Commercial Pecans Controlling Rosette, Diseases and Zinc Deficiency

B-6057 10-97

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 caution when using copper type

4 fungicides. Drift onto fruit trees such as peaches, plums, nec- Table 7. Zinc Sources and Rate/100 Gallons of Water. tarines and apricots can cause Source Rate/100 Gallons of severe leaf and fruit shed. Be Spray Solution sure to clean up equipment after Zinc Sulfate™ (36% WP) 2 lb using copper materials. Copper is corrosive to equipment if not Zinc Nitrate™ (17% L) 20 fl oz handled properly. Tracite-N-Zinc™ (17% L) 1 qt NZN™ (6% L) 1 qt Zinc Nutrition ZN Special™ (13.5% WP) 2 lbs

ecans require zinc for nor- mal stem and leaf growth. Aerial Application Residues PTrees not receiving zinc do The EPA has established pestici- not produce sufficient of Fungicides dal residue tolerances on indoleacetic acid. Indoleacetic pecans. These regulations estab- acid (IAA) is a naturally occur- lish the amount of a specific ring growth hormone responsible erial application of fungi- chemical that can be present in for shoot elongation, leaf devel- cides either by fixed wing or on pecans at harvest. Always opment and other critical plant Aor rotary aircraft has not consult the product label for functions. Internodes between proven as effective as ground specific restrictions, and be sure the leaves and stems are short- applications. During periods of the pesticide used is registered ened. unfavorable weather conditions for use on pecans and is used This compaction of the annual that prevent use of ground equip- only in accordance with specific growth is known as zinc rosette. ment, it may be necessary to application instructions. Leaves are smaller, thickened make an aerial application if dis- and somewhat distorted. When ease potential is severe. Tree Caution severe, affected leaves develop height, density of leaf canopy All pesticides are poisonous; necrotic areas between the and requirements for maximum some are poisonous to man, ani- veins. Fungi are often associated coverage must be considered to mals, nontarget crops, etc. They with the necrotic lesions. achieve satisfactory disease control. should be used with caution and Zinc sprays are essential for stored out of reach of children, early season pecan growth. irresponsible persons, livestock Early, frequent applications are Chemical Use and household pets. Properly the most effective. Several for- dispose of leftover spray solution mulations of zinc are approved Precautions and empty containers. for use on pecans. Elemental zinc is the most toxic to plants Pesticide Drift other than pecans and grapes. elect suggested materials Avoid drift to protect nearby for most effective, safe, Avoid spray drift into urban plants from phytotoxicity. If drift Seconomical control. All sug- areas, rivers or lakes, or crops is a possibility, use NZN™ or a gested materials are poisonous, that will be used for food for similar formulation. Do not use but proper handling reduces the human consumption or livestock any zinc product at higher than hazards associated with use. feed unless the product is the labeled rate. If applying Read and comply with manufac- approved for use on that crop more than one zinc spray within turers’ label directions for stor- and the rate and timing follow 2 weeks, reduce the rate by one- age and handling of toxic chemi- label recommendations. half. Never spray young trees cals. that are not actively growing.

