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Several of these were on my potato plants in Washington state, USA. This one about 7mm in length, some were a bit larger. They were moving in an inchworm-like fashion, but only by touch - I don't think they have eyes.
This specimen was photographed after placing in isopropyl alcohol, which changed the color (it was almost white while alive) and the shape somewhat.
One notorious pest of potato plants are cutworms. Unfortunately due to the the discoloration of the species I am not able to identify for sure which species of cutworm it is.
Cutworms attack a wide host of plants (more info here). According to that same website, the main ways to avoid the damage these larvae can cause are to:
Remove all plant residue from soil after harvest or at least two weeks before planting…
… plastic or foil collars fitted around plant stems to cover the bottom 3 inches above the soil line and extending a couple of inches into the soil can prevent larvae severing plants; hand-pick larvae after dark; spread diatomaceous earth around the base of the plants (this creates a sharp barrier that will cut the insects if they try and crawl over it); apply appropriate insecticides to infested areas of garden or field if not growing organically
These larvae come from a large variety of insects so don't associate them too quickly with one insect or another (many websites associate them with moths but that is not always necessarily accurate).
Here's a source that elaborates a bit more on how to treat them plus another source for how to use pesticides in a garden safely (if no other option is convenient).
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Potatoes can be attacked from the time seed pieces go into the ground until they are harvested. Insects can feed on tubers, seed pieces, leaves, and stems from planting to harvest.
COLORADO POTATO BEETLE
The most devastating pest of potato in Indiana is the Colorado potato beetle (CPB). The adult is a yellow, ovalshaped beetle about 1/4 to 1/3 inch long with 10 black stripes on its wing covers. Larvae are bright pink to red with black heads, and older larvae have two rows of black dots on the sides of their bodies.
Colorado potato beetle (top) larva and (bottom) adult
(Photo Credit: J. Obermeyer)
The adult overwinters about 6-10 inches below the soil surface, usually outside the field where it fed as a larva. CPB move to fence rows, waterways, etc. at field edges to burrow into the soil and overwinter. In early spring, when soils are warm enough to plant potatoes, CPB emerge and begin searching for a suitable host plant. When they find one, they immediately begin to feed. CPB will feed on any plant in the potato family, such as tomato, potato, pepper, eggplant, tobacco, and weeds, such as buffalo bur and nightshade, but they prefer potato.
CPB adults mate, and each female beetle lays groups of 10-20 eggs (a total of several hundred), usually on the underside of lower leaves. Eggs hatch in 4-10 days, depending on temperature, and larvae begin to feed on tender young foliage immediately. First and second instars do not consume much leaf tissue because of their size. Third and fourth instars cause the majority of defoliation and tend to feed on older leaf tissue. Larvae have a habit of feeding on leaves in the top portion of the plant. After 2-3 weeks of feeding, larvae drop from the plant, burrow into the soil, and pupate. Adults then emerge from the soil 2-3 weeks later. These adults will also feed, mate, and lay eggs. In late summer, the second generation larvae drop, burrow into the soil and pupate. These adults will emerge, feed for a few days, and then burrow into the soil for the winter.
Although both adults and larvae feed on the leaves of potato and related plants (tomato, eggplant), the most damage is caused by the third and fourth instar larvae. These larvae are large (1/2 inch) and can defoliate a plant within 1-2 days. Potatoes can be defoliated by as much as 30% before flowering or during tuber fill and yields are unaffected. However, when potatoes are flowering, they cannot tolerate more than 6-8% defoliation.
Colorado potato beetle damage
(Photo Credit: J. Obermeyer)
One of the major concerns for growers in Indiana is the problem of CPB resistance to insecticides. CPB develop resistance when they are exposed to the same insecticide or class of insecticides year after year. Thus, relying solely on frequent applications of chemical insecticides is not a good economic or long-term strategy for CPB control.
