[1.1] Varieties that are susceptible to cedar apple rust include: Arlet, Braeburn, Fuji, Gala, Ginger Gold, Goldrush, Golden Delicious, Idared, Jonathan, Lodi, Mutsu (Crispin), and Rome. All varieties are susceptible to quince rust under favorable weather conditions. See Table 9 for a precise listing of temperature and wetting periods necessary to cause cedar-apple rust infections. Maintain short intervals during periods of wet weather in orchards where quince rust fruit infections have been a problem. Quince rust infections are most likely to develop when long wetting periods (48 hours or more) occur between tight cluster and first cover and the average temperature is greater than
50° F.

Refer to the reference materials list at the end of this publication for a Fact Sheet containing more details on the biology and management of this pest.

• Pesticide Application Notes

[1.2] Where apple rust diseases are a problem, sprays normally must be applied at 7- to 10-day intervals from pink until 2–3 wk after petal fall. Nova, Rubigan, *Procure, Bayleton, and Bayleton/Triadimefon have kickback activity against cedar apple rust; if an infection period should occur when foliage is poorly protected, it is recommended that one of these materials be applied within 3 days of the start of the infection period or as soon thereafter as weather conditions permit. The strobilurin fungicides (Sovran, Flint) provide moderate protection against rust diseases when applied on a 7-day schedule, but they have little or no kickback activity.

[1.3] The EBDC fungicides (mancozeb, maneb, Polyram) are labeled for use on apples in one of two different ways: (i) at a rate of 1.5–2 lb/100 gal (maximum 6 lb/A, no more than 24 lb/A per year), not to be applied after bloom; OR (ii) at a reduced rate of 3 lb/A (maximum 21 lb/A per year), which may be applied to within 77 days of harvest. The latter rate is adequate for control of rust diseases, and the extended timing is necessary to control rust infections on terminal leaves. It is illegal to combine or integrate the two treatment regimes.

[1.4] Where apple rusts are a problem, include a suitable rust fungicide in the first two cover sprays.

Apple Scab

• Biology & Cultural

Refer to the reference materials list at the end of this publication for a Fact Sheet containing details on the biology and management of this pest.

• Pesticide Application Notes

[2.1] See discussion of inoculum reduction in the disease management section. Scab fungicide sprays beginning at green tip are absolutely essential in orchards with high carry-over inoculum or orchards where scab control with SI fungicides was less than satisfactory in previous years. If early season infections are allowed to become established, even the best fungicide programs will not prevent development of fruit scab in orchards where the scab fungus has developed resistance to all three of the fungicide groups (dodine, benzimidazoles, SI’s) that previously provided presymptom and postinfection activity against apple scab.

[2.2] Fungicide rates per acre should never be reduced below either (i) 50% of the per-acre rate listed on the label or (ii) 1.5 multiplied by the rate/100 gal listed on the label. This applies even when spraying small trees. Although tree-row volume calculations may suggest that lower rates are appropriate, applying less than 50% of the per-acre rate has frequently resulted in unsatisfactory scab control and/or more rapid development of fungicide resistance.

In orchards with SI-resistant scab, a combination of a mancozeb fungicide at 3 lb/A plus a captan formulation that supplies 1.5 lb of active ingredient/A has provided excellent scab control when used in prebloom and bloom sprays. (A captan rate of 1.5 lb active ingredient/A translates to 3 lb/A of Captan 50W, 30 oz/A of 80W, or 1.5 qt/A for the 4L formulations.) This combination provides a better residual activity through heavy rains than would be available from either product used alone and it preserves the option of using mancozeb sprays after petal fall. The mancozeb-captan combination cannot be used close to prebloom oil sprays because of captan-oil incompatibilities.

For reasons of economy and resistance management, it is recommended that SI and strobilurin fungicides not be used until tight cluster, even when fungicidal protection is needed earlier; in such cases, make a single application of an alternative fungicide (captan, copper, EBDC) at green tip and half-inch green, then begin the SI/strobilurin program at tight cluster. Do not apply captan or sulfur within 10 days of an oil spray. Do not apply liquid captan formulations with sulfur on sulfur-sensitive varieties. A further discussion of apple scab fungicide characteristics is presented in the section “Apple Scab Fungicides” and in Table 6.

