Posts Tagged: water stress
Colletotrichum Shoot Dieback of Citrus
Figure 1: Citrus shoot dieback (top) and gummosis (bottom) caused by Colletrotrichum. |
A new disease of citrus has been found in the main growing regions of the Central Valley of California. The causal agents of this disease were identified as species of Colletotrichum, which are well-known pathogens of citrus and other crops causing anthracnose diseases. Several growers and nurserymen in various orchards in the Central Valley first noticed the disease in 2013. Symptoms include leaf chlorosis, crown thinning, gumming on twigs and shoots dieback, and in severe cases, death of young trees. The most characteristic symptoms of this disease are the gum pockets, which appear on young shoots either alone or in clusters and the dieback of twigs and shoots (Fig.1). Field observations indicate that symptoms initially appear during the early summer months and continue to express until the early fall. These symptoms were primarily reported from clementine, mandarin, and navel orange varieties. In order to determine the main cause of this disease, field surveys were conducted in several orchards throughout the Central Valley. Isolations from symptomatic plant samples frequently yielded Colletotrichum species. Morphological and molecular phylogenetic studies allowed the identification of two distinct species of Colletotrichum (Colletotrichum karstii and Colletotrichum gloeosporioides) associated with twig and shoot dieback. Interestingly, these Colletotrichum species were also isolated from cankers in larger branches. Although C. gloeosporioides is known to cause anthracnose on citrus, a post-harvest disease causing fruit decay, it has not been reported to cause shoot dieback of citrus. C. karstii however has not been reported previously from citrus in California and our research team is currently conducting field and green house studies to determine the pathogenicity of this species in citrus. At present, it is unclear how widespread this disease is in California orchards or how many citrus varieties are susceptible to this disease. Pest control advisors are monitoring citrus trees for the presence of the disease in the Central Valley (particularly clementine, mandarin, and navel varieties) during the early summer months. Continuing research led by Dr. Akif Eskalen in collaboration with Dr. Florent Trouillas is focused on further understanding the biology of the fungal pathogens as well as factors influencing disease expression in order to develop management strategies against this emerging disease.
Champions of the Forests Researchers receive $2.5 million to study the effects of climate and climate change on trees along river channels
Riparian forests — the ribbons of trees that grow along river channels — play an important ecological role as refuges for endangered species in dry areas. But these natural havens are increasingly threatened by the changing frequency and intensity of drought, both of which are byproducts of climate change.
Scientists at UC Santa Barbara are studying how riparian forests respond to climate change that manifests as hotter and drier conditions over time. With $2.5 million in combined funding from three grants, Michael Singer, a researcher with UCSB's Earth Research Institute (ERI), and colleagues seek to understand the impact of nonstationary climate — trends in temperatures and precipitation — on riparian forests.
“As a river starts drying up, groundwater-dependent trees like those in a riparian forest might disappear, or the moisture within the soil might dry up, affecting more shallowly rooted trees and shrubs,” explained Singer, who also is a lecturer at Cardiff University in the United Kingdom.
Through the National Science Foundation's Geography and Spatial Sciences Program, one project — led by associate professor John Stella of the State University of New York College of Environmental Science and Forestry (SUNY-ESF) — is being conducted near UCSB in Ventura County's Santa Clara River Valley. A basin with competing water needs — ecological, urban and agricultural — the Santa Clara, because it goes dry, relies largely on subsurface groundwater. Continual pumping of groundwater from the aquifer for agriculture, when that aquifer is not recharged by rainfall, causes wells to go dry and forces pumping efforts to reach deeper and deeper.
Innovative new legislation in California, the Sustainable Groundwater Management Act (SGMA), shifts the management of groundwater resources from the state to local basins, requiring regional stakeholders to create action plans for managing water resources. With the grant, Singer and Stella will collaborate with UCSB geography professor Dar Roberts and The Nature Conservancy to develop an improved understanding of forest health along the Santa Clara River. They'll investigate matters including what happens to trees that are rooted at depths below the surface with diminishing groundwater, and their findings can be used to administer SGMA.
Through another NSF grant, in its Hydrologic Sciences Program, Singer, Stella and ERI director Kelly Caylor, also a professor in UCSB's Bren School of Environmental Science & Management, will study riparian forests along a major European river. The Rhône, which flows through France from Lake Geneva to the Mediterranean Sea, warms 2 degrees Celsius along its climate gradient. The researchers plan to measure the variation in temperature, precipitation and climate to model what might happen under climate change and determine how water availability to forests shifts due to climate and how trees are using water, as well as their corresponding growth and health outcomes over time.
The scientists also will core trees to determine their age and will extract cellulose from individual rings for isotopic analysis. Oxygen isotopes are used to distinguish water sources such as groundwater or rainfall, while carbon isotopes reveal how efficiently trees are using that water — a calculation of photosynthesis versus water loss.
The third project is funded by the Department of Defense through the Strategic Environmental Research and Development Program. Singer, Stella, Roberts and Caylor will develop a toolkit and provide quantitative support for land and water conservation management to promote the sustainability and resilience of riparian forest ecosystems located on DOD lands. The endeavor focuses on three dry area bases in drought-prone regions: Vandenberg Air Force Base near Lompoc; Marine Corps Base Camp Pendleton in San Diego County; and the driest, U.S. Army Fort Huachuca in southeastern Arizona.
