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Here are two articles from the July 2009 issue of Western Fruit Grower discussing almond scaffold diseases and pruning.
Do you agree with the minimal pruning strategies as recommended by the University of California? Click on the comment link to voice your thoughts!
Wednesday, July 29, 2009
Monday, July 27, 2009
Almond Leaf Scorch
In late July a variety of leaf issues occur which include premature leaf drop due to improper irrigation, salt burn from poor quality water, and in rare cases, almond leaf scorch.
A summer farm call to an orchard close to the Merced River yielded my first confirmed case of almond leaf scorch. This orchard consisted of a 12th leaf planting of Monterrey, Nonpareil, Carmel, and Sonora all on Nemaguard rootstock, planted in the Snelling Sandy Loam soil series, and irrigated by microsprinklers.
The orchard looked relatively healthy from afar, but a notable discoloring of the leaves was seen in the Sonora variety. A closer inspection revealed a large percentage of trees (i.e. 80%) that appeared to be infected with of almond leaf scorch. Some Nonpareil trees were symptomatic, but very few of the other pollinators (i.e. Monterrey and Carmel) had symptoms.
Picture 1: A tree severely affected with almond leaf scorch. Trees "bronze" over in late summer. This picture was not from the farm call listed above.
Upon seeing the symptomatic leaves, it became clear that Almond Leaf Scorch was the suspected disease due to the large yellow halo that bordered the scorched part of the leaf. Furthermore, the yellowing and scorch did not have any particular pattern across the leaves. This is unlike many salt issues that typically have scorching int he tip of the leaf due to accumulations of salts.
Picture 2: Symptoms of almond leaf scorch on an almond leaf. Note obvious yellow halo surrounding the necrotic leaf region.
For a true confirmation of almond leaf scorch, a diagnostic PCR assay must be completed. Leaves were taken from infected and healthy looking trees and sent to Dr. Bruce Kirkpatrick's lab in the Department of Plant Pathology at UC Davis. The diagnostic assay came back positive for the diseased trees, and negative for the healthy trees, confirming that the pathogen was present within the orchard.
Almond Leaf Scorch is caused by the xylem-limited bacterium, Xylella fastidiosa. The bacteria is very fastidious and is hard to culture in media. Artificial inoculations of almond trees made within the laboratory has shown that it can take several years for the first leaves to show symptoms after inoculation. Eventual tree death occurs through the clogging of the vascular tissues, which prevents the flow of nutrients to the branches. Leaf symptoms are caused by bacterial produced toxins that accumulate within the leaves.
The bacterium can not directly infect the almond tree by itself. It requires infested xylem feeding insects to carry and introduce the bacteria into the tree. Within almond, this is primarly limited to sharpshooters (Cicadellidae) and spittlebugs (Cercopidae), with green sharpshooters (Draeculacephala minerva) being the most commonly found in orchards. Leaf hoppers have not been shown to transmit the disease at high levels.
Picture 3: A close up of a green sharpshooter.
Xylella fastidiosa is commonly found in riparian areas due to the high diversity of plants that can serve as hosts for the bacterium. Coincidentally enough, these areas are also the same locations in which sharpshooters and spittlebugs overwinter and feed year round. Sharpshooters transfer the bacteria to the almond tree by feeding on infected ground cover and weeds and then move to feed on the tree. Upon piercing into the xylem tissue of the tree, the sharpshooter injects the bacteria into the xylem, thus infecting the tree. Tree to tree transmission of the disease has not been demonstrated and is thought not to occur. Known weed hosts include fillory, chickweed, London rocket, shepherd's purse, malva, ivy, clover, bluegrass, and stinging nettle.
Picture 4: A close up of several spittlebugs found in California.
Research by Dr. Kent Daane (UC Berkeley) has shown that X. fastidiosa is detected within weeds only between October and April, and within insects from April to July. This suggests that the ground cover and weeds are infected with almond leaf scorch in the winter months and the sharpshooters acquire the bacteria when emerging from diapause around mid-April. Tree infection is thought to occur between April and July as emerged sharpshooters can feed on the soft tissue of almonds, infecting the trees upon feeding. Sharpshooter populations within the orchard were found to be the highest during these months. Evidence suggests that orchard practices that remove the sharpshooter habitat, such as year-long weed management, may decrease the populations of shapshooters, therefore decreasing the incidence of almond leaf scorch within orchards.
