Over the next couple of weeks, I will be presenting information regarding weed control in an orchard system. Since herbicide resistant weeds are becoming more prevalent in the San Joaquin Valley (think Hairy Fleabane, Horseweed/marestail), it is becoming more important for growers to utilize practices that reduce the chance of herbicide resistance.
Herbicide resistance is defined as the inherited ability of a plant to survive and reproduce following an exposure to a dose of herbicide that would normally kill the wild type (Think: "We used to get good control of this weed with this herbicide..."). This is different than herbicide tolerance, which is the ability of a species to survive and reproduce a herbicide treatment with no implied selection or genetic manipulation that would make the plant tolerant (Think: "We've never gotten dependable control of this weed with this herbicide...").
Since 1980, cases of herbicide resistant weeds within California has increased from 0 to 21 reported cases. This is mainly due to the change in tillage and herbicide use practices within agriculture. In perennial crops, growers have shifted away from orchard tillage and have become more reliant on herbicide "burn downs" to control weeds in the tree rows. Glyphosate is one of the most widely used herbicides for this practice, and, until recently, has provided good control.
The formation of herbicide resistant weeds is an evolutionary process that occurs due to the application of herbicides. Since most herbicides are reliant upon a single site mode of action, it only takes a minor mutation within the plants genome to become resistant. Furthermore, the high genetic diversity of weed populations provides the opportunity for weeds to contain a mutation, thus yielding an "escape." Once the weed is unable to be controlled by the herbicide, it produces progeny that is also resistant. These seeds tend to move outward from the point of origin, causing a "hotspot" pattern within the orchard.
To control these hotspots, growers need to rotate to different herbicide modes of action. The mode of action of an herbicide is the way it alter or inhibits specific physiological or biochemical processes. This is not to be confused with active ingredient or trade name. This can be found on some herbicide labels as the WSSA or HRAC group number found below the herbicides active ingredient. Growers should also avoid the year-after-year use of the same herbicide/mode of action. In some cases, a tank mix of two products that target the escaped weed must be used.
Growers should also apply herbicides using the proper rate and at the proper timing. Herbicides give the greatest control when the weed is no larger than a silver dollar (1.5 inch diameter). As the weed grows larger than this, it becomes harder and harder to control. Growers also need to reduce the spread of weed seeds throughout their orchards. Spread may occur from harvesting equipment, spray rigs, and also natural conditions such as wind. Keeping notes of the herbicides used and escapes observed is also advised.
If you feel that you may have a resistant weed population, it is best to use any means necessary to control the weed. This may include hand weeding, herbicide tank mixes, and/or tillage. Controlling a small patch of resistant weeds is much easier than an entire orchard. It may also be of interest to contact you local farm advisor to report the incident, but the weed MUST be controlled before it goes to seed.
Monday, December 28, 2009
Monday, December 21, 2009
Making a Zinc Dormant Spray
Question came in this week regarding the decision on the timing of a zinc spray.
When should I make a Zinc Spray?
Research by UC Specialist Dr. Scott Johnson at the Kearney Agricultural Center has shown that a zinc foliar spray is the most effective when made during the post harvest period. Applications of zinc should be made to the tree around late October - early November. The idea is to have a leaves still on the tree when the application is made. Dr. Johnson has shown that a roughly 3% of the zinc applied is taken into the tree from a fall foliar spray, but this is dependant upon the source of zinc. Defoliation may occur after the application, but do not worry as sufficient zinc should have made its way into the plant tissues.
Is making a dormant zinc application a bad idea?
If a fall application of zinc was not made and the orchard is suspected to be deficient in zinc, making a dormant application of zinc will increase zinc tissue levels. The percentage of uptake is slightly less, around 2.0-2.8%, and it is harder to get a large amount of zinc into the tree. This is due to the fact that the shoots, buds, and bud scars only account for roughly 3% of the surface area of a peach/almond branch. Therefore the amount of spray landing on the tree surface is significantly less than when the leaves are still attached (Leaves make up the other 97% of the surface area). To counter this, higher rates should be used during the dormant period.
What type of material should be used in a zinc spray?
Dr. Scott Johnson's (UC Specialist) work has shown that the "biggest bang" for your buck comes from Zinc Sulfate (high uptake, moderate phytotoxicity). There are other formulations that have higher uptake, but have high phytoxicity as well (Zinc chloride, zinc nitrate). Chelates (Zinc EDTA, Zinc Leonardite, Zinc Oxysulfate) have shown to have lower uptake efficiency (bad) and phytotoxicity (good) than zinc sulfate.
I hope this helps!
When should I make a Zinc Spray?
