Manitoba Grasshopper Forecast for 2019

 
                                

Grasshopper surveys have been conducted in Manitoba in various degrees of detail since 1931. The current grasshopper forecast is based on counts of grasshopper populations in August (which estimates the egg-laying population), weather data (which helps estimate whether those female grasshoppers present are capable of laying their optimum level of eggs), and recent trends in grasshopper populations. In some years, natural enemy populations may significantly affect the number of grasshopper eggs that survive and hatch, and such data may be pertinent to the forecast as well. Counts are generally done in or alongside crop fields in Manitoba. The goal is to estimate levels of the 4 species of grasshoppers that have potential to be pests of crops in Manitoba.
 
Purpose of a grasshopper forecast
 
All stages of grasshoppers, except the egg stage, feed on plants. Some species will feed on crops, while other species do not, or rarely will. Older grasshoppers of these crop feeding species can do the most damage to crops, particularly later in the season as these grasshoppers can move greater distances. In annual cropping systems, the young stages of these species are often highly concentrated around field edges early in the season, particularly around fields that had sparse green vegetation late in the previous summer. If grasshopper populations get quite high, these younger, concentrated populations of grasshoppers are much easier to control than older and more dispersed populations later in the season.
 
Knowing the risk of grasshoppers being a problem alerts farmers and agronomists to the importance of monitoring field edges, vegetation surrounding the fields, and other preferred egg laying areas in late-May and June for these younger grasshoppers. This information can also help farmers choose crops and plan seeding practices for the following year.
 
Interpreting the grasshopper population map
 
The grasshopper population map for Manitoba is based on counts of adult grasshoppers per m2 done by farm production extension specialists, agronomists, and entomologists in August 2018. Grasshopper counts from 107 locations in Manitoba were used to produce the map. The legend on the map shows the average grasshopper counts in an area, and relates these to risk for many of our crops. Factors affecting grasshopper development, survival and behaviour will determine whether these August populations are likely to increase, decrease, or remain fairly stable for the next year and are also important factors in the overall forecast for 2019. The small circles on the map show where data was collected. White areas on the map are areas where data was not collected. Note that the averaging of counts in a region will result in a density category for a region representing the cumulative data, not the value from a specific count.

Figure 1. Average density of grasshoppers in Manitoba during August 2018.
 
 
The Grasshopper Forecast for Manitoba for 2019
 
What the grasshopper population map shows
 
Most of the surveyed area (95 out of 107 counts) rated as very light risk, having counts from 0 to 4 grasshoppers /m2. Nine count were in the light risk category (>4-8/m2), two counts were in the moderate risk (>8-12/m2), and one count was in the severe risk category. The Rural Municipality with the highest counts was Portage la Prairie, with estimates of 14.5 and 11.75 grasshoppers per m2 at two of the locations. No counts from the northwest or southwest were above 4 per m2.
 
Recent trends in grasshopper populations
 
Grasshopper outbreaks usually develop after a few years of conditions that are favourable for a steady increase in numbers of those species of grasshopper that can become pests of crops. Comparing the current August grasshopper counts with those of previous years can determine if the populations tend to be rising or falling.
 
The following figures show the area in Manitoba survey maps in each of the grasshopper population density categories for data collected for the 2015 to 2018 grasshopper forecasts.
 

Grasshopper populations had been increasing in surveys done in 2012, 2013 and 2014 (data for the 2015 grasshopper forecast). Grasshopper populations decreased to quite low levels in surveys for the 2016 to 2018 grasshopper forecasts . The data collected in August 2018 for the 2019 forecast showed an increase in grasshopper populations compared to surveys from the previous 3 years.
 
Weather for 2018 Growing Season
 
(Report from: Timi Ojo, Agricultural Meteorology Specialist, Manitoba Agriculture).
Coming off one of the driest winters on record with three-quarters of agro-Manitoba receiving less than 40% of regular winter precipitation, many areas had a relatively dry spring. The months of May and June were about 3°C warmer than normal and this likely provided a boost to the vegetative growth of crops during the early stage. July and August were about 1°C warmer than normal at most regions. Apart from the increased heat, the main highlight of the season was the lack of precipitation. In late June and July, many areas only had about half of the historical average precipitation. August was even drier with many locations having less than 40% of historical average precipitation. September precipitation impacted harvest operations and about 60% of agro-Manitoba had above historical precipitation in September.
 
Summary
 
Although the forecast is for very light risk for most of Manitoba in 2019, there was an increase in grasshopper levels in some areas compared to previous years. Whether populations continue to increase will depend on factors such as weather and natural enemies and needs to be monitored. Grasshopper populations have more successful development in dry years and generally increase more over a series of dry years. The risk of economical populations of grasshoppers developing in 2019 varies, depending on location, but overall is generally low to moderate. If weather is favourable for grasshopper survival and development there may be localized areas where grasshoppers are a concern to crops.
 
When they have the opportunity, farmers and agronomists are encouraged to monitor grasshopper populations along roadsides, field edges, and other areas where populations tend to be concentrated or at high levels early in the season. This monitoring should begin in late-May or June.
 
For more information on the grasshopper forecast or monitoring for grasshoppers, please contact John Gavloski at (204) 750-0594. The protocol for doing the grasshopper counts for this survey can be found at: http://www.gov.mb.ca/agriculture/crops/insects/mb-grasshopper-survey.html 
 
Produced by: John Gavloski; Entomologist; Manitoba Agriculture, Box 1149, 65-3rd Ave. NE, Carman, Manitoba, Canada, R0G 0J0                                                                        January 2019