You are correct- I was reading from dated material and misread it entirely, confusing the division between brown rot and scab which in the manual were one on top of the other. However, that is where my confusion came from- I didn’t assume peach and apple scab would respond to the same materials the same way.
Here’s what Rutgers has to say about peach scab now. Lots more commercial stonefruit production in Jersey than NY, I think.
TREE FRUIT PESTS AND CONTROLS
93
Scab
The fungus Fusicladosporium carpophilum causes peach scab. The pathogen overwinters in lesions produced on current season‘s fruiting shoots. In New Jersey, spore production on these lesions begins during bloom and ends early- to mid-July. The spores are not readily released into the air until they become wetted. The period between infection and visual symptoms of the disease on the fruit is very long, from 40 to 70 days. Because of this long period, early maturing cultivars may be harvested before the fruit spots are visible to the naked eye. Infections can occur on the fruit, green twigs, and leaves. Infections occur most readily at temperatures between 65 and 75°F, when rainfall is abundant. Infections can occur at temperatures as low as 40 -45°F and as high as 90-95°F.
Lesions formed on current season twigs are light brown, diffuse, and small initially (0.0625 to 0.125 inches in diameter). As they increase in size, they become circular with a darker brown color. A slightly raised bark callus surrounds the margin of the lesion. In the spring, velvety-textured, olive-colored spots appear within the lesion.
On fruit, tiny spots appear around third cover (early July in southern counties) when the fruit are about one-half their final size. The spots develop quickly into very dark, olive-colored, circular spots. Later the spots appear almost black in color. The spots do not “break” the skin as do the fruit spots caused by bacterial spot. However, the skin frequently cracks open in the areas where numerous infected spots occur, and the Brown Rot or Rhizopus Rot fungus then attacks the flesh of the fruit. The spots are usually more numerous on the stem end of the fruit.
Topsin M (0.5 lb/100 gal), when applied at petal fall, has resulted in “burn out” of many of the overwintering lesions on the twigs. Thus, disease pressure can be measurably reduced as a result of a lower inoculum level. Fruit infections are most common from shuck-split through third cover. Foliar sprays are effective in protecting the fruit from infection, and a single fungicide spray applied around first cover will provide reasonably good control of twig infections in nonbearing blocks.
The disease is troublesome in commercial blocks when the trees did not receive a regular spray program in the preceding year. This occurs when the block was “frozen-out” the previous year and when a new block is first coming into production. The disease can be troublesome during periods of drought, since only 3 hours of 100% RH is necessary for sporulation to occur. Where disease is troublesome, apply Gem, Topsin M + Captan, Bravo, Abound, or Quadris Top; use higher rates and shorter spray intervals if frequent rains occur. In addition to protectant activity, Gem and Abound also act as antisporulants, thereby reducing inoculum production on twig lesions. Sprays should be applied until 40 days before harvest.
Rutgers is one of the few sources for free information about commercial production recs. Here’s the link to download their manual. file:///C:/Users/aland/Downloads/e002.pdf
