Vegetables - Assignment Point
Vegetables
Subject: Zoology

INTRODUCTION

Vegetable crops occupy an important status in the agricultural economy though it may not be of the same level as the major cereals and cash crops like rice, cotton, sugarcane, tea and coffee.The vegetables form an essential component of the human diet specially in the case of India and some South-east Asian countries where sizable population basically consists of vegetarians.

The variability in the crops that are used as vegetables is enormous; there are some like potato, tomato, brinjal, cabbage and cauliflower which are grown throughout the world; while there are others like drumstick, little gourd, pointed gourd and round gourd which are specific not only to a country but also to a particular region of the country as is found in India.

Inspite of the importance of vegetables in Indian diet, it occupies only about 1.2 per cent of the total area under cultivation. The total production is about 16 million tonnes per year which is rather very low. Keeping in view the vast multitude of people who generally take one or the other vegetable with the cereals, it is estimated that per capita consumption of vegetables is only 40 g while for nutritiously balanced vegetarian diet it should be about 400 g.

Vegetables are rich source of proteins, carbohydrates, minerals, vitamins as also provide the necessary roughages. Cabbage, carrot, spinach and amaranthus contain vitamin A, cabbage, beet-root, bitter gourd and chillies are rich sources of vitamin C; beans and peas provide lot of proteins while leafy vegetables supply calcium and iron.

Significant progress has been made in improving and introducing high yielding varieties of major cereals and cash crops, however, relatively very little attention has been paid to the improvement of vegetable crops. Since the last decade spectacular achievements under the ‘green revolution’ have been projected in different forums but there is hardly any mention about the improvement in the yields of vegetable crops. There are only a few vegetables like okra, tomato, cabbage and cauliflower in which new improved varieties have been evolved by using the modern technology of breeding and high yield potential realised by developing suitable agronomic practices. However, due to various constraints their cultivation is restricted only to limited areas and thus there has hardly been any impact on the overall production of even these crops.

Objectives

  1. To evaluate various poly phagous insects of winter vegetables.
  2. To determine the nature of damage of polyphagous insect in winter vegetables.
  3. To estimate the damage of winter vegetables by various polyphogous insects.

MATERIALS AND METHODS

This paper mainly depends on the secondary data. Different published report of different journals mainly supported in providing data for this paper. It has been prepared by comprehensive studies of various articles published in different journals, books and proceeding available in libraries of SAU, Banghabandhu SheikhMuziburRahmanAgriculturalUniversity, BAU, BARI. Variable information has been    collected  through contact with respective persons and with the help of computer CD Rom search and Internet facilities.

DISCUSSION

Tomato infected by hornworm

Hornworms

Tomato hornworms are the most familiar insect pests. These caterpillars grow to an awesome size, three inches or longer, with a fearsome looking “horn” on their back end, the purpose of which is unknown other than to scare gardeners. The rapid loss of tomato leaves as well as big green droppings at the plant’s base, signals a hornworm at work. While the caterpillar stage usually takes three to four weeks to complete, hornworms grow so much in the last few days, they seem to appear almost overnight.

Despite their size, hornworms are quite easy to control. They are very susceptible to Bacillus thuringiensis, the biological insecticide sold under trade names such as Dipel, Thuricide, and Caterpillar Attack. Most other garden insecticides (Sevin,   Malathion) also are effective.

I hunt hornworms as a form of recreational pest control, and I recently met a man who trained his dog to find them! Because they are large, hornworms are easy to hand-pick or to cut with a knife or scissors. They are, however, difficult to find, as they blend into their background. Hornworms are most visible early in the morning, when they likely are on the plant’s exterior

Psyllids

Though hornworns are large, the most damaging tomato insect often is the over-looked potato/tomato psyllid. Developing psyllids are small (aphid-sized), pale green or yellow, and somewhat scale-like in appearance. Adults are banded black and white and jump readily when disturbed.

Psyllids feed on the underside of leaves, sucking plant sap and introducing a saliva that disrupts plant growth. New growth may appear twisted and discolored. Tomatoes from psyllid-infested plants are small and mealy textured. Psyllid-injured Big Boy and other tomato varieties may grow no larger than a small marble.

Tomato psyllids do not occur regularly, as they overwinter in southern areas and are carried by winds into Colorado. Heavy flights were detected in several locations earlier this year. Check plants for evidence of psyllids, and look for their characteristic droppings that consist of small waxy beads. These droppings also resemble granulated sugar or salt.

