Anthracnose

Symptoms of anthracnose on almond include blossom blight and fruit infections often with spur and limb dieback. Infected flowers look similar to brown rot strikes. Leaves on infected spurs develop marginal necrosis, beginning with water-soaked areas that fade in color; leaves die but remain attached to branches.

Infected nuts show round, orangish, sunken lesions on the hull. These symptoms may appear about 3 weeks after petal fall; nuts remain susceptible and can be infected later in the season if conditions are favorable. Profuse gumming occurs as the infection progresses into the kernel. Diseased fruit die and turn into mummies that remain attached to the spur. The shoots or branches that bear infected nuts often die. Although the fungus may invade fruitwood, it is seldom cultured from affected branches. Death of the wood may result from a toxin rather than from direct colonization of the wood by the fungus.

All cultivars appear to be susceptible to anthracnose. The disease has been most damaging on Thompson, Merced, Price, Peerless, Winters, Monterey, Fritz, and Butte; moderate on Harvey, Carmel, NePlus Ultra, Padre, and Mission. Nonpareil is considered to be less susceptible. Ideal conditions for the development of this disease are warm, rainy weather.

Fungicide treatment is the most important control strategy, but must be coupled with cultural practices to achieve the best control. In orchards that have a history of anthracnose, apply fungicide sprays beginning at 5-10% bloom or pink bud and repeat every 10 to 14 days if rains persist. Late spring rains may necessitate additional applications into May. Alternate materials as follows: make the first application at pink bud using either a demethylation (sterol) inhibitor (DMI; FRAC group 3) or quinone outside inhibitor (QoI; FRAC group 11) fungicide; follow this with a premixture (FRAC groups 3/11 or 7/11) fungicide application or a tank mix of captan or mancozeb mixed with iprodione or thiophanate-methyl applied at full bloom.

As long as conditions are conducive to disease development, alternate applications of demethylation (sterol) inhibitor (DMI), quinone outside inhibitor (QoI), captan, chlorothalonil, or mancozeb (FRAC Groups M3, M4, M5, 3, 11, respectively). Prune out dead, infected wood to reduce inoculum. If sprinkler irrigation is practiced, use low angle nozzles to prevent the tree canopy from being wetted by the sprinklers as a means of reducing disease spread.