Postharvest Care for Almonds

We are mid way through almond harvest. As we finish up shaking our Nonpareils, we need to keep in mind the list of orchard tasks to help maintain crop production for the next year. For almonds, flower bud differentiation takes place during the month of September. This means that next year’s bloom and subsequent crop is being formed in the middle of this year’s harvest. During this time period, there are three important cultural practices that need to be considered by almond growers.They include irrigation, nitrogen fertilization and pruning. 1. Post-harvest irrigation is very important to keep the leaves active and functioning until normal leaf drop, which typically takes place at the end of October, early November. By preventing premature defoliation, we let the tree transition its nutrients from the leaves back to the fruiting spurs. The nutrients that are known to migrate from the leaves to the spurs at the onset of leaf fall are nitrogen, potassium and phosphorous. These nutrients play major roles in bloom development and fruit set. If the orchard does prematurely defoliate due to lack of water, irrigate to encourage re-growth. This may reduce yields in the following year, but yield loss will not be as significant as not watering at all. If watering does not occur, not only will fruit bud differentiation be poor, the orchard will suffer from premature flower drop in late winter. The best advice is to avoid this situation all together by properly managing your water during the harvest period. 2. After irrigation, nitrogen fertilization is the most important cultural practice in an almond orchard. For most of our orchards, split nitrogen applications provide the most efficient use of nitrogen. A post-harvest nitrogen application can be of 20 to 40 pounds per application – dependent upon tree age- totaling no

September 1, 2009

Potassium thiosulfate toxicity on almond

During periods of high heat and the corresponding high evapo-transpiration, several unique orchard problems can occur. Most of these are due to fertigation methods which have been widely adopted to increase fertilizer application efficiency. The benefits of fertigation greatly outweigh most negative impacts, but caution must be used as a simple mis-calculation can cause orchard damage. A field call from a grower in late June demonstrated the potential problems that can occur with fertigation. Observations of yellowing leaves, leaf drop, and death of lower limbs raised concerns by the grower and pest control advisor (PCA), prompting an orchard visit. Initial Observations: Upon arriving to the 11th leaf Sonorra/Nonpareil/Carmel (all on Nemaguard) orchard I noticed excessive leaf drop across all varieties (Picture 1). Most of these leaves were coming from the interior of the canopy, suggesting the possibility of drought stress from improper irrigation scheduling. Lower leaves found on the interior of the canopy were burnt back, with a crispy texture. Leaves closest to the trunk that were completely yellow were beginning to abscise, while leaves on the tips of the branches remained green (Picture 2). This is in contrast to lower limb dieback, which causes soft yellow leaves found on the ends of interior branches. Picture 1: Leaf drop associated with the over-application of potassium thiosulfate. Picture 2: Leaf wilting and “dieback” associated with the over-application of potassium thiosulfate. Note how the interior branches are more affected than the branches on the outside edge of the canopy. Up-Close Observations: Close inspection of the leaves revealed a necrotic tip, or burnt region of the leaf. This leaf was surrounded by a yellow halo (Picture 3). Typically, a yellow halo around a necrotic area would suggest the possibility of almond leaf scorch, but due to the widespread occurrence of the problem, this

July 20, 2009

Mid-July Leaf Sampling for Almonds

Leaf analysis of almond is a useful tool in diagnosing deficiencies, toxicities, and future nutrient needs of the tree. It provides an up to date analysis of the mineral composition of the tree, with desirable concentration of different elements known through extensive University of California research. Reasoning for sampling. As almond trees increase in size, their demand for nutrients also increases. Tree nutrient concentration is dependent upon the growth rate of the crop and the amount of nutrients that have been supplied naturally or through fertilizer. Under certain conditions, plant tissue may become deficient which could limit further growth and crop quality. Depending upon the nutrient and level of deficiency, remediation is possible in the current season, dormant period, or early spring of the following year. Leaf concentrations of major elements (nitrogen, phosphorous, and potassium) can be used along with kernel yield per acre to determine the nutrient budget for the next season. Process of sampling. Sampling should be distributed in a regular pattern across the block, with fully expanded leaves pulled from non-fruiting spurs on branches at least 6 feet high. About 100 leaves are needed for each sample. Leaves should be picked from trees of the same variety, age, rootstock, and soil type. Trees samples should be at least 100 feet apart and 20 trees are needed to ensure accuracy and confidence with the results. Partitioning of larger sampling blocks is advised to determine tree size and yield variability. Label the samples so the sampling location is known, and keep cool until they are sent to an analytical lab. Interpreting the results. Leaf analysis results are recorded either in percentages (%) or parts per million (PPM) of each element in a given weight of dried leaves. The table below contains the critical values for almond leaves sampled in