“In all of these studies, we're developing water stress indicators, which can be physical manifestations such as dropping leaves or branches or trees becoming less green,” Singer explained. “Such markers can be seen in remote sensing imagery and tree-ring isotopes, but we're also looking at climate records for precipitation and temperature, along with numerical modeling to determine what type and how much water has been delivered to a basin in the first place. If we see trends that tell us the forest is really suffering, we hope to establish an early warning response window in which managers can act quickly before important patches of forests are lost.
“Combined, those various metrics give us a good idea of how well trees are doing,” Singer added. “We hope to integrate the results of these projects to eventually predict the thresholds of species collapse and perhaps even forest collapse. If we can identify what the dominant controls on those thresholds are climatically, we may be able to assess whether trends in temperature are more relevant than those for precipitation.”
Blueberries Looking Sad?
Advice From the Help Desk of the
UC Master Gardener Program of Contra Costa County
MGCC Help Desk Client: I've attached photos of our Patriot blueberry bush. Why are the leaves turning brown and curling? The problem began about a month ago. We tried to treat with acidifying powdered fertilizer, applied to the soil and cultivated in prior to watering. We water every other day or as needed (we check soil moisture with a short stick). The plant is now sending out new growth which looks relatively healthy.
Blueberriy showing sun burn/scald and/or water stress...
MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with your blueberry question. You wrote that the leaves were turning brown and curling.
Your photographs were helpful. We think the plant has been experiencing sun scald and/or water stress. Several different factors may be contributing to this.
1. Blueberries have a shallow root system. During times of high moisture demand the roots may not be able to keep the leaves hydrated. This is especially true for container plants in full sun where during significant heat spells they will likely need water every day. To help the roots function, we recommend that you put an inch or two of mulch such as wood chips, or well-decomposed compost on the top of the soil (but keep it at least an inch away from the stems). This will help the soil to remain cool and reduce water loss.
2. Shallow rooted plants are susceptible to damage from cultivation. When you apply fertilizer or acidifier, just water it in without cultivating. Plants with damaged roots will have a much more difficult time absorbing sufficient water.
3. Shallow rooted plants need room to expand sideways in order to have an adequate root volume. We recommend that you re-pot your blueberry plant into a wider container in the fall once the weather cools down (e.g. November). Wait at least 4 weeks after re-potting before applying any fertilizer.
Additional information on growing blueberries can be found at this University of California website http://ucanr.edu/sites/gardenweb/files/29062.pdf.
I hope that this information is helpful.
UC Master Gardener Program of Contra Costa County (JL)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (//ucanr.edu/blogs/CCMGBlog/).
Drought Induced Problems in Our Orchards
Drought Induced Problems in Our Orchards
Abiotic disorders are plant problems that are non-infective. They are not caused by an organism, but through their damage, they may bring on damage caused by organisms. Think of a tree hit by lightning or a tractor. The damage breaches the protective bark which allows fungi to start working on the damaged area, eventually leading to a decayed trunk. It was the mechanical damage, though that set the process in motion.
Too much or too little water can also predispose a plant to disease. Think of Phytophthora root rot or even asphyxiation that can come from waterlogging or too frequent irrigations.
Salinity Effects from Lack of Water
Lack of water and especially sufficient rainfall can lead to salinity and specific salts like boron, sodium and chloride accumulating in the root zone. This happens from a lack of leaching that removes native soil salts from the root zone or the salts from the previous salt-laden irrigation from the root zone. These salts cause their own kind of damage, but they can also predispose a tree to disorders, disease and invertebrate (insect and mite) damage.
Lack of water and salt accumulation act in a similar fashion. Soil salt acts in competition with roots for water. The more soil salt, the harder a tree needs to pull on water to get what it needs. The first symptom of lack of water or salt accumulation may be an initial dropping of the leaves. If this condition is more persistent, though we start to see what is called “tip burn” or “salt damage”. Southern California is tremendously dependent on rainfall to clean up irrigation salts, and when rain is lacking, irrigation must be relied on to do the leaching
As the lack of leaching advances (lack of rainfall and sufficient irrigation leaching) the canopy thins from leaf drop, exposing fruit to sunburn and fruit shriveling.
Leaf drop and fruit shriveling in avocado.
In the case of sensitive citrus varieties like mandarins, water stress can lead to a pithy core with darker colored seeds, almost as if the fruit had matured too long on the tree.
Total salinity plays an important factor in plant disorder, but also the specific salts. These salts accumulate in the older leaves, and cause characteristic symptoms that are characteristic in most trees. Boron will appear on older leaves, causing an initial terminal yellowing in the leaf that gradually turns to a tip burn.
Often times it is hard to distinguish between chloride, sodium and total salinity damage. It is somewhat a moot point, since the method to control all of them is the same – increased leaching. There is no amendment or fertilizer that can be applied that will correct this problem. The damage symptoms do not go away until the leaf drops and a new one replaces it. By that time hopefully rain and/or a more efficient irrigation program has been put in place.
