Impact of Insecticides on Silverleaf Whitefly and Tomato Yellow Leafcurl Virus (TYLCV) on Staked Tomato, 2000

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P. A. Stansly, J. M. Conner and D.R. Peach
University of Florida/IFAS
Southwest Florida Research and Education Center

TOMATO: Lycopersicon esculentum Mill. ‘Neptune'
Silverleaf whitefly: Bemisia argentifolii Bellows & Perring

TYLCV is a devastating whitefly-vectored disease of tomato which has spread from the Mediterranean to the Caribbean region including Florida. Along with cultural control such as host free periods, insecticidal control of the vector is the key to present-day management of TYLCV. Greenhouse-raised seedlings were planted 9 Mar at 18-inch spacing on 2 sets of 3 drip irrigated beds , 240 ft long on 6 ft centers. The outer 2 beds of each set were divided into 7 plots, each 34 ft long and assigned to treatments in a completely randomized block design with 4 replications. The middle row of each 3-bed set was left untreated to serve as a source of whiteflies. On 16 Mar 2 tomato plants which had been exposed to TYLCV infected whiteflies were transplanted in the center of each plot to provide a source of virus inoculum. Admire® 2F and Platium 2 SC were applied as soil drenches on 13 Mar in 10 ml of water per plant. Two treatments, one with the half rate of Admire and one with no Admire received weekly applications, 11 total, of Neemix® beginning 1 Mar while the plants were still in the transplant trays. Actara 25 WG was applied as a foliar spray on 21 Mar, 11 Apr and 2 May. Applaud 70 WP was applied 11 Apr and the same plots sprayed with Knack .86 EC on 2 May. Foliar applications were made using a high clearance sprayer driven by a hydraulic pump operating at 200 psi and delivering the spray through two drop booms equipped with 2 yellow hollow cone ceramic Albuz® nozzles each for a rate of 44 gpa until 11 Apr when another nozzle was added to each drop for an output of 66 gpa for the remaining applications. Seven weekly evaluations of whitefly adults were made beginning 10 Apr by beating 1 side of 4 plants at 4 locations per plot with a 9 x 13 inch pie pan painted black and coated with a 9:1 mixture of vegetable oil and liquid detergent. Immature stages were monitored from 1 leaf removed from the 6th node of 4 centrally located plants in each plot. All whitefly stages were counted that appeared in a 2-cm2 ring placed 4 times on each leaflet using 3 leaflets from each leaf collected. Plants were monitored every 3 or 4 days for symptoms of TYLCV. On 26 May, 15 plants per plot were harvested and the number and weights of insect, disease and marketable fruit were recorded.

Whitefly populations were sufficient to move virus rapidly from inoculum plants into treated plants. Soil drenches of Admire or Platinum provide the most rapid response in whitefly numbers, with significant differences from the control throughout the study period. Significant differences were seen in plants treated with Actara by the second week, and with Knack rotated with Applaud by the 3rd week. Significantly fewer adults than the control were seen on plants sprayed with Neemix on 10 Apr, 15 May and over all dates. Fewest whitefly adults over all dates were seen on plants treated with Admire at the full rate; significantly less than plants treated with Platinum or the Knack and Applaud rotation and all treatments were significantly different from the untreated check. Fewer eggs were seen over all dates on plants treated with Platinum, although not significantly less than with Admire at the full rate, Neemix or Actara. Fewest nymphs were seen on plants treated with Platinum, and all treatments were significantly less than the control except for no overall effect of Knack + Applaud. Best control of nymphs + pupae overall was obtained with Platinum, with no significant difference between the full and half rates of Admire + Neem with all treatments were significantly different from the control. Incidence of TYLCV at 25 and 32 days was significantly reduced by all treatments except for Knack + Applaud. Fewest symptomatic plants were seen from 32 through 60 days in plots drenched with Admire or Platinum. Only plants treated with Platinum produced significantly greater numbers of fruit than the control, although fruit weight was significantly greater from plant treated with Admire at the full rate as well. This trial demonstrated that only soil drenches of choronicotinoid insecticides were able to protect plants from an early and heavy attack of viruliferous whiteflies. Nevertheless, significant whitefly control was also observed from Actara, Knack + Applaud and Neemix.

Florida Agricultural Experiment Station Journal Series No. N-02006.

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