Crop advisor casebook: Winter kill woes. Did this timothy crop suffer from the cold winter and cool, dry spring?

A Crop Advisor's Solution from the January 21, 2019 issue of Grainews

This UAV (drone) photo shows the extent of the damage due to necrosis and poor growth caused by a pest outbreak in Nick’s timothy crop.
Corey Pearse. photo: Supplied

Following an abnormally cold winter and cool, dry spring, Nick thought his timothy crop was suffering from winter kill. Large, random areas within the field were exhibiting plant necrosis as well as poor and unusual growth and vigour.

Nick — who farms about 6,000 acres of mixed cereals, pulses, oilseeds, alfalfa and timothy near Picture Butte, Alta. — called me at the end of May last year to ask if I could have a look at the field.

When I arrived, Nick explained the symptoms started appearing around mid-May. The environmental conditions could have caused winter kill, but I thought we should also rule out a nutrient imbalance as well as disease.

After scouting the field in question, we also checked neighbouring timothy fields for winter kill symptoms. These fields were not showing any symptoms, so it was unlikely winter kill was the issue. The large, random patches of affected plants were only occurring in that one field.

A nutrient imbalance was also ruled out as Nick’s fertility plan was sound, and a tissue analysis and soil tests revealed all nutrients were present at normal levels.

This field had been a top-yielder of timothy in previous years. I thought the probability of a disease or infection causing the injury was low for a few reasons — for the past five years, there were no diseases present in the field that timothy hosts, there were no symptoms of root disease and no lesions on the leaf blades, and environmental conditions weren’t conducive for disease development.

While I was digging up some plants in order to examine their root structures, I discovered the cause of the necrosis and poor growth. Nick’s crop had a large pest outbreak!

Crop Advisor’s Solution: Glassy cutworm diminishes timothy yields

Within the soil’s top two inches, I found a heavy glassy cutworm infestation. These pests were causing the plants’ symptoms. Glassy cutworm larvae are shiny and greenish-white to grey in colour, with a reddish-brown head. Mature larvae are about 35 to 40 mm (1.5 inches) in length. Glassy cutworms feed on or near the crowns of grass plants.

After this discovery, Nick applied an insecticide for cutworm control on the timothy field. The glassy cutworm population was greatly reduced, but not before large areas of the field were deemed non-productive. Thus, the field’s stand and yield were greatly diminished.

When insecticide is required, as it was in Nick’s field, choose a residual rather than a contact-only product. Use higher water volumes (20 gallons per acre) to ensure best coverage and penetration into the crown of the plant. Also, apply the insecticide prior to a rain event, if possible, for greater efficacy — the moisture will carry the insecticide into the plant’s crown and the soil’s upper level where the cutworms are present.

To minimize cutworm populations, begin scouting for the pest in the fall until freeze-up and early spring in newly-broken sod as well as established grass fields, such as tall and creeping red fescues, bluegrass, timothy and brome. In the fall, also remove grassy weeds from the field, especially on newly broken sod.

Continuous field scouting is essential for the establishment of a healthy and vigorous crop stand. Early detection and monitoring of pest populations, such as glassy cutworms, by frequent and thorough scouting will also minimize the risk of outbreaks.

Corey Pearse works for Richardson Pioneer Ltd. in Nobleford, Alta.

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