Management of the disease is through removal of disease tissues. Typically, by time a strike of almond leaf scorch is seen, the infection took place 2-3 years prior. Prune out branches that are infected with almond leaf scorch by cutting back as far as possible from the last visibly affected leaf. It has been demonstrated that cuts need to be as far back as five feet from the last infected leaf. Removing too little of the branch may not remove all of the pathogen, thus allowing the bacteria to continue infecting the tree. If a high percentage of the orchard is infected, it may be in the best interest to remove the orchard. Orchard removal of older blocks may not be necessary as the progression of the disease may take longer to kill the tree than the planned orchard life.
Chemical control options are very limited for trees infected with almond leaf scorch. Tree recovery has been demonstrated with injections of the antibiotic tetracycline. This process is very expensive and time consuming and may not be worth the effort. Research also has demonstrated that it is nearly impossible to to reduce the number of vectors through applications of insecticides. There is some possibility that a "cold curing" may occur, in which bacteria titer and disease progression are reduced after cold temperatures, but this has not been clearly demonstrated.
Almond leaf scorch is found more frequently in the Peerless and Sonora varieties. Nonpareil is often affected as well. Rarely is the disease seen in Carmel or the Butte varieties. It is also thought that some varieties may "cold cure" more easily, but, again, this has not been thoroughly researched.
My recommendations for an orchard infected with almond leaf scorch is as follows:
Young Orchards (3-8 yrs): rogue out infected branches aggressively, making cuts five feet from the last infected leaf. If tree removal is necessary, replant to maintain orchard.
Old Orchards (5-7 years before planned orchard removal): It is not necessary to remove infected branches as it will take the disease longer to kill the tree than planned orchard life. Furthermore, replanting young trees may be more trouble than it is worth as they may not bear almonds before orchard removal.
Mature Orchards (8-16 years): This becomes a management decision. If the infected tree yields are low, remove the trees. Rogue branches, if it is economically possible. In the orchard described above, the decision was made to remove all of the Sonora trees and aggressively rogue out infected branches within the Nonpareil.
Publication 8106 provided by the University of California Agricultural and Natural Resource Division is available for more information.
A summer farm call to an orchard close to the Merced River yielded my first confirmed case of almond leaf scorch. This orchard consisted of a 12th leaf planting of Monterrey, Nonpareil, Carmel, and Sonora all on Nemaguard rootstock, planted in the Snelling Sandy Loam soil series, and irrigated by microsprinklers.
The orchard looked relatively healthy from afar, but a notable discoloring of the leaves was seen in the Sonora variety. A closer inspection revealed a large percentage of trees (i.e. 80%) that appeared to be infected with of almond leaf scorch. Some Nonpareil trees were symptomatic, but very few of the other pollinators (i.e. Monterrey and Carmel) had symptoms.
Picture 1: A tree severely affected with almond leaf scorch. Trees "bronze" over in late summer. This picture was not from the farm call listed above.
Upon seeing the symptomatic leaves, it became clear that Almond Leaf Scorch was the suspected disease due to the large yellow halo that bordered the scorched part of the leaf. Furthermore, the yellowing and scorch did not have any particular pattern across the leaves. This is unlike many salt issues that typically have scorching int he tip of the leaf due to accumulations of salts.
Picture 2: Symptoms of almond leaf scorch on an almond leaf. Note obvious yellow halo surrounding the necrotic leaf region.
For a true confirmation of almond leaf scorch, a diagnostic PCR assay must be completed. Leaves were taken from infected and healthy looking trees and sent to Dr. Bruce Kirkpatrick's lab in the Department of Plant Pathology at UC Davis. The diagnostic assay came back positive for the diseased trees, and negative for the healthy trees, confirming that the pathogen was present within the orchard.
Almond Leaf Scorch is caused by the xylem-limited bacterium, Xylella fastidiosa. The bacteria is very fastidious and is hard to culture in media. Artificial inoculations of almond trees made within the laboratory has shown that it can take several years for the first leaves to show symptoms after inoculation. Eventual tree death occurs through the clogging of the vascular tissues, which prevents the flow of nutrients to the branches. Leaf symptoms are caused by bacterial produced toxins that accumulate within the leaves.
