Soybean and Bees

Soybean pest control
and the impact on pollinators
There are several insect pests attacking soybeans during its life cycle, since sowing to almost
harvest. Major pests are defoliators, pod sucking and feeders. The critical period for negative
impacts of chemical pest control on pollinators occurs when flowers are present on soybean
plants. This period may range from 15 to 30 days, depending on several aspects, but especially
if soybean cultivars are determinate or indeterminate. On determinate types, the R2
stage is characterized by full bloom, and the uppermost node develops flowers, so vertical
plant growth stops. At R3 stage (pod set or beginning pod) the blooming period is over and
almost no flowers are present on the plants. The blooming period for a determinate cultivar
averages 15 days, the maximum being around 20 days.
In the case of indeterminate cultivars, blooming continues after R3, sometimes up to R5 (beginning
seed), extending for ca. 30 days. This is a very important and crucial difference as
far as impact of pest control on pollinators is involved, because, on determinate varieties,
the blooming period does not overlap with pod formation and filling. Therefore, it is not
necessary to control pod sucking or pod feeding pests while flowers are open in the plants.
Contrarily, on indeterminate varieties – which are the most commonly cultivated in Brazil
– pods and flowers are present on the same time on the plants. Therefore, while flowers attracts
pollinators, pods might (or not) be attacked by pests, needing control practices (Figure
24).
In the majority of the soybean cultivars grown in Brazil, the vegetative part of the cycle
(VE to Vn) represents roughly one third of the whole cycle. Nevertheless, this general rule
depends on the cultivar, the latitude and altitude, climatic conditions (rain and daily and
night temperature) and on soil pH and fertility (FERREIRA et al., 1983). To illustrate, higher
temperatures induces shorter soybean cycles, and the first flower appears earlier than under
normal temperatures. The same is valid for hydric or nutritional stresses (low N, P and
K levels on the soil).
SoybeAn and bees
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