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Sweetpotato Whitefly, Bemisia tabaci Bstrain (Silverleaf Whitfly, Bemisia argentifolii
The adult has its body and wings covered with a white powdery wax. It is 1-1.5 mm long. Eggs are oval
shaped and about 0.2 mm. They are yellow and attached to the leaf surface. Eggs darken in color as they get
ready to hatch. Both adults and eggs of Silverleaf Whitefly are found on the underside of young leaves and the
scalelike nymphs are found on the underside of older leaves.
The first yellowish instar nymphs of Silverleaf Whitefly are mobile and move about until they find a minor
vein to feed on. Then they become immobile for the next four instars. The 3rd and fourth instars of the
Sweerpotatoe Whitefly nymph have red eyespots. They are referred to as redeye nymphs. They pupate after
the fourth instar. The pupal case is dome shaped and 0.7-0.8 mm in length. The Silverleaf Whitefly life cycle
takes as little as 16 days in fall weather.
Their damage includes sucking out the carbohydrates and amino acids. They destroy the chlorophyll and
reduce photosynthetic activity. They can and do cause desiccation of leaves and plant death. They exude
honey dew producing sooty mold. Sample for Silverleaf Whitefly early in the morning when the adults are
sedentary.
Field Crickets, Gryllus spp., 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.
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.
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.
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. Wireworms 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 trapping technique consists of digging a hole 2 to 3 inches deep and 6 to 9 inches wide at the soil
surface. Place into the hole a half cup of an equal mixture of untreated corn and wheat seed which has been
presoaked for 24 hours prior to use in order to facilitate germination of the seed. Fill and slightly mound each
station with soil. Cover each mound with an 18-inch square of black polyethylene plastic (appropriately sized
trash bag) topped with a 1-yard square sheet of clear polyethylene or similar clear plastic bag. Cover the edges
of the plastic layers with soil to hold them in place. The black plastic layer absorbs heat and the clear plastic
helps retain heat in the soil, thus allowing for more rapid germination of the bait seed. Carbon dioxide is
produced during the germination process and attracts wireworms to the bait. Just prior to planting, remove the
plastic layers and soil from the bait and count the number of wireworm larvae in and around the bait. If the
average number of wireworm larvae collected in all bait stations located in the field average one or more per
bait station, the economic threshold has been exceeded and treatment is justified. An average of one wireworm
per station is equivalent to 40,000 wireworm larvae per acre.
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
Beet Armyworm, Sodoptera exigua (Hubner) is a year round pest of seedlings and mature vegetables.
Beet armyworm adult moths have a wingspan of 1 1/4 inch. The beet army worm 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
The seedcorn maggot, delia platura, 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.
Salt Marsh Caterpillars, Estigmene acrea,
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 Salt Marsh
Caterpillar 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.
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 leafminors 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 leafminor 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
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 cabbage looper 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.
Thrips, Western Flower Thrips, Frankliniella occidentalis. Onion Thrips, Thrips tabaci.
Thrips are present all year, but they build up during warm spells.
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. Thrips eggs 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 in
the leaves.
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.
Cultural Methods of Pest Control
Land Preparation
Plant residues from the previous crop can feed and harbor large populations of insects that damage young
emerging crop seedlings. Weeds that grow on the edges of fields are another source of seedling insects.
Adjoining fields with crops that are near maturity or have been harvested are a source of seedling insects.
Pesticide treatment of maturing crops is restricted because of the probability of chemical residues on
harvested products. The buildup of insects occurs during harvest and plow down of the harvested crop
residue. Crops that require several passes of the harvest crew can result in large populations of insects that can
move into neighboring fields of young emerging seedlings.
One cultural control for field crickets, Rove beetles, ground beetles, white fly and other insects that migrate
from neighboring fields is to disc or plow these fields as soon as possible after harvest
Disking the nearby harvested fields of Sudan grass and cotton will destroy most of the crickets.
A cultural practice for cutworm control is the plowing of fields with a history of cutworm at least two weeks
before planting. This operation destroys the organic matter that cutworm female moths lay their eggs on.
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 Disking fields that have high amounts of exposed organic
matter will reduce the area needed by the seed corn maggot eggs to hatch.
Fallowing the field.
Wireworm control by letting the field lay fallow has been successful if the grower can spare the time. By
leaving the field without planting or irrigating for several weeks will allow organic matter to decompose.
Wireworms need moisture and organic matter to survive. Wireworms will increase their populations in turf or
any other crop that increases organic matter and receives enough moisture.
Crop Rotation:
Crops like alfalfa hay where the soil moisture is reduced during the several harvests during the year reduce
the wireworm population. Alfalfa can be rotated with other crops to reduce wireworm infestations.
Field Sanitation:
Keeping the field edges, roads and ditches free of weeds reduces breeding areas for a large host of seedling
insects.
Timing of Planting.
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. Waiting for soils to warm up has always been an excellent cultural control of seedling insect
damage.
Delaying planting to allow time for the soil microorganisms to decompose the residue is a method of
removing heavy crop residues where cutworm, wireworm and seedcorn maggot are problems.
Even transplant operations can cause seedling insect problems. A favorite site for adult Seedcorn Maggots to
lay their eggs is the growing medium for transplants spilled at planting.
Barriers:
Salt marsh caterpillars do not like to cross barriers and barriers of aluminum foil, irrigation pipe or water
filled ditches with detergent or oil will protect the field.
Plant Growth As A Control Method
Once the plant is out of the seedling stage it can take off and grow away from leafminor damage.
The use of beneficial insects
There are several predators that work on cabbage looper these include the wasps and a nuclear poluhidrosis
virus.
Natural enemies like parasitic wasps in the Diglyphus, Olpius and Chrysocharis genera, can maintain
leafminer populations below the economic injury level.
Chemical Control
Baits: 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. Ambush treated baits are effective.
For cutworm control baits should be applied in the early evening.
Pre-plant treatment of the soil with pesticides may be required for wireworm control when a wireworms
have been a problem pest in the past. Both granular and liquid pesticides are available.
Insecticide drenches of transplants and seed treatments will control seedcorn maggots.
Adding insecticides to the sprinkler system or applying pesticides by air after the water is shut off on
irrigated fields are control methods used on beetles and crickets.
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.
Bacillus thuringiensis is an effective control insecticide for cabbage looper.
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.
Leaf minor nsecticides 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.
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,
For seedling insect control one of the chemicals that has controlled many of the hard to control pests like
Silverleaf Whitefly has been the systemic, Admire. It is a chlornicotynl. Admire is a nicotine mimic and acts by
binding to the nicotinic receptor, thus simulating the action of acetylcholine. This action results in continual
stimulation of the nerve cells and eventual death of the insect.
In heavy clay soils Admire is not very mobile and stays where it is injected. Admire is very sensitive to ultra-
violet light and has a half life of four hours in direct sunlight. If applied to the soil surface it should be covered or
sprinkled into the soil.
Admire must remain in solution in order to be taken up by the plant roots. Research at the University of
Arizona has demonstrated that Admire performance depends on placement at the soil root interface.
Application labeled techniques include sub-seed furrow injection, in-furrow spray, transplant drench, or
through drip or trickle irrigation. They state that the key to obtaining successful performance with Admire is to
place the product where it will stay in an aqueous solution within the root zone of the plant.
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
Bailey, Wayne: Wireworm baits and preplant decisions for corn
Integrated Pest & Crop Management Newsletter University of Missouri-Columbia
Vol. 10, No. 1 Article 6 of 9 March 17, 2000