Research by UC Specialist Dr. Scott Johnson at the Kearney Agricultural Center has shown that a zinc foliar spray is the most effective when made during the post harvest period. Applications of zinc should be made to the tree around late October - early November. The idea is to have a leaves still on the tree when the application is made. Dr. Johnson has shown that a roughly 3% of the zinc applied is taken into the tree from a fall foliar spray, but this is dependant upon the source of zinc. Defoliation may occur after the application, but do not worry as sufficient zinc should have made its way into the plant tissues.
Is making a dormant zinc application a bad idea?
If a fall application of zinc was not made and the orchard is suspected to be deficient in zinc, making a dormant application of zinc will increase zinc tissue levels. The percentage of uptake is slightly less, around 2.0-2.8%, and it is harder to get a large amount of zinc into the tree. This is due to the fact that the shoots, buds, and bud scars only account for roughly 3% of the surface area of a peach/almond branch. Therefore the amount of spray landing on the tree surface is significantly less than when the leaves are still attached (Leaves make up the other 97% of the surface area). To counter this, higher rates should be used during the dormant period.
What type of material should be used in a zinc spray?
Dr. Scott Johnson's (UC Specialist) work has shown that the "biggest bang" for your buck comes from Zinc Sulfate (high uptake, moderate phytotoxicity). There are other formulations that have higher uptake, but have high phytoxicity as well (Zinc chloride, zinc nitrate). Chelates (Zinc EDTA, Zinc Leonardite, Zinc Oxysulfate) have shown to have lower uptake efficiency (bad) and phytotoxicity (good) than zinc sulfate.
I hope this helps!
Monday, December 14, 2009
Inquiries about Bacterial Canker on Almond
This week I have had a few questions regarding post harvest treatments for Bacterial Canker of almond. I thought it would be a good idea to use these questions as the theme for this weeks post.
What is bacterial canker?
Bacterial canker is commonly found on Prunus species (Peach, cherry, apricot, plum, almond, etc.). Caused by Pseudomonas syringe, a common surface inhabiting bacteria, the disease is often observed in the spring. Symptoms include limb dieback with rough, irregular cankers (Figure 1). Cankers do not extend into the soil and a very unique smell is present. In some cases, cankers do not form, but a "sour sap" stage occurs. This stage is characterized by brown inner bark with a distinctive fermentive, sour smell - hence the name. Generally, almond trees in the 2nd through 5th leaf are affected.
Figure 1: Almond tree killed by bacterial canker. Note that the canker has an irregular shape and does not extend into the soil.
How does bacterial canker spread?
Pseudomonas syringe survives on plant surfaces and is spread by splashing rain. The bacteria is found throughout the entire orchard and is impossible to eradicate. The disease commonly occurs in the spring during periods of mild temperatures and high humidity. It does not spread like other diseases, but is common on trees that are stressed. Therefore, soils that have poor water/nutrient holding capacity (i.e. sand), have been replanted with several generations of Prunus sp. orchards, and have the presence of ring nematode are prone to this disease.
Figure 2: Photo of an almond with a scaffold infected with bacterial canker. Note the irregular margin of the canker.
What can I do to prevent the problem?
In soils that have exhibited the disease, pre-plant fumigation with Telone or Methyl Bromide (if it is still available) provides the ability for the tree to establish a healthy root system while it is young. This is mainly due to reduction of nematodes and replant disease. It is important to note that nematodes will still find their way to the roots as fumigation does not kill all of the nematodes in the soil. In this case, fumigation serves as a means to "buy time" before the soil surrounding the tree becomes re-infested.
All the almond rootstocks differ in their susceptibility to the disease, which is due to their ability to be parasitized by the ring nematode. Marianna 2624 and peach almond hybrids (Brights, Hansen, etc.) are more susceptible than Nemaguard, Lovell, and Viking. Lovell and Viking are the most resistant.
Studies by Roger Duncan in Stanislaus County have demonstrated that low biuret urea foliar sprays made BEFORE leaf drop can reduce the incidence of bacterial canker. Duncan's research showed that a foliar spray with 100 lbs/acre of low biuret urea applied to unfumigated trees gave the same level of bacterial canker control as pre-plant soil fumigation with methyl bromide. It is unknown if 100 lbs/acre are needed, but it is clear that a fall foliar spray of nitrogen is helpful in preventing bacterial canker. It is thought that the additional foliar nitrogen reduces tree stress, thus increasing resistance to bacterial canker.
Since the disease is correlated with infestation by the ring nematode, fall treatments of Enzone nematicide have also been shown to be effective. Recently, the systemic insecticide Movento was released. This product has been shown to reduce lesion nematode populations in walnut, but studies have not been carried out in almond.