One very effective way to reduce CPB populations is to rotate out of potato to a nonhost crop (e.g., corn, soybean, alfalfa, sorghum). When CPB emerge in the spring in a field that has been planted with a nonhost crop, they are forced to walk or fly to find another potato field. If the field in rotation is located at least 1/2 mile away from any other potato field, only a few beetles will reach the new fields.
CPB can develop resistance to a particular chemical used or to the whole class of insecticides. For example, beetles that are resistant to Asana would probably also be resistant to Ambush. Thus, for chemical control, if a particular insecticide is not working in your field, a switch to another class of chemicals might be helpful (for example, from an organophosphate to a carbamate). Insecticides recommended for control of Colorado potato beetles on potatoes include:
- Organophosphates - Thimet, Monitor,
- Carbamates - Vydate, Sevin
- Pyrethroids - Asana, Ambush, Baythroid, Mustang Maxx, Pounce, Warrior
- Nicotinoids - Admire Pro, Actara, Assail, Belay, Cruiser, Platinum
- Other - Agri-Mek, Avaunt, Coragen, Entrust, Kryocide, Novodor, Radiant, Rimon, Torac
(see ID-56, Midwest Vegetable Production Guide for Commercial Growers, web site: http://www.btny.purdue.edu/ Pubs/ID/ID-56/.)
Figure 1. Third instar potato beetles fill up but don't overlap a 5/16" diameter circle
This method works for two reasons. First, although not all adults emerge at the same time, by the time third instars appear in the field, almost all adults have emerged. Second, potatoes can withstand some defoliation at this time, making it possible to wait until all adults are present. However, the field should be sprayed before too many third or any fourth instars are present. Another consideration is that keeping the number of insecticide applications to a minimum will delay CPB resistance.
For second generation CPB, no sprays should be applied until eggs begin to hatch, because insecticides do not affect CPB eggs. However, it is possible to control most of the second generation with one or two well timed applications.
The potato leafhopper is usually present each year, but it is only an occasional problem. The adult is about 1/8 inch long and yellow-green. Adults are blown to Indiana from southern U.S. regions in the summer. For this reason, they are rarely a problem in the early part of the season, but can be a problem by mid- to late May. Once in the crop, reproduction is continuous, with three to four generations a season. Nymphs are basically smaller versions of the adult but are unable to fly.
Potato leafhoppers feed by sucking juices from the potato plant. The first signs of leafhopper feeding are a subtle paling of veins and a curling of leaflets. Continued feeding causes a characteristic triangular yellowing or browning of the leaf tip known as “hopperburn,” in which potato foliage becomes curled and yellow. Injured plants usually are stunted, and yields are reduced. Leafhoppers cause the greatest amount of damage as tubers are filling.
Potato leafhoppers, while difficult to see, are easily controlled with insecticides. However, growers should not wait until the symptoms of leafhopper damage (i.e., hopperburn) appear in the field, because yield has already been reduced by this time. Growers should treat when they find one or more nymphs per 10 leaves. Fields should be watched closely beginning in mid- to late May for the appearance of leafhoppers.
Aphids, or “plant lice,” are a pest of many crops, including potato. These small (1/20 - 1/10 inch long), greenish- to blackish-colored, soft-bodied insects usually are found on the underside of leaves. Immatures look like adults, except smaller.
Potato leafhoppers - nymphs and adults
(Photo Credit: J. Obermeyer)
Potato leafhopper damage on potato
(Photo Credit: J. Obermeyer)
Adult winged aphids first move into potato fields between mid- to late April in southern Indiana and early to mid-May in northern Indiana. These aphids will “test” each plant they land on until they find an acceptable plant to feed upon. Aphids then will move to the underside of a leaf, lose their wings, and begin to feed by sucking juices out of the plant.
After feeding for a time, the female will begin to give live birth to female offspring. Within 5-7 days, these offspring to give live birth to daughters. Aphid populations can build very quickly, especially in hot weather
The sucking of plant juices can lead to wilting and loss of yield. Large populations of aphids can cause the upper leaves of plants to develop light green spots, usually followed by curling of the leaf margins. As with leafhoppers and “hopperburn,” once these symptoms of aphid damage appear, tuber yields are already greatly reduced. This reduction in yield can be as great as 64%. Virus problems in potato in Indiana are usually not a problem.