Controls are warranted when psyllids are present. Sulfur dusts, permethrin, esfenvalerate or insecticidal soaps are effective treatments. Apply thoroughly, including on leaf undersides, where psyllids nymphs occur.

Greenhouse Whitefly

Greenhouse whitefly is another common tomato pest. The flying adult stage is familiar to most gardeners, but the pale, motionless nymphs that feed on leaf undersides are not. Nymphs and adults remove sap and reduce plant vigor. Whiteflies also may excrete sticky honeydew, which is more of a nuisance than a serious problem.

Once established, whiteflies are difficult to control. They resist most insecticides. Sprays must cover the leaf undersides to kill the nymphs. Pyrethrins and malathion may provide some control, but insecticidal soaps probably are the best. (NOTE: Most whitefly sprays sold in nurseries contain resmethrin, and are not legal to use on edible crops such as tomatoes.)

Greenhouse whitefly is not native to Colorado, and it cannot survive our outdoor temperatures. Problems arise annually, however, from plants grown in whitefly-infested greenhouses or other indoor areas. Therefore the best means of managing whitefly is to just say no: Don’t grow or purchase transplants that may have come from whitefly-infested places.

Flea Beetles

Flea Beetles (damage seen above) are small, black chewing insects that create pits in the leaves and fruits of many plants including tomatoes. They are first seen in the spring as they favor the early growth of the plants they affect.

By Judy Sedbrook, Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver County

Looking forward to the flavor of a home-grown tomato after months of the tasteless fare offered in grocery stores? Unless you are vigilant, diseases, pests, and environmental problems can rob you of that perfect tomato.

Insects

There are a number of insects that can cause tomato problems. Most noticeable are the hornworms. These 3-4 inch caterpillars devour the foliage near the top of the plant. They are easily picked off and disposed of. Bacillus thuringiensis, rotenone or Sevin insecticides can control them when they are small.

Aphids suck the juices from the plant. They can be found on the underside of leaves and identified by the sticky honeydew they produce. Aphids can be effectively controlled with insecticidal soap.

Psyllids, another small insect that sucks plant juices, are more of a problem some years than others. They cause the foliage to turn yellow and curl. Plants are stunted and often produce no fruit. Insecticidal soap is also effective against psyllids.

Flea Beetles chew small holes into the leaves, leaving it looking as though it had been “blasted” with fine shot.

Environmental problems

Distortion of the tomato is often the result of an environmental problem.

With blossom end rot, a small water-soaked spot appears near the blossom end of the tomato. As it enlarges, the spot becomes dark brown to black, sunken and leathery.  This happens when calcium is not readily available to developing fruit. Calcium imbalance can result from fluctuations in soil moisture caused by improper irrigation or prolonged dry weather. Other causes are high nitrogen levels from fertilizer, or a disruption of the root system. You can prevent blossom end rot by the correct application of nitrogen, and keeping the plants mulched to maintain moisture. Mulching also helps to control weeds and eliminate the need for cultivation that can damage roots.

 Blossom End Rot

SUNSCALD

The sudden exposure of fruits to direct sunlight in hot, dry weather can cause sunscald. This results in white or yellow patches on the side of the tomato exposed to the sun. To avoid sunscald, limit pruning and keep foliage healthy to provide shade and protection for the ripening fruit.

 Sunscald

Misshapen or malformed fruit can be caused by cool weather occurring during fruit set or from herbicide exposure.

Catfacing is an abnormality that develops on the blossom end of susceptible tomato varieties. It results from cool weather at blossom time and causes the fruit to pucker and have deep crevices.

Catfacing

GROTH CRACKS

Growth cracks occur as a result of the rapid growth stimulated by wet weather following a dry period. Two types of growth cracks affect the stem end of tomatoes: concentric and radial. Concentric cracking produces circular cracks around the stem end of the fruit. Radial cracks spread outward from the stem scar.

Growth cracks

LEAF ROLL

Leaf roll, or leaf curl, is a physiologic distortion that may develop with periods of cool, rainy weather. It cause the lower leaves to roll upward and become thick and leathery. Leaf roll does not affect plant growth or fruit production and requires no treatment.

