Control of Insects Attacking Forage and Pasture Crops
Grasses and legumes, permanent or temporary, are important assets to the Mississippi livestock producer. You can manage these crops to provide grazing for summer, fall, and late winter or cut for high-quality hay. These crops are subject to attack by several insects, and although the per-acre value is relatively low, you can justify some control. The armyworm complex, chinch bugs, aphids, and weevils are among the insects that may feed on these plants. These pests defoliate the plants or cause them to wilt by drawing out plant juices. Examine your crops frequently during peak insect activity.
Armyworms
The two types of armyworms that attack pasture crops are the true and fall armyworms. The adult armyworms are rarely seen during the day but become active in the late-evening and night hours. The females lay eggs on the lower leaves of host plants, and feeding starts as soon as the new larvae hatch. The small larvae feed close to the ground and often go unnoticed until they are about 1 inch long; by this time, they can consume large amounts of foliage.
True armyworm larvae feed at night and seek shelter during the day. The fall armyworm larvae remain active in daylight and night hours.
Start looking for true armyworm outbreaks in early spring and for the fall armyworm from mid- to late July. Check fields regularly during periods of armyworm activity. Do this by brushing your hand through grasses to knock worms to the ground; part the grass and count the worms in a 1-square-foot area. For successful control and to prevent extensive damage, start treatment when you find five to seven small worms per square foot of surface area.
Alfalfa Weevil
The larval stage of the alfalfa weevil can be one of the most destructive insects to alfalfa stands. You can find larvae feeding on stem tips, on upper leaves as they unfold, and eventually on lower leaves. Severe losses of dry matter and a decrease in forage quality can result if you don't control this insect.
Effective control requires a timely application of an approved insecticide based on number of larvae per stem. To determine larval numbers, scout your fields weekly starting in mid-February. If larval populations reach one to two per stem, apply an insecticide, using 10 to 20 gallons of spray per acre.
Aphids
Aphids are one of the most commonly found insects on stands of grasses, clovers, or alfalfa. Aphids are small, soft-bodied insects that have mouthparts suited for piercing plant tissue. The insects can damage plants by sucking plant juices, injecting toxic substances, or injecting diesease organisms. A heavy aphid infestation can cause a sticky "honeydew-type" material to form on the leaves. This material is rich in sugars and makes an ideal medium for fungus growth (sooty mold), which may damage plants or make them unpalatable to grazing livestock. Also, "honeydew" can cause seed heads to become sticky, which creates conditions unfavorable for seed-crop harvesting.
Watch for the appearance of small, circular areas in fields that show dead plants in the center, surrounded by yellowed plants. Aphids are usually controlled by parasitic wasps; however, if examination of these areas shows high numbers of aphids, consider using chemical control.
Grasses Permanent and Temporary
| INSECT |
INSECTICIDE |
ACTIVE INGREDIENT PER ACRE |
REMARKS |
|---|---|---|---|
| Aphids |
methyl parathion |
.75 lb |
15-day waiting period |
| malathion |
.50 lb |
7-day waiting period |
|
| Armyworms |
carbaryl |
1 to 1.5 lb |
14-day waiting period |
| malathion |
1 lb |
7-day waiting period |
|
| methyl parathion |
.75 lb |
15-day waiting period |
Alfalfa and Clover
INSECT INSECTICIDE ACTIVE INGREDIENT REMARKS Spotted
alfalfa aphid methyl parathion .25 to
.50 lb Leaves
curl, turn yellow, die, and drop. Treat when you find two or three
aphids per ten seedlings. malathion .75 to
1 lb methomyl .25 to
.50 lb permethrin .05 to
.20 lb Three-cornered carbaryl 1 lb Girdling
of stem; leaves will become yellow and drop. Cutting at early bloom
stage helps reduce the infestation. malathion .75 to
1 lb Guthion .25 to
.50 lb permethrin .05 to
.20 lb Clover
leaf weevil methyl
parathion .25
to .50 lb Larvae
feed on flowers and seed heads. Treat when clover is 50 percent
of full bloom stage. Alfalfa
weevil methyl parathion .25 to
.50 lb Larvae
feed within plant tips, on upper leaves as they open, and then on
lower foliage, skeletonizing the leaves. malathion (larvae
only) .75 to
1 lb methomyl 1 lb Guthion .25 to
.75 lb Furadan .50 to
1 lb permethrin .10 to
.20 lb
PER ACRE
alfalfa hopper
Restrictions and Limitations Alfalfa and Clover
carbaryl Do not
apply more than once per cutting. Do not apply within 7 days of
harvest or grazing. Furadan Do not
apply more than once per cutting. Do not apply more than twice per
season. Harvest or grazing interval: .5 pound per acre = 14 days;
1 pound per acre = 28 days. Guthion Harvest
or grazing interval: .25 pound per acre = 14 days; .5 pound per
acre = 16 days; .75 pound per acre = 21 days. malathion No time
limitations for harvest or grazing. methomyl Do not
apply within 7 days of harvest or grazing. methyl
parathion Do not
apply within 15 days of harvest or grazing. permethrin Do not
apply more than 0.2 pound per cutting. If 0.1 pound or less is applied
per acre, there is not waiting period for harvest or grazing. If
more than 0.1 pound is applied per acre, wait 14 days before harvest
or grazing.
Read the Label
Always read the label
before buying or using any insecticide. Be sure to observe the restrictions
and limitations on the label. You can reduce the danger of skin exposure
to insecticides by wearing protective clothing and by using safety equipment
specified on the label.
By Dr. Douglas M. Gaydon, Extension Entomologist
Mississippi State University does not discriminate on the basis of race, color, religion, national origin, sex, age, disability, or veteran status.
Information Sheet
722
Extension Service of Mississippi State University, cooperating with U.S.
Department of Agriculture. Published in furtherance of Acts of Congress,
May 8 and June 30, 1914. Ronald A. Brown, Director
Copyright by Mississippi
State University. All rights reserved.
This document may be copied and distributed for nonprofit educational
purposes provided that credit is given to the Mississippi State University
Extension Service.
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