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Archive for May, 2013

Obsolete pesticide collection – coming to Ontario this fall.

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Thinned Kentucky bluegrass turf showing the melting out phase of leaf spot

Thinned Kentucky bluegrass turf showing the melting out phase of leaf spot

Leaf spot lesions on Kentucky bluegrass leaf blade

Leaf spot lesions on Kentucky bluegrass leaf blade

There is a lot of leaf spot on home lawns, sports fields and golf course fairways. This is generally not a problem, but with the hot, humid weather in the forecast it could become a problem. When we get some hot weather following cool, wet weather, these are the perfect conditions for the melting out phase of leaf spot to occur. What is happening is that the individual leaf lesions (small watersoaked spots with a dark brown to purplish border) coalesce and and girdle the whole leaf, or even worse the entire tiller. This phase of the disease is called melting out and can lead to thinning turf or completely dead areas.

If this phase of the disease occurs, the best control is to raise the mowing height. A light application of nitrogen fertilizer after the hot, humid weather passes will help the turf recover from melting out damage. If the turf is irrigated, avoid over-irrigating.

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Early bloom of lilac

Early bloom of lilac

White iris in early bloom

White iris in early bloom

The plant phenological indicators that predict the start of dollar spot are late bloom of lilac and full bloom of iris. Lilacs are in early/full bloom depending on species and iris is in early bloom in the Guelph area at the moment. This is a reminder that a prevenative dollar spot program should begin sooner than later. The temperature is cooling off for the next six days, so that will probably delay the onset of the disease and buy some time.

Dollar spot is favoured by warm, humid days followed by cool nights that produce heavy dew formation. Removing dew by mowing, rolling or polling greens and adequate nitrogen fertilization are practices that will help to minimize this disease, but preventative fungicide applications are the backbone of dollar spot management.

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Leatherjackets washed up on pavement

Leatherjackets washed up on pavement

Leatherjackets feed in the late fall through to late spring but the bulk of the feeding damage occurs in the late spring (mid-May to mid-June). Once we hit mid-June the feeding stops. Whether we see leatherjacket feeding damage has a lot to do with how well the grass is growing during that one month period. A cool, wet spring favours leatherjacket feeding. Also, leatherjackets prefer moist habitats and are often more of a problem in low lying, poorly drained areas. Sometimes it is the secondary damage from starlings that is more noticable than the turf damage. The very dry conditions over the past week may have driven the leatherjackets down in the soil and may have slowed the feeding damage.

What will be evident, especially in urban areas that are infested with leatherjackets, is large numbers of leatherjackets forced out of the turf after rain storms like the ones that are currently moving through the area. Don’t be alarmed, this is actually a good control measure as the leatherjackets will usually end up dying once they are forced out of the turf.

Our research on leatherjacket control for home lawns has been focused on using insect parasitic nematodes and we have had very low success when the nematodes were applied in the spring (<30% control). Our results with fall applied (late October/early November) nematodes have been inconsistent with good results some years and poor results in other years.

For golf courses, both carbaryl and clothianidin can be used at this time of year. The other insecticides that are labeled for control of leatherjackets are best applied in the fall as a preventative application.

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Crabgass seedlings in a thin turf area

Crabgass seedlings in a thin turf area

We (Dr. Michael Brownbridge and his gang) and my gang seeded a new research trial on a sandy site near Fergus last week. The thin grass areas around our site had loads of crabgrass in them already. Of course this makes sense because Forsythis were in peak bloom last week. For lawn care this means that it is now too late to apply any of the corn gluten products against crabgrass. For the golf course sector, there is still time to apply a product like dithiopyr. It can be used up to the three leaf stage for post-emergence crabgrass control. This round of thundershowers that are moving through southwestern Ontario now will provide the soil moisture that is needed for another flux of crabgrass germination.

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Our twice a week soap flushes for annual bluegrass weevil adults put the peak adult migration in the Guelph area around May 6th this year. This is consistent with a project that Dr. Brenda Nailor is working on for the Weevil Trak program with Syngenta. She tracked peak adult migration on May 7th. That would have put the timing for an adulticide around that time.

If your preference is to target the early larvae, then the timing for a product like chlorantraniliprole is to apply it 2-3 weeks after the peak adult migraton. This is coming up quickly. We predict the best timing in the Guelph would to be May 20-30th. The product needs to be applied and taken up by the turfgrass plant and be in the plant as the young stem boring larvae start feeding.

If your preference is to use clothianidin, the window of application is slightly later. It is aimed against the 2nd and 3rd instar. We have started our salt solution flotations (place a plug of turf in a mixture of 36 grams of salt per 100 mL of water) this week to track the larvae and will keep you posted as what we find and when. To date we have not found any young larvae.

One last comment, the emergence of the annual bluegrass weevil adults seems to have been very synchronous, mainly due to an extended warm spell during the migration. My gut feeling is that this will greatly help the efficacy of controls whether it be the adulticide or the larvaecides.

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ABW adults collected from soap flushes

ABW adults collected from soap flushes

Yesterday marked the beginning of the annual bluegrass weevil adult exodus from their overwintering sites to their egg laying sites in the Guelph area. We found some here at the Guelph Turfgrass Institute and Dr. Brenda Nailor found some at a local golf course. There is also a confirmation from a Toronto area golf course that they saw their first ABW’s yesterday. Here at GTI we did a dozen soap flushes all within a half metre perimeter of the edge of the pathology research green that has trees surrounding it. We found roughly two adults per flush. Our plan is to do daily soap flushes over the next 2-3 weeks to closely track their migration and I will continue to update this blog with information on their progression. We will also start to do salt flotations in 2-3 weeks to track the young weevil instars.

Just a note on plant phenology, the very first wave of migration seems to coincide with the first bloom of Forsythia. In the Guelph area, they started to bloom a few days ago, so the timing is almost spot on for this first wave of ABW migration.

The suggested timing for an adulticide is when the forsythia are half green/half gold. So, don’t get your sprayers out yet. With this nice weather the Forsythia will probably progress quickly, but I guestimate that we are at least a week away from this stage of Forsythia development. Information on a larvaecide application timing with a product like chlorantraniliprole is less clear. The concensus in the field is that the larvaecides should target the 1-3rd weevil instars. That timing would be roughly the same time, when the Forsythia are half green/half gold. The thing is that both of these products are quite residual so the timing is not so critical and my gut feeling is that you should err on the early side not the late side. The clothianidin label says to target the 2nd and 3rd instar, so it should probably go on a couple of weeks after the half green/half gold stage of Forsythia.

Stay tuned.

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