Potato Leafhopper Yellowing

PLANT CULTURE

Greenhouse

Container................	10 cm clay pots or 55 x 32 x 6 cm flats for seedlings
Medium..................	Sterilized soil mixed with commercial soil mix to improve aeration and drainage
Temp/Light..............	22 to 28†C; 16 hour day length
No. of Plants...........	1 mature plant per pot; 30 seeds per row, 14 rows per flat, spaced 2.5 cm apart
No. of Reps.............	4 minimum

Field

Planting.................	Seed entries in drill-row plots or transplant seedlings 6 to 8 weeks of age
Rate......................	1 gm seed per 3 m row or minimum of 25 seedlings per entry; space rows and plants 30 cm apart
No. of Reps...........	3 minimum

LEAFHOPPER CULTURE

Source..................	Collect adults from alfalfa fields when present; start new colony annually
Rearing.................	Alfalfa, broad bean, or 'Henderson' bush lima bean for mass rearing in the greenhouse
Temp/Light............	24 to 27†C, 50 to 90% RH and 15 hours minimum daylength
Life Cycle..............	Total time from egg laying to adult stage is about 20 days

INVESTIGATION PROCEDURE

Greenhouse

Plant Age.............	Seedlings: 14 to 18 days after emergence; 2nd trifoliate stage. Mature plants: prebud stage
Method................	Seedlings: plexiglass cage is placed on flat and covered with saran screen top. Mature plants: cage 2 stems per plant in a clear cylindrical plexiglass tube and seal bottom of tube with split foam plug and top with nylon netting
Rate.....................	Seedlings: 200, 4 to 8 day old PLH adults per flat. Mature plants: 8, 4 to 8 day old PLH adults per plant
Length..................	Seedlings: approx. 3 to 5 days

Field

PLH Source..........	Natural infestations of adult PLH generally occur after the first cutting
Plant Age.............	New seedlings or spring transplants should be kept insect free for the first year to allow establishment
Length..................	Plants can be scored one or more times during the second and third regrowth after the year of establishment; control of grasses in alfalfa stands has been shown to favor the development of PLH populations

RATING OF SYMPTOMATIC INJURY

Seedlings

Probing and feeding by PLH adults cause collapse of the petioles and subsequent death of the seedling. Because of difficulty in differentiating degrees of PLH feeding in young seedling, those seedlings that survive after 95% of all seedlings have died should be vegetatively propagated and tested as mature plants.

Mature Plants

Most of the alfalfa germplasm which has been classified as resistant to yellowing caused by PLH feeding is fed upon by the PLH and exhibits loss of protein, stunting, reduced yields, and other symptoms. Individual plants are visually scored for percent foliar discoloration (yellowing or reddening) using a 1-5 scale.

1 Hi. Tolerant.........	0 to 20% leaves yellowing
2 Mod. Tolerant......	20 to 40% leaves yellowing
3 Low Tolerant.......	40 to 60% leaves yellowing
4 Susceptible........	60 to 90% leaves yellowing
5 Susceptible........	Leaves necrotic and stems wilted

CHECK CULTIVARS

Plants with little or no yellowing (%)

	Approximate Expected Tolerance	Acceptable Range
Tolerant
MSA-CW3AN3	70	60-80
Susceptible
Ranger	5	0-10

Values are based on percent plant foliage yellowed and correspond to
ratings of 1-2 for MSA-CW3AN3 and 4-5 for Ranger

DISTRIBUTION AND SEVERITY OF
POTATO LEAFHOPPER

Potato leafhopper, Empoasca fabae (Harris)

Click on the map above for a larger version. See also the KEY.

SCIENTISTS WITH EXPERTISE

Name.................	Franklin L. Bedard
Address..............	W&L Research, Inc. 601 Oswell St. Bakersfield, CA 93307
Phone................	805-366-5525

Name.................	Thomas C. Elden
Address..............	USDA-ARS Bldg. 467, BARC-East Beltsville,MD 20705
Phone.................	301 -504-8392

Name.................	Arthur A. Hower, Jr.
Address...............	Entomology Department Pennsylvania State Univ. University Park, PA 16802
Phone.................	814-863-2982

Name..................	Robert A. Byers
Address...............	USDA-ARS U. S. Regional Pasture Res. Lab. University Park, PA 16802
Phone.................	814-863-0941

HELPFUL INFORMATION

Drought stress and certain nutrient deficiencies can cause plant symptoms which appear similar to those caused by PLH feeding. Short, decumbent alfalfa lines often escape PLH damage. Height measurements and nymphal population counts can assist in identifying resistant plants in the field. Germplasm with adequate levels of antibiosis, nonpreference or tolerance to PLH feeding damage have not been identified which would serve as a resistant source in a breeding program. Research to date has indicated that individual plant selection following more than one cycle of seedling selection may increase the level of PLH resistance. Resistance to feeding damage, oviposition, and/or insect survival and development should be considered separately in a screening program and concurrent selection for each trait would be desirable.

REFERENCES

1. Elden, T.C., J. H. Elgin, Jr., and J. F. Soper. 1986. Inheritance of pubescence in selected clones from two alfalfa populations and relationship to potato leafhopper resistance. Crop Sci. 26: 1143-1146.

2.Elden, T.C., and J. H. Elgin, Jr. 1987. Recurrent seedling, and individual plant selection for potato leathopper (Homoptera: Cicadellidae) resistance in alfalfa. J. Econ. Entomol. 80: 690-695.

3.Elden, T.C., and J. H. Elgin, Jr. 1992. Mechanisms of resistance to the potato leafhopper (Homoptera: Cicadellidae) in selected alfalfa clones. J. Econ. Entomol. 85: 576-582.

4.Kindler, S. D., and W. R. Kehr. 1970. Field tests of alfalfa selected for resistance to potato leafhopper in the greenhouse. J. Econ. Entomol. 63: 1464-1467.

5. Newton, R. C., and D. K. Barnes. 1965. Factors affecting resistance of selected alfalfa clones to the potato leafhopper. J. Econ. Entomol. 58: 435-439.

6. Sorenson, E. L., and E. Horber. 1974. Selecting alfalfa seedlings to resist the potato leafhopper. Crop. Sci. 14: 85

7. Webster, J. A., E. L. Sorensen, and R. H. Painter. 1968. Temperature, plant-growth stage, and insect population effects on seedling survival of resistant and susceptible alfalfa infested with potato leafhopper. J. Econ. Entomol. 61: 142-145.