Management of Tomato Late Blight Disease Using Reduced Fungicide Spray Regimes in Morogoro, Tanzania

Abstract

Tomato (Solanum lycopersicum L.) production in Tanzania is affected by late blight disease caused by Phytophthora infestans (Mont.) de Bary. Currently, farmers spray more than 12 per crop per season to control diseases by weekly spraying. Field experiments were conducted at Morogoro to evaluate the  performance of three tomato varieties subjected to different fungicide chemistries and reduced fungicide spray intervals. The treatment factors were tomato varieties Meru, Cal-J and Tanya as main plots; fungicides Ivory 72 WP, Volar MZ 690 WP and Topsin-M 70 WP as sub plots; and reduced number (4, 6, 8 and no-spray) of sprays per crop at a spray intervals of 14-, 10-, 7-days respectively as sub-sub plots. Variety Meru showed low tomato late blight incidence (1.4%) and severity (1.0) (P.0.001) followed by Tanya (81.2%, 4.0) and Cal-J (82.6%, 4.0) respectively. Results show that plots sprayed with Topsin M-70 WP had significantly (P.0.001) higher disease incidence and severity (66.2%, 3) compared to Ivory 72 WP (42.5%, 2) and Volar MZ 690 WP (44.5%, 2). The no-spraying regime (control) had highly significant (P.0.001) disease incidence and severity than other spray regimes. Although there was no significant (P.0.05) difference among the spray regimes plots sprayed 8 times had lowest disease incidence and severity (47.9%, 2) while, unsprayed plots had highest disease incidence and severity (66.3%, 4) followed by plots sprayed 6 times and 4 times (53.9%, 2) and (52.1%, 2) respectively. There were significant differences (P<0.001)) in yield among three commercial tomato varieties. Cal-J variety produced higher number of fruits per plant (27), marketable fruits (26.5 t/ha) and total yield (28.9 t/ha) followed by Tanya with 21 fruits per plant, 19.3 t/ha marketable fruits and total yield of 21.3 t/ha. Meru produced 13 fruits per plant, 13.6 t/h marketable yield and total yield of 17.6 t/ha. Tomato varieties,  fungicides and spray regimes demonstrated significant influence on late blight disease incidence and severity. Results reveal that, variety Meru was resistant to tomato late blight disease while, Cal-J and Tanya varieties were highly susceptible. However, Meru had lowest yield due to production of few number of fruits per plants. Fungicides Ivory 72 WP and Volar MZ 690 WP verified higher field efficacy against P.  infestans. These two fungicides significantly reduced disease intensity to lowest level than Topsin-M 70 WP. Similarly, spray regimes significantly gave appreciable reduction of tomato late blight disease  intensity and consequently increased fruits yield in susceptible varieties Cal-J and Tanya when compared to no spraying regime. It was evident that the number of fungicide sprays was reduced from more than 12 (current farmers practice) to 8, 6 and 4 at intervals of 7-, 10- and 14- days respectively.

Key words: Tomato late blight disease, fungicides, reduced fungicides spray regime, tomato varieties.