By midsummer, black pimple-like dots are visible in the spots. When severe, infected leaflets are killed, causing leaf shed in late summer or early fall. Premature shedding adds to the reduced plant vigor. Fungicides applied following the pecan scab spray program will also control this fungus. Primary infection occurs on developing leaves in the spring from spores produced on last years foliage.
Symptoms usually appear during the summer months on the lower surfaces of leaflets.
Later in the season, the lesions turn brown due to the death of the leaf cells in the disease area. Spores are spread by wind and rain to nearby leaves and neighboring trees. Although all pecan varieties are moderately to slightly susceptible, Pawnee, Moneymaker and Stuart varieties are the most susceptible to the downy spot fungus. Disk or rake under fallen leaves in the fall or early spring before the leafbuds begin to swell. By removing the leaves from the soil surface, spore discharge is stopped.