When the disease is severe, infected leaflets are killed causing defoliation of the trees in late summer or early fall and resulting in reduced tree vigor and increased susceptibility to invasion by other pathogens. Scab is a fungus which invades the young rapidly growing shoots and leaves and later the developing nuts. The black pecan aphid also increases in severity as densely shaded areas become more prevalent, as occurs in orchards needing thinning. Another reason to concentrate on insect control is the fact that pecan fungicides are available only in commercial-size packages. For example, resistance can delay the occurrence of scab during periods of inclement weather when spraying is not possible. The Plant Health Instructor. If you plant scab disease-resistant varieties, you may need to treat only for insects. Also, look for adapted varieties that are less susceptible to pecan scab, a serious fungal disease that attacks leaves and nuts. 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. It was first described from Carya tomentosa (= C. alba) by Winter (1885) as F. effusum Wint. – Crop sanitation Areas where unnecessary insecticide treatments are made tend to have more aphid problems. Pecan scab is a common fungal disease of pecans. 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. It is to control this primary infection that the bud break and pre-pollination sprays are applied. Adapted varieties: One of the most important decisions in growing pecans is choosing a pecan variety that is adapted to the climate of your region of the state. Pecan Scab occurs on leaves, twigs, and nut shucks. Domestication of pecan began in the late 1800’s and much genetic potential remains to be capitalized upon. Premature defoliation will occur. Slow decline, zinc deficiency, nematodes – Root knot on pecans (Nematodes – Meloidogyne incognita) – Small swellings found on rootlets. Pecan trees are also grown for commercial trade in Texas, with the state usually ranking second or third nationally in total pecan pro- duction of approximately 60 million pounds. Overview Texas A&M Veterinary Medical Diagnostics Laboratory, Texas A&M College of Agrculture and Life Sciences. However, before commercial growers and homeowners begin putting trees in the ground, they must consider their fungicide spray options to manage scab disease. 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]. Total coverage is important to achieving effective control. Weak trees, old foliage – Leaf blotch (Fungus – Mycosphaerella dendroides) occurs mainly in trees of poor vigor. weevil infestation. To determine when sprays should be applied within a specific year, the number of hours of 90% relative humidity occurring must be recorded and accumulated. This practice covers leaves with soil and prevents the discharge of spores into the air, thereby controlling primary infections of new leaves. The pecan is a large tree, often growing to 100 feet high or more and has a stately appearance. Available electronically from http : / /hdl .handle .net /1969 .1 /160734 . Crop sanitation The fungus [funlfsc2] causes premature defoliation in the fall. Once the fall rains begin, the fungus is washed off the shuck leaving only the dead epidermal cells of the shuck. Primary lesions develop on the lower leaf surfaces as small dots which gradually enlarge and become reddish-brown with a grayish cast. Although the ten year average gives a clue to scab occurrence at a critical time during the spraying season, it is not sufficient to use only this to determine when applications should be applied. Pink mold rarely occurs on the shucks of nuts in the absence of scab disease. 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. It tends to be a poor-bearing, unattractive tree if it is not well managed. The disease symptoms first appear on the under surface of mature leaves in early summer as small, olive-green, velvety spots. These pecan cultivars do not produce the largest pecans. Apply zinc foliar sprays frequently at the beginning of the season. When infection is severe, the entire nut surface is black, kernel development is stopped, and the nut drops prematurely. 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. Insect and vertebrate pests Major insect pests on native pecans are pecan nut casebear-ers, hickory shuckworms, stink bugs, and weevils. Fungicide Program Example for Managing Pecan Scab. Tested by Auburn University, Mississippi State University and the University of Georgia. Overview Resistant varieties Pecans are susceptible to several foliage, fruit, and root diseases in Texas.