[2.3] Check fungicide compatibility with desired insecticide or oil; see [2.1].

[2.4] Sovran and Flint are excellent protectants, but they have only 48–72 hours of post-infection activity compared with 72–96 hr for the SI fungicides. Sovran and Flint also lack the presymptom activity that makes the SI fungicides so effective (in the absence of SI resistance) for arresting scab epidemics after primary scab lesions become visible in trees. Sovran and Flint have proven very effective against apple scab when applied at 7–9-day intervals to control primary scab, but they have not performed as well when used to control secondary scab in trees where scab lesions are already visible. Sovran and Flint control rust diseases fairly well when used as protectants, but they have little or no post-infection activity against rust diseases.

CAUTION: Sovran has caused moderate to severe phytotoxicity (leaf burning) on several sweet cherry varieties when sprayed directly onto them at high labeled rates. The most sensitive varieties were: Somerset, Sweetheart, Valera, Van, and Vandalay; these varieties might also be injured by spray drift containing Sovran. Minor to moderate injury occurred on Cavalier, Coral Champagne, Emperor Francis, Royalton, Schmidt, Summit, and Viva; there is less danger of injury due to spray drift on these varieties. Many other sweet and sour cherry varieties (including Bing, Brooks, Cashmere, Gold, Hardy Giant, Hartland, Hedelfingen, Hudson, Kristin, Lapins, Lambert, Montmorency, Napoleon, Nelson Black Sweet, Rainier, Royal Ann, Sam, Stark Crimson, Stella, Sue, Tehranivee, Tulare, Ulster, Vega, Vic, Viscount, and Windsor) showed no injury when sprayed directly with high labeled rates. The Sovran manufacturer recommends: (i) Do not apply Sovran near or allow drift onto cherries in the highly sensitive group (Somerset, etc.); and (ii) thoroughly rinse spray equipment (tanks, hoses, nozzles) after spraying Sovran and before using this equipment on sensitive cherry varieties.

[2.5] Although Rubigan, *Procure and Nova have up to 96 hr of kickback activity, this activity depends strongly on rate. Do not use tree-row volume calculations with these products. They provide good curative activity when used at higher label rates (e.g., at least 10 fl oz/A of Rubigan or *Procure, or 6 oz/A of Nova) but are much less active at lower rates if applied more than 48 hr after infection. When applied beyond the effective kickback period, many infection sites are merely suppressed but not eradicated. In such cases, if a 2nd spray is applied 7–10 days later, most of these lesions will finally be killed or inactivated; however, if no additional material is applied, the suppressed lesions may eventually become active again.

IMPORTANT: Good spray coverage is especially critical for SI fungicides. Poor spray coverage not only provides poor control but speeds the selection of scab strains that are resistant to the SI fungicides. Experience has shown that inadequate control occurs more frequently when spray concentrations are greater than 6X than when concentrations are 6X or less. Inadequate control due to poor spray coverage is also relatively common in unpruned or very tall trees.

[2.6] Primary inoculum pressure is generally at a peak from pink through bloom—this is a critical time to maintain full coverage with proper fungicide rates.

