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Now that spring is almost here, it's time to turn our attention to the spray programme.
In the last years the pipfruit industry has made huge progress away from heavy reliance on harsh pesticides such as organo-phosphorus insecticides which eliminate predators to integrated pest management, which relies on soft pesticides such as the insect growth regulators (IGR) that are pest specific and relatively safe towards predator populations.
At the recent NZ Pipfruit Ltd annual grower seminar, Dr Jim Walker from Hort+Research reviewed some of the progress that had been made and highlighted some of the shifts in orchard insect population that have occurred.
Between 1996 and 2002, organophosphorus use declined by 93% from an average of 10 in 1996 to just 0.69 applications now. Whereas azinphos methyl or chlorpiryfos and also diazinon were probably applied eight or nine times during the growing season in 1996 most of the applications now are of chlorpiryfos made in late dormant with oil largely for scale and woolly apple aphid. This spray was only applied to half of the orchard area indicating that around half of the apple area is not receiving any broad-spectrum insecticides at all.
This move away from broad-spectrum insecticides has been of great benefit to insect predator populations which have increased markedly leading to fewer numbers of mealy bug, leaf roller, leafhopper and mite being found on fruit in packhouses. On the negative side there have been increases in scale, codling moth, woolly apple aphid and bronze beetle. These pests will require greater focus.
Scale insects are largely a problem on fruit from later varieties which become infested by summer release crawlers. These crawlers often come from alternative hosts around the orchard such as shelterbelts. The key to this problem lies in managing the scale population in both the orchard itself and surrounding alternative host plants.
With established orchards there is no need for tall shelterbelts because the trees themselves within the orchard tend to become self-sheltering. Boundary shelterbelts are important to provide a barrier against spray trespass onto neighbouring properties. For this purpose they only need to be a couple of meters taller than the apple trees so topping shelterbelts down to about 5 m in height will reduce their capability of spreading scale crawlers, and also make them much easier to spray.
Recent studies by Hort+Research entomologists have shown that predators play an important role in controlling scale populations. This suggests that we should avoid applying broad-spectrum insecticides to shelterbelts and rely on IFP friendly pesticides for scale control. The most appropriate treatment for scale around orchard boundaries is oil in the late dormant period and again in mid summer to catch the summer generation before they move off into the orchard.
IFP friendly products for scale insects include mineral oil, ApplaudTM, and CalypsoTM. With the orchard we would recommend ApplaudTM with either oil or an organosilision wetter for scale control.
Woolly Apple Aphid populations generally blow out once the organo-phosphorus insecticides are withdrawn from the programme and it takes a while for their main predator, Aphelinas mali, to get on top of them. Our experience has been that where orchards are planted on resistant rootstocks such as MM106 or M793 the A.mali will do a reasonably good job of wooly apple aphid control once the populations come into balance. With the exception of very attractive varieties such as Fuji, there is probably no need to consider late dormant sprays for woolly apple aphid control if predation late autumn was heavy. For blocks where woolly apple aphid control is a problem primicarb with the oil is an option that is IFP compatible.
Orchards planted on dwarf rootstocks that are susceptible to woolly apple aphid will need a directed insecticide spray to the base of the tree to control aphids, which may emerge from the roots and climb up the trunk into the tree.
Where there is visual evidence of mite eggs on the wood during pruning, a dormant or late dormant oil spray should be applied.
Codling moth and bronze beetle are late spring early summer pests. Codling moth needs to be carefully monitored with pheromone traps and the appropriate spray programmes applied once the traps indicate time for action.
Bonze beetle is a pest which has a wide host range and spends most of its time as a grub living on the roots of many herbaceous plants. It's the adults which cause havoc in the orchard. These hatch from October to January and will migrate up into the apple trees. Often they are very localized in their distribution within an orchard, or if the main population is outside the orchard, tend to damage trees near the boundary.
Control options compatible with IFP appear limited, however we understand that CalypsoTM recently obtained a label claim for bronze beetle control. This product also gives good codling moth, scale and mealy bug control as well as suppressing woolly apple aphid so it looks as if it will be a very useful late spring, early summer insecticide for apples.
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