Photo 4

Cole (Brassicae) crops:  Aphids  including the turnip aphid, Lipaphis erysimi (Kaltenbach). Hemiptera: Aphididae

Biology:  In Arkansas, cole crops are produced during spring and fall and aphids can usually be detected throughout these periods.  Populations are generally greatest on collard and cabbage. Turnip aphids are small (< 3 mm) soft-bodied insects that feed on cole crops by inserting their stylet into the plant and removing large amounts of plant sap.  Aphids also excrete large amounts of a sticky honeydew on which mold may grow.  Plants with large aphid populations become stunted and unmarketable.  Aphid reproduction is both sexual and asexual and numerous generations occur each year.  As a result population increases can be dramatic (Photo 4).  But just as dramatic, populations often crash due to the action of natural enemies including fungal pathogens, parasitic and predatory insects.  Insecticide application often decreases the effects of the beneficial organisms and large increases in aphid populations may result.

Management:  Aphids are often naturally controlled by beneficial insects (predators and parasites).  In Arkansas, however, most commercial cole crop fields are produced for processing and canning.  While very low numbers of aphids present at harvest may be tolerated and may be washed from the leaves during processing, higher aphid populations usually require management and this generally involves use of foliar insecticide sprays.  Of the insecticides currently available in cole crops, imidacloprid, should control the aphids on cabbage and have minimal effects on beneficials.  Other effective insecticides including pyrethroids, and others are also effective against aphids but their use may cause aphids or other insects to later reach pest status.  Another key concern of the commercial producer is the presence of beneficial insects at harvest.  Lady beetle larvae are effective predators of aphids on cole crops.  However, larvae pupate by cementing thenselves to the leaf surface.  This presents a greater problem to the processor than the aphid.  At times, beneficial insects must be eliminated with insecticides prior to harvest.  Additional efforts at reducing aphid populations include destruction of crop residue following harvest.

Back to top

Cole (Brassicae) crops:  Cabbage looper, Trichoplusia ni (Hubner). Lepidoptera: Noctuidae

Photo 5

Photo 6

Biology:  Cabbage looper adults are dark grey, heavy-bodied moths.  Two silvery-white spots occur on the center of each forewing.  The spots usually just touch each other.   At rest the wings are held back over the abdomen.   After mating, off-white eggs are laid individually on the foliage of cabbage, other cole crops and numerous other plants including beans, potato, tomato and others.  Larvae hatch in four to six days and larvae can be detected feeding on the bottoms of leaves.  Small larvae can be difficult to find and looking for small pin hole damage may be the best method for larvae detection.  Larger larvae are pale green and have numerous longitudinal white lines (Photos 5 and 6).  In addition to the three pair of true legs on the thorax, cabbage looper larvae have two pair of prolegs on the abdomen plus the anal pair.  Larvae movement is characterized by a looping motion.  At maturity, larvae are about 35 mm in length.  Pupation occurs in a web on the plant.   Multiple generations occur each year.

Management: Low numbers of cabbage looper larvae detected on small plants should be tolerated.  If plants are actively growing, they will likely outgrow the damage.  With larger cabbage that is beginning to form a head, damage resulting from cabbage loopers may be severe and management is generally warranted.  Beneficial insects and pathogens often play a substantial role in cabbage looper regulation and their effects should be prolonged by delaying the use of synthetic insecticides.  Use of Bacillus thuringiensis may provide some benefit early in the production season.   In late season  insecticides are generally the tactic of choice.  Cabbage looper populations vary greatly in their susceptibility to insecticides.  Methomyl may provide acceptable control.  Others include organo-phosphates, pyrethroids and spinosad.  Proper spray coverage is important and to achieve this, plant spacing may need to be increased.  Also, use of a surfactant with the spray may increase effectiveness.

Back to top

Cole (Brassicae) crops:  Cross-striped cabbageworm, Evergestis rimosalis (Guenee). Lepidoptera: Pyralidae

Photo 7

Photo 8

Biology:  Cross-striped cabbageworm is a relatively common pest of brassica in Arkansas.  Its biology and management closely resembles that of the imported cabbageworm.    After mating, eggs are laid individually on the foliage of cabbage, collard and other cole crops. Larvae hatch in four to six days and larvae can be detected feeding on the bottoms of leaves.  Small larvae can be difficult to find and looking for small pinhole damage may be the best method for larvae detection.  Larger larvae are pale green and have numerous white and yellowish lines (Photos 7 and 8).  In addition to the three pair of true legs on the thorax, cross-striped larvae have three pair of prolegs plus the anal pair.  At maturity larvae are about 25 mm in length.  Pupation occurs in the soil near the plant.   After about 1 week adults emerge.  Multiple generations occur each year.

