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Lettuce Aphid Information – How To Control Aphids In Lettuce

Lettuce Aphid Information – How To Control Aphids In Lettuce


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Aphids in lettuce can be a real nuisance, even a deal breaker when lettuce is when severely infested. Most folks dislike the idea of ingesting a little extra protein in the form of a bug in their salad, and I am no exception. So what are lettuce aphids and is it possible to control lettuce aphids in the garden? Let’s find out.

What are Lettuce Aphids?

Lettuce aphids come in multiple hues ranging from green to orange to pink. The adults have black markings on their leg joints and antennae. Some have black markings on the abdomen as well, and may be winged or wingless.

Lettuce Aphid Information

Lettuce aphid information informs us about their prolific reproduction, which is definitely no boon to the gardener. Aphids are both viviparous and parthenogenic, which means the females are capable of producing living offspring without any sexual activity. Just a couple of aphids in lettuce rapidly become an infestation if left unchecked.

The problem is how to control lettuce aphids. They tend to be difficult to get at, as they are not only well camouflaged, but hide deep in the center of the lettuce on the tender, new leaves in head lettuce types. In loose-leaved varieties, like Butterhead, the insects are more readily apparent and can be viewed on the inner young leaves.

You may also see quantities of sticky honeydew and black sooty mildew.

Lettuce Aphid Control

Usually, the first thing you read about when controlling aphids is to try to blast them off with a good stream of water. I’ve tried this. Never worked. Okay, maybe it got some of the insects off, but never did much for a true infestation.

Next, I usually try spraying either a commercial insecticidal soap or one I have created out of water and a bit of dish soap. This will work somewhat. Better yet, spray with Neem oil, which will give a much better result. Spray in the evening once the sun has gone down, as Neem and insecticidal soap can damage plants in direct sun. Also, this allows the morning dew to wash off the majority of the oil by morning.

You can start your lettuce under row covers, which in theory, will work. Of course, if even one aphid gets under there, you could soon have an army sucking away on baby greens.

Ladybugs love aphids and can either be purchased or you can plant flowering annuals near the lettuce crop to naturally attract them. Syrphid fly larvae and green lacewing larvae are also connoisseurs of aphids.

You can, of course, resort to chemical controls too, but given that this is a food crop, eaten raw no less, I would steer clear. To me, if it gets that bad, I would prefer to rip the plants out and dispose of them.

Lastly, keep the area around the lettuce crop weed free to mitigate any other cozy hiding places for lettuce aphids.


Lettuce aphid has several color forms, ranging from green to orange to pink. Adult winged and wingless lettuce aphids have black markings on the joints of the legs and antennae. Some of the wingless aphids have many black markings on the top of the abdomen as well. The winged adults are browner than the wingless forms, but also have various black markings.

Lettuce aphid is a relatively new pest of lettuce in California. It can be distinguished from green peach aphid by the fact that lettuce aphid does not have strongly converging antennal tubercles.

Lettuce aphid has a very short life cycle and their numbers can increase rapidly. Lettuce aphids appear to pass the winter as nymphs and adults on lettuce, radicchio, Nicotiana spp., and some other composites.


Pests of Lettuce

Caterpillars attacking the fall crop are usually the most troublesome field pests of lettuce. In the greenhouse, aphid and cabbage looper infestations often give problems. Cutworms, whiteflies, leafminers, and slugs are slightly less important greenhouse pests. Regardless of growing site, aphids cause additional problems by transmitting several virus diseases, including lettuce mosaic.

A. Caterpillars that sever or leave holes in foliage

  1. Beet armyworm – Green or black larva, up to 30 mm long three pairs of legs near head five pairs of fleshy prolegs three lightly colored stripes running length of body black spot on each side of the second segment behind the head (Figure 1) damages bud and young leaves
  2. Cabbage looper – Green caterpillar with longitudinal white stripes body up to 30 mm long, tapers toward the head three pairs of legs near head three pairs of fleshy prolegs (Figure 2) young larva on underside of leaf mature larva deep within head consumes tender leaf tissue, leaving most veins intact
  3. Cutworms – Fat, basically gray, brown, or black caterpillars 40 to 50 mm long when fully grown three pairs of legs near head five pairs of fleshy prolegs (Figure 3) young larva on underside of leaf mature larva deep within head consumes tender leaf tissue, leaving most veins intact
  4. Imported cabbageworm – Velvety green caterpillar up to 32 mm long yellow stripe down back row of yellow spots down each side three pairs of legs near head five pairs of prolegs (Figure 4) feeds deeper in plant and more likely to eat small veins than the cabbage looper leaves wet, greenish-brown excrement deep among leaves

