Do Insecticides Affect Plant Growth And Development ?

THE application of insecticides is often necessary in greenhouse crop production to prevent damage from insect pests that could render the plants unsalable. However, pesticide usage can lead to toxicity issues, which may adversely affect plant growth and development. It seems plausible that applications of foliar insecticides could adversely affect photosynthesis by clogging, or at least partially blocking, plant stomates – the microscopic pores in leaves through which gases (water vapor and CO2) are exchanged. Reduced photosynthetic rates can delay production times or reduce plant quality, in addition to any visible damage due to chemical toxicity. Subtle negative effects of insecticides on individual crops can add up and lead to economic loss when multiple crops are grown. While visible phytotoxicity and the toxicity to humans and animals are tested prior to registration, subtle impacts such as effects on flower production, stunted growth or longer production times are not often tested. We tested various foliar insecticides (including spraying control plants with de-ionized water) on gerbera daisies to determine whether the insecticide applications affect growth, development, physiology and overall plant quality. Gerberas make ideal feeding grounds for a variety of pests including aphids, broad mites, spider mites, whiteflies, leaf miners and likely their worst enemy – western flower thrips. Gerbera daisies are mighty tasty to western flower thrips, which feed on both the foliage and the flowers. It has even been suggested that gerberas could make an excellent trap crop for western flower thrips. Due to this high susceptibility to insect pests, growers need to spray on a regular basis in commercial potted gerbera production. In our evaluations, we chose five insecticides that represented the diversity of chemicals used against gerbera pests, including western flower thrips (See Table 1). Plants were sprayed weekly at the recommended (1×) or at four times the recommended rate (4×) to determine the likelihood of plant damage under normal and overdose conditions. Avid 0.15 EC, Talstar Nursery Flowable and Conserve SC did not reduce photosynthesis, and did not cause plant damage, even when applied at 4× University research tests foliar insecticides to determine whether applications