Of the many fungicides developed between 1940 and 1953 only ferbam has been outstanding for the control of all three forms of rust on apples. It is available for spray purposes as a 76-percent active, dry, wettable powder.

The use of ferbam makes unnecessary the close timing of applications that are necessary when sulfur is used to control rust, because ferric dimethyl dithiocarbamate, the active part of ferbam, is translocated externally and internally to such an extent that new growth is protected. J. M. Hamilton, L. O. Weaver, and I, working at the New York State Agricultural Experiment Station, found that the toxic element in Fermate (ferbam) is taken into the plant in sufficient amounts to give a degree of protection through systemic action, particularly against the cedar-rust fungus. Consequently even a spotty coverage of ferbam controlled rust, whereas a spotty coverage of sulfur failed to control. Ferbam applied to the lower leaf surface prevented infection when the rust spores were placed on the upper leaf surface.

Ferbam (76-percent active) used alone at the rate of 1 or 1.5 pounds to Too gallons of spray at the pink, petal-fall, and 10-day stages of apple development gave satisfactory control of the rust diseases in New York over a 10-year period. When a combination of wettable sulfur and ferbam was used for control of both scab and rust, one-half the usual amount of each fungicide was used, and an extra application during bloom was made. Because the number and timing of sprays for rust control may vary in different sections of the country, owners of apple trees should follow the recommendations issued by their own county agents or State experiment stations.

The use of 4-percent ferbam dust with sulfur as the diluent, applied before or during rainy periods, has satisfactorily controlled apple rust diseases. Such dusts can be applied quickly. Commercial growers like them particularly when special applications are needed, especially during the bloom period. Ferbam dusts applied by plane have also given good control.

So far no other fungicides (except maybe some other carbamates) have equaled ferbam against rust diseases, but many commercial orchardists for whom rust is not a serious problem use other fungicides, such as wettable sulfur, naphthoquinones, and glyoxalidines. Additional rust protection has been obtained by adding one-half pound of ferbam to each 100 gallons of spray when those materials are used during the period of critical rust infection.

Ferbam has also been used experimentally in combination with the phenyl mercury fungicides and with captan fungicides to control both rust and scab.

IF YOU GROW cedar trees as ornamentals, it is well to protect there from rust to keep the rust fungi from disfiguring them and to keep the fungi from producing spores that would infect flowering apples or other ornamental plants susceptible to rust.

If you plan to make new plantings of cedars, it is wise to consider using the cultivated varieties of cedar that are resistant to the rust. For twenty years Anthony Berg selected, propagated, and tested red cedar trees for resistance to cedar-apple rust. In 1941 he published his results with a selection from West Virginia that showed outstanding resistance.

In established plantings you can get partial control by spraying the surrounding apple or other susceptible pome trees with ferbam. That will restrict greatly the source of new infection. Commercial orchards sprayed with ferbam produce few rust spores capable of infecting cedars. Many of the cedar infections now come from spores produced on neglected apple trees which, as likely as not, can be removed.

The direct spraying of cedars with bordeaux and sulfur for rust control is done sometimes. The usual procedure is to make one application in July or August to give protection from spores that are discharged in the summer. Another application in late fall or early spring will kill any spores that may remain on the cedars until spring. Such sprays are said to give 80 to 90 percent control.

Spring applications of sulfur, bordeaux, and dinitrocresylate have been used on rust-infected cedars to prevent the cedar galls from producing viable spores. Rush P. Marshall reported in 1941 the results of tests conducted in Connecticut in which one early spring application of bordeaux 180 (a combination of copper sulfate, lime, monocalcium arsenite, zinc arsenite, and fish oil) gave superior control of spore formation and greatly reduced the number of new rust galls on cedar trees.

THUS THREE METHODS of controlling the fungi that cause apple, quince, and hawthorn rusts are available.

In localities where either the cedar or the pomaceous host can be eliminated the remaining host will be unharmed.

Resistant varieties of both host plants are available and are recommended if both plants are to be used in the same area.

For most commercial apple orchards, nurseries, and estates where wild cedar trees are abundant, however, the use of ferbam in sprays or dusts is the most practical means of control.

Susceptible cedars may also be protected by one or two applications of bordeaux 180 in places where it is desirable to prevent damage to the cedars or to reduce the production of spores that would otherwise reinfect pomes.

D. H. PALMITER has been associated with the New York State Agricultural Experiment Station since 1937. He is a graduate of Oregon State College and received his doctorate in plant pathology at the University of Wisconsin. In New York he has investigated methods of controlling various fruit tree diseases by means of fungicide applications.