The bacterium can not directly infect the almond tree by itself. It requires infested xylem feeding insects to carry and introduce the bacteria into the tree. Within almond, this is primarly limited to sharpshooters (Cicadellidae) and spittlebugs (Cercopidae), with green sharpshooters (Draeculacephala minerva) being the most commonly found in orchards. Leaf hoppers have not been shown to transmit the disease at high levels.
Picture 3: A close up of a green sharpshooter.
Xylella fastidiosa is commonly found in riparian areas due to the high diversity of plants that can serve as hosts for the bacterium. Coincidentally enough, these areas are also the same locations in which sharpshooters and spittlebugs overwinter and feed year round. Sharpshooters transfer the bacteria to the almond tree by feeding on infected ground cover and weeds and then move to feed on the tree. Upon piercing into the xylem tissue of the tree, the sharpshooter injects the bacteria into the xylem, thus infecting the tree. Tree to tree transmission of the disease has not been demonstrated and is thought not to occur. Known weed hosts include fillory, chickweed, London rocket, shepherd's purse, malva, ivy, clover, bluegrass, and stinging nettle.
Picture 4: A close up of several spittlebugs found in California.
Research by Dr. Kent Daane (UC Berkeley) has shown that X. fastidiosa is detected within weeds only between October and April, and within insects from April to July. This suggests that the ground cover and weeds are infected with almond leaf scorch in the winter months and the sharpshooters acquire the bacteria when emerging from diapause around mid-April. Tree infection is thought to occur between April and July as emerged sharpshooters can feed on the soft tissue of almonds, infecting the trees upon feeding. Sharpshooter populations within the orchard were found to be the highest during these months. Evidence suggests that orchard practices that remove the sharpshooter habitat, such as year-long weed management, may decrease the populations of shapshooters, therefore decreasing the incidence of almond leaf scorch within orchards.
Management of the disease is through removal of disease tissues. Typically, by time a strike of almond leaf scorch is seen, the infection took place 2-3 years prior. Prune out branches that are infected with almond leaf scorch by cutting back as far as possible from the last visibly affected leaf. It has been demonstrated that cuts need to be as far back as five feet from the last infected leaf. Removing too little of the branch may not remove all of the pathogen, thus allowing the bacteria to continue infecting the tree. If a high percentage of the orchard is infected, it may be in the best interest to remove the orchard. Orchard removal of older blocks may not be necessary as the progression of the disease may take longer to kill the tree than the planned orchard life.
Chemical control options are very limited for trees infected with almond leaf scorch. Tree recovery has been demonstrated with injections of the antibiotic tetracycline. This process is very expensive and time consuming and may not be worth the effort. Research also has demonstrated that it is nearly impossible to to reduce the number of vectors through applications of insecticides. There is some possibility that a "cold curing" may occur, in which bacteria titer and disease progression are reduced after cold temperatures, but this has not been clearly demonstrated.
Almond leaf scorch is found more frequently in the Peerless and Sonora varieties. Nonpareil is often affected as well. Rarely is the disease seen in Carmel or the Butte varieties. It is also thought that some varieties may "cold cure" more easily, but, again, this has not been thoroughly researched.
My recommendations for an orchard infected with almond leaf scorch is as follows:
Young Orchards (3-8 yrs): rogue out infected branches aggressively, making cuts five feet from the last infected leaf. If tree removal is necessary, replant to maintain orchard.
Old Orchards (5-7 years before planned orchard removal): It is not necessary to remove infected branches as it will take the disease longer to kill the tree than planned orchard life. Furthermore, replanting young trees may be more trouble than it is worth as they may not bear almonds before orchard removal.
Mature Orchards (8-16 years): This becomes a management decision. If the infected tree yields are low, remove the trees. Rogue branches, if it is economically possible. In the orchard described above, the decision was made to remove all of the Sonora trees and aggressively rogue out infected branches within the Nonpareil.
Publication 8106 provided by the University of California Agricultural and Natural Resource Division is available for more information.
Tuesday, July 21, 2009
Almond prices recovering?
