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Manitoba Grasshopper Forecast for 2016

 
                

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 the following season 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 advisors, agronomists, and entomologists in August 2015. Grasshopper counts from 119 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 2016. The small circles on the map show where data was collected. White areas on the map are areas where data was not collected.




Figure 1. Average density of grasshoppers in Manitoba during August 2015.
 
 
The Grasshopper Forecast for Manitoba for 2016
 
What the grasshopper population map shows
 
Most of the surveyed area (114 out of 119 counts) rated as very light risk, having counts from 0 to 4 grasshoppers /m2. Four counts were in the light risk category (>4-8/m2), and 1 count was in the moderate risk category (>8-12/m2). There were no counts greater than 12/m2. The highest count was an estimate of 9 grasshoppers per m2 in the Rural Municipality of Stanley.
 
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 table shows the percentage of area in the Manitoba survey map in each of the grasshopper population density categories for data collected from 2006 to 2015. Note that the averaging of counts in a region will result in a denity category for a region representing the cumulative data, not the value from a speciifc count.
 
     Table 1. A 10 year comparison of grasshopper counts in Manitoba.

Year

Very Light

(0-4/m2)
Light
(>4-8/m2)
Moderate
 (>8-12/m2)
Severe
(>12-24/m2)
Very Severe (>24/m2)
2006
94.60
5.40
0
0
0
2007
56.30
38.26
5.21
0.23
0
2008
33.17
40.73
16.48
7.26
2.36
2009
47.19
24.84
16.86
10.67
0.44
2010
98.01
1.99
0
0
0
2011
99.97
0.03
0
0
0
2012
85.82
13.85
0.34
0
0
2013
62.63
28.78
7.71
0.88
0
2014
60.23
18.31
8.62
12.84
0
2015 99.17 0.83 0 0 0

Grasshopper populations had been increasing from 2012 to 2014, however counts in the 2015 survey were noticeably lower. Highest counts in 2015 were in the Municipalities of Roblin and Stanley, but overall the 2015 survey shows a decrease in grasshopper populations.
 
Summary
 
Grasshopper populations were very-light to light in most areas of Manitoba during the August survey. The risk of economical populations of grasshoppers developing in 2016 varies, depending on location, but overall is lower than the previous few years. 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) 745-5668. 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, Food and Rural Development, Box 1149, 65-3rd Ave. NE, Carman, Manitoba, Canada, R0G 0J0                                                                        January 2016
 
 

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