Do copper dormant sprays reduce bacterial canker?
The short answer is no. In all of the studies held in California since the 1960's within bacterial canker, copper sulfate dormant sprays have given very inconsistent results. It would be better to save the money by not applying copper and use it for either a fall nitrogen foliar spray or application of a post-plant nematicide.
What is bacterial canker?
Bacterial canker is commonly found on Prunus species (Peach, cherry, apricot, plum, almond, etc.). Caused by Pseudomonas syringe, a common surface inhabiting bacteria, the disease is often observed in the spring. Symptoms include limb dieback with rough, irregular cankers (Figure 1). Cankers do not extend into the soil and a very unique smell is present. In some cases, cankers do not form, but a "sour sap" stage occurs. This stage is characterized by brown inner bark with a distinctive fermentive, sour smell - hence the name. Generally, almond trees in the 2nd through 5th leaf are affected.
Figure 1: Almond tree killed by bacterial canker. Note that the canker has an irregular shape and does not extend into the soil.How does bacterial canker spread?
Pseudomonas syringe survives on plant surfaces and is spread by splashing rain. The bacteria is found throughout the entire orchard and is impossible to eradicate. The disease commonly occurs in the spring during periods of mild temperatures and high humidity. It does not spread like other diseases, but is common on trees that are stressed. Therefore, soils that have poor water/nutrient holding capacity (i.e. sand), have been replanted with several generations of Prunus sp. orchards, and have the presence of ring nematode are prone to this disease.
Figure 2: Photo of an almond with a scaffold infected with bacterial canker. Note the irregular margin of the canker.What can I do to prevent the problem?
In soils that have exhibited the disease, pre-plant fumigation with Telone or Methyl Bromide (if it is still available) provides the ability for the tree to establish a healthy root system while it is young. This is mainly due to reduction of nematodes and replant disease. It is important to note that nematodes will still find their way to the roots as fumigation does not kill all of the nematodes in the soil. In this case, fumigation serves as a means to "buy time" before the soil surrounding the tree becomes re-infested.
All the almond rootstocks differ in their susceptibility to the disease, which is due to their ability to be parasitized by the ring nematode. Marianna 2624 and peach almond hybrids (Brights, Hansen, etc.) are more susceptible than Nemaguard, Lovell, and Viking. Lovell and Viking are the most resistant.
Studies by Roger Duncan in Stanislaus County have demonstrated that low biuret urea foliar sprays made BEFORE leaf drop can reduce the incidence of bacterial canker. Duncan's research showed that a foliar spray with 100 lbs/acre of low biuret urea applied to unfumigated trees gave the same level of bacterial canker control as pre-plant soil fumigation with methyl bromide. It is unknown if 100 lbs/acre are needed, but it is clear that a fall foliar spray of nitrogen is helpful in preventing bacterial canker. It is thought that the additional foliar nitrogen reduces tree stress, thus increasing resistance to bacterial canker.
Since the disease is correlated with infestation by the ring nematode, fall treatments of Enzone nematicide have also been shown to be effective. Recently, the systemic insecticide Movento was released. This product has been shown to reduce lesion nematode populations in walnut, but studies have not been carried out in almond.
Do copper dormant sprays reduce bacterial canker?
The short answer is no. In all of the studies held in California since the 1960's within bacterial canker, copper sulfate dormant sprays have given very inconsistent results. It would be better to save the money by not applying copper and use it for either a fall nitrogen foliar spray or application of a post-plant nematicide.
Monday, December 7, 2009
Potassium Applications in Almonds
By: David Doll
Having a major role in many plant processes, potassium promotes root growth, increases kernel/fruit size, and provides key metabolic features that include the formation of starch, translocation of sugars, stomata regulation, and the formation of xylem vessels. In general, plants deficient in potassium tend to have slow growth, with small, pale leaves. Trees that are severely deficient may have necrotic tips and margins. In many cases, the leaf tip curls upwards in a common symptom that is named the “Vikings Prow” (Figure 1).
Figure 1: Potassium deficiency on almonds. Note the upturned leaf tip which is known as the "Viking's Prow."
Since Potassium plays a large role in tree health, it is important to maintain proper levels of the nutrient within the tree. A critical leaf value of 1.4% has been established by the University of California and current research has suggested that levels above this value do not increase yields. Recent field studies by Roger Duncan (UCCE Stanislaus) have demonstrated that leaf potassium levels in excess of the 1.4-1.6% range did not increase yield. Through the study, leaf levels between 1.4-1.6% gave the best yield results, with yield decreasing when potassium levels were below this level. Leaf potassium levels higher than this range did not increase yield, and may actually reduce yields if applied in excess.
