It’s time to get into the fields and check for grasshoppers. Most infestations will still be at the nymph stages and found close to the edges of the fields and in the ditches. If this is the case spraying the edges of the field will still be an option; however, the window for effective control is quickly closing. Once the nymphs mature and get their wings they become much harder to kill.
First, scout the edges of the field, if there are no visible hoppers there likely won’t be any further into the centre. However, it is important to scout from all sides to ensure they aren’t moving from one side through the field to the other.
Manitoba Agriculture, Food and Rural Development suggests conducting a field survey by starting at one corner of the field, walking diagonally past the centre of the field and then turning and walking straight out to one side of the field. Make at least 20-square-foot counts as you walk. By dividing the total grasshoppers counted by two will give the approximate number of grasshoppers per square meter.
Generally, when the population exceeds 12 adult grasshoppers per square meter it is high enough to consider spraying. At this population of adults there is a high risk of yield loss. At the nymph stage the threshold for spraying is 30-35 per square meter.
Grasshoppers thrive under hot dry conditions but are vulnerable to disease under prolonged periods of cool wet conditions. If periods of sunny and drier weather allow the grasshoppers to dry off then they are less susceptible to disease and their populations will increase.
Early-seeded crops will be able to withstand the pressure from grasshopper better than late-seeded crops. Foliar insecticides can be used to treat wheat for grasshopper control but offer little residual activity of the active ingredient. Several other insecticides also help control grasshoppers in field margins as well as in the seeded field itself.
Even though populations will decline through the late summer and fall, they can remain and cause damage through to the first hard frost. It’s good practice to continue to watch the fields for these pests as growers move through the early harvest to planting their winter wheat. Grasshoppers can feed on the winter wheat plants as they are emerging and cause severe damage.
For more information or help with your crop scouting contact one of our GJ Chemical locations.