Seedling Insect Control  By Tim Braun, Instructor, E-mail tbraun783@aol.com

The early season treatments to protect the seed and young seedlings before thinning is the subject of this
presentation. Other insects like aphids, pin worms, and mites will attack seedlings under certain conditions, but
in this course I am attempting to cover information on the insects consistently considered to be a threat to seeds
and seedlings.

Wireworms, Limonius spp., eat seeds and damage roots. They will also bore into underground growing crops
like carrots, radishes and potatoes. By feeding on rootlets, tap roots and the lower part of the stems of
vegetable seedlings they damage the vascular system of the plant, which stops the flow of water and nutrients to
the upper portion of the plant resulting in death or stunting. The wireworm damage to the epidermal tissue of the
plant will result in the entry of diseases into the plant .  
Wireworms are found in every kind of soil and exist throughout the year. They can last for several years in the
soil in their beetle larval stage. Wireworms are most prevalent in fields with high levels of organic matter built up
by plantings of turf, alfalfa, vineyards, citrus and grains.
Wireworm larvae are hard-bodied, slender, yellow to brown, shiny and cylindrical. Depending on the species
Wireworms are about 0.5 to 1.25 inches in length. The adults are tan to black beetles that are from 0.25 to 1.0
inch in length. They are called “click” beetles because when they are turned upside down they can snap and flip
their bodies into the air.
Because the damage symptoms can occur suddenly, monitoring for this insect is difficult. Plant stands are
reduced and seedlings appear yellow, diseased and dead. Where wireworms have been a pest in the past or
where the previous crop residues are a problem pre plant treatments of the soil may be needed.
The cultural and organically acceptable control methods call for fallowing fields to allow the organic residues to
decompose. Because seeds planted in cold, moist soils or that have been planted deeper then 1 1/2 inches take
longer to germinate; these conditions should be avoided. Seeds planted in these conditions are more susceptible
to wireworm damage.
There are several pesticides available: Admire, Diazinon, Di-Syston, Thimet and several others. Always read
and follow label recommendations. These are in liquid and granule formulations.

Field Crickets are annual pests with eggs laid in damp soil. Nymphs and adults are present throughout the
growing season in mild weather. The adults are black or brown and they are 0.5 to 1.0 inch in length.
When crickets are in large numbers they can reduce stands of vegetables. They feed on the emerging seedlings.
Even though crickets will lay their eggs on the field where they become a problem they usually migrate from
nearby cotton or Sudan grass fields. The edges of the fields are first to suffer from their feeding.
Field Crickets feed at night and during the day. They can be found in cracks in the soil or under leaves and
sprinkler pipes. Disking the nearby harvested fields of Sudan grass and cotton will destroy most of them.
Populations are difficult to monitor. When they are a problem the damage is the only way to tell when they are
present; therefore constant checking of emerging crops is necessary. When experience indicates high-risk fields
have been planted, treatment of field crickets should take place when the crop seedlings first emerge. This is  a
precaution against loss of stand.
Pesticides that are registered can often be applied through the sprinkler system or by air when the fields are
drying out but are still too wet for  ground application. Insecticide treated baits can be applied to the edges of
emerging seedling fields. There are several types of Sevin treated baits. Apple and bran are a few of the baits
used.

Darkling Beetles, Blaspstinus spp. are similar to crickets in that they feed on and destroy emerging vegetable
seedlings. They are about a 1/4 of an inch in length. They are shiny dark black or brown with the tips of their
antennae slightly enlarged or clubbed.  

The Ground beetle, Carabids, is often mistaken for the Darkling beetle because they are the same size and
colored black, brown or reddish. Their antennae are not enlarged at the tip. Ground beetles are predators but
they will uncover seeds and damage emerging seedling while digging in the soil for insects.

Rove Beetles, Staphylidids, are another predaceous beetle that creates the same damage to emerging vegetable
seedlings while exploring for insects. Rove beetles are less than a 1/4 inch in length. They are shiny dark black
or brown with short elytra covering their wings, but their abdomen is not covered. When Rove beetles are
excited they elevate their abdomens taking on the appearance of scorpions.

