Bowling Green FAQ 11: How do we repair insect damage?

How do we repair areas of the green damaged by chafer grubs or leatherjackets without using nematodes for control before the start of the season: It is now early March?

The use of nematodes will typically require soil temperatures to be above about 10C, otherwise they won’t be adequately active in attempting to control the grubs. April is usually the earliest month in which consideration for nematode application might occur. Do check that it is grubs which are causing the problem, so take some wide diameter cores and inspect the rootzone to see if any are present and try and estimate the extent of infestation. A discoloured and/or damaged sward might be a consequence of many factors, including damage from grubs. Bird activity is usually a good indicator, especially from March onwards, when the nesting season typically commences, that grubs may the present within the rootzone. However, birds may just be finding a source of bedding to line their nests with and the organic thatch layer within a green is an ideal source of bedding for birds. Many other factors might be causing a green to look sickly or prone to animal damage without grubs being present. Earthworms might be sought out by birds or foxes; squirrels might be digging for thatch or to bury a food source; winter die back of leaves, poor growth due to compaction, waterlogging, high thatch content, drying cold winds, and more.

Assuming that it is grubs, if there are less than about 25 per m² then overall underground damage to roots is going to be quite small; only when significant numbers of grubs are found in each square metre, maybe 75+, will more serious damage be caused.

Either way, some attention is needed to the green. If the weather is mild and the season isn’t opening until the latter part of April, then there is time to put some plans into action. Firstly, mow, by lightly topping, the green to remove any debris from the damage caused by birds, or others, to extract the grubs and this will also tidy up the green. If there is lots of surface debris, then you might want to go over the green with a rotary mower before using a cylinder mower. Next, carry out a thorough double aeration of the green using solid tines, or if the green is quite thatchy then a hollow-tine aeration combined with a solid tine aeration might also be considered.

Give a high sand content top-dressing and work it in to the tine holes – obviously more material will be needed where hollow-tining has taken place. Don’t fully infill all the holes quite yet as you will want to get some seed into the holes, so as to allow the final material worked in to just cover and protect the new seed, about a 5mm-6mm depth of coverage should be fine. Apply a 100% red fescue – Chewings and Slender Creeping Red Fescue - seed mixture at 35 g/m². The reason for not including browntop bent at this time is that the fescue seed will germinate and establish that much quicker than bentgrass seed at this time of year. An application of bentgrass seed within a red fescue mixture could be planned either later in April or for the renovation end of season work.

Now work the top-dressing completely into all the aeration holes, covering much of the seed in the process and producing a nice even surface. Make sure the grass is not smothered by any top-dressing and leaves are clearly visible throughout the entire green.

Firm the green with the use of a light roller and make sure there is water available to the seed otherwise it won’t be able to germinate.

Apply a light application of fertiliser to help encourage seed germination and establishment. This will typically be in addition to the main spring fertiliser, so a rate of 17g/m² might be considered suitable, although the rate and actual type will also be influenced by what you might have put on already or are planning to put on during April. Either way, some additional (but light) feed will typically encourage seed establishment, but do not put too much on as this will force growth and you may end up having an attack of Fusarium patch disease on the green.

The aim of the above is to try and nurture the newly applied seed so that additional ground cover has occurred by the start of the season. Even if the work has been carried out to a high standard, we will still be relying on suitable weather conditions, as that will be the ultimate deciding factor.