Posts Tagged: cherimoya
SACRAMENTO — A portion of Los Angeles County has been placed under quarantine for the Oriental fruit fly following the detection of nine flies in the Hollywood area. The quarantine zone measures 75 square miles. A link to the quarantine map may be found here:https://www.cdfa.ca.gov/plant/off/regulation.html
“California's fruit fly season extends from late summer through the fall,” said California Agriculture Secretary Karen Ross. “These pests like Southern California for some of the same reasons other travelers do: the pleasant climate and the tremendous variety of food. Fortunately, with the help of local residents, we have a great track record of eradicating these infestations.”
To prevent the spread of fruit flies through homegrown fruits and vegetables, residents living in the fruit fly quarantine area are urged to not move any fruits or vegetables from their property. Produce may be consumed or processed (i.e. juiced, frozen, cooked, or ground in the garbage disposal) at the property where it was picked.
The most common pathway for these pests to enter the state is by “hitchhiking” in fruits and vegetables brought back illegally by travelers as they return from infested regions around the world or from packages sent to California. To help prevent infestations statewide, officials asks residents to refrain from bringing or mailing fresh fruit, vegetables, plants, and soil into California unless agricultural inspectors have cleared the shipment beforehand.
While fruit flies and other invasive species threaten California's crops, the vast majority of them are detected in urban and suburban areas.
“That's why it's important for residents to cooperate with quarantine restrictions and allow authorized agricultural workers access to properties to inspect fruit and oriental fruit fly traps for signs of an infestation,” said Secretary Ross.
Following the principles of Integrated Pest Management (IPM), the California Department of Food and Agriculture (CDFA) uses a “male attractant” technique in its eradication effort for this pest. This approach, which has successfully eliminated dozens of fruit fly infestations in California, significantly reduces the amount of insecticide required to eradicate the population, and only targets the fruit flies – no other insects or animals are harmed. The treatment program is being carried out over several square miles surrounding the sites where the oriental fruit flies were trapped.
The oriental fruit fly is known to target more than 230 different fruits, vegetables, and plants. Damage occurs when the female fruit fly lays her eggs inside the fruit. The eggs hatch into maggots and tunnel through the flesh of the fruit, making it unfit for consumption.
The oriental fruit fly is widespread throughout much of the mainland of Southern Asia and neighboring islands including Sri Lanka and Taiwan, and has invaded other areas, most notably Africa and Hawaii.
Residents with questions about the quarantine may call the CDFA Pest Hotline at 1-800-491-1899.
—California Department of Food and Agriculture
Photos: OFF adults and Grapefruit infested with larvae of oriental fruit fly, Dacus dorsalis.
The latest edition of Topics in Subtropics newsletter is out, Elizabeth Fichtner as editor. Read on.
TOPICS IN THIS ISSUE:
Why has California red scale been so difficult to control?
Navel Orange Nitrogen Fertilization
Recent Advances in Understanding the History of Olive Domestication
- Upcoming UC Olive Center Events
Lime-induced Iron Chlorosis: a nutritional challenge in the culture of several subtropical perennial crops in California
Elizabeth Fichtner, UCCE Tulare County and Rachel Elkins, UCCE Lake and Mendocino Counties
Spring, and new leaves are coming out, but this could, but yellow could be a sign of iron chlorosis, as well.
Although iron (Fe) is the 4th most abundant element in the lithosphere, Fe deficiency is among the most common plant micronutrient deficiencies. Fe deficiency in plants is common in calcareous soils, waterlogged soils, sandy soils low in total Fe, and in peat and muck soils where organic matter chelates Fe, rendering the element unavailable for plant uptake. In California, lime-induced Fe deficiency is often observed in soils and irrigation water containing free lime, and is exacerbated by conditions that impede soil drainage (ie. compaction, high clay content), resulting in reductive conditions. Given that over 30% of the world's soils are calcareous, lime-induced Fe deficiency is a challenge in numerous perennial cropping systems including: grapes, pears, apple, citrus, avocado, pecans, and stone fruit (prune, almond, apricot, peach, nectarine, cherry).
