Posts Tagged: pests
Diseases, disorders and other plant problems are critical concerns for the wholesale nursery. These include biotic problems — caused by living organisms such as pathogens, nematodes, and insects and other arthropods — as well as abiotic problems — caused by factors such as temperature and moisture extremes, mechanical damage, chemicals,
nutrient deficiencies or excesses, salt damage and other environmental factors. Many plant problems, especially biotic problems, if not recognized and controlled early in their development, can result in significant economic damage for the producer. Therefore, timely and accurate diagnoses are required so that appropriate pest and disease
management options and other corrective measures can be implemented.
Definition of Plant Diagnosis and Steps
Diagnosis is the science and art of identifying the agent or cause of the problem under investigation. When one renders a diagnosis, one has collected all available information, clues and observations and then arrives at an informed conclusion as to the causal factor(s). Hence, plant problem diagnosis is an investigative, problem-solving process that involves the following steps:
- Ask and answer the appropriate questions to define the problem and
obtain information that is relevant to the case under investigation.
- Conduct a detailed, thorough examination of the plants and production areas.
- Use appropriate field diagnostic kits and lab tests to obtain clinical information on possible causal agents and factors.
- Compile all the collected information and consult additional resources and references.
- Finally, make an informed diagnosis.
Throughout this process compile all notes, observations, maps, laboratory results, photographs and other information. This compilation will be the information base for the present diagnosis and can also be a useful resource for future diagnostic cases. Keep an open mind as the information is analyzed and do not make unwarranted assumptions.
Distinguishing Abiotic and Biotic Problems
The first step is to determine whether the problem is caused by an infectious agent, and this can be difficult. Plant symptoms caused by biotic factors such as infectious diseases and arthropod pests are oftensimilar to damage caused by other factors. Leaf spots, chlorosis, blights, deformities, defoliation, wilting, stunting and plant death can
be common symptoms of both biotic and abiotic problems; therefore, the presence of these symptoms does not necessarily mean the problem is a disease. Some general guidelines for distinguishing abiotic and biotic
problems follow and are summarized in table 1.
Table 1 DISTINGUISHING ABIOTIC AND BIOTIC PROBLEMS
often affects several species or plants of various ages
often affects one species or cultivar of the same age
Pattern of plant symptoms
often related to environmental or physical factors or cultural practices; may be regular or uniform
often initially observed in random or irregular locations
Rate of symptom development
relatively uniform, extent of damage appears similar among plants
relatively uneven, time of appearance and damage severity varies among affected plants
no evidence of the kinds of pests or pathogens known to cause the current symptoms
presence of insects, mites,
is not infectious, is not progressive, commonly caused by one incident and does not spread
infectious, spreads on host over time if environmental conditions are suitable
possibly previously associated with current or prior environmental conditions or cultural practices
possibly caused by pests that
Adapted from Table 18, ANR Pub 3420
Biotic problems. Identifying biotic problems is sometimes facilitated if signs of a pathogen, primarily the growth of a fungus, are present. The most obvious examples of such signs are the mycelium and spores produced by rusts and powdery and downy mildews. However, in other cases nonpathogenic fungican grow on top of damaged plant tissues and appear to be signs of a pathogen, resulting in possible misdiagnoses.
Biotic problems often affect one species or cultivar of the same age and typically are initially observed in random or irregular locations; symptoms appear at varying times, and severity varies among affected plants. Biotic problems are infectious, spreading when environmental conditions are favorable, and may be associated with pests that have affected the crop. This infectious aspect is important, as biotic diseases will many times be progressive and continue to affect
additional tissues and more plants.
Abiotic problems. In contrast to biotic factors, abiotic problems often affect several species or plants of various ages; typically, damage is relatively uniform, doesn't spread and is often not progressive. Abiotic problems are not associated with pests. They are often caused by a single incident and are related to environmental or physical factors or cultural practices. Once the responsible factor has dissipated and is no longer affecting the plant, the plant may grow out of the problem and develop new, normal appearing foliage.
Diagnosing Biotic Problems
Infectious diseases. To confirm if a problem is caused by a pathogenic fungus, bacterium, nematode, or virus, it is often necessary to have symptomatic tissues analyzed by a trained horticulturalist or plant pathologist. Such experts will attempt to microscopically observe the agent and recover it, if culturable, through isolation procedures. Lab analysis is particularly important to determine if multiple pathogens are infecting the plant. A downside is that obtaining a diagnosis from lab analysis is not a fast process. However, quick test kits (fig. 1A) are available that can be used to rapidly identify many common diseases in the field.