Leaf Roll

Herbicides can distort the foliage and fruit of tomatoes. They are especially sensitive to 2,4-D. Damage can bend the leaves down, causing cupping and thickening. New leaves are narrow and twisted and do not fully expand. Fruit may be catfaced and fail to ripen. Exposure can occur when herbicides are applied to lawns for weed control and the spray “drifts”. Resultant fumes can also effect the plants for several days after treatment. Clippings from grass that has been sprayed with a herbicide should not be used as mulch in the vegetable garden. If the exposure is minimal, the plant will outgrow the injury. Be sure to water the affected plants thoroughly and often.

TOMATO FRUITWORM

The tomato fruitworm (Helicoverpa zea) is the most damaging tomato insect pest in South Carolina. Fruitworms occur throughout the Western Hemisphere extending as far north as Canada and as far south as Argentina. The tomato fruitworm feeds on tomato, corn and cotton and is also called the corn earworm or the cotton bollworm. It also attacks soybeans, peppers, tobacco, beans, okra and eggplant. The adult tomato fruitworm is a moth. It is usually light yellowish-olive with a single dark spot near the center of each forewing. It lays eggs singly, usually on the lower sides of leaflets close to the flower or fruits. The eggs are creamy white when laid but develop a reddish-brown band just prior to hatching. Larvae (caterpillars) hatch from the eggs. The larvae are yellowish-white with a brown head. The color of older larvae varies from greenish-yellow to brown or even black with paler stripes running lengthwise on the body. Larvae grow to a size of about 1½ inches in length.

Fruitworms feed on tomato leaves and fruit. Distorted leaves often result when they feed upon the tips of the leaves in the developing bud. Larvae may also bore into stalks or midribs. When fruit is present, larvae enter it soon after hatching. They prefer green fruit and will enter it usually at the stem end, causing extensive direct damage and promoting decay. The larvae are cannibalistic, so there is rarely more than one larva per fruit. Larvae usually complete development in a single fruit, but when fruits are small they may feed in several.

Fruitworms overwinter (survive the winter) as pupae (nonfeeding stage where the larva changes to an adult) in the top 2 inches of soil. Adults emerge from early May to early June. Fruitworms have four to five generations per year in South Carolina.

POTATO APHID

Potato aphids (Macrosiphum euphorbiae) occur throughout North America. They are common visitors to home vegetable gardens in South Carolina.

Potato aphids infest a wide range of host plants. Some important cultivated hosts include potato, tomato, eggplant, sunflower, pepper, pea, bean, apple, turnip, corn, sweet potato, asparagus, clover and rose. Weeds such as ragweed, lambsquarters, jimsonweed, pigweed, shepherdspurse and wild lettuce are also common food plants.

This soft-bodied, pear-shaped insect may be solid pink, green and pink mottled, or light green with a dark stripe. Usually wingless, it is about 1/8 inch long and has a pair of long, slender tailpipelike appendages known as cornicles. The egg stage does not occur in South Carolina. Adult females give birth to live young, called nymphs. Although slightly smaller than adults, nymphs are similar in color and shape.

Sporadic in occurrence, potato aphid infestations are rarely severe enough to kill plants. Aphids pierce veins, stems, growing tips and blossoms with their needlelike mouthparts. As a result, blossoms are shed and yield is reduced. New growth becomes stunted and curled. Heavily infested plants turn brown and die from the top down. Aphids tend to spread rapidly from field to field transmitting a number of viral diseases. These include various mosaics, leaf roll, spindle tuber and unmottled curly dwarf.

In South Carolina, female potato aphids feed and reproduce year round. No eggs or males are produced. Without mating, wingless females give birth to about 50 live nymphs. During warm weather, each of these nymphs matures in two or three weeks. The life cycle continues in this manner until overcrowding occurs or food becomes scarce. At this time nymphs develop into winged adults and migrate to new host plants. Once settled, these aphids begin reproducing and the life cycle continues as before. During the winter, feeding and reproduction occur at a much slower rate. Many generations are produced each year.

STINK BUGS AND LEAFFOOTED BUGS

Several species of stink bugs as well as leaffooted bugs are serious pests of tomatoes and various other vegetable crops in South Carolina. Brown (Euschistus servus) and green stink bugs (Acrosternum hilare) have been reported as far north as Quebec; however, in the United States, they are more injurious in the South. Although more common in the South, leaffooted bugs (Leptoglossus phyllopus) occur as far west as Arizona.