July 13, 2009

Hull Split Part 2: Hull Rot of Almond

As almond trees approach harvest, at about mid hull split, clusters of dry leaves begin to appear scattered through the tree canopy. Individual spurs, small shoots or entire small branches may collapse due to hull rot infections (Photo 1). The loss of fruiting wood, especially in the lower parts of the tree, can negatively affect yield for years to come. Nonpareil is usually the most severely affected cultivar though Sonora and Kapareil can also sustain extensive damage. Hull rot is caused by either of two fungi, Monilinia fructicola or Rhizopus stolonifer. Monilinia fructicola is best known as one of the brown rot fungi and R. stolonifer is often called the bread mold fungus, and will turn bread left out black and moldy. Photograph 1: Hullrot of almond caused by Rhizopus stolonifer. In the southern San Joaquin Valley I believe that Rhizopus is the primary pathogen responsible for hull rot while Monilinia may be more important in the Sacramento Valley. These two organisms are very different but can cause similar disease symptoms on almond. As the name implies, a lesion or dryish rotted area develops on the hull, and dense masses of Rhizopus spores produce a powdery dark gray to black growth between the hull and the shell (Photo 2). Monilinia spores are buff-colored and can be seen on inner and outer hull surfaces. The nut meat is not damaged, but a toxin produced in the infected hull moves from the hull into the neighboring leaves and shoots causing death of these tissues. Neither Monilinia nor Rhizopus are able to invade the healthy outer hull surface. Only after hull split begins can spores gain access to the inside of the hull and initiate infections. Once hull split starts, trees are at risk of becoming infected. One or both pathogens may be

June 30, 2009

Foamy Canker in Almond

This is one of the most visually moving diseases found in almond. Once upon the location of the problem, not only is the disease obvious by looking at the trees, but the air is also filled with a fermented-like smell reminding one a bar when entering for happy hour. Overall Orchard Information: The orchard I was called out to visit was described as a complete loss to foamy canker. To me this came as a bit of a surprise as foamy canker typically comes later in the season. By time I have arrived, the grower was in the process of removing the orchard. The entire orchard was exhibiting symptoms of foamy canker (Picture 1), poor growth and dieing trees. Photo 1: Overview of the almond variety Fritz with foamy canker The orchard was a Nonpareil-Fritz-Monterrey on Lovell planted on clay/clay loam soil. The trees were in their 4th Leaf trees with average growth. Nut set of the trees was decent, but not great. Speaking with the grower, he mentioned that the orchard has a high water table, found at about 7 feet with subbing up to 4-5 feet. Quality of the water was unknown. The site is also high in boron within its soil, and has a history of verticillium wilt (old tomato and melon ground). Overall, the discussion yielded that there were many issues from the start with the orchard – over 30% of the Fritz variety planted in the first year did not survive and needed to be replanted. Irrigation of the trees tends to be minimal due to the high water table. The grower does not irrigate often – only 8 inches last year through double line drip. Nitrogen usage is minimum, but tree vigor is high due to being the first generation orchard on old row

June 16, 2009

Herbicide drift damage to a Butte/Padre almond orchard by 2,4-D

May is the time of the year for the herbicide injury to almonds. High winds, fast growing weeds, and too many orchard tasks to complete in a day are the typical causes of herbicide drift. Herbicide drift can be prevented by following a few simple principles:1). Avoid windy days when applying herbicides,2). Apply the correct herbicide that targets the correct weed,3). and apply the herbicide at the proper rate. A field call in mid-May by a grower yielded a case of typical 2,4-D injury to almond. The 2nd leaf orchard was 50% Butte and 50% Padre on nemaguard rootstock. The orchard was situated in sandy soil with microsprinklers used for irrigation. The grower reported multiple trees showing dieback of new growth. He was uncertain of the cause and thought verticillium wilt may be affecting his orchard. Picture 1 shows the overall symptoms of an affected almond tree. Picture 1: Overall tree symptoms caused by 2,4-D herbicide drift. Note tip dieback and odd growth. Overall, the distribution of the symptoms were found throughout a large percentage of the block. Many trees where showing a “shepherd’s crook” of the new growth indicating either a wilt disease or herbicide/salt issue. Picture 2 shows the severity of the symptoms on the new growth of the almond tree. Picture 2: Branch tip dieback due to 2,4-D herbicide drift. Leaves at the tip of the crook were crispy, indicating a fast wilt. Shoots with contorted growth were found throughout the canopy. Pictures 3 and 4 are of these symptoms. Picture 3: Branch damage from 2,4-D herbicide drift. Branch is showing the “shepherd’s crook” symptom, typical of vascular wilt pathogens or salt/chemical damage. Picture 4: Contorted growth of new growth caused by exposure to 2,4-D herbicide. With the exception of the contorted growth, symtpoms expressed by the

June 9, 2009