Management:  In commercial collard fields produced for canning even low numbers of cabbageworm larvae will require management and this may be based primarily on insecticide application. However, the use of  “hard insecticides” should be delayed for as long as possible particularly in early season.  Beneficial insects and pathogens often play a substantial role in cabbageworm regulation and their effects should be prolonged by delaying the use of synthetic insecticides.  Bacillus thuringiensis (BT) likely offers the best alternative to the “hard insecticide”.  Also, several newer (Biobit) and more effective types of BT may be available and should provide some control.  Again, the objective of early season use of  “soft” insecticides is to promote the development and prolong the effectiveness of beneficial organisms.  In late season, insecticides are generally the tactic of choice.  Cabbageworm populations vary greatly in their susceptibility to insecticides.  Several insecticides currently provide acceptable control and include carbamates, organo-phosphates, pyrethroids and spinosad.  Proper spray coverage is important and to achieve this, plant spacing may need to be increased.  Also, use of a surfactant with the spray may increase effectiveness.  After harvest, crop plants should be destroyed as cabbageworms are host plant specific.  Also, volunteer cole crops should be prevented from growing.  In home gardens some damage can be tolerated and hand picking of the larger larvae may be sufficient. 

Back to top

Cole (Brassicae) crops:  Cutworm, Agrotis spp. Lepidoptera: Noctuidae

Photo 9

Photo 10

Biology:  Adult cutworms are dark grey moths with wingspans approaching 5 cm.  After mating, females lay eggs on the host plant and larvae emerge in three to six days.  Mature larvae are about 40 mm in length and dark gray to brown (Photo 9).  Larvae feed on the stem of seedling plants and often cut the seedling off just above the soil line (Photo 10).  Pupation occurs in the ground and several generations occur annually in Arkansas.  Several species occur in Arkansas and most vegetables are susceptible to attack.

Management:  Adult cutworms are attracted to fields with plants or weeds where they deposit their eggs.  Thus maintaining the field free of plants for at least two weeks prior to planting will reduce the cutworm problem.  Crop rotation is an important practice, especially with legumes.  Although labor intensive and only practical for the home gardener, wrapping the transplants with a paper collar from the root to about 5 centimeters above the ground will reduce cutworm feeding.  Soil insecticides may be used with some success and will likely remain a critical element of cutworm management.  In fields with persistent cutworm problems, incorporating soil insecticides  into the soil prior to planting has been effective.  Application of insecticides to foliage may be attempted in fields with problem cutworm populations but may not provide acceptable results. 

Back to top

Cole (Brassicae) crops:  Diamondback moth, Plutella xylostella (Linnaeus), Lepidoptera: Plutellidae

Photo 11

Photo 12

Photo 13

Photo 14

Biology:  Adult diamondback moths are very small moths commonly found flying around cole crops.  At rest the wings are closed over the abdomen and the light colored markings form a multiple diamond pattern (Photos 11 and 12).  Eggs are laid on the foliage surface and larvae feed directly on the foliage.  Larvae are light green and the anal pair of prolegs is evident on the end of the abdomen (Photo 13).  Also, larvae wiggle violently when disturbed.  Pupation occurs on the leaf (Photo 14) and several generations occur each year.  Non-managed populations may devastate cole crops. 

Management: The diamondback moth is a relatively host specific pest; thus, the first objective of an IPM program should be to limit its access to its host plant for as long as possible.  Since the crop season occurs throughout fall and spring, volunteer Brassica plants should be removed and crop residue plowed under after harvest.  Doing this should greatly reduce the diamondback population at the time of transplanting.  Seedlings should be produced free of the insect.  This can be accomplished by producing plants in areas where field grown Brassica crops do not occur; use of row covers that completely cover the nursery bed; and carefully checking for even low numbers of diamondback moth on nursery plants and using available insecticides prior to transplanting. After transplanting the use of  “hard insecticides” should be delayed for as long as possible.  Bacillus thuringiensis (BT) likely offers the best alternative to the “hard insecticide”.  Also, several newer (Biobit) and more effective types of BT may be more effective.  Again, the objective of early season use of  “soft” insecticides is to promote the development and prolong the effectiveness of beneficial organisms.  Although the diamondback moth has developed resistance to several insecticides in much of the U.S., in Arkansas it is currently susceptible to many foliar insecticides.