Again these beetles are very hard to monitor without discovering some type of feeding damage. Close field
checking is required and where a history of presence has occurred preventive treatment is necessary.
Treating the edges of the field with baits, adding insecticides to the sprinkler system or applying pesticides by
air after the water is shut off on  irrigated fields can become necessary.

Cutworms, Agrotis ipsilon, Peridroma saucia, and Feltis subterranea

Cutworm adults are mid sized adults, brown or gray with spots and light hind wings. Depending on the species
they lay eggs by the hundreds singly or in clusters. These eggs are laid on leaves and stems close to the ground.
Cutworm adults will also lay their eggs on any form of organic matter. This occurs when the only growing plants
in the field are emerging seedlings.
After hatching the larvae feed on the organic debris or the plant that they were deposited on. During the day the
larvae hide under the debris of the organic matter or soil clods and come out at night to feed on the growing
plants. They cut off the seedlings of young plants at or just under the soil level.
The larvae are 1/2 to 1 inch in length. They are gray or mottled brown. When they are disturbed they react by
immediately curling up.
Constant monitoring of the young emerging seedlings for wilted or partially wilted plants that are cut off at
ground level is the best method of finding cut worm populations. Sometimes they will only occur at the edges of
fields but when there is abundant organic matter in the field they may be present throughout the field. Cutworms
feed out from where they hatched. This method of feeding forms circular patterns of damage.    
I found this wilting pattern in a field of cauliflower without the cutting but with the wilting. A circular pattern of
damage was in a couple of areas of the field. I found out after talking to the grower that they had a rain shower
and lightning storm the night before. This was lightning damage on a seedling field, but it looked very similar to
cutworm damage with the circular patterns.
The baits used for control of Darkling ground beetles and Field crickets will  control cutworms. Baits should be
applied in the early evening. Cultural controls include control of weeds near the field. Plowing fields that have a
cutworm history at least two weeks before planting operations begin will reduce populations. Ridding the field
of heavy crop residues from the previous crop will discourage the female moth from laying eggs in the field.
Delaying planting to allow time for the soil microorganisms to decompose the residue is a method of removing
heavy crop residues.

Seedcorn Maggot, Delia platura can be a serious pest on vegetables and melons that emerge in the late winter
and early spring. Cold periods that limit the germination of seeds are ideal for the maggot to infest the seeds.
The seedcorn maggot is a white, legless larva of an adult, small, light gray fly. The larvae will over winter in the
soil or the adult may lay eggs in late winter. Three to four generations occur per year, but the first generation is
economically destructive to young seedlings and seeds.
Larvae bore into and feed on the seed and germinating seedlings. The plants yellow and die within a few days.
Cool wet weather combined with high organic matter where the adult maggot can lay eggs is ideal situations for
populations of maggots to establish themselves. A favorite site for adult Seedcorn Maggots to lay their eggs is
the growing medium for transplants spilled at planting.         
Disking fields that have high amounts of exposed organic matter will reduce the area needed by the eggs to
hatch. Insecticide drenches of transplants and seed treatments will control seedcorn maggots. Waiting for soils
to warm up before planting is also a good control method.

