Lettuce drop is one of the most frequent and destructive diseases encountered by commercial lettuce growers throughout the US. The causal agents Sclerotinia minor & S. sclerotiorum produce sclerotia requiring long rotations and annual fumigation in fields where the disease has become established. Heavily infested fields have incurred losses of up to 70%.
SoilGard® 12G Microbial Fungicide contains spores of Gliocladium virens strain GL-21 which has proven to be an effective fungicide in laboratory and field studies. Fungicidal activity occurs via four distinct modes of activity:
SoilGard® 12G was tested under field conditions in Greenfield, CA during 2009 in cooperation with Steffi-Saul Ketzler: BioResearch Inc. The trial was set up as a randomized complete block design with 4 replicate plots/treatment each 2 rows x 6m.
SoilGard® 12G was applied at 4lb/a a total of three times:
CO2 pressurized backpack sprayer w/ wand (3 flat fan 8003 nozzles); 75 gal/acre; 40 psi.
Second and third applications
CO2 pressurized backpack sprayer w/wand (3 hollow cone , D-4 spin nozzles); 85 gal/acre; 40 psi. *All applications were followed by 1hr overhead irrigation.
14 April (1 day post plant), 23 May and 6 June
Disease incidence (fig. 4) was rated on 6 & 23 June and 7 & 16 July.Figure 4: Early season Sclerotinia sp. infected lettuce plant (left). Resulting dead lettuce plant from infection by Sclerotinia sp. (right). Both plants above were rated as infected an represented as such in disease incidence ratings for this trial.
At the conclusion of the study, when the season long total of the diseased plants were calculated and the percent control of each product was determined (fig. 5), significant differences between treatments became apparent. The best performer was the Certis Experimental product 9090 at 4 lb/a, which exhibited excellent control at 83%. This was followed by, SoilGard® 12G at 4 lb/a, and the Certis Experimental product 9090 at 1 lb/a, with 67, 65 and 61% control, respectively (fig. 6). Contans showed control of only 51%.
Soilgard ® 12G provided economically acceptable control of lettuce drop, equivalent to the Endura® Fungicide treatment. Both rates of Certis’ experimental product resulted in economically acceptable control of lettuce drop, with the 4.0lb/acre treatment providing the most effective control.Figure 5: Season total disease incidence showing effects of trial treatments in controlling Sclerotinia sp. on lettuce, where each treatment was applied three times. Greenfield, CA (July 2009). Figure 6: Season total percent control of lettuce drop vs untreated control. Greenfield, CA (July 2009). Percent incidence vs untreated control calculated using Abbott’s Formula (1925): [(x-y)/x] *100; where x=number living plants in untreated and y=number of living plants in treatment group.
Figure 1 photo (left): Howell, R., 2003. Plant Disease 87 (1): 4-10.
Figure 1 photo (right): www.mycolog.com/chapter14.htm
Figures 2 & 3 (all): Courtesy of Mike Dimock, Certis USA
Figure 4 photos (both): Courtesy of Steffi Saul-Ketzler, BioResearch Inc.
Abbott’s Formula: Abbott, W.S., 1925. A method for computing the effectiveness of an insecticide. J. Econ. Entomol. 18 (2): 265-267.