- Author: Ben Faber
RECOGNIZING NATURAL ENEMIES Proper identification of pests, and distinguishing pests from natural enemies, is essential for effective biological control. Carefully observe the mites and insects on your plants to help discern their activity. For example, some people may mistake syrphid fly larvae for caterpillars. However, syrphid fly larvae are found feeding on aphids and not chewing on the plant itself. If you find mites on your plants, observe them with a good hand lens. Predaceous mites appear more active than plant-feeding species. In comparison with pest mites, predaceous mites are often larger and do not occur in large groups. Consult publications listed in the References to learn more about the specific pests and their natural enemies in your gardens and landscapes. Take unfamiliar organisms you find to your local University of California (UC) Cooperative Extension office, UC Master Gardener Program, or agricultural commissioner office in your county for aid in identification. CONSERVATION: PROTECT NATURAL ENEMIES Preserve existing natural enemies by choosing cultural, mechanical, or selective chemical controls that do not harm beneficial species. Remember, only about 1% of all insects and mites are harmful. Most pests are attacked by multiple species of natural enemies (Table 1), and their conservation is the primary way to successfully use biological control. Judicious (e.g., selective, timing) pesticide use, ant control, and habitat manipulation are key conservation strategies. Ant Control and Honeydew Producers The Argentine ant and certain other ant species are considered pests primarily because they feed on honeydew produced by insects that suck phloem sap, such as aphids, mealybugs, soft scales, psyllids, and whiteflies. Ants protect honeydew producers from predators and parasites that might otherwise control them. Ants sometimes move these honeydew-producing insects from plant to plant (called “farming”). Where natural enemies are present, if ants are controlled, populations of many pests will gradually (over several generations of pests) be reduced as natural enemies become more abundant. Control methods include cultivating soil around ant nests, encircling trunks with ant barriers of sticky material, and applying insecticide baits near plants. See Pest Notes: Ants for more information. Mark Hoddle at UC Riverside is working on a gel formulation to attract ants selectively for their control: http://biocontrol.ucr.edu/hoddle/. Habitat Manipulation Plant a variety of species that flower at different times to provide natural enemies with nectar, pollen, and shelter throughout the growing season. The adult stage of many insects with predaceous larvae (such as green lacewings and syrphid flies) and many adult parasites feed only on pollen and nectar. Even if pests are abundant for the predaceous and parasitic stages, many beneficials will do poorly unless flowering and nectar-producing plants are available to supplement their diet. To retain predators and parasites, grow diverse plant species well adapted to the local conditions and that tolerate low populations of plant-feeding insects and mites so that some food is always available. Other cultural controls that can help natural enemies include reducing dust and properly fertilizing and irrigating. Dust can interfere with natural enemies and may cause outbreaks of pests such as spider mites. Reduce dust by planting ground covers and windbreaks and hosing off small plants that become excessively covered with dust. Avoid excess fertilization and irrigation, which can cause phloem-feeding pests, such as aphids, to reproduce more rapidly than natural enemies can provide control. REFERENCES Dreistadt, S.H., M.L. Flint, and J.K. Clark. 2004. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide. 2nd ed. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3359. Flint, M.L. and S.H. Dreistadt. 1998. Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control. Oakland: Univ. Calif. Div. Agric. Nat. Res. Publ. 3386. Rust, M.K. and D.-H. Choe. 2012. Pest Notes: Ants. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 7411.
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NATURAL ENEMIES |
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PESTS |
Lacewings |
Lady beetles |
Parasitic flies |
Parasitic wasps |
Predatory mites |
Other Groups and Examples |
aphids |
X |
X |
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X |
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entomopathogenic fungi, soldier beetles, syrphid fly larvae |
carpenterworm, clearwing moth larvae |
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|
|
X |
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entomopathogenic nematodes |
caterpillars (e.g., California oakworm) |
X |
|
X |
X |
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Bacillus thuringiensis, birds, entomopathogenic fungi and viruses, predaceous bugs and wasps,Trichogramma spp. (egg parasitic wasps), spiders |
cottony cushion scale |
|
X |
X |
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Cryptochaetum iceryae (parasitic fly), vedalia beetle |
elm leaf beetle |
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|
X |
X |
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Erynniopsis antennata (parasitic fly),Oomyzus (=Tetrastichus) spp. (parasitic wasps) |
eucalyptus longhorned borers |
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|
X |
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Avetianella longoi (egg parasitic wasp) |
eucalyptus redgum lerp psyllid |
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|
|
X |
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Psyllaephagus bliteus (parasitic wasp) |
giant whitefly |
X |
X |
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X |
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Encarsia hispida, Encarsia noyesi, Entedononecremnus krauteri, andIdioporus affinis (parasitic wasp), syrphid fly larvae |
glassy-winged sharpshooter |
X |
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X |
