What is in this article?:
- Effective pest management tools in desert-grown alfalfa
- Potato leafhopper
- Pest-resistant alfalfa varieties, natural insect enemies, insecticides, and flexible harvest schedules help manage pests in Southern California and Arizona desert alfalfa production;
- Common alfalfa pests include the spotted alfalfa aphid, pea aphid, blue alfalfa aphid, cowpea aphid, and potato leafhopper;
- Aphid problems generally begin in the fall months with the cowpea aphid, followed by the pea and blue alfalfa aphids during the winter;
- The potato leafhopper is a mobile insect but not a persistent alfalfa pest in southern California.
Switching gears to Blythe-area alfalfa production, Vonny Barlow joined the UCCE Riverside in 2009 during a heavy potato leafhopper infestation in the Palo Verde Valley.
The potato leafhopper overwinters from northern Florida to Texas. Trade winds transport the pest back to the West annually. The pest has a host range of more than 200 plants. The leafhopper is a mobile insect but is not a persistent alfalfa pest in southern California.
According to the UC Statewide Integrated Pest Management Program, potato leafhopper feeding causes a yellow V-shape on the leaf tip; the leaf margin and tissue surrounding the area turns red. Symptoms can be confused with boron deficiency. The presence or absence of the leafhopper can determine whether the insect is the culprit.
Potato leafhopper feeding causes stunted plants with short internodes. Stunting can occur into the next cutting cycle even after the insect is controlled.
“The plant leaf can die, fall off the plant, and reduce the marketable yield,” Barlow told the crowd. “This is why the potato leafhopper is an issue for some desert alfalfa growers.”
Three-to-four generations of potato leafhopper are common per season. The population peaks from May to September. Three-to-10 days after mating, the female deposits eggs into the stem, petiole, or thick leaf blades. Eggs hatch in 7-to-10 days.
Many wingless immatures are killed during the alfalfa harvest.
“If potato leaf hoppers are at threshold levels (0.2/sweep at 3”, 0.5/sweep at 6”, and 2/sweep >12”) and harvest is near, do not spray,” Barlow said. “Harvest the alfalfa early, bale it, and remove it from the field.”
Barlow conducted an insecticide-potato leafhopper trial from May through September last year in three, 20-acre fields in early spring alfalfa stubble located adjacent to irrigation drainage ditches heavily populated with host plants and the pest. The fields were split down the middle. The half closest to the irrigation ditch was treated with a 2.8 ounce/acre application of Baythroid XL.
Preliminary results from the first-year study indicate no treatment impact on season-long potato leafhopper populations. An alfalfa stubble application would only indirectly manage leafhopper populations if the pest continuously emerged from protected areas including irrigation ditches. The study will be continued this year.
Many alfalfa varieties resistant to aphids are also resistant to the potato leafhopper. Varieties with a glandular-haired trait perform as “fences across the fields,” Barlow says, impeding insect movement and causing the insect to move to less “unfriendly” plants.
The Fall Desert Crops Workshop was sponsored by Western Farm Press with commercial sponsor support from: BASF and Bayer CropScience (Platinum sponsors); Dow AgroSciences, Tessenderlo Kerley Inc., and Valent U.S.A. (Gold sponsors); FMC Corporation (Silver sponsor); and Certis U.S.A. and CDMS (Bronze sponsors).