Root Aphids, Fungus Gnats, and Spider Mites: How to Eliminate These Cannabis Pests
Root Aphids, Fungus Gnats, and Spider Mites: Eliminate These Marijuana Pests Completely
- 1 Root Aphids, Fungus Gnats, and Spider Mites: Eliminate These Marijuana Pests Completely
- 2 Root Aphids
- 3 Fungus Gnats
- 4 Spider Mites
- 5 Final Tips on Preventing and Removing Pests from Your Cannabis Garden
- 6 Root Aphid Info: Learn About Killing Root Aphids
- 7 Root Aphid Info – What are Root Aphids?
- 8 How to Get Rid of Root Aphids
- 9 Root Aphid
- 10 Aphids on Greenhouse Crops
- 11 Identification
- 12 Damage
- 13 Biology and Descriptions
- 14 Detection and Monitoring
- 15 Preventive Strategies
- 16 Aphid Predators
- 17 Aphid Parasitoids
- 18 Treatments
Marijuana has been grown outdoors for thousands of years. During that time, cultivators have faced dozens of threats in the form of disease and pests. While humans don’t usually eat raw cannabis, it seems to fit the palate of many bugs, insects, and other animals. If you are unable to spot an infestation in time, there’s a chance that your entire crop will be ruined.
A simple and effective way to deter and kill pests is to use chemical insecticides. However, these products can damage the crop too, and ruin the taste. Think about it for a second. Would you like to smoke weed that has been heavily sprayed with commercial-grade chemicals?
In this guide, we provide you with natural methods of removing three of the most common cannabis pests. These are: Root aphids, fungus gnats, and spider mites.
Rhopalosiphum rufiabdominale, the Rice Root Aphid, is a soft-bodied insect that infests the foliage and root systems of its host plants. These bugs can range from reddish-brown to bright green in coloration.
If a plant is heavily infested, the leaves become yellow and begin to wilt. Aphids also produce a large amount of honeydew, a sugary liquid waste. The honeydew emitted from the aphid’s anus often attracts sooty mold, which accumulates on leaves and branches, turning them black.
Your cannabis garden can become infested when a winged aphid lands and lays eggs. It only takes a handful of aphids to cause an infestation. The eggs quickly hatch to produce ‘nymphs’ which begin feeding on your crop. These young aphids mature in 7-10 days, and when they shed their skin, they leave behind silver-colored exoskeletons.
Removing Root Aphids
A root aphid colony can get out of control within a couple of weeks, so you have to act fast. Examine your plants at least once a week and look beneath new leaves for clusters. If you spot some, it is a sign that several colonies are well-established in your garden. Here is a quick list of things to do once you spot an infestation of aphids:
- Insecticidal soaps: These soaps suffocate or dissolve the exoskeleton of aphids. As soaps don’t stay on plantsfor long, we recommend several follow-up applications.
- Neem oil: Azadirachtin, the active ingredient in Neem oil, is effective against most pests. The chemical can, however, be damaging to buds (and is potentially harmful to humans), so spray carefully.
- Spinosad: They kill aphids on contact, but aren’t very strong. As a result, you need to use them numerous times.
- Introduce predators (like ladybugs and lacewing larvae): You can introduce these insects to your garden for the most natural of solutions. One issue with ladybugs is that they tend to fly away after a couple of days.
- Remove ants: Ants farm aphids to collect their honeydew. As a result, you have to get rid of ants in your garden because they keep the aphid population high!
These pests look similar to tiny mosquitoes and are just 2-4mm long. They produce larvae up to 6mm long, which live in your growing medium. The problem with these larvae is that they damage the roots of the marijuana plant. A severe infestation reduces a plant’s strength and makes it susceptible to diseases such as root rot.
Fungus gnats thrive in moist conditions, which means they love it when growers overwater their soil. After fungus grows or overwatered matter decays into the soil, gnats lay their eggs in the wet soil’s top layer.
How to Remove Fungus Gnats
To reduce the risk of a fungus gnat infestation, make sure the humidity in your grow room is low. Signs of gnats include:
- Tiny black bugs crawling on the soil or flying around the plants.
