Potato leafhopper resistant alphalpha varieties

DES MOINES, Iowa – Researchers at The Ohio State University will begin research this spring to determine when insecticides should be applied on potato leafhopper-resistant and tolerant alfalfa varieties to prevent economic losses.

Although PLH-resistant and tolerant alfalfa varieties became commercially available in 1997, economic thresholds for chemical treatment of these varieties to prevent yield loss from high infestations have been unclear.

“Both public and private industry trials have shown that PLH varieties can reduce yield losses to less than one-half of the losses seen with standard susceptible varieties when PLH populations are high,” said Mark Sulc, associate professor, Department of Horticulture and Crop Science, The Ohio State University.

However, prior research has not confirmed the infestation levels at which it is economically justified to treat the most recent commercialized PLH-resistant or PLH-tolerant alfalfa varieties with insecticide. Determining valid economic thresholds is the goal of The Ohio State University research.

“Leafhopper-resistant varieties provide a significant new tool in integrated pest management strategies and potentially may greatly reduce or even eliminate the need for chemical control of this alfalfa pest in many areas,” said Ronald B. Hammond, professor, Department of Entomology, Ohio Agricultural Research and Development Center. “The goal of our research is to provide information that will help alfalfa growers reduce their losses and optimize their profits in an environmentally sound manner.”

Research award.

Sulc’s and Hammond’s research project on PLH-resistant alfalfa is one of three projects selected to receive a 2001 Pioneer Crop Management Research Award. The other two grants were awarded to researchers at the University of Illinois for studies on soybean varieties with moderate resistant to Soybean Cyst Nematode and soybean responses to early planting dates.

“Potato leafhopper is one of the most common and destructive insects affecting alfalfa production in North America,” said Tom Doerge, agronomy research manager, for Pioneer Hi-Bred International, Inc., in Johnston, Iowa. “Having valid economic thresholds for PLH-resistant/tolerant varieties available will help alfalfa growers optimize their profits. Pioneer Hi-Bred is pleased to collaborate with public institutions on research that brings valuable crop management information to growers.”

Methods.

Alfalfa stands will be established in April 2001 and in April 2002 at field research facilities at the Ohio Agricultural and Research Development Centers near Wooster and South Charleston. Potato leafhopper population density and forage yield will be monitored in a highly resistant/tolerant variety and in a susceptible variety over the course of the experiment. The following treatments will be imposed on each variety:

1. No insecticide.

2. Insecticide applied early in the growth cycle (six to seven inches of growth).

3. Insecticide applied late in the growth cycle (12 to 15 inches of growth).

4. Absolute insecticide control of PLH in seeding year, no insecticide in following years.

5. Absolute insecticide control of PLH in first two years, no insecticide in third year.

“A combination of control strategies – chemical control, mechanical or agronomic practices and host plant resistance – is required to effectively minimize the damage caused by leafhoppers in alfalfa,” said Hammond. “Understanding proper economic thresholds for resistant/tolerant varieties will give alfalfa growers greater confidence in using these products to economically maximize their forage production in an environmentally sound manner.”