Fig.1. Diagnosing biotic
problems. Plant pathogens can sometimes be rapidly diagnosed using
commercially available quick tests, such as these test strips for
viruses (A). Arthropod pests such as Cuban laurel thrips (shown here on Ficus) cause feeding damage, which can help in pest identification (B). Photos: S.T. Koike (A), J. K. Clark (B).
It is worthwhile to emphasize that diagnosing plant diseases requirescareful examination of the entire plant specimen. Symptoms on leaves, stems, or other above ground plant parts might lead one to suspect that afoliar pathogen is involved. However, these symptoms could also resultif the roots are diseased. Therefore, it is important to conduct a
complete examination of the symptomatic plant.
Because biotic diseases are caused by living microorganisms, the collecting and handling of samples is particularly critical. Samples that are stored for too long a time after collecting or that are allowedto dry out or become hot (if left inside a vehicle, for example) will sometimes cause the pathogen in the sample to die, making pathogen recovery and identification impossible. Plants that have been diseased for a long time and that are in the late stages of disease development will often be colonized by nonpathogenic saprophytic organisms. If these tissues are collected, it will be difficult to recover the primarypathogen of concern because of the presence of these secondary decay organisms. Root samples should be collected carefully as diseased rootsare sometimes difficult to dig out of the potting mix or soil, are
usually colonized by the pathogen as well as secondary agents, and are very sensitive to high temperatures and drying conditions.
Arthropod and other invertebrate pests. Insects,mites, slugs and snails cause damage while feeding on the plant (fig. 1B). Feeding damage is usually associated by the type of feeding characteristics and mouthparts of the insect or pest. For example, mites and insects such as whiteflies, aphids and mealybugs have tubular sucking mouthparts that suck plant fluids, causing buds, leaves, or flowers to discolor, distort, wilt, or drop. Thrips have rasping mouthparts that result in dried out, bleached plant tissue. Caterpillars, weevils, snails and slugs have chewing mouthparts that
make holes and cuts in foliage or flowers. They can also prune plant parts and sometimes consume entire plants.
If present, these pests are visible with the naked eye, a 10 X hand lens, or stereomicroscope, all depending upon their size. An assessment of whether the identified arthropod or invertebrate matches the plant damage it is associated with must be determined. Sometimes the identified arthropod or invertebrate may not be the sole problem or
could, in fact, be a beneficial organism or insignificant pest.
Aphids, whiteflies, thrips, leafhoppers and some other insects that suck plant juices may vector pathogens such as viruses and phytoplasmas (and to a lesser extent fungi and bacteria). They can feed on infected plants, acquire the pathogen, feed on healthy host plants and transmit the pathogen to the new host. The insects do not necessarily have to bepresent in large numbers to cause a significant disease outbreak. The insect vectors are not always present at the same time the disease symptoms are being expressed.
The excrement and byproducts from these pests can also provide clues that the pests have been or are actively present. Caterpillars and other chewing pests produce dark excrement or droppings. Greenhouse thrips and plant bugs produce dark, watery, or varnish-like droppings onfoliage. Aphids, whiteflies, soft scales, and some other sap-sucking insects excrete excess plant fluids as honeydew, a sticky sap, which provides a medium for the growth of sooty mold.
Diagnosing Abiotic Problems
Nutrient deficiencies and toxicities. Nutrientdeficiencies and toxicities reduce shoot growth and leaf size, cause leaf chlorosis (fig.2A), necrosis and dieback of plant parts. However, nutrient deficiencies cannot be reliably diagnosed on the basis of symptoms alone because numerous other plant problems can produce similarsymptoms. There are general symptoms that can be expressed by deficiencies of nutrients but usually leaf and/or soil samples are
needed to confirm the problem.
Fig. 2. Examples of abiotic problems. Iron deficiency on sweet gum (Liquidambar styracifolia) showing interveinal chlorosis (A). Chorotic spots on Hedera caused by a miticide application at a higher dosage rate than specified on the pesticide label (B). Photos: E. Martin (A), S. A. Tjosvold (B).