[2.7] Serious losses from apple scab are usually the result of secondary spread to developing fruits. Therefore, it is important to carefully check blocks for the presence of primary scab lesions from petal fall through the early cover spray period. This is particularly important because fruit are most susceptible to infection during the first few weeks of their development. If scab is detected, the management strategy should be to (i) thoroughly protect the sensitive young fruitlets from fungal spores that are present, AND (ii) limit the number of new spores that can be produced. To protect fruitlets, use (a) the full rate of captan (e.g., 2 lb/100 gal of the 50WP formulation), or (b) the reduced rate of an EBDC fungicide (if allowable) supplemented with a half rate of captan, or (c) a strobilurin fungicide combined with a contact fungicide. To limit new spore production, use (a) an SI fungicide through 2nd cover (to prevent new leaf lesions), or (b) a registered strobilurin fungicide (to prevent new leaf lesions and suppress spore production from existing lesions), or (c) dodine (to “burn out” existing lesions). SI’s and dodine should be used only in orchards where there is no resistance to these fungicides. (CAUTION: Applications of dodine after bloom may cause russeting on russet-sensitive varieties). With repeated use, all three of these options will speed the development of resistance. Thus, they should be viewed as emergency “rescue” operations, and increased care should be taken in future seasons to avoid the development of primary scab that necessitated their use.

[2.8] It is illegal to use the 6 lb/A rate of the EBDC fungicides after bloom. It also is illegal to use the reduced rate (3 lb/A) after bloom if the rate for any of the sprays prior to petal fall exceeded 3 lb/A.

[2.9] The danger of primary scab is over after 1st cover except when drought conditions delay spore release. If primary scab has been well controlled, fungicide schedules and rates can be relaxed after the danger of primary infection is past. For best control of mildew, apply an SI or strobilurin fungicide through 2nd cover on bearing trees and through 4th cover on non-bearing trees.

[2.11] The use of Nova, Rubigan or *Procure beyond 2nd cover is specifically NOT recommended, except in non-bearing orchards where they may be needed for mildew control during the summer. Spraying them during the summer increases the likelihood of selecting strains of the scab fungus that are tolerant of these compounds. Excessive use of Bayleton, Nova, *Procure, or Rubigan also increases the possibility of developing powdery mildew resistance to these sterol-inhibitor compounds.

• Pesticide Resistance

[2.12] Apple scab and powdery mildew resistance to Topsin M and Thiophanate-methyl is very widespread throughout New York. Once resistance develops it will persist indefinitely. Thus, these products should NOT be relied upon for apple scab or mildew control in orchards or regions with a long history of use.

[2.13] Sensitivity to the SI fungicides (Nova, *Procure, Rubigan) is declining among some populations of the apple scab and powdery mildew fungi. These materials still provide apple scab control in some orchards, but they are totally ineffective in other orchards. Declining efficacy usually appears in orchards with a history of regular SI use (3–5 applications for 10+ yr) under high disease pressure, whereas no decline is apparent in orchards where the materials have been used sparingly or in tight schedules with low levels of inoculum. In order to maintain the usefulness of these products, it is recommended that they be used: (a) at full rates with thorough spray coverage; (b) only in tank-mix combinations with another effective scab fungicide; and (c) no more than 2–3 times per season.

[2.14] Sovran and Flint are prone to resistance development, and resistance to one member of this class confers resistance to other products in the class (cross-resistance). The primary strategies for reducing this risk are to rotate the strobilurins with unrelated fungicides, to limit the number of seasonal applications of a strobilurin (e.g., 3-4 per year), and to tank mix strobilurins with full rates of captan when treating trees with visible scab lesions.

Bitter Rot

• Pesticide Application Notes

[3.1] Although the EBDC fungicides are effective against bitter rot, the 77-day PHI does not allow them to be used in late summer when most bitter rot infections occur. Captan and Pristine are the best materials available. Bitter rot has the potential for “explosive” development, thus captan rates should be increased to their upper labeled range (equivalent to 1.5–2 lb/100 gallons of the 50WP formulation) if the disease begins to develop and hot, wet weather is anticipated. Under such conditions, tight spray schedules should be maintained until 2 wk before harvest. The higher captan rates should be used even in combinations with Topsin M, since these fungicides have very little effect against bitter rot. Flint at 2.5 oz/A is also effective against bitter rot.

