Dimilin (diflubenzuron) – It is unlikely that Dimilin will ever have a label for use on apple, however our experiences on apple may help develop use patterns for the same pests on pear. Dimilin is another selective insect growth regulator. Dimilin inhibits chitin synthesis, which makes its mode of action unique compared to Intrepid or Esteem.
Lepidopteran pests
Codling moth – Dimilin does have activity against the codling moth
egg. When Dimilin is applied at the beginning of the egg-laying period
(100DD) it will disrupt normal egg development. To obtain adequate control
two applications of Dimilin will be required. In apple Dimilin has not
provided the same degree of control as products like Guthion or Imidan.
Leafrollers – Dimilin has not been evaluated as a possible control for leafrollers.
Lacanobia fruitworm – We have not tested Dimilin against Lacanobia.
Indirect/secondary pests
Dimilin has no known effect on mites, aphids, campylomma, scale, or leafhopper.
When originally tested it was quite effective on leafminer, but this
diminished over the course of a few years (not really an issue on pears,
and no projected registration on apple).
Pear pests
Dimilin has been tested extensively in pear for pear psylla and codling
moth control for over two decades. Dimilin has been shown to have moderate
activity against pear psylla; it will control a low to moderate population.
Like Esteem, Dimilin affects the eggs and early instars of pear psylla,
although there are likely sublethal effects on later instars and adults.
Dimilin has been found to be most effective when applied to the first
generation of pear psylla, from delayed dormant through petal fall. The
optimal timing to target pear psylla is at clusterbud, where maximum
effects against eggs and early nymphs would occur. When using Dimilin
in a pear psylla program it is important that Thiodan, sulfurs, and oil
are used at delayed dormant to help reduce the pest pressure and better
synchronize the generation. Applications in the summer also can provide
some degree of control; however, the level of effectiveness is decreased
as more and larger instars become present in the developing populations.
Codling moth is another target pest for Dimilin applications in pear. Dimilin has been shown to be effective against codling moth, but the level of control is lower than other available products. Dimilin should be used only against low populations of codling moth, except in situations where other control tactics such as mating disruption are being used. There is concern that codling moth populations resistant to organophosphates may also be tolerant or resistant to Dimilin due to OP mediated cross-resistance. This may lead to variable results in observed efficacy.
Beneficial arthropods
Dimilin is not acutely toxic to beneficial arthropods. However, we found
in one study that Colpoclypeus florus females directly exposed to Dimilin
laid eggs that were not viable. Dimilin apparently sterilized the female
or had some other sublethal effect on normal egg development.