- White/translucent larvae with black heads on the soil.
If left untreated, fungus gnats can result in a nutrient deficiency, a halt in plant growth, and reduced yields. If you find gnats, here’s how to get rid of them:
- Yellow sticky cards: These are special traps designed for gnats, which love the color yellow. The glue traps the gnats and severely reduces their numbers. You can monitor the cards to see if an infestation is being managed. If your cards become less covered in gnats, it is a sign that the population has been severely reduced.
- Use a fan: Place a fan in a position where it blows air out the top of the growing medium. It helps dry out the top layer and stops gnats laying more eggs.
- Dry out the soil: Avoid watering your plants for a few days to dry out the soil. This should kill a large percentage of larvae. Once the first few inches have become dry, the next step is to add a treatment.
- Kill the larvae: Spray the top layer of soil with neem oil. Make sure you don’t use the oil less than a week before harvest, and that it doesn’t touch the buds. Alternatively, sprinkle food-grade diatomaceous earth overexposed parts of the growing medium.
If there are still larvae remaining after your treatment, it’s time to switch things up because they are resisting treatment. Products such as Bacillus thuringiensis (a species of bacteria), SM-90, and Essentria IC3 Insecticide should do the job. That is if you don’t mind going down the chemical route. After a fungus gnat infestation, water your crop less often and keep using your sticky cards.
These mites are the most common cannabis pest. As they are only 0.4mm in size, they are tough to spot with the naked eye. You will probably need a magnifying glass to spot these insects.
As small as they are, spider mites can ruin a crop. They have sharp mouths that pierce the individual plant cells, removing the contents.
You may spot orange, white, or yellow specks on your plant’s leaves and wonder what they are. We’re afraid to say; they are probably spider mites! Their diminutive nature means it can take days or even weeks to spot them. Here are a few reasons why growers dread spider mites:
- Spider mites easily re-infest a crop if they are not entirely eradicated, including ones in nearby areas.
- Spider mites produce silk webbing, which covers buds and leaves. Even if you get rid of the mites, their webs can still ruin the quality of your crop.
Spider mites become resistant to different methods of eradication.
Removing Spider Mites
Even when you destroy a spider mite infestation, it can quickly repopulate. Early detection is vitally important. You can only do so by thoroughly inspecting both sides of the leaves of your plants. Once you spot them, you must assume your garden is infested for the duration of the marijuana plant’s growth cycle. Here is how to get rid of spider mites once you have found them:
- Because they are exotherms, consider increasing the temperature above 30 degrees Celsius. This is because spider mites cannot regulate their body temperature in excessive heat.
- Spinosad products such as Mighty Wash and Azamax work well when sprayed directly on the roots.
- Stethorus punctillum is the Spider Mite ladybeetle, and it feeds on spider mites voraciously. Phytoseiulus persimilis is another predatory mite that evolved specifically to feed on spider mites as well!
- Be sure to rotate treatments as part of an integrated pest management approach.
- After your initial treatment, follow up in 2-3 days with a different method. Let’s say you used neem oil. This time, try the DIY alcohol spray remedy. You will need to repeat the treatment at least once more. Remember, it must be different from the first two treatments.
Prevent spider mites by carefully checking new plants and clones by ensuring good airflow and maintaining a comfortable room temperature. It is also worth sprinkling diatomaceous earth on top of your soil and around the grow room.
Final Tips on Preventing and Removing Pests from Your Cannabis Garden
Growing cannabis can be challenging, and there is nothing worse than having your hard work ruined by unwelcome pests. Prevention is better than cure. If you find root aphids, spider mites, or fungus gnats damaging your crop, you have to act fast. Otherwise, you risk the ruination of your crop. Here are some quick tips to kill pests and keep them at bay:
- Don’t use anything other than sterilized soil or fertilizer. To sterilize the soil, put it in the oven at a temperature of 160-180 degrees Fahrenheit for 30-45 minutes.
- Consider growing ‘companion’ plants such as basil, garlic, mint, or marigolds. Leaf eating pests tend to hate the smell of these plants and steer clear.
