INSECTS FOUND IN FORAGE AND PASTURE
Stephen Bambara & Wes Watson
Department of Entomology
The alfalfa weevil (Hypera postica) is the most important insect
pest of alfalfa in North Carolina. Unlike the situation in more northern states,
the adults often remain active throughout much of the winter when mild temperatures
persist. Although peak egg laying occurs December through January, unseasonably
warm winters will result in earlier-than-usual larval activity and continued
egg laying into spring. In some years, treatments for alfalfa weevil
have begun as early as late February in some south-central counties. As a result,
scouting is necessary for effective and economic weevil control.
Scout for alfalfa weevil by selecting 30 stems at random throughout the field. Cut the stems carefully to avoid dislodging any larvae. Then beat them against the inside of a plastic bucket, dislodging the larvae into the bottom of the bucket where they can be counted. Young alfalfa weevil larvae are about 1/16 inch long and are yellowish-green with shiny black heads. Older larvae reach a length of about 1/4 inch and are light green with a white stripe down the middle of the back. Finally, the length of each stem is measured and the tips are examined carefully for damage and for other larvae. Treatment decisions are based on the thresholds of (plants < 6" tall) 1 1arva/stem with >50% foliar damage OR (plants >6" tall) 1.5 larvae/stem with >50% foliar damage. Sample 30 stems.
One of the factors complicating alfalfa weevil control is the unpredictable nature of the weather during early spring. Cool or cold weather slows feeding and oviposition activity, sometimes extending weevil activity beyond the effective period of foliage protection provided by an insecticide treatment. Because temperatures at this time of the year are quite variable, most growers choose an insecticide with longer residual (such as carbofuran) and reserve less persistent chemicals (such as malathion) for secondary use. Under most circumstances, a single well-timed application will provide adequate foliage protection. Fall applications are rarely needed or useful except to protect newly established stands against other pests such as grasshoppers. Other suggested chemicals for use in alfalfa weevil management can be found in the North Carolina Agricultural Chemicals Manual. Since pesticide labels change frequently, always use the most recent issue of the chem manula and always read the product labels before deciding which chemical to use. In selecting the proper insecticide for use against alfalfa pests, plan ahead and always consider the preharvest or pregrazing intervals for each product.
The potato leafhopper (Empoasca fabae) is a pest of occasional importance in alfalfa. Potato leafhoppers are not known to overwinter in North Carolina. They migrate north from the Gulf Coast and make their initial appearance in North Carolina around April and peak in July to August when the weather becomes hot and dry. While feeding, leafhoppers inject a toxin into the leaves causing a yellowing that is commonly referred to as "hopper burn". This damage reduces stand vigor and can shorten the lifespan of the stand. Once hopper burn becomes apparent, it is too late to protect that cutting by chemical spray. Early cutting can be done in lieu of spraying if the crop is at 60% bud. However, early cutting will also reduce stand vigor and should not be done more than once per season. Spraying for leafhoppers is rarely needed and should be based on a threshold determined by taking five sets of 20 sweeps (100 sweeps) with a sweep net across the field. Treatment thresholds for the potato leafhopper are 1 leafhopper/sweep for plants < 6" tall OR 2 leafhoppers/sweep with plants >6" tall. Suggested chemicals are listed in the NC Agricultural Chemicals Manual.
The most important insect pests in forage grasses are the true armyworm (Pseudaletia unipuncta) and the fall armyworm (Spodoptera frugiperda) . Damage from these pests can kill or severely stunt grass in pastures. Armyworms are a greater problem during spring and early July, after which time, natural controls keep the population below threshold level. Armyworms feed primarily at night and remain hidden in ground litter by day. They may be particularly numerous following a cool, wet, spring which tends to limit the suppression by natural controls. Coloration can be deceiving in identifying the two species.