There are many natural enemies of aphids, such as lady beetles (adult and larvae), lacewing larvae, syrphid larvae, and parasitic wasps. These predators can be very effective in reducing and controlling aphid populations. These predators, however, are very sensitive to insecticides. Therefore, growers should try to keep their insecticide applications to a minimum when controlling other primary pests such as Colorado potato beetle. (See Colorado potato beetle section.) Several insecticides can be used to control aphids when populations reach an average of two aphids per leaf.
Green peach aphid
(Photo Credit: University of Wisconsin)
Flea beetles are small (1/25 - 1/16 inch long), usually dark colored (black with no stripes, black with two yellow bands on wing covers, or metallic) chewing insects. They have enlarged hind legs and when disturbed, jump in long, rapid “flea-like” leaps (hence their name).
Adult flea beetles overwinter in or near fields under plant debris. They become active in early spring, feed on weed seedlings, and disperse readily when temperatures reach 68°F.
Adult beetles chew small holes in the potato leaves, which creates a shot-hole appearance. Unless beetle populations are very high (2 beetles/sweep with net), damage usually is not economic. If enough defoliation does occur, however, there are numerous insecticides available that will control the population. Most insecticides applied to control CPB or potato leafhopper will also control flea beetles.
Potato flea beetle and damage
(Photo Credit: J. Obermeyer)
Potato flea beetle damage
(Photo Credit: J. Obermeyer)
Wireworms are slender, hard-bodied, wire-like larvae of the click beetle. They are yellow-brown and range from 3/4 - 1 1/2 inches long. They can remain in the larval stage for 3-7 years, depending upon species. The larvae will feed on and in seed pieces soon after planting. They usually are only a problem if the field was in sod, was fallow the year before, or if there was a wireworm problem in the field in the past.
One way to test for wireworms is by placing four or five baits in the field 3-4 weeks prior to planting. Baits can be a handful of untreated wheat, corn, potato or flour buried 6-8 inches deep in the soil and marked with a flag. In 10 days, the baits can be dug up and searched for wireworm. More than one wireworm per bait station will result in economic damage, and treatment will be necessary.
(Photo Credit: J. Obermeyer)
Wireworm damage to potato
(Photo Credit: University of Wisconsin)
EUROPEAN CORN BORER
European corn borers are rarely pests of potatoes in Indiana. They overwinter as larvae and pupate in spring. Moths emerge in mid- to late May, then lay eggs in late May to early June. The adult female moth is 3/4 inch long and yellowishbrown. While they prefer corn, they will lay eggs into the leaf axil of potato if the moth population is large.
Larvae that emerge from eggs feed on the inside of the stem for approximately 2-3 weeks. They then pupate inside the plant and emerge as moths 1-2 weeks later (mid- to late July).
Larvae bore into the stem soon after hatching and are not controllable once inside the plant. Growers, therefore, have only a short time period to control this pest. Once inside the stem, the larvae plug their entrance hole with frass and begin to tunnel. Often, infested plants will have dead stems. If the base of the stem is inspected, the frass covered entrance hole of the ECB can usually be found. Fortunately, this pest is usually not severe enough in Indiana to warrant control measures.
European corn borer adult male (l) and adult
female (r) (Photo Credit: J. Obermeyer)
European corn borer larva (top) and damage (bottom)
(Photo Credit: (l) B. Christine, (r) G. Brust)
READ AND FOLLOW ALL LABEL INSTRUCTIONS. THIS INCLUDES DIRECTIONS FOR USE, PRECAUTIONARY STATEMENTS (HAZARDS TO HUMANS, DOMESTIC ANIMALS, AND ENDANGERED SPECIES), ENVIRONMENTAL HAZARDS, RATES OF APPLICATION, NUMBER OF APPLICATIONS, REENTRY INTERVALS, HARVEST RESTRICTIONS, STORAGE AND DISPOSAL, AND ANY SPECIFIC WARNINGS AND/OR PRECAUTIONS FOR SAFE HANDLING OF THE PESTICIDE.