Back to top

Cole (Brassicae) crops:  Grasshoppers and katydids, Orthoptera: Arctiidae and Tettigoniidae

Photo 15

Photo 16

Photo 17

Photo 18

Photo 19

Photo 20

Photo 21

Biology:  Large insects such as grasshoppers present major problems to the vegetable canner.  The large flat leaves of spinach and greens can easily obscure detection during processing.  Also, if even a single grasshopper makes its way into the can, its large size will almost guarantee detection by the consumer.  In Arkansas common grasshoppers include the American (Photo 15), Carolina (Photo 16), red legged (Photo 17), green striped (Photo 18), and differential (Photo 19).  Katydids (Photos 20 and 21) and several additional grasshoppers occur in lower numbers.  As the “grasshopper” name implies, grasses are the preferred host plants and while brassica greens are not preferred, their production during the cool seasons of spring and fall constitutes a “green island” for grasshoppers.  Although most grasshoppers overwinter as eggs in the soil, several species are capable of surviving winter in Arkansas as adults and nymphs.  Green striped grasshoppers are commonly observed throughout warm periods in winter.  In spring overwintering grasshoppers move from resting sites into the first green area regardless of host plant.  In fall months grasshoppers move from mature or harvested agronomic crops like soybean and corn and dormant Bermuda grass into adjacent “greens”.  Boarder areas of these fields generally hold the greatest numbers of grasshoppers although low numbers can be detected throughout the greens fields.  Most grasshopper species have only one generation per year in Arkansas but stages overlap and both nymphs and adults are often found.

Management:  In small commercial fields produced for fresh market and in home gardens low numbers of grasshoppers may be tolerated with no effect on yield.  A slight reduction in quality due to consumption of leaves may occur.  However, in commercial fields the lack of tolerance for even low numbers of grasshoppers and their characteristic of moving into greens requires that grasshoppers be intensively managed and this generally is in the form of insecticide applications.  Luckily grasshoppers in the Arkansas/Missouri/Oklahoma region are highly susceptible to several currently labeled insecticides.   Reasons for this susceptibility are not well documented but are likely related to the historical lack of exposure to modern insecticides.  Insecticide effectiveness against grasshoppers may be greatly reduced in regions in which the insecticide load is greater, especially in cotton production areas.

Pyrethroid insecticides are currently the insecticide of choice for grasshopper management.  Following application, grasshopper mortality can be detected in a few hours and most pyrethroids will persist for a few days.  Grasshopper movement back into greens, however, may require additional insecticide applications.  Other efforts at grasshopper management include location of fields away from grasses, especially Bermuda in turf farms and hay fields; mechanical removal with “bug knockers”, i.e., boards attached to the front of harvest machines; and even the use of “bug vacuums” attached to harvesters.  Finally, truck drivers should be advised not to park under lights during warm nights.  This may be a source of night flying katydids.

Back to top

Cole (Brassicae) crops:  Harlequin bug, Murgantia histrionica (Hahn). Hemiptera: Pentatomidae

Photo 22

Photo 23

Photo 24

Photo 25

Biology:  Adult harlequin bugs are about 10 mm in length and are black with orange and white markings (Photo 22).  After overwintering in plant debris in and adjacent to cole crop fields, adults fly into newly planted fields, mate and deposit eggs on foliage.  Harlequin bugs are generally host plant specific and usually only occur on brassica plants.  Eggs are barrel shaped and white with 2 black bands and a black cresent on the top (Photo 23).  Adults usually lay a long double row of eggs.  Nymphs hatch in 5 days to several weeks depending on temperature.  Nymphs resemble adults in shape and color but do not possess wings (Photo 24). Both adults and nymphs feed through a stylet mouth by injecting digestive fluids into the plant and extracting plant sap. This feeding results in a distinct discoloration on the leaf surface (Photo 25).  In Arkansas collard and cabbage are the preferred host plants and multiple harlequin bug generations occur each year. 

