Monday, April 27, 2015

You’re All Wet if You Don’t Take Almond Disease Management Seriously in a Drought Year

Farmers are quick to tell you that no two years are the same. They come to expect the unexpected. Past performance doesn’t necessary predict future results.

Almonds are well into fruit development at this time.
This certainly is the case with almond growers. Their crop has been doing well so far this season with nuts developing about a month faster than normal.
“Every year is different with the progression of the crop. This year we’re ahead,” says Gurreet Brar, a farm advisor and almond expert with the University of California Cooperative Extension in Fresno County.
As a result, it’s important that almond growers stay on top of monitoring the trees in the orchard and not simply relying on the calendar as a guide. At this stage, almonds are well into fruit development (have you seen the size of some almonds already?)
Moisture build up can lead to diseases in trees.

Brar says growers should be looking this spring and summer for any signs of diseases in the orchards. Post-bloom diseases could linger if there is high amount of moisture in an orchard. For example, microsprinklers may be angled high up toward the canopy and that could cause moisture build-up in the canopy, creating an environment ripe for diseases to spread. Here are some of the things to look for this spring:

Alternaria damage on a leaf.  - UC IPM photos
·        Alternaria: large brown spots form on the leaf. Alternaria develops when there is a lot of humidity or stagnant air. Leaf spots can spread quickly in June and July and can completely defoliate trees by early summer.

Rust damage is evident on leaves.
·        Rust: Rust colored spores appear on leaves and can spread by air movement. It’s a serious problem in orchards near waterways or areas with high humidity in the spring and summer. Leaves can fall prematurely, causing trees to become weak.

Sacb is evident by grayish black spots the nut.
·        Scab: Grayish black spots show up on leaves, fruit and twigs in the late spring or early summer. Usually, the disease thrives during prolonged wet spring weather. As Brar points out, orchards irrigated by sprinklers can get this disease if the water reaches the foliage.

Hull rot causes leaves to wither and die.
·        Hull rot: This disease surfaces several weeks before harvest when leaves wither and die. Fungi will invade hulls and produce a toxin that kills the shoot attached to the fruit. This will impair maturity of other green fruit on the shoot. The fruit will stay on the tree after harvest. 

Brar points out the drought doesn’t have direct affect on almond tree diseases. Indirectly, though, the lack of water will weaken tree health and make them more susceptible to diseases in the future.

Reports of canker are up.
Right now, Brar has been fielding a lot of calls from growers concerned about canker in the stems and lower canopy. Called bacterial canker, this disease becomes evident in the spring and includes limb dieback with rough cankers and amber-colored gum. Also, leaf spots and a blast of young flowers, spurs and shoots can develop.

 UC IPM notes orchards with nitrogen-deficient trees, young trees 2 to 8 years old or high populations of ring nematode are prone to bacterial canker. Prevention is the best way to manage the disease. Here’s what UC IPM recommends:

  •         Maintaining proper nutrition, especially nitrogen.
  •        Applying low-biuret urea before leaf drop can reduce the canker size of infected trees.
  •      Using a nematicide treatment in October can help reduce the disease severity

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