The wet summer and harvest period means grass grub and slugs are likely to cause problems for arable growers.
Arable farmers are being advised to keep a good eye on grass grub and slug populations as they head into the busy autumn sowing period.
In the case of grass grub, FAR researcher Richard Chynoweth says that in a dry year, many eggs are lost to desiccation, but that this season’s wetter than average December and January means a lot of the eggs have survived and hatched into larvae. He says they’re going to be tricky to manage and there are a lot of factors to consider.
“It's quite easy to find grass grub larvae now as the good feeding season means they are bigger than they would usually be at this time of year. On the up side, this means they are potentially more susceptible to cultivation damage, but on the down side, they’re hungry. The wet season has led to some good weed strikes so there's actually quite a lot of food there for grass grub larvae at present, but once those weeds are removed, pre-sowing, they'll be sitting there waiting for the new crop to come through and can cause enormous damage at that point. The use of a short term cover crop that provides a food source may actually provide some protection of the main crop planting by advancing larval development so the stop feeding earlier in winter.
“Naturally occurring pathogens are another thing to factor in. The wet season will have suited them as well, but it’s really difficult to know what impact they will have on larval populations. My suggestion to all growers is to get out with a spade and look at the number of larvae they've got, especially relative to how many seeds of the crop they're going to plant and make a call as to whether they need to need to put some treatment on.”
Richard says in the case of slugs the story is slightly different.
“Slugs’ major reproductive period is just beginning, so the summer rainfall may not have influenced numbers to any great extent, yet. However, it’s important to note that thanks to the wet season, unirrigated farms are sitting on the same conditions as irrigated ones, and may need to be more vigilant than usual. As with grass grub, monitoring for slugs is going to be absolutely key, especially in the high risk crops like brassicas and clovers. Slug numbers could be quite a bit higher in crops following clover and plantain; and if the weed pressure on the cereals has kept them ticking away, then there's the potential for them to explode in almost any paddock.”