In most soils, Fe oxides are the common source of Fe for plant nutrition. Solubility of Fe oxides is pH dependant; as pH increases, the free ionic forms of the micronutrient are changed to the hydroxy ions, and finally to the insoluble hydroxides or oxides. In calcareous soils, the bicarbonate ion inhibits mobilization of accumulated Fe from roots to foliage and directly affects availability of Fe in soil by buffering soil pH. When irrigation water is also high in bicarbonate, probability of Fe deficiency is enhanced because bicarbonate is continuously supplied to the soil, and more importantly, the roots may become crusted with lime as water evaporates, thus inhibiting root growth and function. Inside the plant, bicarbonate inhibits nutrient translocation from roots to aboveground plant parts. The adverse effects of high bicarbonate levels are exacerbated in very saturated, very dry, or compact soils, where bicarbonate levels increase concurrent with diminished root growth and nutrient uptake.
Symptoms of Fe deficiency in plants
Fe is immobile in plants; therefore, symptoms appear in young leaves. Interveinal chlorosis (Figure 1) is the main symptom associated with Fe deficiency, followed by reduced shoot and root growth, complete foliar chlorosis, defoliation, shoot dieback, and under severe conditions may result in tree mortality. Overall productivity (yield) is reduced, mainly from a reduced number of fruiting points.
Plant species and cultivars vary in their sensitivity to Fe deficiency, and are categorized as either "Fe-efficient" or "Fe-inefficient". Fe-efficient plants have Fe uptake systems that are switched on under conditions of Fe deficiency. Fe-inefficient plants are unable to respond to Fe deficient conditions. All Fe-efficient plants, except grasses, utilize a Fe-uptake mechanism known as Strategy 1. Strategy 1 plants decrease rhizosphere pH by release of protons, thus increasing Fe solubility. Some plants may excrete organic compounds in the rhizosphere that reduce ferric iron (Fe3+) to the more soluble ferrous (Fe2+) forms or form soluble complexes that maintain Fe in solution. Additionally, roots of Strategy 1 plants have specialized mechanisms for reduction, uptake, and transfer of Fe within the plant. Strategy 2 plants (grasses) produce low molecular weight compounds called phytosiderophores which chelate Fe and take up the chelated Fe with a specific transport system.
Amelioration of Fe chlorosis
Planting sites in calcareous soils should be well drained to provide optimal conditions for root growth and nutrient uptake. Waterlogged and compact soils contain
more carbon dioxide, which reacts with lime to form even more bicarbonate. These conditions, as well as very dry soils, also inhibit microbial activity which aids in
solubilization and chelation of Fe. Prior to planting, soils and water should be tested to determine the pH, lime equivalent, and bicarbonate concentration. Bicarbonate concentrations greater than 3 meq/L in irrigation water increase the hazard of lime accumulation on and around roots. If high bicarbonate water must be used, the pH must be adjusted to 6.0-6.5 to dissolve the bicarbonate and prevent it from negating the effects of soil-based treatments. In microsprinker and drip systems, acidification of irrigation water will also reduce the risk of emitter clogging, a common problem at bicarbonate levels over 2 meq/L. The cost of reducing the pH of irrigation water will more than compensate for the savings incurred from avoiding wasted investment in failed soil- and plant-based remedies. Systems can be set up to continuously and safely inject water with acids such as sulfuric, urea-sulfuric, or phosphoric during irrigations. Specific choice and rate will depend on crop, soil type, other nutrient needs, availability, and cost. Downstream pH meters are available to continuously adjust rate of acid use. Acetic and citric acid can be utilized by organic growers.
Soil based pre-plant treatments to reduce pH include elemental sulfur (S) and acids as mentioned above. It is only necessary to treat a limited area near the root zone to ameliorate symptoms because the tree only needs to take up a small amount of Fe. Material can be shanked in or banded and incorporated in the prospective tree row. One ton of elemental sulfur per treated acre is needed to mitigate three tons of lime, and may need to be re-applied every 3 to 5 years after planting. The addition of organic matter such as well-composted manures will benefit poorly drained or compact soils by increasing aeration for better root growth, fostering chelation of nutrient cations, and reducing pH (depending on source material).
