Potato leafhoppers have been reported feeding on alfalfa in most parts of Iowa. Each year, these small, green insects with milky white eyes reach Iowa from overwintering populations in the southern United States. Once established in alfalfa fields, populations can increase rapidly with feeding damage caused by both adults and nymphs. Scouting alfalfa for potato leafhoppers on a weekly basis can help prevent significant forage yield and quality losses.
The first visual sign of damage is yellowing of leaves, especially on new growth. This yellowing often occurs in V-shaped wedges and is referred to as hopperburn. Severe damage causes stunted plants with shortened internodes. Stunting and leaf loss result in poor hay quality, reduced tonnage, and occasionally the loss of an entire cutting. Long-term losses include reduction in plant vigor that reduces winter hardiness. Stunted alfalfa allows light penetration into the canopy, encouraging weed growth.
|||Severe hopperburn on alfalfa.|
|||Potato leafhopper adult.|
As alfalfa cutting progresses, adult potato leafhoppers often hopscotch among neighboring fields. The regrowth of subsequent cuttings must be scouted carefully. Considerable damage can be caused by large populations of leafhoppers moving from a cut field to the new regrowth of an adjacent field.
Fields should be scouted on a regular schedule. Begin checking regrowth after cuttings and recheck every 5-7 days. Do not wait for hopperburn to appear before scouting. Use a sweep net and take 20 sweeps in five different areas of the field. Consider applying an insecticide if the number of leafhoppers exceeds the following thresholds:
- For hay less than 10 inches tall, consider spraying if you collect more than 0.1 leafhopper per sweep for each inch of plant height. For example, if the hay is 8 inches tall, spray only if the average number exceeds 0.8 leafhopper per sweep.
- If hay is taller than 10 inches, 2 or more leafhoppers is the acceptable threshold.
Some of the insecticides labeled for leafhoppers are listed below. The minimum label rate and preharvest interval are given. Always read and follow label directions.
Insecticides labeled for potato leafhoppers.
|Insecticide||Minimum rate||Preharvest interval (in days)|
|Ambush *||3.2 ounces||0|
|Cygon 400||0.5 pint||10|
|Furadan 4F*||1 pint||14|
|Lorsban 4E||1 pint||14|
|Pounce 3.2 EC*||4 ounces||0|
|Sevin XLR+||2 pints||7|
This article originally appeared on pages 105-106 of the IC-480(14) -- June 15, 1998 issue.