March 15, 2012
Resistance of the Fruit Tree Red Spider Mite
Reduced sensitivity or even resistance of the fruit tree red spider mite to the METI (mitochondrial electron transport inhibitor) miticides Masai and Sequel appears to have been getting worse over the past few years
The problem is thought to have arisen mainly through the overuse of these products on the continent and the transfer of the affected mites to English farms on trees imported from continental nurseries where resistance is well established.
Senior Agrii fruit consultant Colin Bird reckons that the answer to the problem here is the use of an integrated control programme based on Envidor which kills mite eggs and motile stages (and also controls rust mite and mussel scale).
“The sensitivity shifts of the METIs to red spider and rust mites here is largely because we import trees from the continent where there is known resistance,” he affirms. “There is a strong link between the time that our increased sensitivity began five or six years ago and when we started to import large numbers of trees from the continent. However, at present not all of our red spider and rust mite populations are affected.”
Bird recalls that METIs have been available for well over 10 years and we have been reliant on them since the loss of Blex in the 1990s. This was a broad spectrum product that killed typhs, the main red spider and rust mite predator. Envidor is relatively kind to typhs and so its use allows the predator to contribute to the control of these pests although it is not easy to establish a healthy balance between predator and prey.
Last autumn’s warm spell allowed red spider ‘hot spots’ to develop. Where the result was large numbers of overwintering eggs he advises an early application of Apollo (between bud burst and pink bud) then Envidor post bloom, timed at the first egg lay of the surviving red spider mites.
“Because most growers are environmentally sensitive these days they try to maintain biodiversity in their orchards and a product like Envidor helps them to do this,” maintains Bird.
His colleague Andy Bull affirms that red spider mite has tended to become more prevalent in some areas, possibly because typhs took a long time to build up last year or were nonexistent. He has been using Envidor where red spider mite numbers are high enough. “It works very well,” he says, but growers must realise that it takes 10 to 14 days to become fully effective, especially in the case of adult mites.
“Envidor needs to be applied the sooner the better once you see red spider building up,” advisesBell. “If there is a significant number of overwintering red spider eggs I would try to knock them out with Apollo and reserve Envidor for later.”
Note: Envidor belongs to the novel ketoenol chemical group and the active ingredient spirodlofen works by inhibiting lipid biosynthesis. It binds to the leaf wax, ensuring the good product rainfastness and persistence so important for effective, prolonged pest control.
Bayer’s horticultural specialist Peter Newman points out that as a contact product, good spray coverage with Envidor is essential. For mite pests application rates may be adjusted according to tree size down to a minimum of 0.4l/ha in a water volume of 150 to 1500l/ha.