- For mammalian pests, purchase the urine of their enemies. Some stores specialize in these products.
- Make sure all of your cannabis growing equipment is sterile. You must wash your hands before touching plants and remove any debris you find as soon as possible. A clean grow room is a safe one!
- Build a fence around your cannabis garden if it is outside. Animals carry a bevy of pathogens and bugs, so keeping them away from your crop is half the battle.
- If you are growing weed indoors, seal your grow room. Spray foam or caulk is useful to fill in gaps, and also seals windows and doors effectively.
- Change your clothes before entering your grow room if you were outside. Otherwise, you run the risk of bringing in pests.
Root Aphid Info: Learn About Killing Root Aphids
Aphids are an extremely common pest in gardens, greenhouses, and even in potted houseplants. Theses insects live and feed on various types of plants, gradually causing their health to decline. Though aphids are most commonly found the leaves and stems, another type of aphid can be found below the soil surface. These root aphids attack the root system of plants and can cause quite a bit of trouble for growers. Read on to learn about root aphid treatment.
Root Aphid Info – What are Root Aphids?
The physical appearance of root aphids is very similar to that of other aphids. Most often, they can be identified by their tiny and almost translucent bodies. These pests use their mouths to feed on the roots of the plants, causing the plants to begin turning yellow.
While plants begin to yellow for many reasons, growers are able to further investigate by examining the base of the plant. Often, colonies of root aphids will establish at or just below the level of the soil. Upon removal of the infected plant, gardeners are likely to notice small clumps of a white wax-like material throughout the root system.
How to Get Rid of Root Aphids
Like many issues in the garden, one of the best methods by which to avoid root aphids is through prevention. General garden routines, such as weed control and even watering, can greatly reduce the likelihood that root aphids are able to invade. Turning and working the soil in the fall will also help to prevent the overwintering of this pest.
Comparatively speaking, root aphids tend not to spread in the garden. However, these aphids do spread to other plants through irrigation run off and may be “washed” from one planting to another. Root aphids may also be transported from one container to another via transplants or rooted cuttings.
Once established, the process of killing root aphids may become somewhat difficult. Though some chemical treatments are an option (in potted plantings), it is often not realistic as a choice to thoroughly drench the soil. If choosing a chemical control, always make certain to carefully read labels and instructions for safe usage.
Other root aphid treatments, such as predatory nematodes,may also be marginally effective. In most cases, however, the reproduction rate of the aphids will outpace the control. Once established, many growers choose to discard and dispose of the infected plants.
How to spot and organically control root aphids. A growing pest of greenhouse and garden plants.
Root aphids — aphids that stay at or above the soil line — are from the family Phylloxera, a near-cousin of aphids. They are an escalating problem, especially among indoor growers, and spreading through parts of the country where they haven’t been seen before. They’re hard to spot and unlike small colonies of green and other aphids found on stems and leaves, root aphids are more likely to get out of control. They can multiply quickly, unseen, and sap enough vigor from your plants to kill them.
Because they’re small — about the size of a mite — and often colored to blend with roots and soil, Phylloxera is hard to spot. Often, growers will see the white, waxy material that the aphids secrete, a chalkier type of the honeydew secreted by other aphids. Their bodies are more pear-shaped than oval as are mealybugs. They’re about the same size or slightly smaller than stem-and-leaf aphids with shorter legs and antennae. They come in a variety of colors, including pink, but are mostly white and brown. They’re commonly confused with the larger mealy bugs, because of the white substance they spread. In their winged stage, they can be confused with fungus gnats. Like other aphids, they have small cornicals or “tail pipes” at the end of their abdomen which also distinguishes them from mealybugs.
Because of their size and below-soil habitat they can go unnoticed, even through one or more grow cycles. They can be spotted attached to the sides of grow cups when growers take the trouble to look. Root aphid damage is often mistaken for other problems, especially nutrient deficiencies. Plants that appear to be suffering from magnesium or iron deficiency should be checked carefully for root aphids.
