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Commercial Pecans Controlling Rosette, Diseases and Zinc Deficiency

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Commercial Pecans Controlling Rosette, Diseases and Zinc Deficiency B-6057 10-97 Commercial Pecans Controlling Rosette, Diseases and Zinc Deficiency Jerral D. Johnson and George Ray McEachern* ealth and vigor of pecan rain, dew or irrigation. In addi- Late Summer and trees plus satisfactory nut tion to weather condition prob- Early Fall Hquality and yield depend lems, the leaves and nutlets are on a well-planned and executed immature and are most suscepti- Producers must continue to disease management program. ble to the pecan scab fungus monitor weather conditions dur- Losses from diseases and insuffi- during this period. Foliage of ing the late summer and early cient zinc nutrition can be pre- susceptible cultivars is suscepti- fall months. Foliage is mature vented by following effective ble to downy spot fungus during and no longer susceptible to the grove management practices. this period. Although cultural scab fungus, but shucks sur- practices are followed, a protec- rounding the nuts are immature tive fungicide is required in some and susceptible to late season Disease locations and on scab-suscepti- infection. ble cultivars. Continue applica- Development tions on a 14-day interval as long as weather conditions favor Factors that infection. Spring and Early Influence Disease Summer Mid Summer Development The fungi that cause pecan dis- During the summer months, eases require moisture and mild occurrence of rain and dew is temperatures during spore ger- less likely to occur for extended roducers should consider mination and infection of the periods of time. This reduces the the following factors as immature leaves and nutlets. chance of infection. Producers Pthey develop a spray pro- Losses to disease-causing who carefully monitor weather gram: pathogens are reduced by follow- conditions and disease develop- ■ Susceptibility of variety to ing cultural practices that short- ment can reduce fungicide costs pecan diseases, especially en the length of time leaves and by reducing rates and increasing pecan scab, young nutlets are wet following intervals between applications. ■ Current weather conditions, *Associate Department Head, Professor and ■ Predicted weather conditions Extension Program Leader for Plant for next 1 to 2 weeks, Pathology; Professor and Extension Horticulturist (Pecans and Grapes). ■ Status of disease pressure in 1 and near the orchard, Table 1. Observations and Responses . ■ Tree spacing, Nut Development Diseases Most Stages When or Insect Likely to Occur Trees Best ■ Age of trees, Occurrence at This Stage Respond to Zinc ■ Past history of disease in the Bud break Scab, Downy Spot Rosette (Zinc orchard, Deficiency) ■ Date of last fungicide applica- Prepollination Scab, Downy Spot, tions and Vein Spot Rosette ■ Last fungicide applied. Casebearer Scab, Downy Spot, Vein Spot Rosette Periods When 1st Cover (14 days Scab, Fungal Leaf Rosette after Casebearer) Scorch Pecan Diseases Cover Sprays Scab, Brown Leaf Spot, (continue at 14-21 days Fungal Leaf Spot, Are Most Often as long as weather Powdery Mildew conditions favor Observed disease development Water Stage Scab, Stem End Blight roducing high quality Shuck Worm Scab pecans that are both 1The exact time for fungicide applications varies. Fungicide applied, varieties, Pappealing and disease free current and predicted weather conditions, and disease pressure all influence the requires multiple sprays during number and timing of fungicide applications. Rosette treatments are effective only the growing season in most loca- on immature foliage. All foliage is mature on mature trees by mid June. On young tions. Table 1 specifies periods trees the foliage is receptive to zinc during the entire growing season. when pecan diseases are most often observed and when zinc Table 2 gives information on sug- been approved for use on can be used effectively. gested fungicides which have pecans. Table 2. Fungicides Approved for Use on Pecans and Diseases They Are Reported to Control. Brown Fungal Pecan Downy Leaf Powdery Liver Leaf Fungicide Rate/A Scab Spot Spot Mildew Spot Scorch Benlate™ 50 WP 8-16 oz + + + + + + Topsin™ M 70 WP 8-16 oz + + + + – – Orbit™ 45 WP 20 oz/5A Super Tin™ 80WP 25 oz/5A + + + – + + Co-pak* Enable™ 2F 8 fl. oz + + – – – + Super Tin™ 80WP 5-7.5 oz + + + + + – Ziram™ 76 WP 0.5-1.0 lb + – – – – – Basicop™ 2 lb/100 gal + – – – – – Abound™ 9.2-12.3 oz + – – – – – *Orbit™ and /Super Tin™ are packaged in separate water soluble bags. One bag of each is required to spray 5 acres. 