Potassium usage by the almond crop is high. Upon harvesting the hulls and kernals, potassium is removed from the orchard. Studies by Dr. Patrick Brown (UC Davis), have shown that 50 pounds of potassium are removed from the orchard for every 1000 pounds of kernals harvested. From nutrient analysis of the fruit parts, 70-80% of the potassium removed by the harvest is within the hull, while the rest is within the shell and kernel.
Even though a large amount of potassium is used by the almond crop, it doesn’t always mean that large applications of potassium are needed to maintain critical levels. Some soils may have naturally high levels of potassium, depending on the parent material, percent of parent material degradation, soil texture, and the irrigation system. A soil analysis should be made to determine the amount of potassium within the soil and coupled with leaf tissue analysis to see if the potassium within the soil is available to the trees.
Once the potassium level within the soil drops, it will take several years of large applications to bring the levels back to normal. Potassium fertilizer products including sulfate of potash, muriate of potash, potassium nitrate, potassium thiosulfate (K-T-S), and a few others. Organic applications of potassium can be made through manure composts, green manures, guano, and wood ash. It is important to note that some potassium fertilizers may have unwanted chemicals/traits – chloride, sodium, alkalinity, and food safety concerns – which may have a negative impact on the orchard when applied in excess. Applications should be made to maintain the leaf critical level of 1.4%.
With the recent increases in costs of potassium fertilizers, it is important to keep in mind the potential damage caused by potassium deficiency. Inadequate levels will decrease the number of fruiting spurs on the tree, reduce the flowering of the surviving spurs, and reduce shoot and spur growth. In other words, deficient trees will yield poorly. Keep in mind that by the time symptoms of potassium deficiency are visible, yield has already been lost. Therefore, annual leaf samples and proper applications of potassium are recommended to maintain tree health and yield.
Having a major role in many plant processes, potassium promotes root growth, increases kernel/fruit size, and provides key metabolic features that include the formation of starch, translocation of sugars, stomata regulation, and the formation of xylem vessels. In general, plants deficient in potassium tend to have slow growth, with small, pale leaves. Trees that are severely deficient may have necrotic tips and margins. In many cases, the leaf tip curls upwards in a common symptom that is named the “Vikings Prow” (Figure 1).
Figure 1: Potassium deficiency on almonds. Note the upturned leaf tip which is known as the "Viking's Prow."Since Potassium plays a large role in tree health, it is important to maintain proper levels of the nutrient within the tree. A critical leaf value of 1.4% has been established by the University of California and current research has suggested that levels above this value do not increase yields. Recent field studies by Roger Duncan (UCCE Stanislaus) have demonstrated that leaf potassium levels in excess of the 1.4-1.6% range did not increase yield. Through the study, leaf levels between 1.4-1.6% gave the best yield results, with yield decreasing when potassium levels were below this level. Leaf potassium levels higher than this range did not increase yield, and may actually reduce yields if applied in excess.
Potassium usage by the almond crop is high. Upon harvesting the hulls and kernals, potassium is removed from the orchard. Studies by Dr. Patrick Brown (UC Davis), have shown that 50 pounds of potassium are removed from the orchard for every 1000 pounds of kernals harvested. From nutrient analysis of the fruit parts, 70-80% of the potassium removed by the harvest is within the hull, while the rest is within the shell and kernel.
Even though a large amount of potassium is used by the almond crop, it doesn’t always mean that large applications of potassium are needed to maintain critical levels. Some soils may have naturally high levels of potassium, depending on the parent material, percent of parent material degradation, soil texture, and the irrigation system. A soil analysis should be made to determine the amount of potassium within the soil and coupled with leaf tissue analysis to see if the potassium within the soil is available to the trees.
Once the potassium level within the soil drops, it will take several years of large applications to bring the levels back to normal. Potassium fertilizer products including sulfate of potash, muriate of potash, potassium nitrate, potassium thiosulfate (K-T-S), and a few others. Organic applications of potassium can be made through manure composts, green manures, guano, and wood ash. It is important to note that some potassium fertilizers may have unwanted chemicals/traits – chloride, sodium, alkalinity, and food safety concerns – which may have a negative impact on the orchard when applied in excess. Applications should be made to maintain the leaf critical level of 1.4%.
With the recent increases in costs of potassium fertilizers, it is important to keep in mind the potential damage caused by potassium deficiency. Inadequate levels will decrease the number of fruiting spurs on the tree, reduce the flowering of the surviving spurs, and reduce shoot and spur growth. In other words, deficient trees will yield poorly. Keep in mind that by the time symptoms of potassium deficiency are visible, yield has already been lost. Therefore, annual leaf samples and proper applications of potassium are recommended to maintain tree health and yield.
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