Lime-sulfur (a minimum of 6 gallons to 100 gallons of water) is the most effective fungicide for destroying the spore masses in twig lesions. Bordeaux mixture and wettable sulfur do not penetrate under the epidermal covering of the scab pustules and kill only a few of the surface spores. Thorough coverage of the twigs is essential, since the fungicide kills the spores largely by contact.

Some twig infections may not open until after the delayed dormant spray has been applied, and ascospores produced on overwintered leaves usually y mature after that period. Thus it is necessary to apply cover sprays to protect new pear growth from scab infections.

The proper fungicide for use as cover sprays depends mostly on the variety grown and partly on climatic conditions. In that respect we can put pears into two general groups: Those intended for cannery use, or varieties upon which a russet skin does not lower the fruit grade; and the tender-skinned, shipping varieties, which require a smooth skin surface to command top market prices.

Varieties in the first group may be sprayed with lime-sulfur at the pink and calyx stages of bud development or, if needed, until hot weather may be expected. Lime-sulfur has an advantage over many others in being an eradicant spray as well as a protective material. It is dangerous to use any sulfur fungicide on pears when temperatures of 90 F. or over may occur, or if an oil spray will be used within 45 days.

Tender-skinned varieties like Comice and Anjou may be severely russeted by sulfur sprays. The fruit set of Anjou has been cut an average of 30 percent by their use. The spray-sensitive varieties are susceptible to injury early in the season or until the young fruits shed their pubescence about the end of June. As lime-sulfur and other potent eradicative fungicides cannot be used on the tender varieties, milder protective fungicides have to be used. Consequently, the spray applications must be well timed and applied thoroughly to realize satisfactory scab control.

Ferbam (ferric dimethyl dithiocarbamate) and ziram (zinc dimethyl dithiocarbamate) are substitutes for the wettable sulfur sprays. They have been used on tender-skinned pears in the Pacific Northwest since 1944. They have given satisfactory scab control when timed properly and applied thoroughly. They are generally used at the rate of 1 1/2 pounds to 100 gallons of water.

FOLLOWING the delayed dormant spray of lime-sulfur, ferbam or ziram as a first cover spray is usually applied at the pink (preblossom) stage of bud development. If the weather is cool and the buds are slow in opening, it may be advisable also to spray at the prepink, or green-bud, stage before the "pink" spray. If primary infections are not prevented at this early period, the protective fungicides will give only partial scab control later.

Bordeaux mixture or prepared copper fungicides may be substituted for ferbam or ziram on Comice pears, but sulfur in any form is extremely injurious on this variety after the delayed dormant period.

Ferbam or ziram is generally applied at the calyx, or petal-fall, period. Additional applications of ferbam or ziram at 15- to 20-day intervals may be advisable if the season is excessively rainy.

Ferbam and ziram are compatible with most of the newer insecticides, but lime, casein spreaders, or other alkaline materials lower their effectiveness against scab. Applications of ferbam, especially if mixed with oil, are not recommended later than 30 days before harvest because of the difficulty in removing the spray residues. Thorough applications of the earlier sprays will usually make late applications unnecessary.

THE SPRAY SCHEDULE to control pear scab should consist of:

1. The delayed dormant, or green-tip, spray. Use 6 to 8 gallons of liquid lime sulfur (32 Baume) or its equivalent to 100 gallons of water. Maximum control of the twig scab pustules will be obtained if the application is delayed until a few of the outer bud scales are so loose they can be shattered off during the spray operations. Severe injury may result if used after the bud scales have fallen to expose the young pear buds, particularly on Anjou and Comice pears.

2. Preblossom sprays. The first cover spray is applied at the pink, or pre-blossom, period when seasonal development is normal. If weather is cool and buds are slow in opening, an additional spray should be applied at the prepink, or green-bud, stage. Ferbam or ziram (1 1/2 pounds to 100 gallons of water) should be used on spray-sensitive varieties, or lime-sulfur (2 1/2 gallons to 100 gallons of water) on varieties not injured by sulfur. Bordeaux mixture or prepared copper fungicides may be substituted for ferbam or ziram on Comice pears, but beware of sulfur in any form on this variety after the delayed dormant period.

3. Calyx spray. A spray consisting of ferbam or ziram (1 1/2 pounds to 100 gallons) is generally applied at the calyx, or petal-fall, period. On varieties not sensitive to the action of sulfur, lime-sulfur (2 1/2 gallons to 100 gallons of water) is recommended unless hot weather may be expected.

4. Additional cover sprays. Additional applications of ferbam or ziram at 15- to 2o-day intervals may be needed if the season is excessively rainy. Many of the spray materials, except sulfurs, that cause early injury on the spray-sensitive varieties can often be used with safety on them after July. It is too late by then to use them in an efficient scab control program, but they might find usage in special cases. Copper sprays, while not usually causing russet at this time, will intensify any russet already present on the fruit. When scabby fruits or leaves are present on the trees after midsummer, a late outbreak of scab may appear if heavy dews or late summer rains occur. Ferbam or ziram, at the rate of 1 to 1 1/2 pounds to 100 gallons of water, may be added to the last codling moth spray to protect the fruit from late infections or storage scab. This practice is not recommended generally, since the residues are difficult to remove after late applications, and scab should be controlled by the earlier sprays if they are applied in the proper way.

AFTER PEAR FRUITS are picked from the trees at harvest they are no longer susceptible to scab infections. Clean fruits picked from scabby orchards do often develop new scab spots while in common or cold storage, but they result from late infections in the orchard. If rains occur 10 to 14 days ahead of harvest, fruit infections may become visible shortly after the fruit is placed in storage. If the infections occur only a few days before harvest, however, the appearance of scab spots on the fruit in cold storage may be delayed until December or January. To prevent scab from appearing on stored fruit it is necessary to control the fungus in the orchard.

Visible scab spots enlarge only slightly during the storage life of the fruit, but the occurrence of several scabby spots causes the fruit to be discarded or sold for less value. Scabby pears transpire and lose weight more rapidly than sound pears in storage, but generally less than 1 pound per box difference can be measured after 5 months in cold storage.

J. R. KIENHOLZ is a pathologist in the Bureau of Plant Industry, Soils, and Agricultural Engineering. He has been stationed at the United States Fruit Disease Laboratory, Hood River, Oreg., since 1931.