1. Spray with 2.5 percent concentrate 32 Baume lime-sulfur (2.5 gallons in 100 gallons of water) as the blossoms reach the pink stage, just before blooming; or use dried sodium polysulfide at the rate of 3 pounds to 100 gallons of water.

2. Spray with 2.0 percent lime-sulfur after 75 percent of the petals have fallen; or use 2.5 pounds of the dried sodium polysulfide to 100 gallons of water.

3- Spray with 2 to 4 pounds of wettable sulfur 2 weeks later. Micronized sulfur has given adequate control at 2 pounds to 100 gallons.

In orchards sprayed with lime-sulfur or with sulfur, the mildew is held down to 5 to 20 percent until July. As no summer spraying is safe with sulfur :sprays or dusts in the north central area, mildew starts to spread after the last of the sulfur has disappeared from the foliage. By fall mildew may have .arisen to 30 percent or even up to 45 percent or more on trees that had been given only two sprays with lime-sulfur at the pink and calyx stages.

Those suggestions as to rates of application are based on the use of spray guns manually operated from power-driven sprayers, either stationary or portable. Most of the growers now are turning to the use of air-blast sprayers with fixed nozzles. Dosages for them are based on amounts of material per acre. The dosages are computed by determining the amount of material used per tree by the old hand spray gun method multiplied by the number of trees per acre, less about 20 percent. The fixed nozzles forced by an air blast give coverage with little or no spray runoff, hence about 20 percent less spray is usually needed. Some of the so-called concentrate sprayers use very fine jets and apply the spray in :exceedingly fine droplets at relatively high concentrations of material. Proportionately less water is used per acre. Many factors are involved in determining how much material to use per acre.

In the warm valleys of the far West, sulfur cannot be applied after the first cover spray because of the danger of injury from sulfur shock or of fruit scalding. Usually, however, a second cover spray, using 2 pounds of micronized sulfur, is safe on Jonathan. On Delicious and Stayman Winesap, sulfur is generally not recommended at all. In the cooler parts of the northern areas, lime-sulfur is safe on Delicious if it is applied at the pink and calyx stages only. As mildew is seldom serious on Delicious, the early sprays often are not needed. Because scab has appeared in some places, the program for scab control will fairly well eliminate mildew on Delicious. In a few cases ferbam, 1.5 pounds to 100 gallons of water, can be substituted for sulfur. Ferbam is not overly effective against apple powdery mildew and its effect does not last more than 10 or 12 days.

Many experimental materials have been tested at the Tree Fruit Experiment Station in Wenatchee, Wash., and at the Hood River Experiment Station in Oregon against apple powdery mildew. Few proved to be as efficient as lime-sulfur; those few were too costly or were unobtainable on a commercial scale.

Dusting with sulfur from the ground or from airplanes (60 pounds to the acre) was effective in places where water for sprays was not readily available. Dusting in the early part of the season was less effective than the wet treatments, however.

Pruning sometimes helps check mildew in a young orchard. Mildew in young Golden Delicious tends to be restricted to a few terminals. It is sometimes cheaper to prune them than to spray. If the mildew occurs on most of the twigs, pruning may not be practical, or it may not be wise to give such a shock to the young tree in summer.

Mildew-susceptible varieties should be eliminated if possible. A few susceptible trees in an orchard can cause a considerable increase in mildew in the more resistant varieties even if they are some distance away. If susceptible varieties are planted as an integral part of the orchard, the grower must resort to a spray program.

It is not possible to repress mildew by the use of any of the standard understocks. There is no danger in top-working Jonathan to Delicious, however. The Delicious trees grow and flourish with no increase in mildew although Jonathan sap flows through their branches. Of course, if only part of the tree is top-worked to Delicious, the adjacent Jonathan branches will infect the Delicious branches to some extent because of the abundant spores carried to the resistant Delicious from adjacent Jonathan leaves.

In all future breeding programs aimed at development of better apple varieties, mildew should be considered. Susceptibility to mildew appears to be a dominant trait in Jonathan hybrids. Jonathan-type apples said to be resistant to mildew are available, but widespread trials are needed to prove their commercial value.

RODERICK SPRAGUE is a pathologist at the Tree Fruit Experiment Station, Wenatchee, Wash. He is a graduate of Washington State College and received the doctor's degree from the University of Cincinnati.

Peach bacterial spot.