Herbicide, insecticide and fungicide phytotoxicity. Herbicidesused to control weeds in crops or in non-cropped areas sometimes injureornamental crops when they are not used in accordance with label instructions. Examples include when an herbicide is used in or around sensitive non-target crops, when an herbicide rate is increased above tolerable limits, or when an applicator makes a careless application. By understanding the mode of action of the herbicide, one can determine if the symptom fits an herbicide application. Herbicide detection in affected plants is possible with the help of a specialized laboratory but the analysis can be expensive. To minimize the cost of testing, the laboratory will need to know the suspected herbicide or its chemical group to narrow the analysis. Pesticides and fungicides occasionally cause obvious plant damage.
Symptoms can vary widely. Generally, flower petals are more susceptible to damage from pesticide applications than are leaves. The younger and more tender the leaves the more susceptible they are to pesticide applications. Hot weather can exacerbate the damage the chemicals cause. Pesticides that have systemic action can have a more profound effect. Some active ingredients can adversely affect the photosynthetic mechanism or other physiological processes and can resulti n a general leaf chlorosis, interveinal chlorosis, leaf curling and stunting. Emulsifiable concentrate (EC) formulations, soaps and oils can adversely affect the waxy surface layer that protects the leaf from desiccation. Applications with these products can result in the loss ofthe shiny appearance of a leaf, leaf spotting and necrosis. Pesticidesapplied as soil drenches can cause poor germination, seedling death, or
distorted plant growth.
Check label precautions against use on certain species. Make sure thepesticide is not applied more frequently or at a higher rate (fig. 2B) than recommended, or that the pesticide is not mixed with incompatible pesticides. When in doubt as to whether the plant species is sensitive to the pesticide, spray a few plants and observe them for several days to a week for any signs of damage before spraying any more of the plants.
Physiological and Genetic Disorders
There are numerous disorders that can occur because of environmental extremes — too much or too little of an environmental element such as light, temperature, water, or wind. Sunburn is damage to foliage and other herbaceous plant parts caused by a combination of too much light and heat and insufficient moisture. A yellow or brown area develops on foliage, which then dies beginning in areas between the veins. Sunscaldis damage to bark caused by excessive light or heat. Damaged bark becomes cracked and sunken. Frost damage causes shoots, buds and
flowers to curl, turn brown or black and die. Hailstones injure leaves,twigs, and in serious cases even the bark. Chilling damage in sensitive plants can cause wilting of foliage and flowers and development of dark water-soaked spots on leaves that can eventually turn light brown or bleached, and die. Physical and mechanical injury can occur when plants are mishandled during transport or routine cultural practices. Wounds might serve as entry sites for plant pathogens and can attract boring insects to woody stems.
In closed environments such as greenhouses and nursery storage areas,plants can be exposed to toxic levels of ethylene gas. Sources of ethylene include improperly functioning or unvented greenhouse heaters; exhaust from engines of forklifts and vehicles; cigarette smoke; damaged, decaying, or dying plants; and ripe or decaying fruit. Toxic levels of ethylene gas can cause premature abscission of flower buds, petals (fig. 3) and leaves. Other symptoms include wilted flowers, chlorosis, twisted growth or downward bending of stems and leaves and undersized or narrow leaves.
Fig. 3. Poor air quality can
lead to physiological disorders. Shattering (petal drop) on geranium was
caused by plant exposure to low levels of ethylene in the greenhouse or
during postharvest storage (A). Yellowish and brownish patches on
Japanese maple leaves are damage caused by ozone (B), an outdoor air
pollutant. Photos: J. K. Clark.
Outdoors, exposure of nursery plants to air pollutant gases such as ozone (fig. 3), carbon monoxide, nitrous oxides and sulfur dioxide can cause damage. Typical symptoms vary widely, but include slow growth anddiscolored, dying, or prematurely dropping foliage. Damage is often found where plants are located near sources of polluted air such as near
freeways or industries or where weather and topography concentrate the pollutants.
Sometimes plants or plant shoots exhibit an unusual and sudden changeof color producing discrete markings of variegation. For example, a plant with entirely green leaves suddenly produces a shoot that has leaves with edges lacking green pigment, stripes, or blotches. A new shoot such as this is probably a chimera (fig. 4). It is produced when a genetic mutation occurs in a specific region of the growing tip resulting in a section with genetically different cells. The ostensible result of the genetic change is dependent on the arrangement of the genetically different cells in the shoot tip and their expression. This can lead to sometimes bizarre variegation forms or sometimes forms thatare quite desirable. Sometimes variegation can be caused by viruses. Viruses usually cause non-uniform chlorosis, such as mosaics, while
chimeras usually produce patterned forms such as variegation of color onleaf margins, stripes, or complete loss of pigment. Some viroids may also cause bleaching of pigments in leaves; such symptoms, however, are generally produced throughout the plant and are not restricted to a single shoot. Some nutrient disorders can cause variegation but these disorders usually do not arise from a specific shoot as with chimeras.
