CORESTA Congress, New Orleans, 2002, AP 27

The effect of acibenzolar-S-methyl/imidacloprid treatments on the incidence of spotted wilt in tobacco grown from plant house transplants

University of Georgia, Coastal Plain Experimental Station, Tifton, GA, USA
Experiment station trials conducted in 1999 indicated low rates of acibenzolar-S-methyl applied in the plant house a week before transplanting had potential to reduce the incidence of spotted wilt in the field. Farm trials were conducted in 2000 and 2001 to test these results. Nine trials in 2000 compared: 1. acibenzolar-S-methyl (2.3 grams/10,000 plants applied to plant house trays 5-7 days before transplant); 2. imidacloprid (71 grams/10,000 plants applied as a spray on/rinse off tray drench in the plant house 1-2 days before transplant); 3. acibenzolar-S-methyl + imidacloprid (applied as above); 4. untreated plants. Once transplanted plants received various field spray treatments: 1. acibenzolar-S-methyl (17.5grams/hectare beginning at transplant); 2. acibenzolar-S-methyl (17.5grams/hectare beginning at layby); 3. insecticide beginning at transplant (either imidacloprid at 56 grams/hectare or acephate at 840 grams/hectare); 4. No treatment. The acibenzolar-S-methyl was three applications at a 10 day interval. Insecticides were five applications at a seven day interval. The design was a randomized complete block of plant house treatments with an overlaid latin square of field treatments. Plant house treatments reduced spotted wilt across all nine trials (acibenzolar-S-methyl: 21%; imidacloprid: 31%; acibenzolar-S-methyl+imidacloprid: 48%). None of the field spray programs were consistently effective in reducing spotted wilt. There was 1-3% stand loss (NS; p=0.05) and obvious early season growth reduction (p=0.05) with plant house acibenzolar-S-methyl treatments. The 2000 trials showed some risk with plant house acibenzolar-S-methyl treatments. Eight trials were conducted in 2001 to study the effects of: 1. imidacloprid; 2. low rate of acibenzolar-S-methyl (1.15 grams/10,000 plants) + imidacloprid; 3. high rate of acibenzolar-S-methyl (2.3 grams/10,000 plants) + imidacloprid; 4. untreated plants. Acibenzolar-S-methyl and imidacloprid were applied as in 2000. The field sprays in this trial were all acibenzolar-S-methyl at 17.5 grams/hectare: 1. once at transplant; 2. at transplant and weekly for three applications; 3. at transplant and weekly for five applications; 4. untreated. Design was the same as in 2000. The results showed imidacloprid combined with the high or low rate of acibenzolar-S-methyl to be equally effective in reducing spotted wilt (55% vs 52%) and equally risky to plant stand and growth. The negative effects of acibenzolar-S-methyl on plant stand and growth were site specific rather than general. Both rates of acibenzolar-S-methyl with imidacloprid enhanced spotted wilt reduction compared to imidocloprid alone. Field applications of acibenzolar-S-methyl were not consistently effective. The three and five application programs were effective in some cases with untreated plants but not with plants receiving either rate of acibenzolar-S-methyl in plant house.