What is in this article?:
- Will Western winter lettuce growers see a repeat epidemic of last year’s lettuce drop disease caused by a rare aerially-dispersed S. sclerotiorum fungus?
- Probably not, says Mike Matheron, University of Arizona plant pathologist, since last year’s outbreak was caused by a perfect storm of events.
Matheron has tested traditional fungicides and biofungicides in separate YAC trials. The findings suggest traditional fungicides are best applied directly to the plant bed immediately after thinning and cultivation and at the rosette stage to prevent sclerotia germination. The highest level of traditional fungicide effectiveness in the trial was about 50 percent.
A one-year YAC trial evaluated eight biofungicide products. These biofungicides when applied alone, except for the product Contans, were equivalent in performance. All of the tested biofungicides, except for Contans, were less effective than the conventional product Endura. Contans and Endura were the most effective products in the trial for Sclerotinia drop.
“Applied fungicides, traditional and natural, should be applied as a barrier on top of the soil surface to reduce the fungal infection of leaves,” Matheron said.
The extreme S. Sclerotiorum outbreak was rare and it remains unknown if and when a combination of weather and other conditions could occur again.
Growers and PCAs question whether fungicides should be applied each crop cycle as insurance against a sporadic threat. Production cost margins are slim in vegetable production. Extra control costs can mean the difference between profit and loss.
“We are on tens to hundreds of dollars per acre margins,” Boelts said. “It’s a tough call. You can’t easily give up profit to prevent a disease which may or not occur.”