In comparison, Fall armyworms have an inverted Y on the head. Also, fall armyworms are usually a problem later in the season (July to September), after the moths have migrated northward into the state from the Gulf Coast area. FAW larvae are active day and night. Parasites and disease organisms will often keep fall armyworm populations in check. However, extremely hot and dry conditions reduce the activity of the fall armyworm's fungal pathogen and promote larval activity. Though they prefer grasses, they can also do significant damage to young alfalfa. Fall armyworms are somewhat more difficult to control than armyworms, but both species have the same treatment threshold of five larvae per square foot or 10% damaged foliage. Threshold on young alfalfa may be lowered to 2-3 larvae per square foot. Suggested chemicals for use against both armyworm species can be found in the NC Agricultural Manual. Growers are reminded to pay close attention to preharvest and pregrazing intervals and to make certain that they select a chemical that is labeled specifically for the pest species and site.
Cutworms (Agrotis and Feltia) can cause damage in newly planted forage or pasture most often during May in infrequent years. Cutworms feed at the base of the plants during the night and curl up when disturbed. Black and granulate cutworms are the most common. There are no good thresholds, but if damage is apparent and there are two or three larvae per square yard, treatment could be investigated. Soap disclosure treatments may be helpful. All areas of a pasture may not need treatment. There may be two or three generations per season. Any pesticide applications should be made late in the day and when foliage is not wet. Some possible chemicals include Lannate, Warrior, Lorsban, Sevin and B.t. depending upon the crop and use. Read labelling carefully regarding grazing or cutting restrictions.
Green June beetle (Cotinis nitida) grubs feed on organic matter
in the root zone. Heavy feeding activity can dislodge or damage roots of plants.
Periods of drought can magnify the effects, resulting in brown and dying patches.
At night, large larvae may leave the soil and crawl. Holes with small earthen
turrets about the diameter of a finger are sometimes evident. Treatment (with
carbaryl) is hard to justify in pastures, but if needed, is most effective
in September. Sectional treatments may be a viable compromise. The best time
of day to treat is in late afternoon when temperatures are above 70 degrees
F. Problems with green June beetles are often
greater where poultry litter or other high organic
matter fertilizers have been used.
Sod samples about 1 sq. foot and four inches deep may be examined for grubs.
There is no precise threshold, but if 8 or more larvae per square foot of sod
are detected, treatment may be considered. Sevin SL and XLRplus are suggested
at 25 gallons/acre. There is a 14-day grazing interval.
Aphid populations are normally held below threshold by natural forces.
The two most common species to be a problem are the pea aphid (Acyrthosiphon
pisum) and the spotted alfalfa aphid (Therioaphis maculata). The
alfalfa aphid is the more damaging of the two. Thresholds vary depending
upon the height of the plant, aphid species, and abundance of beneficial predators
such as lady beetles and lacewings.
Meadow spittlebug (Philaenus spumarius) nymphs form frothy spittle
around tips and nodes of first growth alfalfa and can cause some stunting. The
adult does little damage, but may be annoying at harvest. This is a serious
pest in other states, but rarely in North Carolina. The
two-lined spittlebug (Prosapia bicinta) is also found in NC pastures,
but rarely the pest that it is in states farther south. Threshold is one larva/stem.
Chlorpyrifos may be used on alfalfa. In grasses, treatment is less common and
Lamda-cyhalothrin or pyrenone may be used. Carbaryl applied at the armyworm rate may give some control.
Clover root curculio (Sitonia hispidula) is
occasionally found in legumes (especially alfalfa and clovers) and is very
difficult to control. This grey or brown
weevil is smaller than the alfalfa weevil. Adults feed on foliage but rarely
to a severe extent except in seedlings. The grublike larvae feed on the roots
and may cause damage, but the severity is hard to assess, especially in an established
stand. Root feeding also allows greater entry of Fusarium and exacerbates
its effects. Fields showing major effects of Fusarium are frequently
subjected to heavy curculio damage.
beetles are rarely considered pests, but sometimes concern alfalfa growers.
Larvae are normally predaceous on grasshopper eggs and serve a beneficial
function. Although adults may consume foliage, the greater concern seems
to be for horses that coincidently ingest the beetles while feeding on
alfalfa hay. Blister beetles contain body fluids that can severely irritate
the mouths and stomachs of horses. Even a few beetles ingested can cause
colic or death to a horse. This beetle is gregarious and growers can watch
for concentrations of these beetles when cutting hay. Avoid harvesting
areas of high concentrations, particularly if the forage is to be fed to
horses. Spot treatment in the field with carbaryl may be used if needed.