Stink bugs feed on over 52 plants, including native and ornamental trees, shrubs, vines, weeds and many cultivated crops. The preferred hosts are nearly all wild plants. Stink bugs build up their numbers on these hosts and move to cultivated hosts as their preferred food becomes overly mature. Among vegetable crops, stink bugs attack bean and cowpea seeds, okra pods, ripening tomato fruit, and stems of melons and asparagus. Bean, cowpea, sorghum, eggplant, potato, tomato, peach, strawberry, okra and watermelon are only a few of the leaffooted bug’s many host plants.

All adult stink bugs are shield-shaped. Green stink bugs are about 9/16 to ¾ inch in length. They are bright green with a narrow orange-yellow line bordering the major body regions. Brown stink bugs are dull grayish yellow and ½ to 5/8 inch long. Leaffooted bugs are about 13/16 inch long. They have dark brown bodies, a narrow cream colored stripe across the back and flattened leaf-like hind legs.

When first laid, the barrel-shaped eggs of the green stink bugs are yellow to green, later turning pink to gray. The white kettle-shaped eggs of the brown stink bug are slightly smaller than those of the green stink bug. Leaffooted bug eggs are slightly keg-shaped.

Nymphs of all three bugs are similar in shape to the adults but smaller. Green stink bug nymphs are mainly black when small, but as they mature, they become green with orange and black markings. Nymphs of the brown stink bug are light green. Leaffooted bug nymphs are bright red.

Nymphs and adults of both kinds of bugs pierce plants with their needlelike mouthparts and suck sap from pods, buds, blossoms and seeds. The degree of damage depends, to some extent, on the developmental stage of the plant when the stink bug pierces it. Immature fruits and pods punctured by bugs become deformed as they develop. Seeds are often flattened and shriveled, and germination is reduced.

Stink bugs overwinter as adults in ditch banks, along fence rows, on roadsides and in other similar places. They become active in spring when temperatures rise above 70° F. Each female deposits up to several hundred eggs, usually in mid- or late June. These eggs are laid in clusters, mainly on leaves and stems, but also on pods. Nymphs hatch from these eggs. Two generations per year occur in South Carolina. Stink bugs usually reach high population levels in July through early October.

The biology of leaffooted bugs is not well-documented. They overwinter as adults and have been collected all months of the year. They are most common from May to the fall months.

HORNWORMS

The tobacco hornworm (Manduca sexta) ranges from southern Canada to Argentina. The range of the tomato hornworm (Manduca quinquemaculata), however, extends only from southern Canada through the southern United States.

Hornworms feed primarily on solanaceous plants (those in the potato family). They include tobacco, tomato, eggplant, pepper and some weedy plants. Tobacco and tomato plants are preferred.

Hornworm eggs are smooth, spherical and about 1/16 inch in diameter. Light green at first, they turn white before hatching. Mature tobacco hornworm larvae (caterpillars) usually have green bodies with fine white hairs and seven diagonal white stripes on each side. The hornlike structure that gives them their name projects from a posterior abdominal segment and is usually curved and red. Tomato hornworm larvae have eight V-shaped markings on each side; the horn is straight and black. Both species are about 3 to 3½ inches long when fully grown.

Hornworms strip leaves from tomato vines. If a heavy infestation develops, these caterpillars also feed on developing fruit. Rather than bore into the fruit, they feed on the surface leaving large, open scars. Fruit damage, however, is much less common than loss of leaves. Hornworm damage usually begins to occur in midsummer and continues throughout the remainder of the growing season.

Hornworms overwinter in the soil as pupae (the nonfeeding stage where the larva changes to an adult). Moths of this overwintering generation begin to emerge in early June and may continue to emerge as late as August. Hornworm moths frequently can be seen hovering over plants at dusk. At night, they lay eggs on the underside of leaves. Each moth deposits one to five eggs per plant visit.

Hornworms emerge from eggs in about four days, depending upon temperature. After feeding for three weeks, hornworms burrow into the soil to pupate (to transform to the nonfeeding stage where the larva changes to an adult form). In summer, the pupal period lasts three weeks, after which a new generation of moths emerges. Heavy egg deposition is common in August and early September. At least two generations occur each year in South Carolina.