A recent article posted by Western farm Press speculates on a price recovery for almonds. The article emphasizes that a slightly smaller crop year will help reduce carry-over and increase prices for almonds, especially for the California varietals. Next year's anticipated El nino year may also reduce yields for 2010.
I would suspect that the June 30th USDA/NASS Objective Crop Estimate is still a little high, but we will see in a couple of months!
I would suspect that the June 30th USDA/NASS Objective Crop Estimate is still a little high, but we will see in a couple of months!
Monday, July 20, 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 (KTS).
Picture 2: Leaf wilting and "dieback" associated with the over-application of potassium thiosulfate (KTS). 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 disease was ruled out. In some leaves, yellow spots, or stippling, occurred throughout the leaf. Again, that pattern of a brown area surrounded by a yellow halo is relevant (Picture 4).
Picture 3: Leaf damage associated with the over-application of potassium thiosulfate (KTS).
Picture 4: Close up symptoms of leaf damage. Note the yellow halo and stippling effect on some of the leaf tissues.
Possible Causes:
Since the symptoms were found across the whole field on all varieties, a biological cause was not suspected. Symptoms are most likely caused by an abiotic disorder, which may include underwatering, salt damage, or improper nutrient application (toxicity).
Diagnosing:
The PCA admitted that the grower is still learning proper methods to calculate evapo-transpiration rates on the orchard. Furthermore, the grower did not make a dormant season irrigation, and we had inadequate winter rain. Therefore, the orchard came into the season with an unfilled soil profile. This suggests that some of the leaf drop could be from inadequate irrigation, as the smaller, inner leaves of the tree tend to fall off when a moderate water stress occurs. This, however, did not describe all of the symptoms.
Inquiries into the fertilizer program for the orchard revealed the want to "push" the trees for a higher production. By "pushing," the grower applies more fertilizer more frequently to ensure vigorous growth. Rates of nitrogen fertilization applications seemed to reasonable, with only 6 ounces of actual nitrogen per tree per application being delivered via fertigation. Questioning into potassium revealed that the soil is high magnesium, which makes it difficult to maintain adequate potassium levels. The PCA then revealed that a recent application of potassium thiosulfate (KTS) was made through the water.
KTS can cause considerable damage to trees if applied at high rates. I had the PCA check with the grower to confirm the rate of application. The application made was 28 gallons of KTS per acre applied through the microsprinklers. This raised a flag as it seemed to be a large dose to make in one application. Furthermore, due to the fact that it was applied through the microsprinklers, only 70-80% of the orchard floor was irrigated, indicating that a higher rate of around 36 gallons per treated acre was applied to the soil. This rate is too high for a safe, efficient, and effective application of KTS.
A compounding factor was the high temperature and the high evapo-transipration rate. As the tree pulls more water from the soil, it also pulls more water soluble nutrients/salts as well. As these salts enter into the tree and accumulate, they can reach high enough levels and become toxic, killing plant tissues. Orchards have been observed when a nutrient application deemed "safe" in cool weather became toxic in hot weather. This occurs most frequently when applications rate are more on the high side.
Solution/Prevention of Problem:
The evidence suggests that the over application of KTS caused the symptoms on the orchard. The trees should recover naturally, most likely dropping a few more leaves. The crop should be unaffected. In the future, lower rates of nutrients should be applied more frequently when fertigating. Consideration must be made when applying rates that are on the "high side," as they can become toxic if the tree is in a high water use period.
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 (KTS).
Picture 2: Leaf wilting and "dieback" associated with the over-application of potassium thiosulfate (KTS). 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 disease was ruled out. In some leaves, yellow spots, or stippling, occurred throughout the leaf. Again, that pattern of a brown area surrounded by a yellow halo is relevant (Picture 4).
Picture 3: Leaf damage associated with the over-application of potassium thiosulfate (KTS).
Picture 4: Close up symptoms of leaf damage. Note the yellow halo and stippling effect on some of the leaf tissues.
Possible Causes:
Since the symptoms were found across the whole field on all varieties, a biological cause was not suspected. Symptoms are most likely caused by an abiotic disorder, which may include underwatering, salt damage, or improper nutrient application (toxicity).
