April Showers Brings Almond Diseases Across the Valley

Farming is like Mother Nature – unpredictable.

That’s certainly true with the gusty winds and April showers buffeting the Valley rich farm lands lately.

Growers spraying fungicides to battle almond diseases.

The on-again and off-again winter-like springtime weather has almond growers working feverishly to battle plant fungi that can trigger a variety of diseases in almonds.

Field scout Jenna Mayfield reports growers applying fungicides at a steady clip to prevent crop-damaging diseases.

University of California IPM advisors point out disease-causing fungi is present in almond orchards all the time. The amount depends on the environmental conditions and the level the previous season. A good disease management program hinges on the choice of fungicides, timing and coverage. It also depends on the grower’s assessment of the disease problem.  Fungicides should be chosen carefully to address the specific problem. Advisors also note it’s good to rotate fungicides use in the orchard.

Here are some of the common diseases in almonds:

Brown rot
Growers usually treat for brown rot at least once during bloom. The brown rot fungus attacks the tree by invading the anthers and pistils of the flower when it is open. The fungus then can kill the spur or shoot.
The most susceptible variety is Butte followed by Carmel. Nonpareil is one of the least susceptible varieties for brown rot.

Shot hole

Almonds infected by shot hole.

Wet years are the most favorable conditions for shot hole to develop. This fungus requires water for all its activities, so periods of extended rainfall create a situation that favors shot hole disease epidemics.
The disease can lead to lesions on leaves and fruit, which emerge at the leaf bud. Infected leaves can lead to defoliation. By May, the almond hull develops enough to resist a shot hole infection.

Scab

Evidence of scab on a almond leaf.

In the past, scab wasn’t a concern for growers locally. But in recent years, the problem has become more serious. The fungus causes black spots on the fruit, leaves and shoots.  Scab can defoliate a tree quickly. Fungicide treatment is effective two to five weeks after bloom.

Rust
Rust also can cause defoliation. High humidity will trigger rust as well as scab problems. Rust and scab emerges in late spring or early summer. The fungus attacks the leaves, but not the fruit. Rust is controlled by one or two applications of sulfur in late spring.

Monitor for Alternaria leaf spot now.

Leaf spot

Alternaria leaf spot is another defoliating disease, which surfaces in early summer and causes lesions on leaves. Carmel, Nonpareil, Butte, Sonora, Mission and Peerless varieties are the most susceptible varieties. UC IPM says growers should look for signs of leaf spot from April through June. If alternaria is discovered, treatment should start around mid-April.

  Of course, spotting these diseases requires regular monitoring of orchard conditions.  “Putting your boots on the ground is the best way to fight diseases and pests,” Jenna says.