Blister beetles are a more common problem from alfalfa hay brought in from
the midwestern states than from hay produced in NC. Since blister beetles
are more common in mid to late summer, feeding horses first-cutting hay
before the insects become active lessens the risk of blister beetle poisoning.
Grasshoppers and crickets may move into fields particularly during hot,
dry seasons. They can be especially destructive to young
seedlings in the fall. Field edges may be treated if found to be a source
of the population and carbaryl may be used. See the USDA site.
White fringed beetle (Graphognathus sp.)
adults roughly resemble alfalfa weevil adults but possess a white margin
around the outer wing edges. They are very difficult to control but are often
very spotty in a field. Adults consume foliage but do not fly. They may be abundant
in the fall before alfalfa weevil adults return to the fields.
Mole Crickets have been reported as pasture
pests in Florida.
Though they are present in North Carolina and a pest in turf, they have not
yet manifested themselves as a pest in pastures,
Pests on Livestock
Four flies (Dipterans) are considered important pests of livestock on pasture.
They are horn flies, face flies, stable flies, and horse flies. The horn
fly, Haematobia irritans, is a small blood-feeding fly that is commonly
found on the backs of cattle. Populations may reach thousands of
flies per animal. Female flies oviposit in undisturbed dung pats in the pasture.
Larvae require about 2 weeks to complete development and pupate in the dung
pat or in the soil beneath the pat. This fly was readily controlled with pyrethroid
ear tags in the 1980's but quickly developed resistance to these insecticides.
Other chemical options include insect growth regulators formulated as mineral
additives or feed-through, organophosphate ear tags or dust bags, and endectocides.
The face fly, Musca autumnalis, feeds on the lachrymal secretions of the eyes of cattle often causing pink eye by mechanically vectoring the bacterium Moraxella bovis. Like the horn fly, the female face fly oviposits in undisturbed dung pats. There are few natural enemies of the horn and face fly. Dung beetles readily break down the dung pats, making them inhospitable for the development of fly larvae. Onthophagus taurus, with its bull-like horns, is abundant in central and eastern North Carolina but little is known of the dung pat fauna in other regions.
The stable fly, Stomoxys calcitrans, is a blood-feeding fly that causes great annoyance to cattle. It is most frequently associated with feedlot or confined livestock, but has recently become a serious pest of pastured cattle. Typically the female fly lays its eggs in mixtures of manure and straw, or other organic matter, but wet hay and round bail feeders also contribute to larval development. Parasitoids readily attack stable fly pupae and rove beetles are commonly observed feeding on the eggs and larvae.
Horse flies and deer flies, in the family Tabanidae, are commonly found attacking cattle in pastures. These insects cause great discomfort for livestock and take large quantities of blood when feeding. The larvae live in an aquatic/semiaquatic environment and are often predatory themselves. There are few natural enemies or effective insecticides for Tabanids. Horse fly traps may help reduce feeding adults and relieve animals from feeding pressure.
Ticks can be a major pest to animals and humans in and around pastures. The lone star tick (Amblyomma americanum) is the major tick problem in NC, although deer ticks (Ixodes scapularis) and American dog ticks (Dermacentor variabilis) are also common. Lone star ticks become active in March as the temperatures begin to warm and remain a problem through June. Then the larval "seed ticks" become a problem from July through August. DEET can be used for personal protection. Any of the pyrethroids labeled for ticks in the yard are good to use. Keep grass and other vegetation cut short under fencing and in a ten foot wide outside perimeter buffer. Carbaryl (Sevin) may be used to treat open areas and the perimeter. Cyfluthrin (Tempo 20WP or 2L), bifenthrin (Talstar) and esfenvalerate (Asana XL) may also be used only as a perimeter spray in noncropland areas where livestock do not graze. Treat in spring when temperatures begin to exceed 60 degrees F. Treatment may need to be repeated in the Fall. Adhere to grazing and preharvest restrictions as stated in the labelling. Direct treatment to the animals may also be part of a pest management program. Consult the NC Agr. Chemicals Manual for those recommendations.
