Ruby, Mission, Monterey and Aldrich seem to be very susceptible to leafhopper damage. Some insecticides which are reported to control leafhoppers, often when spraying for another targeted and labeled pest are oils and soaps, Omite, Lorsban, malathion, AGRI-MEK, and Imidan. Almond rust , caused by the fungus Tranzschelia discolor , will begin to show in May or June, if the disease follows our wet spring, as expected. This disease makes rusty spots which look very much like iron rust on the under side of leaves, and the tops of the leaves show yellow color to match the rust spot below. Rust can cause severe defoliation.
Sulfur is a very effective control if applied before, or at the first sign of rust.
Almond scab , caused by another fungus, Fusicladium carpophilum , makes greasy gray spots on the leaves and on the tops of the nuts. These symptoms will usually start showing about mid-June. Control is best done at 2 weeks to 5 weeks after petal fall. There is still some chance to control scab in orchards where scab has been a problem in the past years. Control is very poor if you wait until scab shows in the orchard - scab control is a preventive program based upon past history and weather conditions.