Management: In small commercial fields produced for fresh market and in home gardens low numbers of harlequin bugs may be tolerated with a minimal effect on yield.  Some reduction in quality due to discoloration of leaves may occur.  However, in commercial collard fields produced for canning even low numbers of harlequin bugs will require management and this may be based primarily on insecticide application.  Beneficial insects are important in harlequin bug regulation and their effects should be prolonged by delaying the use of synthetic insecticides. When insecticides are applied proper spray coverage is important and to achieve this, plant spacing may need to be increased.  Also, use of a surfactant with the spray may increase effectiveness.  After harvest, crop plants should be destroyed as harlequin bugs are generally host plant specific.  Also, volunteer cole crops should be prevented from growing. 

Back to top

Cole (Brassicae) crops:  Imported cabbageworm, Pieris rapae (Linnaeus), and southern cabbageworm, Pontia protodice (Boisduval and LeConte), Lepidoptera: Pieridae

Photo 26

Photo 27

Photo 28

Photo 29

Biology:  Adult cabbageworms (Photo 26) are the white butterflies with grey spots often seen flying through cole crop fields.  Eggs are laid singly on the leaf surface and larvae begin to feed on the foliage after hatching.  As larvae develop, they form many setae which give the larvae a velvetlike appearance. Larvae have four pair of abdominal prolegs plus an anal pair.  Mature imported cabbageworm larvae are light green with a faint yellow line on the top of the body (Photo 27).  Southern cabbageworm larvae are more gray with multiple yellow lines running the length of the body (Photo 28).  Pupation occurs on the leaf surface.  Damage from cabbageworm larvae may be severe (Photo 29).

Management:  After harvest, crop plants should be destroyed as the cabbageworm generally feeds only on cole crops like cabbage and cauliflower.  In the offseason, volunteer cole crops should be prevented from growing.  In small gardens some damage can be tolerated and hand picking of the larger larvae may be sufficient.  After transplanting, the use of  “hard insecticides” should be delayed for as long as possible.  Bacillus thuringiensis (BT) likely offers the best alternative to the “hard insecticide”.  Also, several newer (Biobit) and more effective types of BT may be available and should be tried.  Again, the objective of early season use of  “soft” insecticides is to promote the development and prolong the effectiveness of beneficial organisms.  Foliar insecticides including carbamates, organo-phosphates, pyrethroids and spinosad are currently providing acceptable control of cabbageworms.

Back to top

Cole (Brassicae) crops:  Garden webworm, Achyra rantalis (Guenee) (Photo 30), Hawaiian beet webworm, Spoladea recurvalis (Fabricius) (Photo 31), and Southern beet webworm, Herpetogramma bipunctalis (Fabricius) (Photo 32). Lepedoptera: Pyralidae

Photo 30

Photo 31

Photo 32

Biology:  In recent years, producers of commercial greens in Arkansas and Oklahoma have experienced an increase in the frequency of webworms.  This increase may be related to the widespread use of minimal tillage in soybean.  Farmers are now permitting weeds to grow longer in emerging soybean fields before applying herbicides.  Pigweed, in particular, is now more abundant in late spring and early summer.  Pigweed is a preferred host plant for webworms, especially, the garden webworm.  Populations are building during early season in weedy soybeans and following herbicide application, webworms are moving into non-choice crops like soybean and other vegetables including spinach and greens.  Three webworm species are now common on greens grown in the Arkansas River Valley during the fall.  All have somewhat similar biologies.  Adult moths emerge in spring and deposit eggs on foliage of favorable plants including pigweed.  Eggs hatch in 3 to 7 days and larvae feed for about 3 weeks.  Pigweed can be severely damaged.  Greens are somewhat less susceptible but foliar damage is common especially from the Hawaiian and southern beet webworms.  At maturity, larvae are about 25 mm long and pupate on or just under the soil surface.  Several generations occur annually in Arkansas.

Management:  Beneficial insects often play a substantial role in webworm regulation and their effects should be prolonged by delaying the use of synthetic insecticides.  Use of Bacillus thuringiensis may provide some benefit early in the production season.   In late season,  insecticides are generally the tactic of choice.  Webworm populations vary greatly in their susceptibility to insecticides.  Methomyl may provide acceptable control.  Others include carbamates, organo-phosphates, pyrethroids and spinosad.  Proper spray coverage is important and to achieve this, plant spacing may need to be increased.  Also, use of a surfactant with the spray may increase effectiveness.  Due to the plant shape, webworms are difficult to manage with insecticides on large plants.  Insecticide application through center pivot irrigators has often provided improved control.

Back to top