New Report on Neonicotinoids and Bees
Posted: April 6, 2012
In response to requests from growers for an update on the issue regarding bee colony decline and possible connections to neonicotinoid use, I have summarized a recent white paper I co-authored with the Xerces Society.
Several of these insecticides are highly toxic to honey bees and bumblebees.
Neonicotinoid residues are found in pollen and nectar consumed by pollinators such as bees and butterflies. The residues can reach lethal concentrations in some situations.
Neonicotinoids can persist in soil for months or years after a single application. Measurable amounts of residues were found in woody plants up to six years after application, BUT SO FAR ONLY WITH NON-FOLIAR APPLICATIONS AT MUCH HIGHER RATES THAN NORMALLY USED IN ORCHARDS.
Untreated plants may absorb chemical residues left over in the soil from the previous year.
Products approved for homeowners to use in gardens, lawns, and on ornamental trees have manufacturer-recommended application rates up to 120 times higher than rates approved for agricultural crops.
There is no direct link demonstrated between neonicotinoids and the honey bee syndrome known as Colony Collapse Disorder (CCD). However, recent research suggests that neonicotinoids may make honey bees more susceptible to parasites and pathogens, including the intestinal parasite Nosema, which has been implicated as one causative factor in CCD.
Many neonicotinoid pesticides that are sold to homeowners for use on lawns and gardens do not have any mention of the risks of these products to bees, and the label guidance for products used in agriculture is not always clear or consistent.'
Note that most of these studies were done on honey bees and most from seed treating crops that are not bee pollinated. As expected, neonicotinoids as insecticides can kill bees, but not all are the same, with Assail and Calypso being safer. We have a study we are submitting soon showing significant synergism of neonicotinoidson bees when they are tank mixed with SI fungicides like Nova that can complicate the situation in fruit. Most of the problems are centered around the seed treatments, injections and homeowner uses at rates much higher than allowed in orchards
For tree fruit, I would summarize by cautioning never to use clothianidin (Clutch not labeled in NY) or thiamethoxam (Actara) prebloom, or post-bloom until all the blossoms are gone. 80% petal fall still means 20% bloom, and for growers relying on wild bees, this can really wipe them out. Pre-bloom, I would only recommend Assail or Calypso at pink and early pink, if possible. Clothianidin is a more toxic breakdown product of thiamethoxam.
Never use Assail at bloom, even though it is legal. Synergism with Nova can make it 15X more toxic than by itself. One other lab study shows up to 1,000X synergism of Calypso with an SI funigicide tank-mixed. Other fungicides do not appear to synergize, although mancozeb and captan to a lesser extent can be toxic to wild bee larvae that feed on the pollen. Imidacloprid can only be used post-bloom, but that means when all petals are off, not just when the honey bee hives have been moved out.