Diagnosing:
The PCA admitted that the grower is still learning proper methods to calculate evapo-transpiration rates on the orchard. Furthermore, the grower did not make a dormant season irrigation, and we had inadequate winter rain. Therefore, the orchard came into the season with an unfilled soil profile. This suggests that some of the leaf drop could be from inadequate irrigation, as the smaller, inner leaves of the tree tend to fall off when a moderate water stress occurs. This, however, did not describe all of the symptoms.
Inquiries into the fertilizer program for the orchard revealed the want to "push" the trees for a higher production. By "pushing," the grower applies more fertilizer more frequently to ensure vigorous growth. Rates of nitrogen fertilization applications seemed to reasonable, with only 6 ounces of actual nitrogen per tree per application being delivered via fertigation. Questioning into potassium revealed that the soil is high magnesium, which makes it difficult to maintain adequate potassium levels. The PCA then revealed that a recent application of potassium thiosulfate (KTS) was made through the water.
KTS can cause considerable damage to trees if applied at high rates. I had the PCA check with the grower to confirm the rate of application. The application made was 28 gallons of KTS per acre applied through the microsprinklers. This raised a flag as it seemed to be a large dose to make in one application. Furthermore, due to the fact that it was applied through the microsprinklers, only 70-80% of the orchard floor was irrigated, indicating that a higher rate of around 36 gallons per treated acre was applied to the soil. This rate is too high for a safe, efficient, and effective application of KTS.
A compounding factor was the high temperature and the high evapo-transipration rate. As the tree pulls more water from the soil, it also pulls more water soluble nutrients/salts as well. As these salts enter into the tree and accumulate, they can reach high enough levels and become toxic, killing plant tissues. Orchards have been observed when a nutrient application deemed "safe" in cool weather became toxic in hot weather. This occurs most frequently when applications rate are more on the high side.
Solution/Prevention of Problem:
The evidence suggests that the over application of KTS caused the symptoms on the orchard. The trees should recover naturally, most likely dropping a few more leaves. The crop should be unaffected. In the future, lower rates of nutrients should be applied more frequently when fertigating. Consideration must be made when applying rates that are on the "high side," as they can become toxic if the tree is in a high water use period.
July 15th IPM Field Reporter update for the Central Valley
Trece has released their IPM update in their biweekly "Field Reporter" e-newsletter. Here is the link: Volume 12, July 15th, 2009 Field Reporter.
Monday, July 13, 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. A previous blog highlights the negative effects of nutrient deficiency. 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 kernal yield per acre to determine the nutrient budget for the next season (Please see "The Almond Nitrogen Model" for more information).
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. Label the samples so the sampling location is known, and keep cool until they are sent to an analytical lab. A list of analytical labs in California that perform leaf tissue analysis can be found here.
Partitioning of larger sampling blocks is advised to determine tree size and yield variability. A presentation by Dr. Patrick Brown that discusses orchard growth variability in relation to the nutrient application variability can be found here.
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 using the methods described previously. The critical values for magnesium, manganese, phosphorus, potassium, nitrogen, chlorine, and sodium are correlated highly with the appearances of deficiencies/toxicities. In other words,if symptoms of magnesium deficiency are diagnosed, a leaf sample will provide confirmation.
Table 1: Critical nutrient levels (dry-weight basis) in almond leaves sampled in July.(Source: UC Almond Production Manual, Publication 3364, 1996)
The importance of sampling in July.
Many growers have been submitting samples to laboratories earlier in the season in order to prevent mid-season deficiencies. Sampling in spring time, during periods of active growth can be misleading due to the variability of true nutrient usage. Research has shown that the tree during this period is transferring large amounts of nutrients from source to sink, and may be devoting more nutrients to new growth instead of developed foliage, thus providing inaccurate data (For more information see "The Seasonal Patterns of Almond Production"). Therefore the July sampling period was chosen for tissue analysis due to the relatively steady state of element levels within the leaf tissue. Furthermore, the critical levels established through experimentation and field observations by the University of California were made for sampling during July.
In saying this, it is important to note that leaf samples that are taken for diagnostic work can be taken at anytime, as long as there are leaf samples taken from a healthy tree for comparison.