It is the policy of the Purdue University Cooperative Extension Service that all persons have equal opportunity and access to its educational programs, services, activities, and facilities without regard to race, religion, color, sex, age, national origin or ancestry, marital status, parental status, sexual orientation, disability or status as a veteran. Purdue University is an Affirmative Action institution. This material may be available in alternative formats.
This work is supported in part by Extension Implementation Grant 2017-70006-27140/ IND011460G4-1013877 from the USDA National Institute of Food and Agriculture.
Life Cycle and Biology
Females deposit pale white, oblong eggs in loosely aggregated clusters on the undersides of young, expanding leaves of air potato. The process of oviposition apparently deforms the expanding leaf causing it to curl at the edges becoming cup-like around the eggs (Figure 8).
Females deposit more than 1200 eggs on average during their lifetime. The eggs become yellowish as the embryo develops, and dark reddish eye spots appear mid-way through the incubation period. Embryonic development requires about four days. Larvae feed gregariously and skeletonize the leaves from the underside (Figures 9).
Young tender leaves are preferred but they also consume older, tougher leaves and are able to feed on the aerial bulbils. Complete development of the four instars requires about eight days, with each stage lasting about two days. When fully grown, larvae descend from the host plant and enter the soil where they produce a whitish oral secretion that hardens into a foam-like cocoon. Pupation occurs gregariously, often with several pupae clumped together within a matrix of this material. Adults emerge in 12 to 16 days, begin mating after about 10 days, and initiate oviposition five days later. The adults live for five months or longer. Both adults and larvae feed on the foliage.
Larvae can often be found in aggregations on the growing tips of air potato vines. The host plant senesces during the winter, forcing the adult beetles to go several months without food, presumably in diapause beneath leaf litter and other debris. The overwintered adults emerge in the spring, and females begin laying eggs.
Extensive host range testing by scientists at the USDA/ARS Invasive Plant Research Laboratory in Fort Lauderdale demonstrated that the air potato leaf beetle is a specialist feeder on air potato. It will not complete development on any other plant found in Florida and is only known to feed on Dioscorea bulbifera in its native range (Pemberton and Witkus 2010).
Larvae. Black cutworm larvae vary in size from 3 mm when newly hatched to 4-5 cm when fully grown. Their color ranges from grey to nearly black with a greasy, pebbly skin. There is a pale rather indistinct narrow stripe along the center of the back. When disturbed, the larvae typically curls up into a C-shape.
Adult moth. The moths are relatively large compared to other cutworm species and have wingspans of 40-50 mm. They are brownish-grey with a light silvery band on the wings. Their forewings have small but distinct black dagger-like markings that look like cherries.
Life stages: eggs, larvae, pupae, adult moths.
Female moths lay eggs in groups on grasses, dense patches of weeds and on plant debris. The lower areas of potato fields are the preferred spots for female moths to lay their eggs. After egg hatching, larvae go through 6 molts before turning into pupae in the soil. The small larvae, instars 1 to 3, chew what look like shot holes in the leaves. The larger larvae, instars 4 to 6, cut off stems. It is this larger larva that can chew holes in potato tubers. Black cutworm larvae are loners and feed in the evening or at night and spend the day curled up in the soil.
Black cutworm problems are usually spotty in a field and concentrated in low, weedy areas.
The black cutworm does not overwinter in Ontario. In the spring, the adult moths can be blown long distances in storms along the low level jet stream. The first appearance of moths in Ontario is usually in mid-April.
Black cutworm infestations in potato fields are unpredictable, and damage varies from field to field and from year to year. If not detected, this insect can cause considerable economic losses, so scouting is essential.
Period of Activity
Two generations attack potatoes in Ontario
Larvae of the first generation are active from April until June. They feed on foliage and cut off stems of small plants at ground level. The larvae may be found by removing soil to a depth of 5 cm from around damaged plants.
