Yellow Trees from Being Too Wet

It is very common to see yellow trees in the spring. The lack of color is often due to saturated soils which reduces the movement of oxygen into the soil, killing fine feeder roots. This impacts the ability for the tree to take in water and nutrients, leading to micro-nutrient deficiencies, impacting nut set and tree growth. In severe cases, especially with younger trees, the symptoms are similar to glyphosate drift or zinc deficiency. Later-season carry-over effects are also observed and include a limited rootzone, which leads to severe water stress during hull-split and harvest. Most of the time, this problem is caused by the orchard being irrigated too soon. Many operations apply water because it is perceived as needed or they are wanting to apply fertilizer. The need to apply water, however, is usually very low in the spring due to the cooler conditions and crop stage. Based on the 30-year average almond evapotranspirational values across California, water use from Mid-February (bloom) through the first week of April for almonds across the State ranges from 3.6″ to about 4.25.” This demand is often met by rain and the tree accessing stored moisture within the soil. To determine when to start applying water, plant stress or soil moisture levels should be monitored. The soil profile should be starting to dry at the two to three feet zone and can be checked with with the use of a shovel, auger, or soil moisture sensors. If using the pressure chamber to monitor plant stress, irrigation should be considered when trees are 1.5-2 bars more negative than baseline. For more information on the use of a pressure chamber in perennial crops, please see this document. If wanting to apply nitrogen, applications should occur by ground application or the shortest fertigation set as possible. These practices will help to properly time the first

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Yellow Trees and Saturated Soils

Annually, several calls regarding poor tree growth and “pale trees” are received. This is often due to saturated soils. Too wet of soils reduces the movement of oxygen into the soil, killing fine feeder roots. This impacts the ability for the tree to uptake water and nutrients, leading to micro-nutrient deficiencies, impacting nut set and tree growth. Later-season effects are also observed and include a limited rootzone, leading to severe water stress during hull-split and harvest. The problem is often compounded by farm practices. Too early of fertigations before the tree begins to “suck” water from the soil can lead to an increase in saturated conditions. Spring rains, cool temperatures, and heavy soils compound the problem. Once the symptoms appear, the reaction is to fertigate or chemigate in attempts to manage the symptoms of stunted growth and yellow leaves. Symptoms continue to worsen. Recovery is not always possible. If conditions are prolonged, the symptoms will worsen. Trees may eventually die or shed leaves and crop. In some cases, the roots and crown may become infested with Phytophthora. In many cases, Phytophthora is serving as a secondary problem, infecting only after the tree has been weakened by the saturated soils. The problem can be alleviated by warmer temperatures which increase the transpiration rate of the tree or reduced irrigation until the tree recovers. Recovery is dependent on severity, and may take several months. Optimally, it is best to do what is possible to prevent the symptoms from occurring. Prior to the first irrigation, moisture levels in the soil should be dropping. This can be determined with the use of a shovel or auger, pressure chamber, or soil moisture sensors. If using the pressure chamber, irrigation should be considered if trees are 1-2 bars more negative than baseline. More on using the pressure bomb to

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