A Sustainable Farming Fund (SFF) project-led by Plant & Food Research’s Abie Horrocks-aims to provide tools to help farmers and agronomists use integrated pest management (IPM) in forage and seed brassica crops such as kale, rape, swedes and turnip.
“There are a whole lot of reasons why IPM is a good option,” Horrocks told FAR’s South Canterbury and North Otago field day recently.
“IPM is a good way to reduce unnecessary insecticide use and utilise natural predators in the crops.”
It also incorporates cultural controls such as sowing technique, maintaining a healthy crop that is able to overcome minor pest damage and measures
to encourage pest predators or “beneficials”.
Insecticide resistance cases are increasing around the world, Horrocks said.
While there are no known problems with the insecticides used and brassica pests in New Zealand, that’s not to say they won’t arise, particularly if only one or two broad-spectrum insecticides are used routinely instead of more targeted chemistry used only when there’s a measured threat.
“There are a lot more selective insecticide products available now,” she said.
Selective insecticides are the preferred weapons with IPM because they don’t kill some or all beneficial species but do take out crop pest targets such as aphids and caterpillars.
Horrocks is encouraging growers to assess the ratio of pests to predators, rather than work to thresholds of pest populations at which to intervene with insecticide.
“The thing to keep an eye on is the lag between pests coming in and parasitoid control building up.”
With diamondback moth, for example, it was usually three to four weeks between the moth’s caterpillars hatching in the crop and the activity of predators, notably parasitoid wasps, building to the point where caterpillars are kept in check.
Dirk Wallace outlined research into soil treatments to increase water holding, including polyacrylamide.
Answer in the soil?
Never mind dams and ponds. Are farmers missing a great opportunity to increase onfarm water storage right under their feet – soil?
Plant & Food Research’s Dirk Wallace is testing a range of treatments to improve the water-holding capacity of a Templeton silt loam lifted from FAR’s long-term tillage trial at Chertsey.
Some are conventional, such as compost and dairy shed effluent solids, but others are more whacky: biochar, starch, silicate and polyacrylamide.
The latter is the stand-out performer so far, being the only treatment to significantly increase plant-available water capacity.
Applied as a granule it “sucks up 1000 times its weight in water,” Wallace told the FAR field day.
Extrapolating lab results from 5cm-diameter by 3cm-deep soil cores to field scale he calculated an application of 700kg/ha could increase soil water holding capacity by 22% – effectively another 10mm of water in the top 20cm. That could extend irrigation intervals a couple of days and-or increase crop yields, he said.
Water release is similar to natural soil so plants should be able to access the water held by the acrylamide but the catch is that it is “pretty nasty stuff”, he added.
“If any of it leaches then we won’t be able to use it.”
It’s also expensive at present so applications could run to tens of thousands of dollars per hectare or more. “You might as well build a pond!” one field day delegate quipped.
Sphagnum moss was the next best modifier, adding 6% water-holding capacity, while compost and dairy solid effluent applications equating to about 10t/ha increased water holding by about 2%.
Pocket-sized support
A pocket-sized guide identifying fodder brassica pests and their natural enemies has been produced by Plant & Food Research and IPM Technologies, with sponsorship from Du Pont. Contact Du Pont for copies.