The second generation larvae are active from mid-July until August. The large instars of this second generation chew holes in tubers.
Walk fields shortly after emergence. Look for small shotgun holes in the leaves, wilted stems or stems cut off at ground level. The larvae may be found by removing soil from around damaged plants to a depth of about 5 cm.
Scout in the evening to find larvae actively feeding.
Check 20 plants in 5 areas of the field. Always check low spots and weedy areas. Tentative threshold is 5% affected plants.
Usually larvae of the second generation attacks potatoes from mid-July until the end of August
Pheromone traps should be used to monitor flights of male moths. Hang the traps 1.8-2.1 m above the ground close to trees or shrubs surrounding the fields. Do not hang traps near lights that are on at night. Check the traps daily to determine if there were flights the previous night. Remove captured male moths daily from the traps, and change the sticky surfaces every 2 weeks.
A high number of male moths caught in traps indicate that the moths are mating and that the females are laying eggs. Growers have 10-12 days to apply an insecticide to control small larvae. Large larvae cannot be controlled because they usually feed on tubers and remain underground.
- For spring scouting (first generation), the tentative threshold is 5% affected plants.
- For second generation:
Tentative Thresholds for the second generation of black cutworm using pheromone traps*
9 to 15 moths in a 7-day period
5 per night for at least 2 consecutive nights
*These thresholds are being evaluated in Ontario. They appear to be reliable.
An insecticide application is recommended no later than 10 days after peak moth activity.
Control weeds. The moths are attracted to weedy spots on low areas of fields for egg laying.
Black cutworm infestations are sporadic and unpredictable. If field monitoring indicates that population are at threshold levels, apply a registered foliar insecticide. Sprays should be done in the evening.
Monitoring of potato tuber moth is a critical part of its management. Pheromone traps that attract males have been effective for monitoring potato tuber moth populations. Monitoring is one of the most important components of an integrated pest management (IPM) plan for potato tuber moth. Monitoring gives an indication of insect presence, population and distribution and allows for timing of pesticide applications for its management. Pan-water traps baited with the pheromone can be used for attracting and monitoring adult male populations. These traps are easy to use and clean between readings. Four traps per quadrant of a circle, about 50 ft from the periphery of the circle are suggested for monitoring in field. No economic threshold level (ETL) has been determined for crop damage or yield loss in fields. However, checking traps twice a week is suggested and pesticide application is recommended in case of high population (e.g., 15 to 20 moths/trap/night) (Anonymous 2013).
What is IPM?
Aphids can be serious and persistent pests in the greenhouse. They are difficult to control due to their high reproductive capability and short development time which can quickly lead to their developing resistance to many different insecticides. The presence of aphids, their white shed skins and honeydew can reduce the aesthetic quality of a wide range of greenhouse crops. Aphids can also vector viruses such as cucumber mosaic virus and many different potyviruses.
Biology and Life Cycle
Most types of aphids found in greenhouses do not mate. All of the aphids present are females which can give birth to live nymphs. There is no egg stage. An adult female may live for up to one month. During this time, she may give birth to 40 to 100 live nymphs. About one week is sufficient for young aphids to reach maturity. Migratory winged aphids may appear when the colony becomes overcrowded or when the food supply is depleted. Outdoors, in the fall, winged aphids which mate and lay eggs appear so that aphids overwinter in the egg stage.
Aphids are small (less than 1/8 of an inch long), soft-bodied, pear-shaped insects with long legs and antennae. In greenhouse ornamentals some of the important species include the foxglove aphid (Aulacorthum solani), green peach aphid (Myzus persicae), the melon or cotton aphid (Aphis gossypii) and the potato aphid (Macrosiphum euphorbiae). See Managing Aphids in the Greenhouse for more information.
Inspect incoming plants for aphids. Avoid high nitrogen fertilization that promotes lush growth that is favorable to aphids. Remove weeds and &ldquopet plants&rdquo that can be sources of aphid infestations. See Greenhouse Weed Control for more information.