Fig. 4. Genetic disorder.
Growing points with variegated leaves can sometimes arise spontaneously
from some species such as this Origanum. Genetic variants such as this are sometimes confused with plants with virus disease or nutrient deficiency symptoms. Photo: S. A. Tjosvold.
Steve Tjosvold is Environmental Horticulture Advisor and
Steve Koike is Plant Pathology Farm Advisor, UC Cooperative Extension,
Santa Cruz and Monterey counties.
This article was condensed from: Diagnosing Plant
Problems, Chapter 11. In Newman, J. (ed) Container Nursery Production
and Business Management. Univ. of Calif. Agric. and Nat. Resources.
Publication 3540. Richmond, CA.
Boxer P, Sandmann G. 1989. Target sites of herbicide action. Boca Raton, FL: CRC Press.
Costello L, Perry E, Matheny N, Henry M, Geisel P. 2003. Abiotic
disorders of landscape plants: A diagnostic guide. Oakland: University
of California Division of Agriculture and Natural Resources Publication
Derr JF, Appleton BL. 1988. Herbicide injury to trees and shrubs: A
pictorial guide to symptom diagnosis. Virginia Beach, VA: Blue Crab
Dreistadt SH. 2001. Integrated pest management for floriculture and
nurseries. Oakland: University of California Division of Agriculture and
Natural Resources Publication 3402.
Eagle, DJ. 1981. Diagnosis of herbicide damage to crops. New York, NY: Chemical Publishing Co.
Grogan RG. 1981. The science and art of plant disease diagnosis. Annual Review of Phytopathology 19:333–351.
Ratzinger EJ, Mallory-Smith C. 1997. Classification of herbicides by
the site of action for weed resistance management strategies. Weed
Schubert TS, Breman LL. 1988. Basic concepts of plant disease and how
to collect a sample for disease diagnosis. Plant Pathology Circular No.
307. Florida Department of Agriculture and Consumer Services, Plant
Pathology Circular No. 307.
Sharma MP. 1986. Recognizing herbicide action and injury. Alberta Environmental Centre, Alberta Agriculture. Agdex 641–647.
Shurtleff MC, Averre CW. 1997. The plant disease clinic and field
diagnosis of abiotic diseases. St. Paul, MN: American Phytopathological
Stewart TM, Galea VJ. 2006. Approaches to training practitioners in
the art and science of plant disease diagnosis. Plant Disease
Tickes B, Cudney D, and Elmore C. 1996. Herbicide injury symptoms.
Tucson, AZ: University of Arizona Cooperative Extension Publication No.
The University of California Cooperative Extension conducted an Avocado Pest Management Round Table grower meeting in Fallbrook, CA on September 28, 2017. Approximately 64 growers, industry, Pest Control Advisors, and other stakeholders were present. Sonia Rios, Subtropical Horticulture Farm Advisor, University of California Cooperative Extension (UCCE), Riverside/San Diego Counties gave a talk on “Introduction to Avocado Weed Management.” Tim Spann from the California Avocado Commission (CAC) spoke on a potential threat to California's avocado industry, “A Review: Redbay Ambrosia Beetle & Laurel Wilt Disease.
Growers were able to participate in 2 round table discussions, one on “Old challenges/possible new solutions - pesticide resistance, proper spray application, new pesticides” and another on New Challenges in the Avocado industry. Round Table panel members were: Mary Lu Arpaia, University of California, Riverside/CE, Frank Byrne, University of California, Riverside/CE, Kevin Turner, CAL FIRE, Tim Spann, CAC, Enrico Ferro, Avocado Grower/PCA, Sonia Rios, UCCE, Victor Lopez, Crop Production Services.
The growers will be looking forward to the next Round Table meeting in the Spring. If you missed the meeting, below is a link to a recording of the meeting https://soundcloud.com/user-95194984/controlling-pests-in-avocado-roundtable-meeting
Recently a grower called up with a beautiful scale that the PCA couldn't identify. I could just marvel at the beauty of it and wondered what in the heck it was. It didn't look like any scale I had seen in the area and others who were queried didn't know either.