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assassin bugs, Gonatocerus spp. (egg parasitic wasps), spiders |
lace bugs |
X |
X |
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X |
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assassin bugs and pirate bugs, spiders |
mealybugs |
X |
X |
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X |
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mealybug destroyer lady beetle |
mosquitoes |
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Bacillus thuringiensis spp. israelensis, mosquito-eating fish |
psyllids |
X |
X |
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X |
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pirate bugs |
scales |
X |
X |
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X |
X |
Aphytis, Coccophagus, Encarsia, andMetaphycus spp. parasitic wasps |
slugs, snails |
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X |
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Rumina decollata (predatory snail), predaceous ground beetles, birds, snakes, toads, and other vertebrates |
spider mites |
X |
X |
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X |
bigeyed bugs and minute pirate bugs,Feltiella spp. (predatory cecidomyiid fly larvae), sixspotted thrips, Stethorus picipes (spider mite destroyer lady beetle), predatory mites |
thrips |
X |
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X |
X |
minute pirate bugs, predatory thrips |
weevils, root or soil-dwelling |
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X |
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Steinernema carpocapsae andHeterorhabditis bacteriophora(entomopathogenic nematodes) |
whiteflies |
X |
X |
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X |
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bigeyed bugs and minute pirate bugs,Cales, Encarsia, and Eretmocerus spp. parasitic wasps, spiders |
Predatory mite going after citrus red mite
/table>- Author: Ben Faber
Here are the top 10 blogs from Topics in Subtropics over the last 5 years. The two earliest and latest pertain to how you select products that will truly help you from amongst all those that are being promoted. Some of these have been around a long time, so that's why they are the most read. Do a Ctrl + click on the URL to read the post.
Title Author Date
A predatory mite
/table>- Author: Ben Faber
Silicon is currently under consideration for elevation to the status of a "plant beneficial substance by the Association of American Plant Food Control Officials (AAPFCO). Silicon has been shown in university and field studies to improve cell wall strength and structural integrity, improve drought and frost resistance, decrease lodging potential and boost the plant's natural pest and disease fighting systems. Silicon has also been shown to improve plant vigor and physiology by improving root mass and density, and increasing above ground plant biomass and crop yields.
Silicon (Si) is the most abundant element (27.2%) present in the earth's crust following oxygen (45.5%). Silicon is known for a number of important chemical and physical properties, i.e. semiconductor property that are used in various scientific and technical applications. In most soils near a neutral pH, the composition is a complex of iron, aluminum, oxygen and silicon. Silicon is one of the most important constituents of dust, which is carried by winds all over the world. Geologists know silicon as the rock quartz and the many silicate materials, such as opal. Formally, silica (SiO2) is a silicic acid (H4SiO4), which is water soluble and stable in highly dilute aqueous solutions. There are many forms that silicon can take in the natural environment, often complexed with water. Plants take up a form of silicic acid and in highly leached, low pH environments, much of the silicon may have been removed over time.
It appears that grains, such as wheat and especially rice have an absolute need of supplemental silicon to improve plant growth. Few non-grass plants have shown this need other than cucurbits apparently. Much of the improvement typically is for improved disease control and improved stature (prevention of lodging).
Many of the studies showing benefits of silicon amendment have occurred in low soil pH environments or in solution culture where it has been possible to create low silicon growing media. Several years ago, potassium silicate was being promoted as a fungistat for controlling Phytophthora root rot in avocado. A number of field and greenhouse trials were tried in California during the early 2000s to assay its effect. For whatever reason, the material showed no effect on the disease. Potassium and calcium silicates are liming materials, raising soil pH. The effect that was noticed in its use in other countries may simply have been a soil pH effect on either the avocado tree, the Phytophthora or both.
- Author: Ben Faber
TYPES OF NATURAL ENEMIES
Parasites, pathogens, and predators are the primary groups used in biological control of insects and mites (Table 1). Most parasites and pathogens, and many predators, are highly specialized and attack a limited number of closely related pest species. Learn how to recognize natural enemies by consulting resources such as the Natural Enemies Handbook and the Natural Enemies Gallery.
Parasites
A parasite is an organism that lives and feeds in or on a host. Insect parasites can develop on the inside or outside of the host's body. Often only the immature stage of the parasite feeds on the host. However, adult females of certain parasites (such as many wasps that attack scales and whiteflies) feed on and kill their hosts, providing an easily overlooked but important source of biological control in addition to the host mortality caused by parasitism.
Although the term “parasite” is used here, true parasites (e.g., fleas and ticks) do not typically kill their hosts. Species useful in biological control, and discussed here, kill their hosts; they are more precisely called “parasitoids.”
