July 28, 2017
Countering late-drilled wheat slug risks with integrated control
Wetter conditions and slower crop growth make first class slug control crucial with later-drilled wheats; especially where they follow oilseed rape. But pelleting should be very much the last resort, believes Agrii regional technical adviser, Tim Horton.
Although periodic cultivation can be very useful and mid-late October drilling gives more time for it, he does not advise this approach either. Not least to avoid compromising the key purpose of delayed drilling in the first place – black-grass control.
“A split-field slug monitoring study we ran several years ago clearly underlined the value of an extra cultivation in killing eggs and exposing adults to predation,” noted Tim. “However, our Stow Longa black-grass technology centre work shows the best approach with late-drilled wheat is to cultivate early then move as little soil as possible ahead of and at drilling.
“In my experience it’s perfectly possible to reconcile these two apparently conflicting approaches with minimal reliance on pelleting. The twin keys to success here are effective trash and drilling management. Get these right and you’ve done a good 80% of the slug control job.”
Concentrations of surface trash simply have to be avoided, Tim Horton has no doubt. As well as maintaining the moist environment they need, rows of trash protect slugs and their eggs from predation by birds. So good straw, chaff and (with OSR) pod trash chopping and spreading is an essential first step.
Alongside this, he stresses the importance of early cultivation to both bury the trash and bring slug eggs to the surface to desiccate.
“The depth of cultivation will depend on your soil type and condition,” he said. “The priority is to set up the ground to weather so you can create a seedbed from mid-October with the least extra soil movement, keeping as much black-grass as you can soundly asleep.
“You may need an extra cultivation to achieve the trash incorporation you want and open-up the clods that shelter eggs and adult slugs in heavy land. But if it’s necessary, do it early and at an angle to the first cultivation, then use no more metal until you drill.”
While monitoring with non-toxic baits ahead of drilling can be beneficial in assessing slug risk, Tim Horton generally finds it unnecessary as, in most cases, the level of threat is highly predictable from the wetness of the soil, the amount of trash and the quality of the seedbed.
“Monitoring can give you a false sense of security if conditions are on the dry side,” he noted. “Also, I like to avoid feeding pests wherever I can !”
Alongside the most effective trash management, Tim Horton stresses that what you drill, the way you drill it and, most importantly, the quality of your drilled seedbed are all especially critical in late-drilled wheat slug control.
“Two things matter above all else in this respect,” he insisted. “Limiting slug activity on the one hand, and boosting crop establishment on the other.
“Firm, fine seedbeds do both. They seriously restrict slug movement to minimise both seed hollowing and surface grazing. And they maximise seed-to-soil contact and moisture retention so the crop grows away from the slug challenge as rapidly as possible.
“Achieving them can be difficult at this time of the year, however. So you need to stay off the land until you can drill at an even 3-4cm into a seedbed without clods. With such a narrow weather window, it’s tempting to cut corners. But it really isn’t worth the risk. If conditions aren’t in your favour it’s best to hold off and drill in the spring.
“As conditions usually only make it possible to roll once after drilling, it’s vital to get this right too. Essentially this means rolling within two days of drilling and not too fast. Remember, the degree of consolidation you get depends on the time the roller is actually pressing down on the soil as much as its weight.”
Tim Horton also recommends using good quality seed that has been vigour as well as germination-tested, treating it with Deter to reduce seed-hollowing and a manganese or nutritional dressing to encourage rooting, and providing sufficient available phosphate in the seedbed.
While he accepts that slug pelleting may be needed in many cases, he sees it as very much a last resort for highly targeted application to support the best cultural controls.
He prefers either quality durum-based ferric phosphate or 3% hybrid metaldehyde pellets for their balance of palatability, spreadability and longevity, pointing out that, used correctly, more environmentally-benign ferric phosphate should be no more expensive. And it will have to be used around every field this autumn with the new 10m non-pelleting zone under the metaldehyde stewardship guidelines.
To ensure the pellets remain on the surface where slugs feed rather than being pressed into the soil where they can be wasted, he always advises applying them after rather than before rolling.
“Late-drilled wheats are at particular risk from slugs,” concluded Tim Horton. “Even so, if you get your trash and drilling management right, one pelleting may be quite sufficient and you may not need even this. Conversely, if your cultural controls are ineffective you’re unlikely to be able to solve your slug problems with any number of pellet applications.”