I took it into the Ag Commissioner's office and they sent it off to see if it was a new species. Images were sent off to various entomologists and David Haviland in Bakersfield identified it as a Ceroplastes, possibly a Chinese wax scale or Barnacle scale. Others had identified it as Florida wax scale.
It was sent into Paul Rugman-Jones at UC Riverside Entomology for DNA identification. His identification and that of CA Dept of Food and Ag entolomogists came back as Barnacle scale, Ceroplastes cirripediformis.
All of these scales turned out to have been seen in California before, so there was no quarantine issue. It also turned out that all of the adults that were turned in for identification had also been parasitized by some wasp. So there is biological control already in place for it. The issue at stake here, though, is that it's important to be watching for new visitors in the orchard. Joe Morse now retired from UC Riverside Entomology lead a team that intercepted avocados coming into the US. They found a number of scale insects that were new to California and new to the identification world. A number of these scale are parthenogenic, meaning they can reproduce without males, and just one lone female could possible balloon into a massive population in a short time. And on a scale like that, trees would have a hard time without some serious intervention.
Argentine Ant is a very aggressive invader that disrupts native ant populations and at the same time disrupts biocontrol agents that help control, such pests as scale, aphids and mealy bugs in citrus and other tree crop species. They defend these sugar producing sources of energy from attack by predators and parasites, like parasitic wasps and predatory assassin bugs and lady bugs. They increase the threat of Asian Citrus Psyllid and HLB by protecting the psyllid from attack by parasitic Tamarixia.
A careful, well placed chlorpyrifos spray has been used to control Argentine ants. A trunk spray and/or spray on irrigation lines has disrupted their activity with minimal impact on beneficials. This protectant spray keeps the Argentine ants out of the canopies and allows the beneficials access to the pests. Controlling this one species, can have significant impact on biocontrol and the whole need for controlling pests.
Chlorpyrifos is a pesticide that might lose registration and other materials and techniques have been examined over the years as a replacement. A recent procedure has been proposed and used successfully on Santa Cruz Island to control introduced Argentine ants. The ant has caused tremendous disruption in biocontrol and it appears to have been controlled by this new technique. We are in the process of evaluating it's use in citrus. The application technique, costs and materials would need to be modified for use in citrus orchards. The current procedure would not be considered an organic practice since the pesticide material is not registered organic. It might be possible to use an organically registered material in the future.
Protocols for Argentine ant eradication in conservation areas
L.Boser1,C.Hanna2,D.A.Holway3,K.R.Faulkner4,I.Naughton3,K.Merrill5,J.M.Randall1,C.Cory1,D.-H. Choe6 & S. A.Morrison
Journal of Applied Entomology
The Argentine ant (Linepithema humile) is a widespread, abundant and ecologically disruptive invader that is present throughout major portions of coastal California and on half of the California Channel Islands. On Santa Cruz Island, the Argentine ant had invaded about 2% of the island's area in four distinct locations as of 2012. Given the negative ecological effects resulting from Argentine ant invasions,we sought to develop a cost-effective method of eradication. Here, we describe the results of large-scale, field-tested methods for Argentine ant eradication and post-treatment detection. Our eradication protocol employs a novel toxicant-delivery system: an aqueous solution of sucrose and 6 ppm of thiamethoxam mixed with hydrating polyacrylamide beads. Ants feed on the solution present on the bead's surface for about 24h after which time bead dehydration prevents feeding. We distributed hydrated beads by helicopter over 74 ha of infested areas plus a 50-m buffer on 14 occasions between June 2013 and September 2014. Treatments reduced Argentine ant activity to subdetectable levels within four months. In 2014, we conducted a high-intensity detection protocol using lures (n = 55 363) in areas treated in 2013.This effort did not detect Argentine ants. In 2015, we conducted a medium-intensity detection protocol using lures (n=2250) in areas treated in 2013 and 2014 but not searched in 2014; this sampling effort did not detect Argentine ant activity except for a single remnant infestation (c.0.3ha in area),which was retreated in2015.Thec ost of treatments was approximately $1400 per ha; this cost is comparable to other ant eradication efforts. The cost of our preferred detection method, which used lures spaced every 10m,was $500 per ha.These results demonstrate sufficient protocol efficacy to justify expansion of treatments to other infested areas in ecologically sensitive areas.
Photo: Argentine ant and scale
The Orange County Master Gardeners have lived up to their name with their website information on citrus. It's a truly impressive information site for not only homeowners, but also growers:
The “Citrus Problem Diagnosis Chart” is especially work perusing: