: Table 1. 'Jenkins' (Jenkins 1, Alabama Jenkins)(Nut Photo) 'Seedling selection of pecan grown from seed of unknown parentage planted about 1977 by Travis Jenkins, Rena Lara, MS. Under these conditions, spores of the fungus in contact with the wet leaf surface of a pecan leaflet germinate rapidly, invade the tender tissues, and initiate infection within 6 hours. Also when carbamates or pyrethroids are used in the early season, one can almost be assured of aphid and mite problems later. – Root knot on pecans (Slow decline, zinc deficiency, nematodes) Infection occurs in spring near budbreak. (even susceptible cultivars like Wichita can be planted). Lesions of vein spot disease develop on the veins or petioles of leaves and are usually less than 1/4 inch in diameter and are characteristically dark brown to black. Trees which are invaded by the bacteria are more subject to stress factors due to their reduced root system. When the foliage is infected, it becomes slightly distorted and covered with a faint white, powdery substance. Nuts infected with this disorder drop from 1 to 2 weeks early. Pecan growers across Georgia and the southeastern US are taking a new look at phosphite fungicides for control of pecan scab and glomerrella. When the tree is severely affected, it should be destroyed to protect nearby healthy trees from infection. Foliage infection is a problem only on the lower, immature leaves of a tree and on nursery trees. An irrigation system is recommended for all The pecan is the state tree of Texas and has an important place in the state’s history. FOliage of susceptible cultivars is suscepti-ble to downy spot fungus during this period. Physiological, nut drop, variety reaction – Shuck die back (Physiological – possible hormone imbalance) is commonly associated with Success and Success hybrids. Even as pecan harvest is under way across Alabama, soon it will be time to plant new pecan trees. On the nuts, scab lesions [scab1] appear as small black dots which become sunken with age. The fungus lives in fall leaves over the winter. Another reason to concentrate on insect control is the fact that pecan fungicides are available only in commercial-size packages. Mycoplasm, sucker growth – Bunch disease (Mycoplasm) – Evidence indicates it is a mycoplasm [bunchdis].