Aphids are susceptible to many natural enemies, including aphid parasitoids or parasitic wasps, predators and entomopathogenic or insect killing fungi.
Parasitoids (parasitic wasps) develop in a single host and kill the host as they grow and mature. In general, parasitoids are more effective than predators in reducing aphid populations. However, it may be difficult for some parasitoids to search effectively on some crops with hairy or sticky leaves. Aphid parasitoids are host specific. If you are unsure of the species of aphids you may have or have multiple species, mixtures of different aphid parasitoids are commercially available. Parasitoids are shipped as either adults or &ldquoaphid mummies&rdquo from which the adults emerge.
Aphidius lays its eggs in aphids and the larvae develop within the aphid. The aphid is killed as the developing larvae feed upon it. The swollen exoskeleton of the aphid remains and is referred to as an &ldquoaphid mummy.&rdquo As the adults emerge from this mummy, one can see the small round exit hole.
Figure 1 : Aphid mummies. Photo by L. Pundt
Figure 2: Aphidius emerging from an aphid mummy on the right. Note the round exit hole.
Young green aphid nymph is on the left. Photo by L. Pundt
Aphidius colemani is a tiny (2 mm.) long wasp that is used against green peach aphids and melon aphids. The adult wasp lays one egg inside an aphid. This egg hatches into a larva that feeds inside the aphid. When mature, a new adult wasp will emerge from the tan aphid mummy. This active searcher is not as effective at temperatures above 86 °F.
Aphidius ervi attacks larger aphids such as the foxglove (Aulacorthum solani) and potato aphids (Macrosiphum euphorbiae). It resembles A. colemani but is about twice as large and darker in color.
Aphidius matricariae attacks green peach aphids, (Myzus persicae) including the closely related tobacco aphid (Myzus persicae subsp. nicotianae).
Aphelinus abdominalis attacks foxglove (Aulacorthum solani) and potato aphids (Macrosiphum euphorbiae). Adults feed on the small aphid nymphs and parasitize the larger aphids. Apelinus is better able to withstand higher temperatures than Aphidius sp. This species works more slowly for a longer period of time than the other parasitic wasps. Look for the elongated black mummies that are less swollen than Aphidius mummies.
Figure 3: Black mummy from which Aphelinus will emerge. Photo by L. Pundt
Tips for Use
- Release preventively
- Remove yellow sticky traps.
- Temperatures should be between 65 and 77° F and relative humidity between 70 and 85%
- Release at the end of the day in shaded locations.
- Look for aphid mummies after about 2 to 3 weeks, depending upon greenhouse temperatures.
- Consult with your supplier on release rates.
Aphid Banker Plants
One way to reduce the costs of biological control is to rear or grow your own natural enemies. This helps to reduce your shipping costs with releases of fresh, newly emerged biological control agents. Some biological control suppliers are selling &ldquoAphid Banker Plants&rdquo consisting of wheat or barley plants with bird cherry oat aphids (Rhopalosiphum padi) (these aphid species feed upon cereal grains, and are only used in the banker plant system). The bird cherry oat aphid is a small, brownish to olive green aphid. Aphid banker plants need to be well watered, distributed thoroughout the greenhouse with new replacements started every two weeks. See references at the end for more information on how to use aphid banker plants.
Figure 4: Starter Aphid Banker Plant with bird cherry oat aphids. Photo by L. Pundt
Predators consume many prey during their lifetime. Repeated releases of aphid predators are often needed in order to keep pace with the aphids' high reproductive rate in the greenhouse. Their effectiveness depends upon their predation rate, ability to locate prey and increase in number.