Information used in this article has been abstracted from:
Brown, P.H., and K. Uriu. 1996. "Chapter 26: Nutrition Deficiencies and Toxicities" Diagnosing and Correcting Imbalances. "University of California Almond Production Manual." University of California Division of Agricultural and Natural Resources. Publication 3364, Oakland, CA.
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. A previous blog highlights the negative effects of nutrient deficiency. 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 kernal yield per acre to determine the nutrient budget for the next season (Please see "The Almond Nitrogen Model" for more information).
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. Label the samples so the sampling location is known, and keep cool until they are sent to an analytical lab. A list of analytical labs in California that perform leaf tissue analysis can be found here.
Partitioning of larger sampling blocks is advised to determine tree size and yield variability. A presentation by Dr. Patrick Brown that discusses orchard growth variability in relation to the nutrient application variability can be found here.
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 using the methods described previously. The critical values for magnesium, manganese, phosphorus, potassium, nitrogen, chlorine, and sodium are correlated highly with the appearances of deficiencies/toxicities. In other words,if symptoms of magnesium deficiency are diagnosed, a leaf sample will provide confirmation.
Table 1: Critical nutrient levels (dry-weight basis) in almond leaves sampled in July.(Source: UC Almond Production Manual, Publication 3364, 1996)
The importance of sampling in July.
Many growers have been submitting samples to laboratories earlier in the season in order to prevent mid-season deficiencies. Sampling in spring time, during periods of active growth can be misleading due to the variability of true nutrient usage. Research has shown that the tree during this period is transferring large amounts of nutrients from source to sink, and may be devoting more nutrients to new growth instead of developed foliage, thus providing inaccurate data (For more information see "The Seasonal Patterns of Almond Production"). Therefore the July sampling period was chosen for tissue analysis due to the relatively steady state of element levels within the leaf tissue. Furthermore, the critical levels established through experimentation and field observations by the University of California were made for sampling during July.
In saying this, it is important to note that leaf samples that are taken for diagnostic work can be taken at anytime, as long as there are leaf samples taken from a healthy tree for comparison.
Information used in this article has been abstracted from:
Brown, P.H., and K. Uriu. 1996. "Chapter 26: Nutrition Deficiencies and Toxicities" Diagnosing and Correcting Imbalances. "University of California Almond Production Manual." University of California Division of Agricultural and Natural Resources. Publication 3364, Oakland, CA.
Wednesday, July 8, 2009
July 1 IPM update for the Central Valley
Trece has released their IPM update in their biweekly "Field Reporter" e-newsletter. Here is the link:
Volume 11, July 1st, 2009 Field Reporter.
Volume 11, July 1st, 2009 Field Reporter.
Tuesday, July 7, 2009
California Almond Board's July/August Newsletter
The July/August Outlook Newsletter from the California Almond Board covers a variety of topics to help growers prepare for harvest. Content includes a Pre-Harvest Checklist for Orchard Floor Management, Budget Planning, Harvest Sampling, NRCS Air-Quality Incentives, Managing Stockpiles, and more. Check it out!
Monday, July 6, 2009
Lower Limb Dieback of Almond...Still a mystery!
Crops Affected: Almond, Predominantly found on Padre and Butte, but also found on many other varieties including Nonpareil, Fritz, Carmel, Wood Colony, and Mission.
Photograph 1: An almond tree with a branch affected by lower limb dieback.
Photograph 2: The fungal canker associated with lower limb dieback of almond. The canker is usually found on the top of almond branches proximal from the yellowing leaves.
Photograph 3: A proper cut to remove Lower Limb Dieback affected tissue is 4-6" beyond the margin of the canker.
Causal Organisms: Unknown, but high isolation frequency of Botryosphaeria spp. and Phomopsis spp.
Lower limb dieback (LLDB) has become an emerging problem within many almond orchards throughout California. Observations of orchards with LLDB occur independent of soil types, irrigation systems, varieties planted, and planting spacings, while typically affecting orchards that are in their 8th leaf or older.
Photograph 1: An almond tree with a branch affected by lower limb dieback.
