Pests and Birds 109
output, production of many seeds and low construction cost of hollow stems, petioles
and fruits production due to faster absorption of water, nutrients and chemicals as
applied and available in soil make it very sensitive against inorganic pesticides and
nutrients. Papaya plants are very sensitive to pesticide(s). Particularly, two pesticides
diamethoate for aphid control and omite for management of mites have shown pho-
totoxic effect on young papaya plants. High dose and repeated use of diamethoate
(≥2.0 mL/L of water) cause toxicity on newly emerged leaves showing light green
colour of leaf veins (Figure 9.7a and b), but the damaged leaves of papaya recover
within 15–20 days after application. Therefore, we should use recommended pesti-
cides only. Sometimes, farmers and extension workers used to apply chlorpyriphos
(at 1.5–2.0 mL/L of water) in papaya orchards (Figure 9.7d) for mealy bug control in
papaya and other fruit crops. Papaya plants are also very sensitive to soil application
of boron, especially in sandy to sandy loam soils. Soil properties such as texture,
temperature, moisture, microbial activity and pH may also influence phytotoxicity.
At higher pH, soils are less binding hence may enhance phytotoxicity, while high
microbial activity may reduce it. Basal application of borax at ≥6.0 g/plant causes
burning of leaf tip and margins (Figure 9.7c). Seed germination of papaya was
severely affected by seed coating and treatment by propiconazole at 1.5–2.0 mL/kg
of seeds before sowing in nursery (Figure 9.7e). Phytotoxic properties of pesticides
are usually associated with specific formulations or specific plants rather than group
of pesticides or plants.
Least toxic pesticides (natural or organic in nature) are not necessarily harmful
to plants or environment. Many are quite safe to use. Calibration of the equipment
and chemical quantity prior to each application is important in order to avoid heavy
stresses, fruit damages and burning of leaves. A pesticide label may indicate whether
the pesticide is phytotoxic and may list plants or varieties that are sensitive. Reading
and following label directions, especially the correct rates and timing, and being
aware of potential weather effects, avoiding application of pesticides when drift is
likely to happen, waiting for the correct planting times. If unsure, it is always advis-
able to conduct a simple field bioassay by treating only a few plants, before treat-
ing the whole block for phytotoxic effects, especially when growing new crops and
cultivars.