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Show Washington Co. Peach Growers Urged To Combat Powdery Mildew By WILLIAM E. RADER Graduate Assistant In Plant , Pathology XT. S. A.C. Each year the powdery mildew of peaches causes considerable loss in Washington county. This disease dis-ease causes a tough brown spot of the fruit and makes a U. S. No. 1 a cull peach. Losses in Washington county range from none in some orchards to thirty per cent of the total crop in others. Mildew has been increasing increas-ing in recent years and will continue con-tinue to spread unless growers make a county-wide and concentrated concen-trated effort to control it. Same As Apples Fungus The powdery mildew (Sphaer-otheca (Sphaer-otheca pannosa (Wallr.) Lev.) which affects the peach is similar in appearance to the mildew of the apple. The fungus affects either side of the leaf, usually developing de-veloping more abundantly on the under surface and appearing as white patches of powdery material. ma-terial. The leaves become curled and the edges roll downward, parallel par-allel to the midrib. Only young, vigorously-growing shoots are attacked, at-tacked, the infection usually spreading from diseased leaves. White, frosty patches of fungus ap-(Continued ap-(Continued on page six) Peach Mildew Control (Continued from first page) pears on the surface of the bark. As the organism establishes itself, the underlying bark becomes brown and dry. When the attack is severe se-vere the bark also becomes shriveled shriv-eled and the young tips often become be-come distorted. As in the case of the apple, the most noticeable and destructive damage occurs on the fruit. The fungus generally appears on the young, immature fruits, the ripening ripen-ing fruit seems to be more immune. im-mune. When young fruits are attacked at-tacked they frequently drop prematurely. pre-maturely. The mildew appears first as white, musty patches, the undelying flesh becoming hard and the skin taking on a brown or dead color. In severe cases the diseased areas may become cracked. crack-ed. These blemishes lower the grade of the fruit. Symtoms Disappear Later in the season the early symtoms on the leaves, twigs and fruits usually disappear. The leaves previously attacked may dry up and fall from the tree. The white powdery material on the shoots and the fruit turns brown and disappears, leaving brown, dried areas. The fungus develops in the bud scales during the growing season, hibernates during the winter, and the following spring attacks the unfolding leaves. Powdery mildew of the peach was first reported from Utah in 1907 and since that time has become be-come generally distributed thru-out thru-out the state. The severe infestations infesta-tions of peach mildew are confined con-fined largely to the warmer areas of the state. This organism attacks the nectarine nec-tarine causing similar injury to that on the peach. Means of Control In Utah no experimental work has been done to determine effective ef-fective control measures. The following fol-lowing methods have proven satisfactory sat-isfactory in other areas in the West: (1) pruning and elimination elimin-ation of diseased twigs as this procedure will greatly decrease the amount of fungus that will start the diease the following spring; (2) practice of such measures meas-ures as will promote and maintain main-tain the normal vigor of the plant. In some areas such sanitation and cultural practices do not control con-trol these mildews. Under such conditions applications of the following fol-lowing spray is most generally recommended for the control of both apple and peach mildew: Lime sulphur 1-50 plus 3 pounds of iron sulphate (per 50 gallons of spray). Do not use lead arsenate arsen-ate with this spray! Four pounds of dry-lime sulphur equal one gallon of 32 Baume' liquid lime sulphur. The addition of the iron sulphate sul-phate increases the fungicidal and adhesive properties of the spray and also will aid in the control of chlorosis. The spray should be applied as soon as the mildew appears. ap-pears. Under Utah conditions this is about the time of husk fall. The additional applications are made at 10-day intervals. The subsequent abundance of the disease dis-ease will determine the numbei of additional applications neces sary. Controls Peach Mildew The delayed dormant line sulphur sul-phur used for the twig borer control con-trol also aids in controlling the mildew on the peach. Growers must remember that spraying should be started as soon as the mildew appears. This spray does not kill the organism but only protects pro-tects the plants by preventing the germination of the spores, which spread the disease, and by inhibiting inhibit-ing the further growth of fungus body that is already established. Lime sulphur when applied during dur-ing periods of high temperatures will cause severe sulphur sun scald. Unless the disease is controlled in all orchards it will continue to spread from trees not sprayed, to orchards where growers are spraying spray-ing to control it. Because of this, it is important that all growers cooperate in controlling this disease. dis-ease. It is possible to elminate the mildew entirely from all the county if every peach tree were properly sprayed for two seasons. All growers must cooperate in making this program effective and until this is done, there will always al-ways be some trees to carry over the disease from year to year. The mildew on apple will not attack peach trees and peach mildew mil-dew does not grow on apples. |