In outdoor gardens, root aphids may be accompanied by ants. Once established in soil or hydroponic systems, root aphids are difficult to completely remove.
Root aphids are surprisingly adaptable and their lifecycle can vary tremendously. They reproduce asexually during the growing season. Eggs over-winter in soil or, in warm seasons, are attached to leaves and stems above the root line where they hatch and fall to the ground. The aphid bores into the root, creating scars that leave plants vulnerable to mildew and disease. As infestations increase, “crawlers” will move up the stem to feed. Once a plant is nearly destroyed, some root aphids will develop wings that enable them to seek new plants to attack. In the fall, winged aphids, now male and female, mate in brush and trees and produce more eggs. Ants are known to carry aphids from exhausted plants to un-colonized ones.
Damage from root aphids is usually visible in a lack of vigor from plants. Withered, curled, and yellow leaves, similar to signs of nutrient deficiencies, appear and plants fail to reach the size of uninfested plants. Fruits and blossoms on aphid infested plants will be small, stunted, and generally less desirable as nutrition is siphoned away from them.
Attacks from root aphids can leave plants vulnerable to root rot, mildew, and disease.
Visible symptoms, like yellowing leaves, often lead growers to consider adding certain minerals, usually magnesium, to their nutrient mixture, often with no result.
In addition to greenhouse and garden perennials, various types of root aphids attack rice crops, the roots of a variety of trees including fir, walnut, and hickory. Root aphids can also cause problems for perennial herbs, including those grown in pots.
Root Aphid Control
Detecting the first signs of root aphids, especially when growing indoors, is crucial to saving your plants vegetating and fruiting abilities. At a certain point, usually sooner rather than later, affected plants and containers should be removed from the grow space completely and destroyed.
Waiting for fruits or flowers to mature in an attempt to save something of a crop is not advised. This only gives root aphids a chance to inoculate themselves into your entire grow area. It’s best to start over, sanitizing all containers and growing equipment that’s been used. Indoor growers should clean their entire grow space.
- Avoid introducing commercial grade soils, including bagged composts, that may contain aphids and their eggs. This is probably the most usual way that aphids have been spread to gardens throughout the country. Buy soil and compost from a reliable, local source, make your own.
- Attract birds who will pick aphid eggs from trees and the ground.
- Several types of parasitic wasps attack aphid eggs. Ladybugs will also predate aphids they find on the surface but not those burrowed in the soil.
- Introduce beneficial nematodes (link below) into soil at the first sign of root aphid infestation or, better, in anticipation of them. Nematodes will attack a number of soil-borne pests yet are harmless to earthworms, pets, and humans. Make sure the soil is moist when applying nematodes.
- Use AzaMax as a preventive treatment to keep aphids from feeding on roots. Because it’s slow acting, AzaMax is not a good choice for treating infestations, but can be effective, over time, for minor infestations.
- Neem oil can help stop aphid infestations from growing, especially as crawlers move up stems.
- Do not use insecticidal soaps to control soil-borne aphids. While they will kill crawlers moving up plant stems, they will do little to stop aphids in the soil and may harm your plants’ roots.
- Pyrethrum-based sprays can be effective if used early enough in the infestation. Water lightly after applying to disperse this chrysanthemum-based botanical into the soil. Reapply every two weeks (eggs in soil may continue hatching) until plants regain vigor and all aphid sign disappears.
- When removing infected plants, be careful not to drop soil or spread aphids into other parts of your garden. Put plants, roots and all, in a bucket, and take away with minimum disturbance. Removal, in conjunction with preventive spraying, may be your most effective form of control.
- Avoid importing soil or other growing medium of unknown origin into your growing space. Many nursery plants, especially those from large, commercial growers, have been found to carry root aphids and their eggs into green houses.
- Use yellow sticky traps across indoor grow spaces to discover signs of root aphids on the move.
- Pay careful attention to your plants. Roots that are visible in grow cups and other hydroponic methods should be periodically inspected. The small, usually white mite stage may be noticeable attached to the sides of grow cups, tanks and trays.