If possible, choose a Fe efficient species or cultivar. In perennial systems, lime-tolerant rootstocks may be the first line of defense in combating Fe deficiency. Some rootstocksmentioned are peach-almond and Krymsk-86 for stone fruit, Gisela 5 for cherry, and Pyrus communis for pear. Ongoing research studies in Europe focus on screening rootstocks of grape and olive for lime tolerance.
Once soil and water quality improvements are made, post-plant management strategies may also be implemented to ameliorate lime-induced Fe chlorosis in the short term. Soil can be acidified as described above. Individual trees can be treated by digging four to six 12-24 inch
holes around the drip line and burying a mixture of sulfur and Fe fertilizer. Historically, two principal methods have been utilized: 1) foliar application of inorganic Fe salts (ie. ferrous sulfate), and 2) soil or foliar application of synthetic chelates. Application of Fe salts to foliage may have mixed results due to limited penetration of Fe into leaves and inadequate mobilization within the plant. Use of Fe chelates may be of benefit; however, they are expensive and pose an environmental concern due to their mobility within the soil profile. Because soil lime interferes with Fe mobility with the plant, repeat application of inorganic Fe salts or Fe chelates may be necessary throughout the growing season.
Choice of nitrogen (N) fertilizer may also influence solubility of rhizosphere Fe. When N is applied in the ammonium form (NH4+), the root releases a proton (H+) to maintain a charge balance, thus reducing rhizosphere pH. Alternately, fertilization with nitrate (NO3-) results in root release of hydroxyl ions (OH-), resulting in an increase in rhizosphere pH. Solubility of Fe3+ increases 1000 fold with each one unit decrease in pH; therefore, fertility-induced rhizosphere pH changes may significantly influence Fe availability.
New methods for amelioration of Fe chlorosis are under investigation. For example, container studies have demonstrated that inter-planting sheep's fescue, a Strategy 2 plant, with a Fe-inefficient grape rootstock may ameliorate Fe chlorosis in grape. In this system, the grass produces a phytosiderophore that enhances Fe availability to the grape. Additionally, soil amendment with Fe3(PO4)2• 8H2O), a synthetic iron(II)-phosphate analogous to the mineral vivianite, has been effective at preventing Fe chlorosis in lemon, pear, olive, kiwi, and peach. Vivianite has a high Fe content (~30%) and serves as a slow release source of Fe in calcareous soils.
Figures below: Shoot dieback in citrus and iron chlorosis in avocado
A call from a small grower, surprised at the sudden decline of the avocado trees. It must be a disease was the grower's thought. Well driving up to the site, there were numerous trees with canopies indicating drought stress. In fact most of the trees looked like they had had the water turned off. When I got to the orchard, all the trees had a similar look (see photo below). The fringe of the canopy had turned brown/red where the leaves had collapsed rapidly, while the interior leaves were often still green. All the trees had a similar cast. It turns out the water district had required a cutback just when temperatures were going into the 100's. NO water, no cooling effect of transpiration and the outer fringe of leaves collapsed. This is called the “clothesline” effect. It's like a sheet on a clothesline where the margins of the sheet dry first and gradually the body of the sheet dries. The same thing happens in a canopy. The outside leaves are the first to dry out and then the rest of the canopy goes. When you see a whole orchard go down suddenly, that does not fit into a disease pattern. There's usually an epicenter where it starts – where it's colder, wetter, dryer, hotter, more overgrown, etc. and spreads out from there if it is going to spread. It turns out that the automatic irrigation system had gone down and the grower hadn't noticed until too late. When you see reddish tinged leaves, it means the leaves went down fast. When they are brown, it means they slowly went down over weeks or months.
With all the dead points in the tree, it is now open to disease – twig/leaf blight caused by one of the Botryosphaerias. These decay fungi are everywhere in an orchard decaying organic material on the orchard floor. With the dead material in the tree, now the tree becomes a potential feast for the fungi. The dead stuff has to come out, or the fungus will start eating into the tree. I suggested that instead of pruning out all those little points of death, that they cut back the whole canopy to major scaffold branches. In doing so, it would rapidly and cheaply remove the dead material and reduce the water demand.
Published in the Los Angeles Times from Aug. 6 to Aug. 7, 2016 - See more at: http://www.legacy.com/obituaries/latimes/obituary.aspx?pid=180988990#sthash.UTYo4NSS.dpuf