Natural parasitism often occurs, where Brachonid wasps oviposit eggs into the hornworms, the larvae feed inside, and then pupate on the backs of the hornworms. These pupal cases are seen as white projections on the back of the hornworm. If parasitized hornworms are found on the crop, feeding will have ceased, so leave it for the next generation of beneficial wasps to hatch.

Actively feeding hornworms may be hand picked from the plants.

SILVER LEAF WHITEFLY

Silverleaf whitefly (Bemisia argentifolii) occurs around the world in tropical and subtropical areas and in greenhouses in temperate areas. It has been reported from all southeastern states. Additionally, it has been reported from Arizona, California, the District of Columbia, Maryland and Texas.

This pest feeds on many different kinds of plants. The most frequently reported hosts in the southeastern U.S. are poinsettia, gerbera daisy, tomato, squash, cucumbers, melons and cotton.

The silverleaf whitefly is small, about 1/32 inch long and whitish yellow. The head is broad at the antennae and narrow toward the mouthparts. The wings are held roof-like at about a 45-degree angle, whereas other whiteflies usually hold the wings nearly flat over the body. As a result, the silverleaf whitefly appears more slender than other common whiteflies.

The eggs are whitish to light beige. They are inserted on end in the undersides of new leaves. Nymphs (immature stage) hatch from the eggs. The nymphal stage appears glassy to opaque yellow. Its body is flattened and scale-like with the edge of the body relatively near the leaf surface. The pupa or fourth nymphal instar will be somewhat darker beige-yellow and opaque.

Silverleaf whiteflies damage plants in two ways: directly and indirectly. Direct damage results from their feeding activity, which involves them sucking plant sap. Both the adults and nymphs contribute to direct damage. Chlorotic (yellow) spots sometimes appear at the feeding sites on leaves. Heavy infestations cause leaf wilting. In addition, as they feed they excrete honeydew (a sugary substance), which the sooty mold fungi feed on. The resulting dark splotches on the leaves may reduce photosynthesis and other physiological functions of the plant. Indirect damage results from their activity as disease vectors (carriers). The silverleaf whitefly carries and spreads several important viral diseases of tomatoes, lettuce and melons in the southeastern United States.

The number of eggs laid by each female over her lifetime varies considerably but appears to be around 80 to 100. Nymphs that hatch from the eggs are called “crawlers” because they crawl about until they insert thread-like mouthparts into the undersides of leaves to feed. Once they begin feeding, they tuck their legs and antennae underneath their bodies and settle down closely to the leaf surface and do not move again.

Crawlers molt into scale-like nymphs that also suck out sap. Nymphs molt a second and third time. The fourth stage eventually becomes a nonfeeding pupa.

The adult whitefly develops within the pupa. Adults emerge from the pupa through a T-shaped slit about a month from the time the egg was laid. Females live about two weeks.

Wireworms on Sweetpotatoes

At least 3 species of wireworms damage the roots of sweetpotatoes in North Carolina. They are the tobacco wireworms, the southern potato wireworm and the corn wireworm. Damaged roots are downgraded or discarded. Adult wireworms are commonly known as “click” beetles. They acquired the name by their ability to “click” themselves upright when placed on their backs.

Although wireworms are present throughout NC, comparatively few fields suffer economic damage. Wireworm abundance is greatly dependent upon such factors as soil type, rotation, drought, previous crop, insecticide program, and other cultural practices. An assessment of the need to treat must be based on the above factors, knowledge of the life history of wireworms and previous experience. One can also monitor adult click beetle flights with a black light insect trap or use soil baits of corn or wheat to detect larvae present. Bait may be placed 6 inches in the soil at 6 or so locations in the field in early Spring and checked for insect species and numbers 3 weeks later.

Tobacco Wireworm

Conderus vespertinus (F.) Coleoptera: Elateridae

Biology – The eggs, averaging 240 per female, are laid singly on or slightly beneath the soil surface in the summer. Larvae hatch and feed on roots of corn, tobacco, potatoes and other plants. The winter is passed in the larval stage. Pupation in June occurs in the soil. Adults emerge during early summer with the greatest activity from late June through July. There is only one generation per year. The typical life cycle requires about 348 days in North Carolina as follows: egg, 10 days; larva, 315 days; pupa, 10 days, and pre-oviposition period, 13 days.