- Beneficial nematodes introduced to hydroponic solutions at the first sign of infestation may slow the spread of root aphids.
- With lights off, saturate the growing medium with a solution of Nuke Em (1 oz/ 31 oz water). Slowly pour near the plant stem into the soil and let stand for at least 1 hour — longer contact times are best. Rinse the media before turning lights back on.
- BotaniGard ES is a highly effective biological insecticide containing Beauveria bassiana, an entomopathogenic fungus that attacks a long-list of troublesome crop pests – even resistant strains! Weekly applications can prevent insect population explosions and provide protection equal to or better than conventional chemical pesticides.
- When treating aphids in various indoor growing mediums, complete and thorough coverage of infected areas is critical to control. Submerge infested grow cups and root balls completely in a pyrethrum concentrate for a half-minute or more, gently swirling roots and medium to insure complete saturation.
- Remove badly infested plants. No orchid, no herb or flowering perennial is worth risking your other plants and the health of your entire grow space in an attempt to wait out harvest on an affected plant.
Dealing with root aphids, indoors or out, is an evolving and ever-changing set of practices. Don’t be tempted to use harsh, chemical treatments if you already have an infestation. A University of Maryland Cooperative Extension study conducted inside two greenhouses with root aphids on gallardia, aster and boltonia perennials found applications of Talstar (bifenthrin) and Marathon (imidacloprid) applied as a soil drench gave poor results. Keeping aphids out of your garden or grow space in the first place is the most effective practice. And with this problem spreading, it is becoming harder and harder to do.
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Aphids on Greenhouse Crops
About 30 different species of aphids can be found in greenhouses, depending on the crop. Aphids are generally less than 1/8 inch long, soft-bodied insects with long legs, long antennae and a pair of tube-like structures call cornicles projecting from the posterior end. Aphids may occur in large colonies on new growth, the base of buds, or the undersides of mature leaves. There are many species of aphids which range in color from greenish-yellow to very dark green, dark brown to black and even pink. Some have wings, which are transparent with very few veins and are held vertically over the body when not in use.
Resources for Aphid Identification:
- Fact Sheet: Common Greenhouse Aphids, C.E. Frank & M. Skinner, University of Vermont, Entomology Research Laboratory 2013.
- Powerpoint: Tips on Scouting Vegetable Bedding Plants, Pest and Disease ID. Leanne Pundt, UConn Extension.
- Taxonomic Training Videos: Aphids under the Microscope, USDA-APHIS-PPQ.
- BugGuide.Net, Iowa State University.
Aphids are sucking insects that remove plant sap and cause distorted growth. Aphids void waste as a sugar-rich liquid called honeydew, which attracts ants and promotes growth of black-colored fungi called sooty mold. In addition, some aphids also transmit viral plant diseases.
Biology and Descriptions
Many aphid species reproduce sexually only under specific environmental conditions, often those associated with the onset of winter. During spring and summer, reproduction is asexual, with unmated adult female aphids giving birth directly to live young, all of which are female. This process, coupled with the high funcundity of many aphids (some species giving birth to as many as 60 to 100 young nymphs over a period of 20 to 30 days) and the quick maturation of aphids (as little as 7-10 days between generations) allows populations of aphids to increase quickly. At high densities, winged females may appear in aphid colonies. These winged individuals then move to new, less crowded host plants. Outdoors, many aphid species pass the winter in the egg stage. In greenhouses, aphids may continue to reproduce asexually, via live birth, indefinitely. Many species are found on only one, or at most, a few host plants. The common aphid species that are encountered in greenhouses include green peach aphid (Myzus persicae), melon/cotton aphid (Aphis gossypii), foxglove aphid (Aulacorthum solani), and root aphid (Pemphigus spp.).
The green peach aphid is mentioned most often because of its worldwide distribution, very wide host plant range (more than 400 host plants), virus disease transmission (vectors more than 150 virus strains) and difficulty of control.
