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Manage Heightened Almond Stress Caused by Recent Weather Events

March 1, 2018
This image shows an illustrated almond tree in bloom.

Parts of California have experienced higher-than-average temperatures and lower-than-average precipitation over the past year. Then there was the recent freeze and now a forecast for strong storms to sweep across the state. All of this weather variability means almond orchards are facing severe stress during the critical bloom phase.

During these times of extreme weather changes, it may be tempting to make 2 incorrect assumptions:

  1. Almond trees are drought tolerant, so they are better able to withstand periods of stress.
  2. Precipitation levels are currently down, so the risk of bloom disease is likely low.

Both assumptions can be costly for trees that face unexpected stress and disease outbreaks. Here are 4 tips to optimize tree health through almond bloom.

  1. Monitor orchard stress. While almond trees are drought tolerant, a lack of water can have a high impact on yield potential. Water stress reduces a tree’s ability to produce carbohydrates, which is a critical nutrient for proper almond development. Water-deficient trees may experience early-season leaf drop and, in extreme cases, total tree defoliation. Growers can use a portable pressure chamber to measure “midday stem water potential” for signs of stress. Minimizing stress increases photosynthesis and growth potential.
  2. Manage water usage. Water demand is lower during bloom compared to demand in the heat of summer. However, extreme heat and dry spells may tempt you to over-irrigate, which creates the perfect conditions for diseases to thrive. Limiting irrigation to 24 hours and draining any standing water from the crown will help minimize disease risk.
  3. Identify disease warning signs. While moisture levels have been low, freeze protection led many growers to run irrigation. That standing water combined with the forecast for heavy storms creates a ripe environment for disease. Two key diseases that may be problematic this year are anthracnose and root rot, and affected orchards can lose vigor quickly. Oftentimes, trees are already in a declining state when disease is identified. Here are some early warning signs to aid in proactive management:
    • Anthracnose – Look for yellow lesions that begin at the leaf margin or tip and advance toward the middle of the leaf. The disease overwinters in dead wood or mummified fruit that remain attached to the tree, so infection can occur from the previous year.
    • Root rot – Keep an eye out for leaves that wilt, dry and remain attached to the tree. Chronic infections, usually of the roots, cause reduction in growth and early senescence and leaf fall. Younger trees are particularly threatened because their root structures are smaller than mature trees.
  4. Prepare with a fungicide application. A fungicide application at bloom can help mitigate environmental stress and help boost trees’ natural defenses.

A fungicide application – among other management practices – provides multiple physiological benefits to help improve the overall health of your orchards year after year.

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