By: Pam Charbonneau, OMAFRA Turfgrass Specialist
Crabgrass
The rule of thumb of apply preventative crabgrass herbicide treatments when forsythia is in full bloom is very conservative. Forsythia traditionally starts blooming in May. Usually the crabgrass doesn’t germinate until the forsythia blooms have fallen. Now that products like Dimension have taken over the crabgrass market, the crabgrass application window is much longer. Dimension can go on after forsythia blossoms have fallen and still be effective. To try to promote Integrated Pest Management (IPM) in lawn care, we recommend that only customers who have had a crabgrass problem in the past season be given a preventative treatment with Dimension.
European chafer grubs and other insects
The grubs will usually pupate in late May. It is important to make note of customers who had grub infestations this spring and target them for Merit control during the months of June and July. This product is recommended to be used preventatively during peak grub egg hatch and while the grubs are still very small. As with all the insecticides registered for use on grubs, Merit must be watered in to be effective. All of these insecticide products need to get in contact with the developing grubs or they will not work. Merit is registered for use in Ontario on European chafer and Japanese beetle grubs. It can be applied only once per season.
Turfgrass scale is an insect that we become aware of during late April and May. It is evident when small areas of turf fail to green up in the spring. If grass plants in these small patches are examined, we can see the mature female scale nymphs and adults at the base of these plants, sucking the juices. The mature nymph is pink in colour and is the size of a rice kernel. The adults are the shape of a hemisphere and are brown with a white strip down the centre. There are no registered controls for turfgrass scale in Ontario.
We usually see the first indications of European crane fly damage at the beginning of May. These larvae are legless and grayish-green in colour. They can be found at the top of the soil in amongst the turf. Insecticide treatment in early May should be successful, but usually by then, the bulk of the damage to the turf has already been done. Again, I would like to invite anyone who encounters this new turf insect in areas outside of Ancaster, Burlington, Niagara and Sarnia to contact me. I can be reached at (519) 824-4120 x 2597.
Diseases
By now, the turf should have outgrown any snow mould damage. When May is a rainy month, we can see diseases such as red thread and leaf spot. With sudden changes from cool and wet to hot and dry weather, leaf spot could develop into "melting out". To determine if this has occurred, examine the base of the grass plants. If you find oval lesions with black borders and straw-coloured centres on the base of the plants, it is likely that you have "melting out." Raise the mowing height and fertilize lightly to help plants recover.
Weed control
During the month of May both the perennial weeds like dandelion and the annual weeds such as prostrate knotweed flourish. Now is a good time to control these broadleaf weeds with a two- or three-way post-emergence herbicide treatment. If conditions become too dry and too hot and the weeds stop growing, herbicide applications should stop until we receive some rain to spur on the weed growth. We also strongly advocate spot spraying lawns with broadleaf herbicides as opposed to blanket sprays to be consistent with IPM.
Aeration
Conditions are usually excellent for core aeration in May. The soil should be neither too dry nor too wet. If the soil is too dry, it is difficult for the core aerators to penetrate the soil. If it is too wet the process of core aeration will cause as much compaction as it alleviates. There is also a rule of thumb that you need 30 good growing days until the summer drought period for the core holes to fill.