Black Rot, White Rot (frog-eye leaf spot and fruit infections)

• Biology & Cultural

[4.1] Black rot inoculum is retained within trees in dead wood (e.g., old fire blight strikes) and fruitlet mummies; therefore, it is important to remove these sources to whatever extent possible. The critical periods for controlling black rot fruit infections are (a) from the 1st through 3d cover sprays, when fruitlets killed by thinning sprays become infected (they become inoculum sources), and (b) during late summer, when maturing fruit are especially susceptible. Where black rot was not controlled well the previous year, protectant sprays may be needed at 2–3-week intervals until late August.

Black rot cankers cannot be controlled with fungicide sprays. Cankers develop primarily after wood has been weakened by other factors (e.g., drought, winter injury). However, the white rot fungus may establish superficial cankers on trees that receive only mancozeb and/or SI sprays during the primary scab period. Those superficial cankers can suddenly girdle limbs if trees become severely drought-stressed. Using a copper fungicide at green tip and/or including a fungicide with activity against black rot/white rot in the prebloom scab control program should help to control superficial white rot cankers.

• Pesticide Application Notes

[4.2] Many sprays aimed at scab and rust are also effective against the black rot fungus. Topsin M and Thiophanate-methyl are highly effective. Captan and the strobilurin fungicides (Sovran, Flint) provide good control. The SI fungicides (Bayleton, Nova, *Procure, Rubigan) do not control black rot. Polyram and mancozeb fungicides are effective at the maximum label rate but have little activity when used at the lower rates that are labeled as applications after petal fall. Ziram at 1.5–2 lb/100 gallons (dilute basis) is only moderately effective (OK when inoculum levels are low), but is often ineffective at 1lb/100 gallons (dilute basis) or less.

NOTE: The frog-eye leaf spot phase of black rot is sometimes misdiagnosed, because identical symptoms can be caused by (a) spray materials that are phytotoxic to leaves; or (b) cedar apple rust infections whose development is arrested by the application of an SI fungicide or by a host-resistance response such as occurs when the rust fungus begins attacking unsprayed McIntosh, Empire, or Liberty leaves. Mancozeb and Polyram are the best materials for protecting against rust-induced leaf spotting.

Blister Spot

• Pesticide Application Notes

[5.1] This is an economic problem primarily on the Mutsu cultivar, but Fuji occasionally shows symptoms when planted near Mutsu. Apply the 1st spray 10–14 days after petal fall. A delay in applying this spray will significantly reduce control in most years. Two additional sprays should be applied at weekly intervals if any rain occurs. Do not apply more than 3 sprays. The use of 2–4 lb Kocide or C-O-C-S/100 gal between green tip and 1/2-inch green in the spring may reduce overwintering inoculum and provide a small amount of additional control. Additionally, application of Aliette (or phosphorous acid or phosphite products) during pink, petal fall, and early cover sprays may also reduce infections.

• Pesticide Resistance

[5.2] Streptomycin-resistant blister spot bacteria are present in many Mutsu orchards in Western New York. Streptomycin will continue to provide some control after resistance is first detected, but this degree of control will gradually diminish in succeeding years if strep is continuously used. Recent research indicates that resistance levels within an orchard diminish significantly after one season if no strep is applied. Thus, once resistance becomes pronounced, strep is likely to be most effective if used only in alternate years.

Blossom End Rots

• Biology & Cultural

[6.1] Blossom end rots can be caused by Botrytis cinerea, Sclerotinia sclerotiorum, and Botryosphaeria obtusa. It occurs sporadically and is most likely to become a problem if the weather is warm and wet between bloom and 1st cover and in orchards where only mancozeb, Polyram, or SI fungicides were applied during bloom and at petal fall. McIntosh, Delicious, Rome, and Paulared are most commonly affected. Vangard and Scala should control infections caused by Botrytis, but they are may be less effective against blossom end rots caused by Sclerotinia or Botryosphaeria.

• Pesticide Application Notes

[6.2] Where blossom end rot has occurred before, use captan, Sovran, Flint, Scala, Vangard, Topsin M or Thiophanate-methyl in the bloom, petal fall, and 1st cover sprays if the weather conditions are favorable for infection. Vangard and Scala should control infections caused by Botrytis, but they are may be less effective against blossom end rots caused by Sclerotinia or Botryosphaeria.