The problem tends to be associated with smaller diameter branches in the lower canopy of orchards. Often enough, however, the problem extends to larger diameter branches, causing branch loss that can extend to 10 feet or more from the ground. Symptoms include wilted, yellow leaves that eventually fall from the tree. Bark removal will reveal a brown canker with little or no gumming that usually does not completely girdle the branch. The fungal canker can be observed on the top side of the affected branches, which is often found proximal to the yellowing leaves. Often, the canker is associated with a dead spur or small branch. The fungus appears to move up the branch to the point of attachment with the main scaffold, but does not appear to enter into the main scaffold. The first appearance of symptoms has been reported in April, with shoots continuing to collapse throughout the summer. Branch collapse is often noticeable about a week after a hot spell in which the evapotransipiration rates are very high.
Photograph 2: The fungal canker associated with lower limb dieback of almond. The canker is usually found on the top of almond branches proximal from the yellowing leaves.
Isolations made by Themis Michailides (UC Extension Plant Pathology Specialist) from almond trees in orchards affected by LLDB have identified two commonly isolated genera of fungi, Botryosphaeria and Phomopsis. Sampling of diseased limbs from 10 orchards in 2005 (Glenn, Madera, and Stanislaus Co.) and 18 orchards in 2006 (Butte, Colusa, Fresno, Glenn, and Kern Co.) identified Botryosphaeria spp. and Phomopsis spp. from 52% and 56% of the isolations made, respectively. Isolation of these pathogens was higher in late summer/fall than in spring/early summer. Interestingly enough, in the Sacramento Valley, fall isolations frequently occurred from both limbs with AND without symptoms.
Corresponding pathogenicity tests of isolated fungi on thrifty and unthrifty trees indicated that the isolates of Botryosphaeria spp. and Phomopsis spp. can cause disease on almond trees. It was also found that the isolates of Botryosphaeria spp. tend to be more virulent than Phomopsis spp. There is some uncertainty of these fungi being the true cause of the disease, however, as they have been considered to be fungi that colonize weak tissues that are predisposed from some other stress.
Several fungicide trials by Roger Duncan (UCCE Stanislaus) and Bruce Lampinen (UC Extension Pomology Specialist) have consisted of spring and fall applications of several fungicides. Fall (October – December) applications of copper hydroxide, liquid lime sulfur, Pristine©fungicide, Nutriphyte P© (0.5 gallons per acre), and Plant Shield©, a commercial formulation of Trichoderma harzianum(a biological control agent), did not lower the incidence of LLDB the following year. May applications of Captan 80 WDG©, Pristine©, and Agri-fos©, all applied with a bark penetrant, also failed to reduce LLDB symptoms. These trials indicate that chemical control for LLDB is either not possible or has not been identified.
Orchard water management may play a role in the incidence of LLDB. Through the use of soil moisture monitoring systems and a pressure chamber, research by Bruce Lampinen has demonstrated that orchards with LLDB frequently are over-watered in the early season (April-June). Research is ongoing, but evidence suggests that excessive water in the early season can prevent proper root growth and development, which would lead to increase tree stress during periods of high evapo-transpiration. This stress would lead to the reduction of tree resources being sent to branches of the lower canopy, weakening these branches, and allowing invasion by the above mentioned fungi. Growers with LLDB affected orchards should evaluate their water management practices to prevent over-watering during the early season.
Other orchard problems may also contribute to LLDB. Hull rot, scale infestations, and herbicide drift can damage the lower branches and kill spurs, providing an entrance for fungi. These problems occur frequently on younger trees (less than 8th leaf), before the onset of LLDB, which suggest that they may predispose the tree to LLDB. Therefore, it may be important for growers to implement orchard practices that will reduce damage to the lower canopy. Then again, any practice that reduces tree damage should be adopted to increase orchard longevity.
Until the true cause of LLDB is determined, it is advised that growers prune out infected limbs. Work done by Roger Duncan showed a reduction of LLDB in orchards in which affected limbs were removed, and suggests that this is currently the best way to reduce LLDB. Affected limbs should be removed as soon as possible by pruning 4-6” beyond the canker margin to ensure complete removal of the fungal pathogens. It is not advised to make major cuts on scaffolds or large branches to ensure a full 4-6.” Aggressive rouging out of infected branches during the summer months may reduce inoculums levels and prevent infections in the fall or dormant period.
Photograph 3: A proper cut to remove Lower Limb Dieback affected tissue is 4-6" beyond the margin of the canker.
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