Will be a challenging growing season for pests

Meghan A. Vankosky, Ph.D. a research scientist with Field Crop Entomology Agriculture and Agri-Food Canada says it will be a challenging year in regards to the crop pest situation, but like most aspects of agriculture, future weather will predict a lot of the impact the insect pests will have. 

"The maps for wheat stem sawfly, bertha armyworm, pea leaf weevil, and cabbage seedpod weevil illustrate the distribution and approximate density of these insects in 2019," explains Vankosky. "In general, regions with high densities in 2019 are most likely to observe high densities again in 2020. However, there are certain abiotic factors, such as precipitation and mean daily temperature, that can have drastic impacts on insect populations. For example, grasshoppers fare poorly in cool, wet conditions. If these conditions prevail this spring, the forecasted grasshopper risk will drop, but the risk due to wheat midge might increase. Scouting fields on a regular basis is the best way to know for sure what insects are most active and are most likely to be pests in any given year."

According to Alberta Agriculture, the main trouble areas for farmers in the south include:

Grasshoppers: "In southern Alberta, consecutive dry summers is resulting in increasing grasshopper numbers. This is especially true in the M.D. of Acadia, Vulcan, Willow Creek, Lethbridge, Cardston, Magrath and Forty Mile. The grasshopper species found in southern Alberta are a blend of Melanoplus bivitattus, M. packardi, M. sanguinipes and Camnula pellucida. The rest of the province shows light to low grasshopper populations.Portions of southern Alberta indicating moderate to severe risk could experience problems with grasshoppers if environmental conditions favour grasshopper hatching and development in late May through June. Localized factors such as light soils or south-facing slopes result in an elevated risk of grasshopper infestations. Conditions in late spring 2020 will determine the extent of the grasshopper problems later this growing season. Infestation levels in individual fields are NOT indicated in this forecast map."

Cabbage seedpod weevil: "The cabbage seedpod weevil was once again found at economic levels in southern Alberta; however, many fields were below threshold levels and on average the numbers were lower than normal. This is the third consecutive year that cabbage seedpod weevil numbers have been lower than normal but this insect still requires close monitoring for all producers in southern Alberta, especially in its traditional range south of Highway 1. In 2019, Alberta saw a return to the northern range extensions of 2016, with individual weevils found in Wetaskiwin, Strathcona and Lamont. Despite lower numbers in 2019, it will still be important to scout canola in early flower to make control decisions in southern Alberta. We have seen economic threshold levels as far north as a line between Red Deer and Consort in the past and those areas should monitor very early flowering canola."

Wheat stem sawfly: "The sawfly survey conducted in fall 2019 clearly shows an increasing population in various parts of southern Alberta. Increased levels of sawfly damage were found in Willow Creek, Vulcan, and Forty Mile.

Overall, the sawfly risk remains lower than the outbreak levels of the early 2000s but the increase sawfly damage in many spots of southern Alberta signals a resurgence due to the drier conditions over the past few years. The random nature of the survey means that individual fields may still have higher wheat stem sawfly populations than are indicated in the survey map."

Pea leaf weevil: "The level of pea leaf weevil (PLW) feeding damage increased in the northwest portion of central Alberta and the population continues to be lower than normal in southern Alberta. The highest damage ratings were west of Edmonton with the population in southern Alberta still at levels that could cause concern into the 2020 crop year. Although numbers remain low in the Peace River region, PLW is now established from southern Alberta through large areas of the Peace.

There has also been a very noticeable increase of PLW activity to the northeast of Edmonton although the numbers there are still mostly below economic levels. Survey locations shown with black circles had no evidence of PLW feeding on any of the plants assessed.

While this is not a strict forecast, experience has shown us that activity levels greater than 9 notches per plant is sufficient to cause significant damage if conditions are favorable in the spring of 2019. This covers the irrigated and foothills area of southern Alberta and much of northwest central Alberta. For any producers in these higher areas in 2019, there is a risk of damaging levels of PLW in 2020. Producers should use this information along with their own experience to plan control strategies such as seed treatment for the 2020 crop year. Research has shown that seed treatment is much more effective in reducing losses from PLW than foliar treatments."

Wheat midge: "The forecast for Alberta shows areas of risk for midge damage in 2020. It is important to note that over such a wide range, populations in individual fields can be and often are highly variable. Producers should plan to monitor their fields when the midge adults are flying and their wheat is in the susceptible stage. In all areas of the province growers are urged to monitor their wheat fields from wheat head emergence to anthesis for the presence of midge adults. Regular field scouting on multiple nights in succession is important in understanding the population in a particular field."

Grasshoppers are always the pests which tradition get a lot of attention. Vankosky says the spring weather across the province will determine the hopper numbers. Each area is different

 "Most insect pests can be affected by winter conditions, to some extent. While winter temperatures may not have been sufficient to kill overwintering insects, these conditions, including prolonged cold temperatures in the spring can slow insect development or delay emergence and dispersal to crops," explains Vankosky. "Grasshoppers are particularly sensitive to cool, wet conditions in the spring - these conditions result in increased nymph mortality and incidence of fungal diseases that kill grasshoppers. Other insects react positively to wet conditions though. Wheat midge are an important example: rain is necessary for immature wheat midge to complete their development."

 She notes one cannot generalize on how all pests will fare this year and it is very specific in regards to pests, regions and even individual fields and farming practices.  

"I cannot comment on general trends up or down in terms of population densities. We have made observed some interesting trends across the prairies though. For example, in the past, bertha armyworm populations reached outbreak densities on a regular cycle, but we have not observed an outbreak recently and we are overdue for one. This is good news for farmers, but odd for this species. Other pests have had significant population increases in some isolated patches, while others have experienced population declines in some isolated patches of their range. There are a few factors that could affect insect populations, including pesticide use and climate change.”

NOTE: to see the Alberta maps with these pests, visit https://www.alberta.ca/alberta-insect-pest-monitoring-network.aspx and scroll down to the pest map of your choice.

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