The Impact of Drought on Nutrient Deficiencies
Salinity and drought stress can also lead to mineral deficiencies. This is either due to the lack of water movement carrying nutrients or to direct completion for nutrients. A common deficiency for drought stressed plants is nitrogen deficiency from lack of water entraining that nutrient into the plant.
This usually starts out in the older tissue and gradually spreads to the younger tissue in more advanced cases.
The salts in the root zone can also lead to competition for uptake of other nutrients like calcium and potassium. Apples and tomatoes are famous for blossom end rot when calcium uptake is low, but we have also seen it in citrus. Low calcium in avocado, and many other fruits, leads to lower shelf life. Sodium and boron accumulation in the root zone can lead to induced calcium deficiencies and increased sodium can also further lead to potassium deficiencies. Leaching can help remove these competitive elements.
Drought Effect on Tree Disease
Drought and salt stress can also lead to disease, but in many cases once the problem has been dealt with the disease symptoms slowly disappear. They are secondary pathogens and unless it is a young tree (under three years of age) or one blighted with a more aggressive disease, the disease condition is not fatal. Often times, in the best of years, on hilly ground these diseases might be seen where water pressure is lowest or there are broken or clogged emitters. The symptoms are many – leaf blights, cankers, dieback, gummosis – but they are all caused by decomposing fungi that are found in the decaying material found in orchards, especially in the naturally occurring avocado mulch or artificially mulched orchards. Many of these fungi are related Botryosphaerias, but we once lumped then all under the fungus Dothiorella. These decay fungi will go to all manner of plant species, from citrus to roses to Brazilian pepper.
Another secondary pathogen that clears up as soon as the stress is relieved is bacterial canker in avocado. These ugly cankers form white crusted circles that ooze sap, but when the tree is healthy again, the cankers dry up with a little bark flap where the canker had been.
Drought Effect on Pests
Water/salt stress also makes trees more susceptible to insect and mite attack. Mites are often predated by predacious mites, and when there are dusty situations, they can't do their jobs efficiently and mites can get out of hand. Mite damage on leaves is often noted in well irrigated orchards along dusty picking rows
Many borers are attracted to water stressed trees and it is possible that the Polyphagous and Kuroshio Shot Hole Borers are more attracted to those trees.
And then we have conditions like Valencia rind stain that also appears in other citrus varieties. We know it will show up in water stressed trees, but we aren't sure what the mechanism that causes this rind breakdown just at color break. Could it be from thrips attracted to the stressed tree or a nutrient imbalance, it's not clear?
Water and salt stress can have all manner of effects on tree growth. It should lead to smaller trees, smaller crops and smaller fruit. The only way to manage this condition is through irrigation management. Using all the tools available, such as CIMIS, soil probes, soil sensors, your eyes, etc. and good quality available water are the way to improve management of the orchard to avoid these problems.
Scroll down for Images
Tip Burn, notice sun burn bottom right hand fruit
Endoxerosis with dried out core
Boron toxicity
Nitrogen deficiency
Blossom end rot
Potassium deficiency
Bot gumming in lemon
Black Streak in Avocado
Bacterial Canker
Citrus red mite
Polyphagous Shot Hole Borer damage on avocado
Valencia Rind Stain
avocado drought canopy
nitrogen deficiency
endoxerosis 4
boron toxicity citrus 1
blossom end rot lemon
potassium deficiency avocado
gumming dothiorella
avocado black streak 1
bacterial canker avocado
citrus red mite
PSHB damage
Citrus Endoxerosis - Drought Effect?
Recently some 'W. Murcott' mandarins were shown to me. Brown spots in the core of the fruit. Another problem caused by drought and lack of leaching rains? Endoxerosis, also called internal decline, dry core, yellow tip, dry and blossom end decline is often confused with Alternaria rot which frequently accompanies or follows it. Internal tissues back of the stylar end break down, dry and become pinkish or brownish in color. Gum commonly forms in the core and either in or nest to the rind. Green fruits lose luster and frequently but not always develop a yellow color in circular areas surround the stylar end. The cut fru9i shows the gummy pinkish to brownish mass of partially dried and collapsed tissue. Gumming may even extend into the twig bearing the affected fruit. When the fruit turns color, the malady is more difficult to detect without cutting.
The cause is believed to be related to water and the physiological conditions within the tree and fruit and temperature conditions in the air and soil influencing transpiration and water stress. It is suggested therefore that water conditions in the soil be kept as favorable for tree heath as possible and pick on time so that they are not over mature.
From: The Citrus Industry, Volume IV, Editor: Walter Reuther, UC Press
In other words, make sure to leach the root zone of accumulated salts from previous irrigations and pray for rain.
Craig Kallsen in Kern County says he often sees this in young mandarins especially on the south and west sides of the canopy, to the point that growers will not even bother to harvest this fruit until the trees are older. The fruit just transpires so much water when it's not shaded that the fruit just dries out.
If my Latin serves me right: endo - inside, xeric - dry. Dry Inside.
endoxerosis 3