B. Small (less than 4 mm long) piercing-sucking insects that extract sap and create discolored areas on foliage

  1. Aphids – Soft-bodied, pear-shaped insects with a pair of dark cornicles and a cauda protruding from the abdomen may be winged or wingless - wingless forms most common feed in colonies cause discoloration or mottling of foliage often transmit virus diseases excrete honeydew on which sooty mold grows.
    1. Bean aphid – Dark green to black body with white appendages adult up to 2.6 mm long cornicles about same length as cauda (Figure 5A) nymph green, last instar with 5 to 7 pairs of white spots on abdomen (Figure 5B)
    2. Green peach aphid – Pale yellow to green wingless adult up to 2.4 mm long winged adult with dark dorsal blotch on yellowish-green abdomen cornicles over twice as long as cauda and slightly swollen toward tip (Figure 6A) yellow-green nymphs with 3 dark lines on abdomen (Figure 6B)
    3. Potato aphid – Adult and nymph both solid pink, green and pink mottled, or light green with dark stripe adult up to 3.5 mm long long slender cornicles about twice as long as cauda (Figure 7)
    4. Turnip aphid – Adult and nymph both dull green adult up to 2.2 mm long swollen cornicles slightly longer than cauda (Figure 8)
  2. Greenhouse whitefly – White moth-like insect about 1.5 mm long found in conjunction with tiny yellow crawlers and/or green, oval, flattened, immobile nymphs and pupae (Figure 9)
  3. Leafhopper – Spindle-shaped pest up to 4 mm long green body with yellowish to dark green to black spots (Figure 10) usually jumps instead of flies extracts saps from underside of leaf causing leaf to crinkle and curl upward can also cause yellowing of leaves.


Thrips

Thrips are present season long in leafy vegetables, but are usually most abundant during the spring after temperatures begin to increase. They are most important in head, leaf, romaine and baby mix lettuces, cabbage and spinach because of the cosmetic scarring they cause to leaves and contamination of harvested plant parts. Thrips can build up in weedy areas, and other surrounding crops, moving to lettuce in large numbers when host plants begin to dry down. Further, once adults disperse onto plants, they can readily reproduce and rapidly colonize in high numbers. We are uncertain what the developmental rate of thrips is on leafy vegetables, but field observations suggest that they can complete development from egg to adult in less than 3 weeks when temperatures are near 70 ° F.

Species Complex. Western flower thrips, Frankliniella occidentalis and Onion thrips, Thrips tabaci are the main thrips species that occur on leafy vegetables. Because western flower thrips are generally more difficult to control with insecticides than onion thrips, it is important to correctly identify species composition. Identifying thrips can be very difficult because of their small size and similarities in color. Adult western flower thrips are about 1/20 in. (1.5 mm) in length and immatures are generally light yellow in color. Western flower thrips have reddish-orange ocellar pigmentation and eight-segmented antennae. Onion thrips are slightly smaller than western flower thrips, being only 1/25 in. (1.2 mm) long and their body is yellow with brown blotches on the thorax and abdominal terga. The legs are yellowish-brown and the antennal segment I and the base of segments III to V are brownish-white, the rest of the antenna is brown. Their ocellar pigment is gray, and they have seven-segmented antennae. If necessary, contact an Extension agent or specialist for assistance in identification.

Monitoring. Like aphids, thrips can disperse onto crops at anytime, thus it is important that fields be monitored regularly. Thrips can generally be found throughout the plant, feeding on the undersides of leaves, but prefer to hide in complex plant parts, flowers and other folded tissue where they are difficult to detect and reach with insecticides. There are several methods for sampling for thrips on leafy vegetables:

  • Direct observations: involves careful examination of plant parts for the presence of thrips and feeding scars. Can be done when sampling for aphids and other pests. Care should be taken to carefully examine folds in leaf tissue near the base of the plant for immatures. If 3-5 thrips are found on a small plant, there is probably 3 times as many hidden within folds in the leaves or that had dispersed from the plant.
  • Sticky Traps: placed on field margins, can indicate when adult thrips begin to disperse into field from adjacent vegetation. Adults fly when temperatures exceed 63-65 ° F during the day when light is intensity is moderate-high. Also allows for identification of species.

were observed immediately following sharp increases in the number of winged aphids caught on traps in the spring. Used properly, yellow traps placed within fields near upwind edges, can provide an early indication of when economic colonization by aphids is beginning. However, proper identification of aphid species is important because many aphid species are dispersing to wheat and alfalfa also (pea aphid, blue alfalfa aphid, greenbug, etc.). If necessary, contact an Extension agent or specialist for assistance in identification.