Beet Armyworm, Sodoptera exigua  (Hubner) is a year round pest of seedlings and mature vegetables. During
extremely cool temperatures they slow down but in the milder temperate area beet armyworm are a continual
threat to seedling vegetables. Beet armyworm feed on a wide variety of crops, including melon and vegetable
crops.
Beet armyworm adult moths have a wingspan of 1 1/4 inch. The moth has grayish brown forewings and a pale
spot in the mid front margin. The hind wings are white with a dark anterior margin.
The adult will lay an average of 500 to 600 eggs over a four to ten day period. These eggs are laid in masses of
50 to 75 eggs. The Beet Armyworm moth covers the eggs with white scales from her body. This gives the egg
mass a cottony appearance. The eggs are light green when first laid and then darken before they hatch in about
2 to 5 days.
The larvae are olive green in color. Beet armyworms have light colored stripes down the back with a broader
stripe down each side. They have a dark spot above the second true leg on each side of the body. The larvae
have five instars and grow to a length of 1 1/4 inches in length.  
The young beet armyworm larvae will spin a web over them on the underside of the leaf when they first start
feeding. When in the first instars they feed together then they disperse feeding as individuals. The larger beet
armyworms are very mobile and will feed on several plants before they pupate. Their larval stage lasts for 2 to
3 weeks in warm weather. The entire life span of a beet armyworm is about 36 days in 80 degree F. weather.
Young seedlings can be entirely consumed by beet armyworms. More often they stunt or kill the seedlings.
Monitoring the young seedlings often will let you know when to treat. As eggs darken you know that the hatch
is near. When a high percentage of eggs have hatched spraying of the young 1st and 2nd instars are most
effective as a control measure.
Because of the high amount of chemicals used on beet armyworm many insecticides are no longer effective on
them. Higher rates of older insecticides and the use of newer chemicals are required for good control.

There are other types of armyworms besides the beet armyworm that attack young vegetable seedlings. These
include the fall armyworm, the southern armyworm and the yellow striped armyworm. These are larger then the
beet armyworm. Because they do not often inhabit fields that receive constant insecticide treatments like the
beet army worm, they are more susceptible to insecticide sprays.
I saw an outbreak of the fall armyworm in the spring of 1960 in Kern County that was very severe to seedlings
and many full grown crops. The white cottony scales covering the egg masses in the green alfalfa fields were in
circular masses that were 10 to 20 feet in diameter. Scouting from your vehicle was easy.  The larvae were
black and over an inch and a half long with a yellow and red stripe down both sides. The roads were made
slippery for cars to drive on when the worms moved over roads going from field to field..
They where very easy to control with just about any insecticide. We used Malathion. Other worm infestations
(looper, beet armyworm and corn earworm) were a problem in the fields for the entire spring and summer that
year. We killed most of the predators with our early season applications and the mite populations were
uncontrollable during that entire summer. I only saw this happen once in all the years that I’ve scouted fields but
it was an entomological spectacular event.

Salt Marsh Caterpillars

Salt Marsh Caterpillars, Estigmene acrea, under the right conditions for this insect, they will migrate as larvae
from neighboring crops like alfalfa and cotton to vegetable seedling in vast numbers causing considerable
damage.
The adults have white to yellowish colored wings with many black spots. They have a wingspan of around 2
inches. They lay their eggs in clusters of twenty or more on the leaves of the host plant. The larvae are 2 inches
long with yellowish brown bodies covered with red and black hair. They are often called wooly bear
caterpillars.         
As they migrate across the field Salt Marsh Caterpillars devour the entire young emerging seedlings . On full-
grown plants they skeletonize the leaves as they feed through them.
Treatment of the caterpillars in the field from where they migrate is the best form of control for salt marsh
caterpillars. Spraying with bacillus thuringiensis (BT.s) which they are very sensitive to, will give some control.
Putting up barriers of irrigation pipe or aluminum foil on the ground that channel their migration to holes
containing cups of oil is another method of control. Cotton seed oil or vegetable oil can be used.
Salt marsh caterpillars do not like to cross barriers and these barriers of aluminum foil, irrigation pipe or water
filled ditches with detergent or oil added will protect the field. Spraying the edges of the field with Seven will
also produce some control.