Fire Ants may be a minor or major irritant to livestock as they graze. Mounds can also interfere with equipment. Insecticidal control can be formulated as baits or contact poisons. Some are applied broadcast and some are only for direct mound treatment. For effective pasture control, a good overall management program is required. For a table covering chemical options is pasture, see Forage note #4. For information in horse operations, see Forage note #5.
Many forage crops depend on or are improved by bee pollination for seed formation. This is true for alfalfa, clovers, and vetches. In some states, bees are rented to provide pollination on these as seed crops. Though few growers in this state produce forages for seed, the plants produce a large amount of nectar and are highly attractive to several types of bees when in bloom.
Alfalfa is normally cut for hay during flower budding. If cutting is delayed, a field may become highly attractive to many pollinator species. The alfalfa plant may bloom about two weeks. Individual flowers can remain open for several days, but will wilt within hours once pollinated. Vetches and clovers have flowering patterns similar to alfalfa. All species are attractive to bees and usually have the opportunity to reach flowering stage when grown mixed with grasses. Red clover is less preferred by honey bees and more preferred by bumble bees, presumably due to the depth of the flower and the difficulty of the honey bee to reach the nectar with her shorter tongue. Varietal differences in pollinator attractiveness also exist among most of the legumes. Soil pH may also affect flower nectar production.
The presence of valuable pollinators should be considered in timing treatments and selecting pesticides for use on a forage crop or on an adjacent crop while forages are in bloom. Most insecticide labels contain a warning statement about their application hazard to bees. Very few chemicals may legally be applied to a crop while it is in bloom. Check the product label for such a statement before applying a pesticide.
Lady beetles also have an established reputation as a beneficial. Legume fields in the spring often harbor large numbers of aphids around the stem terminals. Any of several species of lady beetles usually move into the fields and eventually suppress the aphid population. Treatment is rarely needed for aphids if lady beetle populations are allowed to develop. There is also a large collection smaller biological control predators and parasitoids that attack other insects in the field and pasture.
No-till seeding of legumes into grasses
Sodseeding of forage legumes into grasses may be practiced to improve forage quality and reduce the need for nitrogen fertilization. Grass competition and insect feeding pressure can be high on seedlings. Best results for no-till stand establishment occur if planting is delayed until late fall or early winter and sod is prepared to minimize competition. Insect populations should be monitored and dealt with as necessary until the planting is established.
Other links of interest
Pests of Forages and
Fire Ant Management in NC Pastures
Management of Imported Fire Ants in Cattle Production Sytstems PDF by Flanders and Drees
Cantharidin Toxicity to Horses New Mexico State Univ.
Blister Beetle Control from Oklahoma State Univ.PDF
Insects and Related Pests of Man and Animals http://ipm.ncsu.edu/AG369/
http://www.agry.purdue.edu/ext/forages/rotational/Fun/insect.htm Pasture/Forage Insect Pictures
http://edis.ifas.ufl.edu/IG061 Insect Management in FL Pasture
http://ipmworld.umn.edu/chapters/flanders.htm Alfalfa IPM
Green June Beetle Grubs in Pastures http://www.aces.edu/pubs/docs/A/ANR-0991/
Green June Beetle Grubs in NC http://www.ces.ncsu.edu/depts/ent/notes/forage/gjbnote02/note02.htm
Internet Journal of Dermatology Tick Identification
Images source-http://www.ipmimages.org/ Photo credits: Clyde Gorsuch-alfalfa weevil, fall armyworm, red legged grasshopper; Matt Pound-lonestar tick; Joe Pase-tabanid fly; Jim Kalish-stable fly; blister beetle- Gerald Holmes.
This publication is a May, 2003 revision of Chapter 13, "Beneficial and Pest Insects in Forage Crops" by S. Bambara & M. Waldvogel in Production and Utilization of Pastures and Forages in North Carolina. 1995. Chamblee, D.S & J.T. Green, eds. NC Agr. Res. Ser., NC State Univ., Raleigh, NC. Tech Bul. 305.
Web version last reviewed January, 2011.