Host Plants

The tobacco wireworm apparently prefers tobacco, but it feeds on a variety of other plants including cotton, corn, potatoes, sweetpotatoes and various truck crops.

Damage

Damage occurs as a ragged hole on the underground root. Oftentimes, a single root may have 10 or more small holes. Early feeding appears as long, shallow cavities. Late or most recent feeding appears as ragged, deep holes.

Distribution

The tobacco wireworm is common in the southeastern states. In North Carolina, it occurs throughout most of the Coastal Plain. It is much more prevalent in areas where tobacco, cotton or corn are the main crops than in areas planted chiefly with truck crops.

The Southern Potato Wireworm

Conoderus falli Lane. Coleoptera: Elateridae

Biology – While the biology of this insect pest has not been studied in North Carolina, adults are found in fields throughout the year in South Carolina. There are two generations annually. Adults from overwintering larvae begin to appear in large numbers during May, reaching their peak abundance in June. Each first- generation female lays an average of 36 eggs. They hatch into the “short cycle” brood which requires 42 to 109 days to mature. Adults of this “short-cycle” brood are abundant in late August and throughout September. They mate and lay eggs of the “long cycle” brood and the overwintering generation requires 239 to 318 days for the egg to reach adulthood.

Host Plants

The southern potato wireworm appears to prefer potato tubers. Newly transplanted tobacco seedlings, the roots of sweetpotatoes, carrots, corn seedlings, and the stems of tomato transplants are also frequently attacked. Less frequently damaged hosts are the roots of beets, fruit of strawberries, cantaloupes, watermelons, and tomatoes that touch the soil surface.

Damage

Damage occurs as a ragged hole on the underground root. Oftentimes, a single root may have 10 or more small holes. Early feeding appears as large shallow cavities. Late or most recent feeding appears as ragged, deep holes.

Distribution

The southern potato wireworm apparently was introduced into the U.S. from South America. Within the U.S. it has been reported along coasts from North Carolina south to Louisiana. Within N.C., it occurs mainly in the southeastern counties of the Coastal Plain.

The Corn Wireworm

Melanotus communis (Gyll.) Coleoptera: Elateridae

The corn wireworm, a large wireworm, is likely the most damaging species in the more northern sweetpotato growing areas. The injury, often extensive, is similar to that caused by other wireworms. However, the holes are large and deeper.

Not a great amount of information is known about the corn wireworm. This wireworm does spend more than one year as destructive larvae in the soil. Adult click beetles prefer to lay eggs in grassy undisturbed soil. Hence, land put out of production for several years or land previously in sod harbor this species.

Control consists of avoid land previously in sod or out of production. The preplant use of fumigants for nematodes will also provide some control of this soil inhabitant. Traditional applications of a granular insecticide over the row in late July are thought to be of little value against the corn wireworm.

Bean Leaf Beetle

Kathleen Bennett, Mario Carrillo, Eric Burkness, Robert Koch and Bill Hutchison, University of Minn., St. Paul

The bean leaf beetle (BLB), Cerotoma trifurcata (Foster), is a common pest of soybeans and snap (green) beans in Minnesota. In the upper Midwest, populations of BLB have increased during the last 4-5 years, possibly as a result of mild winters, good snow cover, and increasing soybean acreage. Adult BLB prefer to feed on the leaves of soybeans and snap beans although they have been found feeding on other crops such as peas, clover and dry edible beans.

Unlike many of us who prefer to fly south for the winter, BLB are able to overwinter as adults throughout the Midwest. They seek shelter under oak leaves or within curled ash leaves (and other leaf litter) in wooded areas close to bean fields, or within soybean stubble left in fields. In early spring, the beetles disperse from their overwintering sites and rapidly colonize newly emerging snap bean or soybean seedlings. Their feeding damage is characterized by round holes (3-4 mm diameter). Extensive feeding can result in complete defoliation, and possibly death of young seedlings (Bennett et al. 2003). Adult beetles feed and live for about 4-6 weeks. Female BLB lay their eggs in the soil, presumably close to the base of legumes; hatching occurs within one to three weeks depending on temperature. Larvae prefer to feed on root nodules, common in legumes. Later in the year, the F1 adults can also cause significant feeding damage to soybean and snap bean pods.