Photo of Aphids
Here are descriptions of the common aphid species encountered in greenhouses:
Green peach aphid: This aphid species can be distinguished from the melon/cotton aphid by the length and color of the cornicles (the tube-like protrusions extending from the end of the abdomen). Green peach aphids have long (approximately the length of the body) cornicles and only the tips are black. In addition, the head has a distinct indentation at the base of the antennae.
Melon/cotton aphid: The cornicles on melon/cotton aphid are short (approximately 1/3? or 8.0 mm, the width of the body) and vary in color from light yellow to very dark green (making them appear black). The antennae are typically shorter than the body. Melon/cotton aphids do not have a distinct indentation at the base of the antennae like that of the green peach aphid.
Foxglove aphid: Foxglove aphids have green flecks located at the base of their cornicles. In addition, they have black markings on their leg joints and antennae. Foxglove aphids tend to fall off plants when disturbed and they can cause severe leaf distortion, more so than the green peach and melon/cotton aphid.
Root aphid: The primary root aphid (Pemphigus species) overwinters as eggs and infests plants in the spring and fall. Root aphids may be misidentified as mealybugs because they are covered with white wax although they are smaller than mealybugs. Root aphids have reduced cornicles that resemble rings, which are located on the end of the abdomen. These cornicles can be seen when magnified.
Detection and Monitoring
Sanitation is an important part of aphid control. To prevent the introduction of new aphid species into your greenhouse, carefully inspect all new plants before placing them in the growing areas. Eliminating all weeds in or near the greenhouse can be useful because it will help suppress potential reservoirs from which aphids might enter the crop. Winged aphids can easily move from the outdoors into greenhouses through open vents and establish on crop plants. To detect aphids early, several plants on each bench throughout the greenhouse should be checked on a weekly basis, particularly those species of plants that most often host aphids. Inspect the young growing tips, stems and buds of aphid prone plants and note which cultivars are the most susceptible. Signs of an aphid infestation include the presence of white cast (molted) skins, honeydew, and black sooty mold fungi. Yellow sticky cards can capture winged aphids that have entered the greenhouse from outdoors, particularly during spring and early summer. Since most aphids are wingless, the use of yellow sticky cards is not a reliable indicator of the population levels of aphids within the greenhouse. Direct visual inspection of the crop is required.
Young aphids of some species may reside between scales of leaf buds or in flowers. This reduces their contact with nonsystemic pesticides and repeated applications may be needed for control. Pest control materials (insecticides) with contact, translaminar, or systemic activity can be used to control aphids. Translaminar means that after application the material penetrates leaf tissues and forms a reservoir of active ingredient within the leaf. This provides extended residual activity even after spray residues dissipate. It is important to rotate insecticides with different modes of action to delay the onset of resistance. Insecticide applications must be initiated early in the cropping cycle, when plants are small.
Coverage of plant parts with wettable or soluble powder formulations may be improved by the use of surfactants. In some instances, insecticidal soaps and/or horticultural oils may provide control of aphids, particularly when populations are low. However, since these insecticides kill exclusively by contact and have minimal residual activity, thorough coverage is essential. Insect growth regulators and pyrethroid-based insecticides may also provide control of aphids.
Systemic insecticides, including the neonicotinoid-based insecticides imidacloprid (Marathon®), thiamethoxam (Flagship®), acetamiprid (TriStar®), dinotefuran (Safari®), and clothianidin (Celero®), effectively control aphids for extended periods of time when applied early in the cropping cycle. The same is true of the selective feeding blockers, pymetrozine (Endeavor®) and flonicamid (Aria®). A number of insecticides have both translaminar and systemic properties. See the current New England Recommendation guide for more information.
- Practice good sanitation, such as removing discarded plant material and eliminating weeds around plant production areas. Weed host plants often serve as reservoirs for migrating or ant carried aphids.
- Avoid excessive amounts of nitrogen fertilizer which promote soft plant tissue. New, soft plant tissue promote higher aphid populations.
- Use physical control methods if appropriate. These include screens or other barriers. Screens are especially important in stock plant production areas to reduce the threat of virus transmission.
- Thoroughly inspect all incoming plant material and spot treat if necessary.