The predatory midge, Aphidoletes aphidimyze, can feed on more than 60 different species of aphids. This gall midge is nocturnal, and prefers dark and humid areas near the lower plant canopy. They require a period of darkness for mating and egg laying. Only the larvae stage is predacious. Adults feed primarily upon pollen and honeydew. The bright orange larva kills aphids by biting their knee joints, injecting a paralyzing toxin and then sucking out their body fluids. Aphidoletes aphidimyza is typically sold as pupae in bottles or blister packs. Adults that emerge from the pupae lay their eggs near aphid colonies. Larvae move to the ground to pupate and use organic debris to make their pupal cocoons. Plastic or concrete floors that are free of debris will not provide sufficient pupation sites. So sawdust, peat or holes in the weed mat barrier on the ground are needed. Some growers also place their aphid banker plants in trays of moist sand to provide pupation sites.
Adults are short-lived and tend to be active at night, so are rarely seen. This midge is most effective in the summer and will go into diapause (period of resting) between September and March. This is because the larvae need at least 15.5 hours of light to prevent the pupae from diapausing. The adults will lay eggs and larvae will feed upon aphids, but there is no second generation of midges produced. Low light intensities, are sufficient to prevent diapause.
Tips for Use
- Place in greenhouse away from direct sunlight.
- Release in the early morning or evening near aphid colonies.
- Temperatures should be between 60 and 80° F, relative humidity between 50 to 85%
- Look for fed upon aphids that will appear shriveled, and turn brown or black.
- Can be used with Aphidius parasitoids.
The convergent ladybird beetle (Hippodamia convergens) and the two-spotted lady beetle, Adalia bipunctata, are commercially available from many biological control suppliers. .
Lady beetles feed on many different types of aphids and other soft bodied insects. Both larvae and adults feed upon aphid nymphs and adults. Adult lady beetles feed upon pollen, fungi and nectar in the absence of prey. Eggs are laid near prey and the larvae may consume from 500 to 1000 aphids. Older, fourth instar larvae are more efficient at capturing prey than adults.
Figure 5: Ladybird beetle adult. Photo by L. Pundt
Figure 6: Ladybird beetle larvae. Photo by L. Pundt
Tips for Use
- Adults can be refrigerated until released.
- Release in the evening or early morning, near aphid colonies when the vents are closed.
- Repeated applications may be needed.
- Look for aphids that have been fed upon and for ladybird beetle adults, larvae or their bright yellow eggs.
- Flowering, pollen producing plants will attract the beetles.
The green lacewing (Chrysopa rufilabiris and C. carnea) adults are active at night and feed on nectar, pollen and honeydew. The predatory larvae (also known as&rdquoaphid lions&rdquo) feed upon many different species of aphids as well as mites, whiteflies, mealybugs, scales and thrips. Because larvae will feed upon each other, they must be released as far apart as possible to discourage cannibalism. Green lacewings may be less effective on plants with hairy leaves.
Green lacewings are commercially available as eggs on cards, or as larvae shipped with a food source in an inert material in a small container or as larvae shipped in separate cells. Larvae may survive better than eggs and are quicker acting. A reduction in aphid population should occur after approximately two weeks.
Green lacewings also available as adults shipped in a small cardboard container. Look on the underside of leaves for the eggs laid on extended stalks.
Figure 7: Releasing lacewing larvae. Photo by L. Pundt
Figure 8: Lacewing larvae. Photo by L. Pundt
Figure 9: Green lacewing eggs. Photo by L. Pundt
Tips for Use
- Spread larvae over an area because they are cannibalistic.
- Look for clean, new growth as a sign that aphids have been killed.
- Ants and slugs will eat lacewing eggs on the cards so need to be controlled.
- If it&rsquos too warm (above 95° F), they will leave the greenhouse.
Naturally occurring predators
Hover flies, also known as syrphid or flower flies are naturally occurring beneficial, predatory insects that may enter the greenhouse from outdoors. Adults begin emerging in April and May about the same time that aphid populations start to increase outdoors. Hover flies are so named because of the ability of the adult to hover in mid-air, dart a short distance very quickly, and then hover again. Adults are small (3/8 to ¾ of an inch long) and look like small bees or wasps. But, they in the fly (Diptera) family, so only have two wings and also have short antennae and large eyes. Hover flies lay their eggs (resembling a small grain of rice) near aphid colonies. Eggs hatch into small, legless larvae with a tapered head that feed upon aphids.