Management Alternatives. Several predators and parasitoids attack aphids on leafy vegetables. However, natural enemies rarely provide adequate control of high field populations in spring crops. Consequently, control with insecticides is often the only viable alternative to preventing aphids from contaminating harvested products. Below is a summary of management alternatives for aphids in leafy vegetables based on replicated research trials:

Prophylactic Soil Treatment Approach

  • A single preplant, soil application of Admire 2F (imidacloprid) is the standard method for controlling aphids in lettuce and cole crops.
  • Admire 2F can provide season-long control of the aphid complex that occurs in head lettuce, leaf lettuces, spinach and cole crops.
  • Studies have consistently shown that reduced rates (12-16 oz) provide control comparable to full labeled rates. Field performance in commercial fields has not decreased during the past four years.

Responsive Foliar Approach

If a grower decides not to apply an Admire treatment at planting there are options that can provide adequate control of aphids. Studies conducted at the Yuma Agricultural Center over the past 3 years have shown that several foliar insecticides are still effective against aphids on leafy vegetables. Combinations of older products such as Orthene, Endosulfan, Metasystox-R, Dimethoate and pyrethroids can provide suppression of aphid populations on lettuce and cole crops with limited residual. Metasystox-R is particularly effective against cabbage aphids. Repeated applications will probably be necessary, depending on time to harvest and aphid pressure. Provado (foliar formulation of Admire) also provides a foliar alternative to Admire. It can suppress aphid populations for 7-10 days and is very effective when combined with Endosulfan or Metasystox-R. None of these products provides a quick, rapid knockdown of established aphid colonies (ie., phosdrin ) and their reentry intervals and pre harvest intervals vary, depending on rates and crops. Note: Always consult the products label before recommending or applying any insecticide.

  • It is important to rotate chemistries to ensure effective control and for resistance management. A foliar spray program with Provado, in rotation and in combination with other foliar insecticides (see above), can provide an alternative to a prophylactic Admire application.
  • Proper timingof application is critical for successful control of aphids with foliar alternatives . Applications of foliar sprays should be initiated when wingless (apterous) aphids first begin to colonize lettuce plants (>5 /leaf), particularly when associated with sharp increases in winged adult numbers.
  • Plants should be sampled every 4-5 days to assess aphid colonization. Repeated sprays (10-21 days) are usually needed to prevent contamination at harvest, but will depend on aphid immigration, level of colonization, location of colonies on plants and time to harvest.
  • Dislodging: involves beating or jarring plants to dislodge thrips onto sheet or sticky surface where they can be counted and identified. Should be done during the morning when adults are less active. Can be time consuming and does not measure scarring.

Management. Cultural management has only a limited impact on thrips populations because of their ability to rapidly disperse from native vegetation, weeds and crops. Further, there are few natural enemies that feed on them. Consequently, control with insecticides is often the only viable control alternative. The following points should be considered when attempting to chemically manage thrips populations in leafy vegetables:

  • There are no defined action thresholds, but experience suggests that applications should be initiated when population numbers are low (head lettuce and cabbage) and when scarring on young leaves is first observed (leaf and romaine lettuce spinach), particulary when temperatures are increasing. Apply treatments during the afternoon when adults are most active.
  • Several products are registered that when used in combination will provide efficacy with limited residual activity (Lannate, Ammo, Othene, Karate, Endosulfan and Dimethoate). Note: Always consult the products label before recommending or applying any insecticide.
  • Frequency of applications will depend on residual of products and immigration of adults from surrounding vegetation. Plants should be sampled at 2-3 day intervals following treatment. In recent trials, the most efficacious insecticides tested were only able to maintain thrips populations at constant levels, and did not reduce numbers significantly. This should be taken into consideration when determining when to treat.
  • Plant size and temperature may be important factors contributing to the efficacy of these products. The larger the plant, the more difficult it is to obtain good coverage underneath the leaf and near the base of the plant Also, higher temperatures drive thrips development, but may also influence their activity to more readily come in contact with the insecticides.

