Producers were reminded to keep a close eye on insects during this coming crop year, including the pesky wireworm which is having a larger impact in Saskatchewan fields.
John Ippolito, Regional Crop Specialist from Kindersley, spoke about this year’s insect outlook and the economic thresholds for treatment at the recent Regional Pulse Workshop held at the Stockade Feb. 6.
Wireworms - “We’re starting to pay a lot more attention to it. The wireworm itself is the larvae of the Click beetle. There’s about 370 known species, 30 of which have economic importance in western Canada. They have a long life cycle, about four years. They’re in the ground and feeding and move up and down in the ground as the soil temperature changes at the surface, preferring cool.”
Currently, the only control for wireworms is a neonicotinoid seed treatment that must be applied by a commercial seed treater and it only slows down the wireworms; it doesn’t kill them. Neonicotinoid is a class of neuro-active insecticides chemically related to nicotine, and the first new class of insecticides introduced in the last 50 years.
“One of the problems we have with it is very low mortality. They feed a little bit, they ingest the insecticide, they stop feeding but they don’t die off. So it does provide an economic benefit - you’ve stopped the feeding so you don’t have a yield loss because of them - but it’s not making the population go away …. he’s still there next year, waiting for the next crop.”
Crop rotations with crops such as flax that have shown resistance to wireworms can be used to some degree to interrupt the four-year cycle, but larvae can survive for up to two years on humus. Another suggestion was to decrease seeding depth.
“You can seed shallow with the idea that hopefully the wireworms are down below where you’ve placed the seed, or increase the seeding rate to compensate for their feeding.”
Cutworms - Generally, cutworm numbers have been declining since 2011 but the dingy cutworm, which overwinters as a larvae, is more prevalent.
“He’s off to a little quicker start in the spring in terms of feeding on your crop, and it feeds above ground on the foliage and goes back down. They’re all nocturnal feeders.
“Control has always been with foliar-applied insecticides, applied in the evening when they’re coming up to feed. You can get up to 10 days’ control with one application so there shouldn’t be a need to apply twice.
Pea Leaf Weevil - “It’s a nocturnal feeder and spends the days underground, so you’re not likely going to see the adults. An adult female can lay up to 1,000 eggs, and what they’ll do is they will lay them at the base of the pea plant.
“Damage occurs in two ways. Adults come up in the evening and cut those notches in the leaves, and then the eggs that are laid at the base develop into little white larvae that actually feed on the [root] nodules that fix nitrogen, and that’s where a big chunk of the yield loss seems to be coming from is from the nodule feeding.”
The two most common control methods are seed treatment and foliar application.
“If you’re looking at the foliar application, if you’ve got a notch in a clam leaf on every third plant, you should be spraying with an insecticide if you are so inclined,” said Ippolito, although he noted that foliar insecticides aimed at killing adults before they lay eggs have produced inconsistent results.
“The more accepted practice has been to use the seed treatment that has the insecticide in it. The idea there is that the insecticide stays around long enough that it actually kills the larvae that are trying to feed on the root system.”
Grasshoppers - There’s two groups of grasshopper: non-pests and pests. The spur-throated grasshoppers are the pests. The two-striped grasshopper is the most common pest in this region.
The non-pest grasshoppers tend to overwinter as grasshoppers, so they’re out earlier, and are noticeable for their colourful and noisy wings. Almost all the pest grasshoppers overwinter as eggs.
“The grasshopper forecast for 2013 looks really good. In almost all cases we’re below two per square metre. We’ve got a little bit to the Southwest, and a little bit west of Kindersley, which has higher numbers.”
The RM of Maple Creek shows Very Light to Moderate counts and the RMs of White Valley and Reno show areas of Very Light to Light. The RMs of Lac Pelletier, Whiska Creek and Glen Bain also show Very Light counts.
“In those areas for this upcoming year, we would suspect that lentil is the only crop that’s at risk, and that’s because the thresholds in lentils is so low. Lentils they don’t eat the leaves or stems, they just eat flowers and holes in pods, so the threshold for lentil is two adult grasshoppers per square metre at the time of flowering (Very Light). They’re causing enough damage there to warrant control.”
Aphids - “In 2011 we had aphids in lentils,” said Ippolito. “It’s a population that changes a lot from year to year. They overwinter as eggs to some degree but probably the bigger infestations happen when we get southern winds, similar to what happens with Diamondback moths. During the growing season … they can skip that egg stage altogether and birth live young that are able to very quickly create more live young.”
The three main predator insects of aphids include the syrphid fly larvae, Lady beetle larvae and Lacewing larvae. To determine whether a crop has an infestation high enough to warrant the use of insecticide, Ippolito suggests using a sweep net.
“You sweep through the crop 180 degrees. If you’re catching 30 to 40 aphids in that sweep, and you don’t see a lot of predators, you may be at risk - but we would tell you to go back and do it again tomorrow, and if you got the same or higher numbers in the second day, then you’re at a point where you probably should be applying insecticide.”
He said the economic threshold for peas is measured differently.
“You look at how many aphids are on the top 20 centimetres of the plant, so if you’ve got two aphids on the top 20 centimetres, that’s an indicator there’s quite a few more below and you’re going to get about a five per cent yield loss.”
The loss may be less on semi-leafless varieties.