To develop better predictive models of BLB emergence and potential damage, we began collecting additional overwintering data on adult survival. As part of this effort, the purpose of this study was to assess the relationship between monthly winter survival and supercooling points (SCP; i.e., the temperature at which spontaneous freezing will occur) for BLB adults. In this article we summarize the results of our 2003-2004 study. We also contrast these results with another important vegetable pest, the striped cucumber beetle, Acalymma vittatum (Fabricius).

Results—Bean Leaf Beetle

Overwintering BLB appeared to have a fairly high survival rate with 40-45% of the beetles still surviving between March and April 2004 at Rosemount Minnesota (Table 1). Our estimates of BLB survival are similar to observations by Len Dobbins (FMC Corp., Indiana), who recently reported estimates of 50-65% survival in the Midwest. It appears that surface soil temperatures on average did not surpass the mean SCP; therefore, many of the adult beetles were able to avoid freezing of their body contents, and thus able to survive the winter. However, in addition to temperature, it is known that winter mortality is also a function of the time of exposure to low temperatures. For these reasons, mortality observed this spring may have also occurred as a result of chill injury. It is also interesting to note that in April the SCP increased to -5.96 ºC. This finding suggests that the beetles were beginning to acclimate to warmer spring temperatures.

Finally, as noted by Dr. Dave Ragsdale (Dept. of Entomology, University of Minnesota), an additional key mortality factor for BLB appears to be the amount of spring rainfall that BLB is exposed to, particularly in April. BLB may survive winter temperatures very well, then experience high mortality in early spring due to high precipitation. Although there may be some direct affects of rainfall, the primary factor under these conditions is a fungal disease, Beauveria spp. This past spring, however, was relatively dry for much of southern Minnesota, and therefore may not result in significant BLB mortality.

Our results for 2003-2004 are also similar to a previous two-year study in Minnesota during the 1980s (D. Ragsdale, unpublished data). We are in the process of comparing our results with this earlier study, and also plan to repeat the study in 2004-2005. Additional data are needed to better understand the relationship between overwintering survival and SCP measurements. We also plan to conduct further experiments to develop a relationship between the recorded soil surface temperatures, mortality rates, and SCPs to be able to predict the percentage survival of this pest following multiple weather scenarios.

Table 1 . Mean percentage survival, soil temperature and supercooling point (SCP; ±SEM) of bean leaf beetles throughout the 2003-2004 winter, Rosemount, MN.

Month n Survival (%) Soil Temp. (ºC) n SCP (ºC)
January4166-6.70
February4058-3.4019-8.89 ± 0.15
March40400.7014-8.83 ± 0.30
April20458.108-5.96 ± 0.21

Contrasting Bean Leaf Beetle and Striped Cucumber Beetle Survival:  In addition to BLB, we also conducted a striped cucumber beetle survival study this past winter at Rosemount. To date, little information is known about the northern limits of cucumber beetle survival. Although the cucumber beetle is not closely related to BLB (i.e., different genus), the adults are similar in size and shape to BLB. In contrast to BLB, however, we found high mortality of cucumber beetles by December of 2003 with 100% mortality by February 2004. These results with cucumber beetle are also similar to those from the 2002-2003 winter. Although migration of beetles from southern states may continue to play a role in developing summer infestations in Minnesota, our winter mortality results suggest that locally overwintering beetles may only survive, and contribute to summer infestations, under very mild winter conditions.

 Insect Pest Problems

Squash bugs (Anasa tristis) are the major pest for most squash and pumpkin growers. Market gardener and author Steve Salt writes:

Year in and year out, . . . the Public Enemy Number One of pumpkins (on my farm at least)—causing losses greater than rots, frost, and drought combined—is the squash bug. These pungently odoriferous gray-brown insects lay masses of red-brown eggs on leaves and stems in early midsummer. The eggs hatch into hordes of tiny pale gray nymphs which fan out through the pumpkin patch, sucking sap and (some scientists speculate) possibly injecting a poison into the plants. Plants attacked by even a few squash-bug nymphs wither, and the leaves curl and turn a crispy texture with a characteristic bronze color. Immature fruits on affected plants cease development, and frequently rot or fall prey to cucumber beetle predation. Plants fail to recover even after the nymphs move on in search of fresh victims. Losses can be severe; badly infested fields look like someone has gone through the patch with a flame-thrower.