2 on pecans, the movement of the Fungicide Activity fungicide is restricted. They do Label Restrictions not move freely throughout the Control Use of tree. The fungus is exposed to ungicides differ in how they the fungicide both on the surface act on fungi. Fungicides Some Fungicides of the tissue and below the epi- that act on the fungus on F derminal cells (Table 3). the surface of the leaf or nutlet are contact materials. Disease Some systemic fungicides have lthough all the products development is affected when the ability to act on the pathogen listed are approved for use spores of the fungus are exposed even after it has penetrated the Aon pecans, label restric- to the fungicide on the surface of leaf and started to develop out- tions and environmental con- the plant tissue. ward. This is known as “kick cerns may restrict their use. back.” The length of time after These must be considered when Systemic fungicides are taken in infection that the fungicide will selecting products. Always read by the plant and become part of still control the pathogen varies the label and follow it closely the sprayed tissue. These fungi- with fungicides but is normally (Tables 4 and 5). cides must retain their activity from 24 to 72 hours. even after they are taken in by the tissue. With fungicides used Table 3. Mode of Action for Fungicides Approved for Use on Pecans. Systemic Fungicides Benlate™ Orbit™ 45WP/Super Tin™ 80W/Co-pack Topsin M™ Enable™ Abound™ Contact Fungicides Super Tin™ Ziram™ Basicop™ Table 4. Considerations When Selecting Fungicides. Suggested Fungicides to Use Around Homes and Urban Developments Benlate™ Topsin M™ Fungicides to Use Where Cattle Will Be Grazed in the Next 12 Months Benlate™ Basicop™ Ziram™ Fungicide to Use in Organic Program Basicop™ 3 Table 5. Comparison of Toxicity of Approved Fungicides. Table 6. Possible Fungicide Toxicity* Fungicide Rotations to Benlate™ Avoid Fungicide Oral LD50 ..........................................................>10,000 mg/kg Resistance. Dermal LD ......................................................>10,000 mg/kg 50 Rotate Topsin M™ Fungicides With Benzimidazole Type Oral LD50 ............................................................>5,000 mg/kg Dermal LD50 ......................................................>10,000 mg/kg Benlate™ Orbit™ Topsin™ M Enable™ Abound™ Super Tin™ Abound™ Oral LD50 ............................................................>5,000 mg/kg Dermal LD ........................................................>2,000 mg/kg Ziram™ 50 Basicop™ Enable™ Triazole Type Oral LD50 ............................................................>2,000 mg/kg Enable™ Super Tin™ Dermal LD50 ........................................................>5,000 mg/kg Benlate™ Topsin M™ Ziram™ Abound™ Oral LD ..............................................................1,539 mg/kg Ziram™ 50 Basicop™ Dermal LD50 ........................................................>2,000 mg/kg Although Orbit™ is a triazole type Orbit™ fungicide, the new Co-pak with Super Tin™ should prevent or delay develop- Oral LD50 ..............................................................1,310 mg/kg ment of resistant strains of the scab Dermal LD50 ..........................................................5,000 mg/kg fungus. Basicop™ Oral LD50 ..............................................................1,000 mg/kg Management of Dermal LD ........................................................>8,000 mg/kg 50 Pecan Diseases Super Tin™ Oral LD50 ..................................................................156 mg/kg Using Basicop™ Dermal LD50 ..........................................................1,600 mg/kg (Copper Sulfate *LD50 = A measure of pesticide toxicity. The lower the LD50, the greater the toxicity. Oral is ingested. Dermal is skin exposure. Type Fungicide) tions. Tank mixing two types of opper sulfate fungicides Fungicide fungicides can reduce the are considered by many to Resistance chance of fungicide resistant Cbe organic pesticides. strains. The disadvantage of Basicop™ is a formulation of Management this method is that it can copper sulfate and is approved increase fungicide costs. by the Environmental Protection Repeated use of systemic fungi- Agency for use on pecans. o avoid the possibility of cides of the same type increas- Although approved for use on developing strains of pecan es the possibility of fungicide pecans, Basicop™ is not as Tscab fungus that are resis- resistant strains developing. effective as some of the other tant to a specific fungicide When alternating fungicides, fungicides for the control of the chemistry, a rotation of different use the most effective materials pecan scab fungus. Apply only to fungicides should be followed during periods of greatest dis- natives or varieties that have a during the season. Table 6 out- ease pressure. high level of resistance to the lines possible fungicide rota- scab fungus or during periods of low disease pressure. Use cau- tion when using copper type 4 fungicides. Drift onto fruit trees such as peaches, plums, nec- Table 7. Zinc
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