Potato Leafhopper on Vegetables
The potato leafhopper, Empoasca fabae , is a pest that is easy to overlook until the damage - called "hopperburn" - "burns" you. Due to it's feeding habits, it can cause damage that is out of proportion to it's density. Most problems in vegetables show up in snap beans or potatoes, but it is capable of successful reproduction on over 200 plants species in 25 different families, including alfalfa, potatoes, beans, peanuts, and woody ornamentals. Potato leafhopper is a transient pest of apples, grapes, celery, rhubarb, and clover to name a few. Densities are typically highest in alfalfa.
The potato leafhopper overwinters to the south of us. Migrant source populations develop in the Gulf States in early spring, where they overwinter on legume host plants, but may also be found on a variety of native, evergreen plants. It has been tentatively demonstrated that the potato leafhopper feeds on loblolly pine, and the leafhopper's overwintering area spans the entire southern pine region and may extend into coastal areas where evergreen hosts are available.
Most overwintering females are mated and in reproductive diapause (their reproduction is delayed). These migrants arrive in Pennsylvania during the spring and early summer and they move northward, recolonizing its entire range from its overwintering source. The summer range spans most of the temperate latitudes east of 100° longitude. Some authors have suggested a "pied-piper" hypothesis for the broad patterns of northward expansion of many pest species, where agricultural activities have provided temporarily suitable habitats for many highly mobile species that are geographically far from suitable overwintering locations. The possibility of some return flow to the south, along with some adult diapause, is currently an open research question.
The sex ratios of our populations shift during the season. The long-distance migrants are predominantly female. A sex ratio of 25 females to 1 male was recorded entering an alfalfa field in May in Pennsylvania. All females were gravid and able to initiate a new generation. The sex ratio changed to approximately 3:1 on second harvest and 1:1 on third harvest. The sex ratio of eggs is 1:1 and adult populations maintain stable 1:1 sex ratios by midseason and thereafter.
Potato leafhopper develops 3 to 4 generations during its residence in its summer range. One important factor that regulates populations is alfalfa harvest. Harvest destroys eggs and nymphs, and sends adults flying. Recolonization of alfalfa regrowth and vegetable crops occurs by invasion of adults from those populations adjacent to alfalfa fields or neighboring alfalfa fields on adjacent farms.
Eggs are deposited within the plant. Most are in the upper more succulent tissue. On alfalfa, eggs are laid in the top 17 cm or upper one fourth of the plant. In potatoes, eggs are laid more frequently in the terminal leaflets and on leaves between apical and basal leaves. Egg-laying activity is maximum during the dark hours. Very little egg-laying occurs below 18.3° C. Females lay about 2 to 4 eggs per day, and somewhere between 30 and 200 eggs per female over a female's lifetime. In the lab, a female lives about 100 to 120 days.
Egg-hatch occurs in 9 1/2 to 11 days at 75° F. After hatching, nymphs undergo five instars. The newly emerged nymph is nearly colorless with red spots that quickly fade. A yellow color soon appears, changing to pale green in the third instar. The time of development varies greatly with temperature, but average duration of each of the 1st through 5th instars respectively are: 2.6, 2.3, 2.3, 2.5, and 4.7 days. Mating occurs within 48 h of adult emergence with females beginning to lay eggs in three days. The average reproductive life was 30-35 days for females and 33 days for males.
Leafhopper feeding results in symptoms called "hopperburn". The adults use the lacerate-and-flush style of probing in and around vascular tissue. Potato leafhoppers move its stylets steadly through cells, secreting full salivary sheaths only rarely. This lacerate-and-flush feeding style results in disorganization of vascular bundles, enlargement and proliferation of cells, collapse of phloem fibers, and eventual collapse of phloem sieve elements. It seems likely that both introduction of saliva from the leafhopper and mechanical wounding by stylet movememt is necessary to cause the injury, which is a saliva-enhanced wound response associated with vascular blockage. The net result blockage of phloem transport. Gross symptoms of hopperburn probably result from this phloem blockage and subsequent accumulation of photoassimilates in leaves. This interacts with other stresses, such as drought.
Hopperburn shows up as a browning and necrosis along the margins of potatoes. Damage varies with cultivar. In beans, it can cause a curling of the leaves, stunting, reduced root systems, and reduced yields and quality. Greatest damage comes from feeding on young plants. In alfalfa, it causes a distinctive V-shaped yellow wedge, typically first in the terminal leaflets. However, hopperburn symptoms result from the plant's response to the feeding. Therefore, responding to the damage by spraying is not the best option. It does help, because new leaves will be free of injury. But the best management is to scout for leafhoppers. It is easy to do with a sweep net, or by closely examining the undersides of leaves. Both adults and nymphs will include a characteristic "sideways" walking pattern as part of their movement. Adults also have a characteristic deep lime-green color. Scouting and spraying when thresholds are exceeded is the best management. In some states, the early season influx is monitored simply by regional reporting of the scouting data from alfalfa.
Thresholds in snap beans suggested in the midwest are:
|Snap beans, seedling (smaller than 2 true leaves)|
|1 adult per 2 sweeps; or 2 per foot of row|
|Snap beans, 3rd trifoliate to bud stage:|
|1 adult per sweep, or 1 nymph per 10 leaves, or 5 per foot of row|
Spray materials for the respective crops are suggested in the Commercial Vegetable Production Guide.
Emmen, D. A. 1999. Colonization patterns of the potato leafhopper, Empoasca fabae (Harris) (Homoptera: Cicadellidae) in alfalfa. Ph.D. Thesis. Pennsylvania State University. (and references therein).
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