Biological Control Photos
Aphids have many natural enemies and several groups have been studied as potential biological control agents for release in greenhouse crops.
Aphids are susceptible to many natural enemies, both predators and parasitoids, which may serve as effective biological control agents in greenhouses. Aphid predators include ladybird beetles, lacewings, and predatory midges. In general, predators are not as effective in maintaining aphid populations at acceptably low populations, with the possible exception of the predatory midge, Aphidoletes aphidimyza. However, the predatory midge is not effective during short-day conditions.
It is important to realize that not all of the commercially available natural enemies reduce aphid populations to non-damaging levels. This is especially true when aphid numbers are abundant due to their rapid rate of development and reproduction. If high aphid populations are present in localized hot spots within the greenhouse or present on only a few plants, then apply an alternative pest control material. The use of alternative pest control materials may not disrupt already established biological control programs for aphids. Furthermore, if aphids are abundant and widespread, scattered throughout the greenhouse, then it will be essential to apply an alternative pest control material in order to reduce the population before releasing any natural enemies. In general, alternative pest control materials do not leave toxic residues that negatively affect aphid parasitoids and/or predators.
Below are descriptions of several commercially available aphid predators:
Ladybird beetles: The convergent ladybird beetle, Hippodamia convergens, and the two-spotted ladybird beetle, Adalia bipunctata, are commercially available from most biological control suppliers. Some greenhouse growers have been known to collect the multicolored Asian ladybird beetle, Harmonia axyridis, from homes to release into greenhouses. Both the larval and adult stages of ladybird beetles feed on aphids. However, they may not distinguish between parasitized and nonparasitized aphids. Adult beetles feed on pollen, fungi, and nectar in the absence of prey. Ladybird beetles are generalist predators and, in addition to aphids, feed on thrips, whiteflies, mealybugs, and scales. Because ladybird beetle adults can fly, they are difficult to establish in greenhouses. If used, it is recommended to release ladybird beetle adults in the evening, near aphid colonies. Repeat applications may be needed. When scouting the crop, look for aphids that have been fed upon and ladybird beetle adults, larvae, and/or eggs. Eggs are typically bright yellow and are laid in clusters near aphid colonies.
Note about adult Hippodamia convergens (Convergent lady beetle)
When just starting out using biocontrol agents, many growers first think about using the well known and familiar «ladybug» (Hippodamia convergens) for aphid control. Ladybird beetles are relatively inexpensive and can be stored in the fridge. However, there are some concerns with using adult ladybeetles to control aphids. Wild collected ladybeetles for sale are field collected from mountainous areas of the west coast states where the beetles migrate and aggregate in large masses. Beetles are highly dispersive and once released in greenhouses, most will leave, providing little or no control.
Another concern is that harvested lady beetles may have been parasitized by a small wasp that develops as an internal parasite and kills them. And finally, Microsporidia, a disease of ladybugs, has also been detected in some shipments.
For more information see the article: Buying Ladybugs, Why Mother Nature Wouldn’t Approve by Suzanne Wainwright-Evans
Green lacewing: The green lacewing, Chrysoperla rufilabris, is adapted to the environmental conditions typically present in greenhouses. Adults are usually active at night and feed on nectar, pollen, and honeydew. Green lacewing larvae (referred to as ‘aphid lions’) feed on many aphid species as well as mites and whiteflies. The larvae, which are cannibalistic, must be distributed over a wide area throughout the production facility. Larvae may survive better than eggs. You should observe a reduction in the aphid population after approximately two weeks. Repeat applications are typically required, and control may be hampered if low aphid populations are present. Scouting for green lacewings is difficult because the larvae tend to hide within the plant canopy during the day. Examine leaf undersides for the presence of eggs laid on extended stalks.