Figure 10: Hover fly adults. Photo by L. Pundt
Figure 11: Close-up of hover fly larve. Photo by L. Pundt
Several types of entomopathogenic (or insect-killing) fungi have been developed for use against greenhouse pests. The entomopathogenic fungus, Beauveria bassiana, is commercially available for use against aphids. However, because aphids have high reproductive rates and molt rapidly, so repeat applications are typically required. Beauveria bassiana is most effective when aphid populations are low. The fungus works best with a relative humidity >90%. Beauveria may not be compatible with the convergent ladybird beetle (Hippodamia convergens) depending on the concentration of spores applied. The entomopathogenic fungus, Isaria (=Paecilomyces) fumosoroseus is most effective when the relative humidity is 80% or higher for 8 to 10 hours.
Tips for Use
- Thorough spray coverage is needed so that the fungal spores contact the targeted insect pest and begin the infection process.
- Repeated applications (three to five) may be needed for effective control.
- High relative humidity is needed
In summary, aphid parasitoids, aphid predators and entomopathogenic fungi can all be incorporated into a biological control program against aphids.
Ferguson, G, G. Murphy, and L. Shipp. 2006. Aphids in Greenhouse Crops. Ontario Ministry of Agriculture, Food and Rural Affairs Fact sheet.
Gill, S. and J. Sanderson. 1998. Ball Identification Guide to Greenhouse Pests and Beneficials. Ball Publishing. Batavia, IL. 244 pp.
Heinz, K.M., R.G. Van Driesche, and M.P. Parella (Ed). 2004. Bio Control in Protected Culture. Ball Publishing, Batavia, Ill. 522 pp.
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Wireworms, the larvae of click beetles, damage potato by feeding primarily on tubers. The damage appears as straight, round holes with smooth walls. It is not clear whether the wireworm feeding is due to a search for shelter or due to thirst and not actually eating. Early in the season around planting, wireworms may drill into seed tubers or seed-pieces thereby weakening them possibly resulting in secondary infection especially by soft rot, in reduced stands and in weakened young plants. Wireworms also can feed on young sprouts with the same results. During the season, although not common, wireworms could damage roots and underground stem. For potato, the major damage is later in the season when tubers are maturing after bulking. Late-season damage will result when larvae feed on tubers causing feeding scars or feeding tunnels. The result of this feeding is reduced quality of the harvested tubers. Wireworm damage is most likely the result of feeding by larvae that are 2 or more years old. In most situations larvae of several ages can be found in an infested field. This does not affect seed production as seed vigor is not affected but the damage causes culling for the fresh market. In processing, potato chips will show gaps along the margin where the hole was located and likewise french fries will show the gap at their ends.
Damage caused by cutworms
Cutworms are general feeders that can attack a wide range of plants. Common vegetables they like to feed on include asparagus, beans, cabbage and other crucifers, carrots, celery, corn, lettuce, peas, peppers, potatoes and tomatoes. A few species feed on turfgrass.
Cutworms curl their bodies around the stem and feed on it. This feeding causes the plant to be cut off just above the soil surface. The number of cutworms found can vary a lot each year. When their numbers are high, there can be severe damage to a garden.
Cultural and Biological Control in Alfalfa
1. Alfalfa-oat mixtures tend to have fewer potato leafhoppers than pure alfalfa stands.
2. Pubescent, or hairy, varieties tend to me more tolerant to leafhopper feeding than glaborous (smooth) plants. Glandular-haired alfalfa causes greater mortality and reproduced reproduction compared to smooth-stemmed alfalfa. Regardless of variety selection, first-year alfalfa stands are considered susceptible to potato leafhopper.
3. Many natural enemies will feed on potato leafhopper adults and nymphs, including lady beetles, predatory bugs, and lacewings. Because these pests are mobile, aphids are preferred prey if co-infesting plants.