5 Steps to Reduce 7. Cut off sprayer when spray mix and require propor- there are open spaces tionately less water. Concen- Spray Drift between trees. trated spraying saves water and time but not pesticides since the 8. Make sure that the upper same amount of pesticide is 1. If an air blast sprayer is 2/3 of the nozzles are needed for each tree to obtain used, the force of the air directed to the upper 70 control. blast should be directed percent of the top canopy, away from the two or but do not go above the Coverage three rows next to a tree. Thorough coverage of the pecan sensitive area. 9. Smaller droplets are more foliage and nuts with spray solu- likely drift. tion is necessary. The fungi that 2. Avoid spraying when the affect pecans infect the tissue wind is blowing in the 10. If there is a drift problem, where they land on the leaf or direction of a sensitive shuck. Coverage is important for area. stop and consider precautions to avoid movement both contact and systemic fungi- 3. Use caution when spray- of pesticides into sensitive cides. ing toward county or areas. state highways. Drift Calibration onto vehicles traveling Symptoms of Poisoning Calibrate sprayers before mak- the road can cause acci- Some symptoms of pesticide poi- ing any pesticide application. dental exposure and soning are headaches, nausea, This is necessary to determine concern. cramps, blurred vision, weak- the amount of chemical to add to the spray tank. One of the easi- 4. Do not spray during ness, muscular twitching and diarrhea. If any of these symp- est methods of determining the periods of fog. Pesticides amount of water being applied can be carried in the toms occurs during or following the handling of a pesticide or per acre is to spray 0.5/A with droplets for some distance clear water. Record the amount from the application site. spraying, consult a physician immediately. of water required to refill the 5. When spraying around tank. Multiply this amount by 2 Always maintain a copy of the and this is the amount applied sensitive areas, use the label and the Material Data least toxic materials. per acre. Table 1 lists the num- Sheet. ber of trees per acre at different 6. Buffer zones can be used spacing and the number of trees to prevent drift onto sen- Spray Application in 0.5/A. sitive areas. A buffer zone If an orchard is not planted in a can be an open space Considerations row but is randomly spaced, where native or planted determine the acres of land grass can be used to involved and the number of trees catch drift. A dense grass omplete coverage of the being sprayed. Divide the num- buffer between the spray- foliage and nuts is essen- ber of trees into the acreage and ed trees and surface Ctial. With conventional, this is the average number of water can filter out much high-volume hydraulic sprayers, trees per acre. It will not be of the pesticide runoff 1/2 to 1 gallon of spray mixture exact but will give an approxi- from pecan trees. Hedge per foot of tree height is a gen- mate number. If trees vary in rows or closely planted eral rule for the volume of fin- size, spray representatives of trees that do not require ished spray required. each tree size when determining spraying can reduce drift. Most high volume sprayers the amount of water being Research has shown that require a pressure of 300 to 400 applied. This is the amount of in some instances the pounds per square inch. Low vol- water used to spray one-half drift will be carried by air ume sprayers (mist blowers, air acre of trees. Multiply this by 2 currents over the plant blast sprayers, speed sprayers, and this is amount of water used material. etc.) use forced air as the carri- per acre. er to deliver a concentrated

6 Table 8. Tree Spacing and Number of Trees Per Acre. Summary of Pecan Spacing No. Trees/A No. Trees/0.5 A Disease and Zinc 35X35 35 17.5 35X40 31 15.5 Management 40X40 27 13.5 Program 45X40 24 12.0 45X45 22 11.0 ffective disease manage- 50X50 17 8.5 ment programs require 60X60 12 6.0 Eproducers to utilize a wide variety of practices. Use the following practices in the control of pecan disease problems: Using this rate and the rate of lons of water can be determined. chemical per acre, the amount of Below are two examples. 1. Select varieties that are pro- pesticide applied per 100 gal- ductive and resistant to pecan scab fungus. 2. Select orchard sites that have Example: good air circulation. A. Tree spacing: 35X35 3. Tree spacing should allow for Sprayer tank capacity: 300 gal air circulation and sunlight. Fungicide rate/A: Enable™ 8 oz/A At midday, 25 percent of the Water required to spray 0.5 A: 85 gal orchard floor should be in Water required to spray 1 A: 85(gal/0.5A) X 2 = 170 gal/A sunlight. No. of acres covered with full tank of spray: 4. Manage orchard floor to 300 (tank capacity)/ 170 gal to spray 1A = 1.8A remove diseased shucks and leaves. Amount of fungicide needed to charge tank: 8 oz/A X 1.8 A = 14.4 oz/300 gal tank 5. Apply zinc as a foliar spray. B. Tree Spacing: 60X60 6. Take soil samples and follow fertilizer recommendations. Sprayer tank capacity: 300 gal Fungicide rate/A: Benlate™ 2 lb 7. Remove trees that are susceptible to pecan scab and can- Water required to spray 0.5 A: 200 gal not be properly sprayed. Water required to spray 1 A: 200(gal/0.5A) X 2 = 400 gal/A 8. Apply insecticides when pest No. of acres covered with full tank of spray: populations reach levels that 300 (tank capacity)/400 (gal/A) = 0.75 A require treatment. (Refer to Amount of fungicide needed to charge tank: current Extension publica- 2(lb/A) X 0.75 A = 1.5 lb/300 gal tank tions that have pest thresh- olds.) 9. Apply fungicides as needed.

7 Suggested pesticides are registered and labeled for use by the Environmental Protection Agency and the Texas Department of Agriculture. The status of pesticide label clearances is subject to change, and many may have changed since this publication was printed. County Extension agents and appropriate specialists are advised of changes as they occur. The USER always is responsible for the effects of pesticide residues on livestock and crops, as well as problems that arise from drift or movement of the pesticide from one’s property to that of others. ALWAYS READ AND CAREFULLY FOLLOW THE INSTRUCTIONS ON THE CONTAINER LABEL. For further information, contact your county Extension agent.

The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.

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Educational programs of the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin. Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 20, 1914, in cooperation with the United States Department of Agriculture. Zerle L. Carpenter, Director, Texas Agricultural Extension Service, The Texas A&M University System. 10M copies–New PP,HORT