Pryor Laboratory - Focusing on Lettuce Diseases, Mycology, and Alternaria at The University of Arizona School of Plant Sciences, Tucson, Arizona USA Disease management is a principle activity for growers of all types of lettuce. Viral, bacterial, and most importantly, fungal diseases can seriously impact quality and yield.

Lettuce Drop Biological Control

Lettuce Drop in Head and Leaf Lettuce

Considerable research has been conducted on evaluating biological control agents to manage Sclerotinia disease in a number of cropping systems. Trichoderma spp., Sporidesmium sclerotivorum, and Bacillus subtilis have been evaluated against Sclerotinia spp. but have not performed well under field conditions (Chitrampalam et al 2008, Plant Dis. 92:1625-1634).

In striking contrast, Coniothyrium minitans has shown much higher efficacy. Two applications of recommended rate of C. minitans (Contans) (2lb /acre)one at planting and one at post thinning outperformed commonly used chemical fungicide Rovral (Iprodione) for controlling lettuce drop caused by S. sclerotiorum. However, C. minitans had less effect on S. minor (Chitrampalam et al 2008, Plant Dis. 92:1625-1634).

Effects of biocontrol products on lettuce drop infestations

Chitrampalam et al 2008. Plant Dis.92:1625-1634

Studies were continued to develop a biocontrol strategy mainly with Coniothyrium minitans to manage lettuce drop caused by S. minor in lettuce production areas of both Yuma County, AZ and Imperial Co, CA. Results from this study revealed that lettuce drop caused by S. minor could also be successfully managed with Coniothyrium minitans in desert agroecosystem. However, the rate of application of C. minitans required to manage S. minor was much higher than that required to control S. sclerotiorum (2lb/acre).

Effects of Contans and Endura on lettuce drop infestations