Cucumber beetles are another insect pest to watch for. There are several kinds, and they vary in importance around the country. The striped cucumber beetle is about 3/16-inch long, greenish-yellow, with three longitudinal black stripes. The spotted cucumber beetle is the same color but with 12 black spots. These beetles feed on young plants as they emerge and can decimate a planting. They also spread bacterial wilt, a disease that can cause severe plant losses later in the season. Row covers can provide a barrier to cucumber beetles when the plants are young. (They must be removed when plants begin to bloom so that insect pollinators can reach the blossoms.) Natural enemies include soldier beetles, tachinid flies, brachonid wasps, and bats, but they may not be effective in substantially reducing beetle damage. A botanical insecticide, such as rotenone, may be helpful if damage is intolerable. Research done by Cornell University entomologist Michael Hoffmann has shown that fall cultivation, if done while the beetles are still active, can cause more than 40% mortality. (6)

Squash vine borers (Melittia cucurbitae) appear when vines begin to run. The borer is a fat, 1-inch-long, brown-headed white caterpillar, the larva of a ¾-inch-long moth with dark front wings, clear hind wings, and a red abdomen. The moths lay single eggs in late spring or early summer along the stem near the base of a vine. The larvae emerge in about a week and bore holes to enter the stem. Evidence of borer activity are the small hole and a pile of greenish frass (excrement) beneath the hole. The vine wilts suddenly and dies. Since damage occurs inside the stem, it is difficult to spot and treat. For ways to deal with this pest, see the ATTRA publication Squash Bug and Squash Vine Borer: Organic Controls.

SOUTH FLORIDA VEGETABLE PEST HOTLINE

Insects

Insect numbers continue to rebound as the season progresses. Leafminers Growers and scouts in Southwest Florida report that leafminer numbers have increased and are building rapidly in most locations. Respondents from the Manatee/Ruskin area indicate that leafminer pressure is up across the area. Reports from the Homestead area note heavy leafminer pressure in a range of crops including beans, eggplant and tomato. East Coast growers also report increased leaf miner activity. With the on-set of cooler weather across the peninsula, growers across the state can expect to see an increase in leafminer pressure. Leafminers attack many row crops but are particularly damaging on celery, crucifers, cucurbits, okra, potato and tomato. Florida growers report that leafminers are the second most important tomato insect pest especially in south and central production areas. Leafminers are present for much of the year in Florida. In south Florida, populations peak between October and March while in central Florida they are a problem in both spring and fall.

The two major species of leafminer that cause problems in vegetables in Florida are the vegetable leafminer (L. sativae) and most commonly (Liriomyza trifolii) – sometimes referred to as the celery leafminer but which has no approved common name. The adults are small yellow and black flies about the size of a gnat. The female punctures or “stipples” the leaves with her ovipositor to lay eggs in the leaf tissue or to feed on sap. Leafminer damage is easily recognized by the irregular serpentine mines in leaves, which are caused by feeding larvae. Heavy leafmining damage can reduce photosynthesis and cause leaf desiccation and abscission. The yellow maggots with black, sickle-shaped mouthparts feed on the mesophyll or chlorophyll tissue between upper and lower leaf surface leaving a winding trail or pattern through the leaf. The tunnel is clear with the exception of a trail of black fecal material left behind as the maggot feeds. There are three larval stages. Each larval instar is completed in 2 – 3 days. The maggots feed approximately 7 days growing to about 1/10 to inch in length prior to exiting the leaf to pupate on the ground or mulch under infested plants. Leafminer injury is readily visible to the grower but healthy plants can tolerate considerable damage without excessive loss of vigor and yield. The Florida Tomato Scouting Guide sets action thresholds at 0.7 larva per plant for young plants with less than 2 true leaves and 0.7 larva per 3 terminal leaflets for larger plants. Heavily damaged leaves will often drop, due in part to entry of pathogenic organisms into old mines.

CONCLUSION

Leaves are the most affected plant parts in all crops; by the polyphagous insects such as “heads of cabbage; inflorescence and pods of other vegetables are eaten up by pest larvae. In most cases the older leaves arernost infested; younger leaves are als6 damaged at the time of high infestation/of the pest. Severe pod infestation is noticed in broccoli, radish and mustard. Central leaves of cabbage or cauiiflowe- may be riddled with holes due to larval feeding, and such leaves are unfit for hurran consumpt on. Severely infested cabbage fields show poorly developed cabbage heads formed by riddled dried leaves.

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Vegetables

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