Palumbo, J.C. 1996. Timing and frequency of Provado applications for management of aphid populations in head lettuce, pp.128-136. In 1996 Vegetable Report, Univ of Ariz, Coll. of Agric.

Palumbo, J.C. 1997. Evaluation of foliar insecticide approaches for aphid management in head lettuce, pp.171-177. In 1997 Vegetable Report, Univ of Ariz, Coll. of Agric.

Palumbo, J.C. 1997. Evaluation of conventional and experimental insecticides for control of thrips in head lettuce, pp.179-189. In 1997 Vegetable Report, Univ of Ariz, Coll. of Agric..

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.

The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.

Any products, services, or organizations that are mentioned, shown, or indirectly implied in this web document do not imply endorsement by The University of Arizona.


Identification

Identifying Aphids

Aphids are tiny (adults are under ¼-inch), and often nearly invisible to the naked eye. Various species can appear white, black, brown, gray, yellow, light green, or even pink! Some may have a waxy or woolly coating. They have pear-shaped bodies with long antennae the nymphs look similar to adults. Most species have two short tubes (called cornicles) projecting from their hind end.


A close-up view of a rose aphid.

Adults are usually wingless, but most species can develop a winged form when populations become crowded, so that when food quality suffers, the insects can travel to other plants, reproduce, and start a new colony. Aphids usually feed in large groups, although you might occasionally see them singly or in small numbers.

While aphids in general feed on a wide variety of plants, different species of aphids can be specific to certain plants. For example, some species include bean aphids, cabbage aphids, potato aphids, green peach aphids, melon aphids, and woolly apple aphids.


Some aphids are darker colors, like brown. The potato aphid is a common brown aphid. Photo credit: GrowVeg.com.

What Does Aphid Damage Look Like?

Nymphs and adults feed on plant juices, attacking leaves, stems, buds, flowers, fruit, and/or roots, depending on the species. Most aphids especially like succulent new growth. Some, such as the green peach aphid, feed on a variety of plants, while others, such as the rosy apple aphid, focus on one or just a few plant hosts.

  • Look for misshapen, curling, stunted, or yellowing leaves. Be sure to check the undersides of leaves aphids love to hide there.
  • If the leaves or stems are covered with a sticky substance, that is a sign that aphids may have been sipping sap. This “honeydew,” a sugary liquid produced by the insects as waste, can attract other insects, such as ants, which gather the substance for food. When aphids feed on trees, their honeydew can drop onto cars, outdoor furniture, driveways, and so on.
  • The honeydew can sometimes encourage a fungal growth called sooty mold, causing branches and leaves to appear black.
  • Flowers or fruit can become distorted or deformed due to feeding aphids.
  • Some aphid species cause galls to form on roots or leaves.
  • Aphids may transmit viruses between plants, and also attract other insects that prey on them, such as ladybugs.


Aphids can be various colors, including yellow, and produce a sticky honeydew substance. Photo Credit: John Obermeyer/Purdue University.


9) Hoops & Row Covers

One final organic aphid control method is to physically block their access to plants. Individual plants, raised beds, or sections thereof can be shrouded with row covers. Also called “floating row covers”, their purpose is to block out or otherwise protect plants from undesirable elements. Some row covers are designed to stop insects, while others are used for shade or frost protection.

I put this option last on the list intentionally. We absolutely love using hoops and row covers as a means for organic pest control in our garden. However, because aphids are so dang tiny, hoops and row covers aren’t always 100% effective at keeping those little suckers out. If you cover young plants early on, and use the right type of fine row covers with it tucked in tightly around the edges, they can certainly help. Read all about using hoops and row covers in the garden here, including details on various hoop and cover material options.

And that is how to get rid of aphids, in a natural and organic manner!

In closing, I hope this article gave you plenty of new ideas of how you can get rid of aphids in your own garden. As you can see, there are tons of effective options – and most of them are very quick and simple! Not sure where to start? Experiment with a few methods, and then come back to let me know how it goes. Thanks for tuning in, and best of luck!

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