Crown Rot (Collar Rot)

• Biology & Cultural

[7.1] Crown rot is primarily associated with trees on moderately to highly susceptible rootstocks (particularly MM.106 and young trees on M.26). It can also develop on moderately resistant rootstocks planted in poorly drained sites or in very wet years. Seedling and M.9 appear to be the least susceptible of the common rootstocks.

Refer to the reference materials list at the end of this publication for a Fact Sheet containing more details on the biology and management of this pest.

• Pesticide Application Notes

[7.2] Ridomil should be considered in sections of the orchard where crown rot has been a problem, or where the combination of marginal drainage and rootstock susceptibility indicates a potential problem. Make a solution containing 8 fl oz Ridomil Gold 4EC/100 gal of water and apply this solution to the soil around the trunk at the following rate:

Trunk diameter (in.)	Solution (qt)
1	1
1–3	2
3–5	3
5	4

Apply just as growth begins in the spring and repeat immediately after harvest. Do not apply to newly planted trees. Ridomil is an effective protective fungicide, but is unlikely to cure trees in moderate to severe stages of decline.

[7.3] Apply 4 lb/A of Aliette 80WP as a foliar spray, or use one of the phosphorous acid or phosphite products labeled for this use. Make 1st application in spring after sufficient foliage is present to absorb chemical. Repeat every 60 days; maximum 4 applications/yr. Unlikely to cure trees in moderate to severe stages of decline.

Fire Blight

• Biology & Cultural

[8.1] Fire blight is a potentially damaging disease on highly susceptible varieties such as Crispin (Mutsu), Fuji, Gala, Gingergold, Honeycrisp, Idared, Jonathan, Lady Apple, Monroe, Paulared, R. I. Greening, and Wayne. Many other varieties can become diseased if conditions are particularly favorable for disease development. The potential for tree loss is especially high when susceptible varieties are grown on susceptible M.26 and M.9 rootstocks (or interstems), since blight can move into them from the scion or infected root suckers and kill the tree.

[8.2] Pruning out infected shoots to limit the spread of shoot blight is of doubtful benefit on large trees but is recommended on young or small trees, particularly those on M.9 or M.26 rootstocks or interstems. To effectively limit damage, strikes should be pruned out as soon as they appear throughout the terminal growth period; begin checking for symptoms about 90–100 degree days (base 55° F) after an expected infection event such as rain during bloom or a summer hailstorm. Degree day information can be sourced from the NYS IPM NEWA network web site at http://newa.nysaes.cornell.edu. Should blight develop, it is also important to maintain control of pear psylla and potato leafhopper because these insects can contribute to shoot blight infections. Recent research indicates that aphids and white apple leaf hopper are less important in spread of fire blight.

Refer to the reference materials list at the end of this publication for a Fact Sheet containing more details on the biology and management of this pest.

• Monitoring & Forecasting

[8.3] Serious fire blight problems are usually the result of infection during bloom. The need for streptomycin sprays during bloom depends upon a combination of both orchard risk factors and weather risk factors. If weather conditions favor blossom blight infections, streptomycin is strongly recommended for orchards where risk factors are high (highly susceptible scion and rootstock cultivars, active fire blight or past history of fire blight in the orchard or in neighboring orchards).

Streptomycin is effective in preventing blossom infections. However, precise timing is required because only those blossoms that are open at the time of the application are protected and there is no redistribution to new blossoms by rainfall. It is currently recommended that in orchards at moderate or high risk, streptomycin should be applied if weather has been relatively warm since full pink AND forecasts indicate the probability of rain or showers in the next 24 hr at temperatures greater than 60° F. A program to initiate spraying once 200 degree hours (base 65° F) have accumulated since full pink (first open blossom in the orchard) has proven effective in several locations and s

Pest Management Guidelines A Cornell Cooperative Extension Publication	Cornell Guide for Pest Management of TreeFruits
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