Cabbage Looper, Trichoplusia ni, is found year round and is a special problem in the fall planted vegetable
seedlings in the desert. The spring and summer build up of populations of cabbage loopers are at a peak period
in the fall and can be very destructive, but the cabbage looper can be a problem in any mild temperature zone.
The moths of cabbage looper are mottled brown in color, and have a small silvery spot near the middle of its
front wing resembling a figure eight. This is unique to the cabbage looper. The moth lays single dome shaped
eggs on the under side of leaves. One cabbage looper moth can lay as many as 275 to 350 eggs. Eggs darken
as they hatch which takes about 2 to 5 days.
The larvae of the cabbage looper are light green in color with a white stripe down either side. This color makes
them often hard to find in a green salad. Unless they move. The larvae of the cabbage looper have two sets of
legs in the front of the body and three sets of heavier, unjointed prolegs at the rear of their bodies. This allows
them to move in a looping movement, arching the leg less middle of their body as they move forward. They go
through five instars in two to four weeks.
Their pupae are brown in color, wrapped in a white cocoon of fine threads. The cocoon is found attached to
the underside of a leaf. The cabbage looper pupation stage lasts 10 to 16 days. They have 3 to 5 generations a
year.
Cabbage loopers can kill vegetable seedling or stunt their growth when the populations of cabbage looper are
high. Bacillus thuringiensis is an effective control insecticide for this insect. There are several predators that
work on cabbage looper these include the wasps and a nuclear poluhidrosis virus.

Vegetable Leafminer Liriomyza sativae, are prevalent in seedling vegetables in the late summer and fall and the
leafminer, liriomyza trifolii, attack young seedling vegetables in the spring.
The two have subtle differences in color between the adults. Knowing that the trifolii is prevalent in the spring
and that stivae are dominant in the late summer and fall is a form of identification used. L. trifolii is more
resistant to pesticides than the L. stivae. Another form of identification is the use of phermone sticky traps that
attract the leaf minor by species.
The adult is the size of an eye gnat. The adult leafminers are flies that are shiny, black and yellow. They have a
yellow triangular spot on the upper thorax between the wings.  Both male and female feed at puncture sites.
Several puncture sites are made. The female will deposit her eggs in some of these puncture sites.
Eggs hatch within a few days after being laid. The larvae feed on the plant mesophyll tissue just below the upper
surface of the leaf. As the larvae mine through the leaf they leave a trail of their fecal matter that forms easily
identifiable lines throughout the leaf. After completing three instars the larvae emerge from the leaf and drop to
the ground where they pupate. Adults emerge from the soil in a period of  7 to 25 days. The entire life cycle is
complete in 3 weeks if temperatures are in the 85-90 degree F. range. This means that many generations can
be produced in a year’s time.
Damage of leaf minors consists of reduced photosynthesis when chlorophyll is removed by the mining of the
leaf minor larvae. The leaf minor mines between upper and lower leaf surfaces creating winding tunnels that are
initially small and narrow, but increase in size as the larvae grow. Mines and feeding punctures provide
entrances for disease systems to infect the plant.
In seedlings most of the mines occur on the cotyledons and the first true leaves. When seedlings only have three
to four leaves and most of them are mined treatment is usually recommended. If plant-growing conditions are
good, the vigorously growing seedling can tolerate high populations of leaf minors and treatment can be avoided.
Natural enemies like parasitic wasps in the Diglyphus, Olpius and Chrysocharis genera, can maintain leafminer
populations below the economic injury level. Once the plant is out of the seedling stage it can take off and grow
away from leafminor damage.
Insecticides include Agri-Mek, Trigard and Neemix. Neemix is an organically approved insecticide. Agri-Mek,
used under a supplemental label, will kill larvae in the mines. Trigard is a growth regulator that is very effective
for control. Neemix does not kill the larvae until it finishes feeding and forms a pupa. Neemix is a restricted use
material in an organically certified crop. Neemix will reduce populations that could attack seedlings planted later
in the area.