Predatory midge: The predatory midge, Aphidoletes aphidimyza, feeds on over 60 aphid species. The midge is nocturnal (active at night), and prefers to reside in dark, humid areas near the lower plant canopy. Only the larval stage is predacious. Adults feed primarily on pollen and honeydew. The bright orange larvae kill aphids by biting their knee joints, injecting a paralyzing toxin and then withdrawing the internal body fluids. Aphidoletes aphidimyza is typically sold as pupae. Adults that emerge from the pupae lay eggs near aphid colonies. Larvae descend to the ground (below greenhouse benches) to pupate, so this predator may be less efficacious in greenhouse facilities with concrete floors. Aphidoletes aphidimyza is most effective during the summer because exposure to short days and low temperatures during winter induces diapause, which is a resting stage. Initiate releases early in the morning or evening near aphid colonies. Greenhouse temperatures should be 60-80F (15-26C), with 50-85% relative humidity. Aphidoletes aphidimyza may be used preventively in combination with aphid parasitoids. When scouting, look for fed-upon aphids, which may appear shriveled and brown or black. The adults are rarely observed since they are active at night.
In general, parasitoids are more effective than predators in reducing aphid populations, although parasitoids may fail to provide acceptable control under warm conditions or at times when aphid populations tend to increase rapidly. Four parasitoids are commercially available. Aphid parasitoids are host-specific in terms of the aphid species they attack. For example, Aphidius ervi attacks foxglove aphid, while Aphidius colemani attacks both green peach and melon aphids. Mixtures of different parasitoid species are commercially available and should be used when multiple aphid species are present. Parasitoids are shipped either as adults or ‘aphid mummies’ from which parasitoid adults soon emerge. To increase the parasitoids’ effectiveness, place small groups of the aphid mummies in cups near aphid colonies. Do not let these aphid mummies get wet. Release rates may vary depending on the parasitoid species. Containers often contain approximately 250 aphid mummies, which can treat 5,000 ft2 at the high release rate or 25,000 ft2 at the low release rate.
Greenhouse temperatures should be 65-77F (18-25C), with 70-85% relative humidity. Aphid parasitoids must be applied preventively to suppress aphid populations. They are less effective when aphid populations are high and already causing plant damage. Release parasitoids on a regular basis to sustain their populations during the growing season. Remove yellow sticky cards before releasing parasitoids, as sticky cards attract and capture parasitoids. When scouting, look for aphid mummies that have circular holes on one end. These are the exit holes created by adult parasitoids during emergence. Aphid parasitoids are sensitive to pest control materials. For example, direct sprays and one-day old residues of kinoprene (Enstar II®) are harmful to A. colemani . Direct applications of spinosad (Conserve®) are also toxic to A. colemani.
Release parasitoids preventively on crops you know are susceptible to aphids, so that the parasitoids will be present when aphids are first noticed. Also, identify aphids to species before ordering parasitoids, since parasitoids are selective in the aphid species they attack. For example, release Aphidius colmani for green peach aphid, and Aphidius ervi or Aphelinus abdominalis for foxglove or potato aphid. Some biological control suppliers sell mixtures of parasitoid species, which may be useful when several aphid species are present in the greenhouse simultaneously. Banker plant systems may be useful in controlling aphids and reducing the costs associated with applying pest control materials. Banker plants support colonies of aphids that are not greenhouse crop pests, along with parasitoids. Information on banker plants is available at:http://negreenhouseupdate.info/ (type in banker plant in the search tool for details).
Also see the fact sheet: Aphid Banker Plant System for Greenhouse IPM, Step by Step (from UVM and Biobest).
If aphids are already abundant then you must reduce their numbers before releasing natural enemies. You can reduce aphid populations by applying the pest control material pymetrozine (Endeavor®), which kills insects with piercing-sucking mouthparts, including aphids. Endeavor® has been demonstrated to be compatible with aphid and whitefly parasitoids, and predatory mites used to control thrips and spider mites. Do not attempt to suppress high aphid populations with predators, as this is typically not effective.
Entomopathogenic fungus: The entomopathogenic fungus, Beauveria bassiana, is commercially available for use against aphids. However, because aphids have high reproductive rates and molt rapidly, especially during the summer, repeat applications are typically required. Beauveria bassiana is most effective when aphid populations are low. This fungus may not be compatible with the convergent ladybird beetle (Hippodamia convergens) depending on the concentration of spores applied.
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