Most parasitic insects are either flies (Order Diptera) or wasps (Order Hymenoptera). Parasitic wasps occur in over three dozen Hymenoptera families. For example, Aphidiinae (a subfamily of Braconidae) attack aphids. Trichogrammatidae parasitize insect eggs. Aphelinidae, Encyrtidae, Eulophidae, and Ichneumonidae are other groups that parasitize insect pests. It's important to note that these tiny to medium-sized wasps are incapable of stinging people. The most common parasitic flies are the typically hairy Tachinidae. Adult tachinids often resemble house flies. Their larvae are maggots that feed inside the host.
Pathogens
Natural enemy pathogens are microorganisms including certain bacteria, fungi, nematodes, protozoa, and viruses that can infect and kill the host. Populations of some aphids, caterpillars, mites, and other invertebrates are sometimes drastically reduced by naturally occurring pathogens, usually under conditions such as prolonged high humidity or dense pest populations. In addition to a naturally occurring disease outbreak (epizootic), some beneficial pathogens are commercially available as biological or microbial pesticides. These include Bacillus thuringiensis or Bt, entomopathogenic nematodes, and granulosis viruses. Additionally, some microorganism by-products, such as avermectins and spinosyns are used in certain insecticides; but applying these products is not considered to be biological control.
Predators
Predators kill and feed on several to many individual prey during their lifetimes. Many species of amphibians, birds, mammals, and reptiles prey extensively on insects. Predatory beetles, flies, lacewings, true bugs (Order Hemiptera), and wasps feed on various pest insects or mites. Most spiders feed entirely on insects. Predatory mites that feed primarily on pest spider mites include Amblyseius spp., Neoseiulus spp., and the western predatory mite, Galendromus occidentalis.
AUGMENTATION
When resident natural enemies are insufficient, their populations can sometimes be increased (augmented) through the purchase and release of commercially available beneficial species. However, there has been relatively little research on releasing natural enemies in gardens and landscapes. Releases are unlikely to provide satisfactory pest control in most situations. Some marketed natural enemies are not effective. Many natural enemies are generalist predators and are cannibalistic and feed indiscriminately on pest and beneficial species, thereby reducing their effectiveness.
Only a few natural enemies can be effectively augmented in gardens and landscapes. For example, entomopathogenic nematodes can be applied to control certain tree-boring and lawn-feeding insects. Convergent lady beetles (Hippodamia convergens) purchased in bulk through mail order, stored in a refrigerator, and released in very large numbers at intervals can temporarily control aphids; however, lady beetles purchased through retail outlets are unlikely to be sufficient in numbers and quality to provide control.
Successful augmentation generally requires advanced planning, biological expertise, careful monitoring, optimal release timing, patience, and situations where certain levels of pests and damage can be tolerated. Situations where pests or damage are already abundant are not good opportunities for augmentation.
A classic example of poor timing for augmentative release of predatory mites for control of broad mite in coastal lemon or persea mite in avocado is right now. Pest populations for the most part have soared and releasing predatory mites is little help. Predatory mites need to be releases into a small growing population, so in both of these cases it would have been better to start small, frequent releases early and throughout the spring to knock their populations back.
Adult predatory mite, Euseius tularensis, and citrus red mite.
/h4>- Author: Ben Faber
Field topworking avocados and citrus can be a prolonged process that can take two years of maintenance before the trees are productive. Often, it's easier and cheaper to just start off with a new tree. Thegrafted tree needs to be pruned back and buds or bud sticks need to be inserted into the old trunk. Birds love to sit on these new perching spots, and can often damage the bud stick, so they need to be protected with some type of covering like a paper bag. The latent buds in the trunk need to be constantly removed to prevent the old scion from outgrowing the new one.
A nurse branch also needs to be maintained so that there is a steady flow of transpired water to cool the trunk. Bud sticks are leafless and when the tree is headed back to graft, the tree no longer has the leaf area to pump water through the trunk. The trunk can heat up and result in sun burn damage. This damage may not appear for a year or so after the incident has occurred. It normally will show up on the south or southwest side of the tree, which catches the afternoon sun. The damage may be so severe that the tree dies, or the tree may begin a healing process as with other wounds and start growing callus tissue along the margins of the sun burn damage. If the damage is nor too extensive, the callus growth can eventually cover over the damage with new bark. If the grafted tree has left some structural branches, damage can show up on upper surfaces of branches, as well as those sides facing the afternoon sun.
To avoid sunburn damage, retain the nurse limb for about a year after grafting and whitewash or cover the trunk with a protective paper. Managing irrigation is important, as well. If grafted trees are interplanted with trees with more mature canopies, the grafted trees should be on a separate irrigation system and schedule. This is to avoid water stress which can enhance sun burn.
Sun burn can happen to any grafted tree, especially those with thin bark, like citrus and avocado. Any time a portion of the bark is exposed to sun that has previously been in the shade, can also set up the tree for sun burn. So excessive pruning going into summer months can also cause significant sun burn.
Sunken area of trunk, showing sun burn damage and callus growth starting to grow along margins of damage. Grafted citrus with nurse limbs and whitewash.