Thrips, Western Flower Thrips, Frankliniella occidentalis. Onion Thrips, Thrips tabaci.
Thrips are present all year, but they build up during warm spells. Their hosts are weedy areas, onions, wheat or
non-irrigated pastures. They move to the crop when their host is destroyed or when the host dries up. Field
observations of the life cycle of thrips indicate the thrips can complete their life cycle from egg to adult in three
weeks during air temperatures of 70 degrees F.
The stages of metamorphosis for thrips are egg, two larval stages, prepupae, pupa, and adult. This is classified
as being between a simple and complete metamorphosis.
The eggs are small, white and bean shaped. They are laid in plant tissue and hatch in 2 to 7 days. Nymphs are
paler in color, smaller in size and without wings when compared to the adult thrips. Otherwise they resemble
the adult. Nymphs have four instars that take 15 to 30 days. The two later instars are spent as  pupae in the soil
or litter beneath the plant where they do not feed.
The difference between the flower thrips and the onion thrips should be known because the onion thrips are
very easy to control when compared to the western flower thrips.
The western flower thrips has many color forms and is difficult to define. The female has color ranges from light
yellow, yellow with brown blotches on the body, to dark brown while the male western flower thrips is light
yellow.
The onion thrips female body is yellow with brown blotches on the thorax and abdominal terga with legs that
are yellowish brown. During warm temperatures the light colored onion thrips adults predominate over the
brown forms which occur during cool temperatures.  
The immatures of both western flower thrips and onion thrips are generally light yellow in color.
The western flower thrips have eight-segmented antenna while the onion thrips have seven segmented antenna.
The onion thrips antennal segment I and the base of segments III to V are brownish white. The rest of the onion
thrips antenna are brown.
The onion thrips have gray colored ocellar pigmentation and the western flower thrips have reddish orange
ocellar pigmentation.
In the United States there are no onion thrips males and the onion thrips reproduce asexually through
parthenogenisis.  
The length of the adult western flower thrips is about 1/20 in. while the onion thrips are smaller at 1/25 inches in
length.
Another method of identification is the use of sticky traps. These can be placed on the field margins when the
light intensity is moderate-high and temperatures exceed 63-65 degree F.
Small plant seedlings can be checked for thrips by examining the folds in the leaves of the plants. Researchers
say that if 3-5 thrips are found on a plant there are probably 3 times as many hidden in the folds.
Thrips feed by making a hole in the epidermis with a single mandible. Then they puncture the cells with their
maxillary stylets and suck the sap that oozes out. When slow growing seedlings are fed on in this way they
become wrinkled. If the weather is warm enough for the seedlings to outgrow this damage, treatment is
unnecessary. If cool weather persists and thrips continue to feed control methods may have to be applied.
The feeding causes brown scarring that has a scorched or speckled appearance. Leaves dry out and drop from
the plant. This damage can be mistakenly diagnosed as wind burn or blown sand damage, but it can be
distinguished by the black specks caused by thrips fecal matter scattered over the burn area. Usually this
damage is evident after the thrips population has reached its peak and does not require treatment.
There are many pesticides that are labeled for thrips control. Always read the label. Thrips populations are
resistant to many of the registered pesticides. This is especially true when it comes to flower thrips control.
Onion thrips control is easier then the flower thrips control,

The use of trade names in this course is solely for the purpose of providing specific information. It is not a
guarantee or warranty of the products named, and does not signify that they are approved to the exclusion of
others of suitable composition. Use pesticides safely. Read and follow directions on the manufacturer's label.


Selected References & Works Cited

W. E. Chaney, UC Cooperative Extension, Monterey Co.
M. LeStrange, UC Cooperative Extension, Tulare Co.
Spinach Insects and Mites
UC IPM Pest Management Guidelines: UC ANR Publication 3467

Johnson, F. A. and Stansly, P. A.     Insects That Affect Vegetable Crops Florida         Cooperative Extension
Service/ Institure of Food and Agricultural Sciences /         University of Florida  June, 1995, Date Revised
September , 2001


Palumbo, J. C. Rev. 8/oo. Management of Aphids and Thrips on Leafy         Vegetables.         Cooperative
Extension, College of Agriculture and Life Sciences,         University of Arizona, Tucson, Arizona         

Palumbo, John C.  & David L. Kerns Melon IPM : Southwestern USA         Department         of Entomology
Yuma Valley Agricultural Center University of Arizona         Yuma, AZ 85364